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mod_ssl - Apache HTTP Server Version 2.4









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Apache HTTP Server Version 2.4



Apache > HTTP Server > Documentation > Version 2.4 > Modules

Apache Module mod_ssl

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Description:Strong cryptography using the Secure Sockets
Layer (SSL) and Transport Layer Security (TLS) protocols
Status:Extension
ModuleIdentifier:ssl_module
SourceFile:mod_ssl.c
Summary

This module provides SSL v3 and TLS v1.x support for the Apache
HTTP Server. SSL v2 is no longer supported.

This module relies on OpenSSL
to provide the cryptography engine.

Further details, discussion, and examples are provided in the
SSL documentation.

Topics

 Environment Variables
 Custom Log Formats
 Request Notes
 Expression Parser Extension
 Authorization providers for use with Require
Directives

 SSLCACertificateFile
 SSLCACertificatePath
 SSLCADNRequestFile
 SSLCADNRequestPath
 SSLCARevocationCheck
 SSLCARevocationFile
 SSLCARevocationPath
 SSLCertificateChainFile
 SSLCertificateFile
 SSLCertificateKeyFile
 SSLCipherSuite
 SSLCompression
 SSLCryptoDevice
 SSLEngine
 SSLFIPS
 SSLHonorCipherOrder
 SSLInsecureRenegotiation
 SSLOCSPDefaultResponder
 SSLOCSPEnable
 SSLOCSPOverrideResponder
 SSLOCSPProxyURL
 SSLOCSPResponderTimeout
 SSLOCSPResponseMaxAge
 SSLOCSPResponseTimeSkew
 SSLOCSPUseRequestNonce
 SSLOpenSSLConfCmd
 SSLOptions
 SSLPassPhraseDialog
 SSLProtocol
 SSLProxyCACertificateFile
 SSLProxyCACertificatePath
 SSLProxyCARevocationCheck
 SSLProxyCARevocationFile
 SSLProxyCARevocationPath
 SSLProxyCheckPeerCN
 SSLProxyCheckPeerExpire
 SSLProxyCheckPeerName
 SSLProxyCipherSuite
 SSLProxyEngine
 SSLProxyMachineCertificateChainFile
 SSLProxyMachineCertificateFile
 SSLProxyMachineCertificatePath
 SSLProxyProtocol
 SSLProxyVerify
 SSLProxyVerifyDepth
 SSLRandomSeed
 SSLRenegBufferSize
 SSLRequire
 SSLRequireSSL
 SSLSessionCache
 SSLSessionCacheTimeout
 SSLSessionTicketKeyFile
 SSLSessionTickets
 SSLSRPUnknownUserSeed
 SSLSRPVerifierFile
 SSLStaplingCache
 SSLStaplingErrorCacheTimeout
 SSLStaplingFakeTryLater
 SSLStaplingForceURL
 SSLStaplingResponderTimeout
 SSLStaplingResponseMaxAge
 SSLStaplingResponseTimeSkew
 SSLStaplingReturnResponderErrors
 SSLStaplingStandardCacheTimeout
 SSLStrictSNIVHostCheck
 SSLUserName
 SSLUseStapling
 SSLVerifyClient
 SSLVerifyDepth

Bugfix checklisthttpd changelogKnown issuesReport a bugSee also

Comments


Environment Variables

This module can be configured to provide several items of SSL information
as additional environment variables to the SSI and CGI namespace. This
information is not provided by default for performance reasons. (See
SSLOptions StdEnvVars, below.) The generated variables
are listed in the table below. For backward compatibility the information can
be made available under different names, too. Look in the Compatibility chapter for details on the
compatibility variables.




 Variable Name:
 Value Type:
 Description:

HTTPS                         flag      HTTPS is being used.
SSL_PROTOCOL                  string    The SSL protocol version (SSLv3, TLSv1, TLSv1.1, TLSv1.2)
SSL_SESSION_ID                string    The hex-encoded SSL session id
SSL_SESSION_RESUMED           string    Initial or Resumed SSL Session.  Note: multiple requests may be served over the same (Initial or Resumed) SSL session if HTTP KeepAlive is in use
SSL_SECURE_RENEG              string    true if secure renegotiation is supported, else false
SSL_CIPHER                    string    The cipher specification name
SSL_CIPHER_EXPORT             string    true if cipher is an export cipher
SSL_CIPHER_USEKEYSIZE         number    Number of cipher bits (actually used)
SSL_CIPHER_ALGKEYSIZE         number    Number of cipher bits (possible)
SSL_COMPRESS_METHOD           string    SSL compression method negotiated
SSL_VERSION_INTERFACE         string    The mod_ssl program version
SSL_VERSION_LIBRARY           string    The OpenSSL program version
SSL_CLIENT_M_VERSION          string    The version of the client certificate
SSL_CLIENT_M_SERIAL           string    The serial of the client certificate
SSL_CLIENT_S_DN               string    Subject DN in client's certificate
SSL_CLIENT_S_DN_x509 string    Component of client's Subject DN
SSL_CLIENT_SAN_Email_n string  Client certificate's subjectAltName extension entries of type rfc822Name
SSL_CLIENT_SAN_DNS_n string    Client certificate's subjectAltName extension entries of type dNSName
SSL_CLIENT_SAN_OTHER_msUPN_n string    Client certificate's subjectAltName extension entries of type otherName, Microsoft User Principal Name form (OID 1.3.6.1.4.1.311.20.2.3)
SSL_CLIENT_I_DN               string    Issuer DN of client's certificate
SSL_CLIENT_I_DN_x509 string    Component of client's Issuer DN
SSL_CLIENT_V_START            string    Validity of client's certificate (start time)
SSL_CLIENT_V_END              string    Validity of client's certificate (end time)
SSL_CLIENT_V_REMAIN           string    Number of days until client's certificate expires
SSL_CLIENT_A_SIG              string    Algorithm used for the signature of client's certificate
SSL_CLIENT_A_KEY              string    Algorithm used for the public key of client's certificate
SSL_CLIENT_CERT               string    PEM-encoded client certificate
SSL_CLIENT_CERT_CHAIN_n string    PEM-encoded certificates in client certificate chain
SSL_CLIENT_CERT_RFC4523_CEA   string    Serial number and issuer of the certificate. The format matches that of the CertificateExactAssertion in RFC4523
SSL_CLIENT_VERIFY             string    NONE, SUCCESS, GENEROUS or FAILED:reason
SSL_SERVER_M_VERSION          string    The version of the server certificate
SSL_SERVER_M_SERIAL           string    The serial of the server certificate
SSL_SERVER_S_DN               string    Subject DN in server's certificate
SSL_SERVER_SAN_Email_n string  Server certificate's subjectAltName extension entries of type rfc822Name
SSL_SERVER_SAN_DNS_n string    Server certificate's subjectAltName extension entries of type dNSName
SSL_SERVER_SAN_OTHER_dnsSRV_n string    Server certificate's subjectAltName extension entries of type otherName, SRVName form (OID 1.3.6.1.5.5.7.8.7, RFC 4985)
SSL_SERVER_S_DN_x509 string    Component of server's Subject DN
SSL_SERVER_I_DN               string    Issuer DN of server's certificate
SSL_SERVER_I_DN_x509 string    Component of server's Issuer DN
SSL_SERVER_V_START            string    Validity of server's certificate (start time)
SSL_SERVER_V_END              string    Validity of server's certificate (end time)
SSL_SERVER_A_SIG              string    Algorithm used for the signature of server's certificate
SSL_SERVER_A_KEY              string    Algorithm used for the public key of server's certificate
SSL_SERVER_CERT               string    PEM-encoded server certificate
SSL_SRP_USER                  string    SRP username
SSL_SRP_USERINFO              string    SRP user info
SSL_TLS_SNI                   string    Contents of the SNI TLS extension (if supplied with ClientHello)


x509 specifies a component of an X.509 DN; one of
C,ST,L,O,OU,CN,T,I,G,S,D,UID,Email.  In Apache 2.1 and
later, x509 may also include a numeric _n
suffix.  If the DN in question contains multiple attributes of the
same name, this suffix is used as a zero-based index to select a
particular attribute.  For example, where the server certificate
subject DN included two OU attributes, SSL_SERVER_S_DN_OU_0
and
SSL_SERVER_S_DN_OU_1 could be used to reference each.  A
variable name without a _n suffix is equivalent to that
name with a _0 suffix; the first (or only) attribute.
When the environment table is populated using
the StdEnvVars option of
the SSLOptions directive, the
first (or only) attribute of any DN is added only under a non-suffixed
name; i.e. no _0 suffixed entries are added.

The format of the *_DN variables has changed in Apache HTTPD
2.3.11. See the LegacyDNStringFormat option for
SSLOptions for details.

SSL_CLIENT_V_REMAIN is only available in version 2.1
and later.

A number of additional environment variables can also be used
in SSLRequire expressions, or in custom log
formats:

HTTP_USER_AGENT        PATH_INFO             AUTH_TYPE
HTTP_REFERER           QUERY_STRING          SERVER_SOFTWARE
HTTP_COOKIE            REMOTE_HOST           API_VERSION
HTTP_FORWARDED         REMOTE_IDENT          TIME_YEAR
HTTP_HOST              IS_SUBREQ             TIME_MON
HTTP_PROXY_CONNECTION  DOCUMENT_ROOT         TIME_DAY
HTTP_ACCEPT            SERVER_ADMIN          TIME_HOUR
THE_REQUEST            SERVER_NAME           TIME_MIN
REQUEST_FILENAME       SERVER_PORT           TIME_SEC
REQUEST_METHOD         SERVER_PROTOCOL       TIME_WDAY
REQUEST_SCHEME         REMOTE_ADDR           TIME
REQUEST_URI            REMOTE_USER

In these contexts, two special formats can also be used:


  ENV:variablename
  This will expand to the standard environment
  variable variablename.

  HTTP:headername
  This will expand to the value of the request header with name
  headername.




Custom Log Formats

When mod_ssl is built into Apache or at least
loaded (under DSO situation) additional functions exist for the Custom Log Format of
mod_log_config. First there is an
additional ``%{varname}x''
eXtension format function which can be used to expand any variables
provided by any module, especially those provided by mod_ssl which can
you find in the above table.

For backward compatibility there is additionally a special
``%{name}c'' cryptography format function
provided. Information about this function is provided in the Compatibility chapter.
ExampleCustomLog "logs/ssl_request_log" "%t %h %{SSL_PROTOCOL}x %{SSL_CIPHER}x \"%r\" %b"

These formats even work without setting the StdEnvVars
option of the SSLOptions
directive.


Request Notes

mod_ssl sets "notes" for the request which can be
used in logging with the %{name}n format
string in mod_log_config.

The notes supported are as follows:


  ssl-access-forbidden
  This note is set to the value 1 if access was
  denied due to an SSLRequire
  or SSLRequireSSL directive.

  ssl-secure-reneg
  If mod_ssl is built against a version of
  OpenSSL which supports the secure renegotiation extension, this note
  is set to the value 1 if SSL is in used for the current
  connection, and the client also supports the secure renegotiation
  extension.  If the client does not support the secure renegotiation
  extension, the note is set to the value 0.
  If mod_ssl is not built against a version of
  OpenSSL which supports secure renegotiation, or if SSL is not in use
  for the current connection, the note is not set.




Expression Parser Extension

When mod_ssl is built into Apache or at least
loaded (under DSO situation) any variables
provided by mod_ssl can be used in expressions
for the ap_expr Expression Parser.
The variables can be referenced using the syntax
``%{varname}''. Starting
with version 2.4.18 one can also use the
mod_rewrite style syntax
``%{SSL:varname}'' or
the function style syntax
``ssl(varname)''.
Example (using mod_headers)Header set X-SSL-PROTOCOL "expr=%{SSL_PROTOCOL}"
Header set X-SSL-CIPHER "expr=%{SSL:SSL_CIPHER}"

This feature even works without setting the StdEnvVars
option of the SSLOptions
directive.


Authorization providers for use with Require

  mod_ssl provides a few authentication providers for use
  with mod_authz_core's
  Require directive.

  Require ssl

    The ssl provider denies access if a connection is not
       encrypted with SSL. This is similar to the
       SSLRequireSSL directive.

    Require ssl


  

  Require ssl-verify-client

    The ssl provider allows access if the user is
       authenticated with a valid client certificate. This is only
       useful if SSLVerifyClient optional is in effect.

    The following example grants access if the user is authenticated
       either with a client certificate or by username and password.

    Require ssl-verify-client
Require valid-user


  



SSLCACertificateFile Directive

Description:File of concatenated PEM-encoded CA Certificates
for Client Auth
Syntax:SSLCACertificateFile file-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl


This directive sets the all-in-one file where you can assemble the
Certificates of Certification Authorities (CA) whose clients you deal
with. These are used for Client Authentication. Such a file is simply the
concatenation of the various PEM-encoded Certificate files, in order of
preference. This can be used alternatively and/or additionally to
SSLCACertificatePath.
ExampleSSLCACertificateFile "/usr/local/apache2/conf/ssl.crt/ca-bundle-client.crt"




SSLCACertificatePath Directive

Description:Directory of PEM-encoded CA Certificates for
Client Auth
Syntax:SSLCACertificatePath directory-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl


This directive sets the directory where you keep the Certificates of
Certification Authorities (CAs) whose clients you deal with. These are used to
verify the client certificate on Client Authentication.

The files in this directory have to be PEM-encoded and are accessed through
hash filenames. So usually you can't just place the Certificate files
there: you also have to create symbolic links named
hash-value.N. And you should always make sure this directory
contains the appropriate symbolic links.
ExampleSSLCACertificatePath "/usr/local/apache2/conf/ssl.crt/"




SSLCADNRequestFile Directive

Description:File of concatenated PEM-encoded CA Certificates
for defining acceptable CA names
Syntax:SSLCADNRequestFile file-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl

When a client certificate is requested by mod_ssl, a list of
acceptable Certificate Authority names is sent to the client
in the SSL handshake.  These CA names can be used by the client to
select an appropriate client certificate out of those it has
available.

If neither of the directives SSLCADNRequestPath or SSLCADNRequestFile are given, then the
set of acceptable CA names sent to the client is the names of all the
CA certificates given by the SSLCACertificateFile and SSLCACertificatePath directives; in other
words, the names of the CAs which will actually be used to verify the
client certificate.

In some circumstances, it is useful to be able to send a set of
acceptable CA names which differs from the actual CAs used to verify
the client certificate - for example, if the client certificates are
signed by intermediate CAs.  In such cases, SSLCADNRequestPath and/or SSLCADNRequestFile can be used; the
acceptable CA names are then taken from the complete set of
certificates in the directory and/or file specified by this pair of
directives.

SSLCADNRequestFile must
specify an all-in-one file containing a concatenation of
PEM-encoded CA certificates.

ExampleSSLCADNRequestFile "/usr/local/apache2/conf/ca-names.crt"




SSLCADNRequestPath Directive

Description:Directory of PEM-encoded CA Certificates for
defining acceptable CA names
Syntax:SSLCADNRequestPath directory-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl


This optional directive can be used to specify the set of
acceptable CA names which will be sent to the client when a
client certificate is requested.  See the SSLCADNRequestFile directive for more
details.

The files in this directory have to be PEM-encoded and are accessed
through hash filenames. So usually you can't just place the
Certificate files there: you also have to create symbolic links named
hash-value.N. And you should always make sure
this directory contains the appropriate symbolic links.
ExampleSSLCADNRequestPath "/usr/local/apache2/conf/ca-names.crt/"




SSLCARevocationCheck Directive

Description:Enable CRL-based revocation checking
Syntax:SSLCARevocationCheck chain|leaf|none flags
Default:SSLCARevocationCheck none
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Optional flags available in httpd 2.5-dev or
later


Enables certificate revocation list (CRL) checking. At least one of
SSLCARevocationFile
or SSLCARevocationPath must be
configured. When set to chain (recommended setting),
CRL checks are applied to all certificates in the chain, while setting it to
leaf limits the checks to the end-entity cert.

The available flags are:

no_crl_for_cert_ok
    
    Prior to version 2.3.15, CRL checking in mod_ssl also succeeded when
    no CRL(s) for the checked certificate(s) were found in any of the locations
    configured with SSLCARevocationFile
    or SSLCARevocationPath.
    
    
    With the introduction of SSLCARevocationFile,
    the behavior has been changed: by default with chain or
    leaf, CRLs must be present for the
    validation to succeed - otherwise it will fail with an
    "unable to get certificate CRL" error.
    
    
    The flag no_crl_for_cert_ok allows to restore
    previous behaviour.
    


ExampleSSLCARevocationCheck chain

Compatibility with versions 2.2SSLCARevocationCheck chain no_crl_for_cert_ok




SSLCARevocationFile Directive

Description:File of concatenated PEM-encoded CA CRLs for
Client Auth
Syntax:SSLCARevocationFile file-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl


This directive sets the all-in-one file where you can
assemble the Certificate Revocation Lists (CRL) of Certification
Authorities (CA) whose clients you deal with. These are used
for Client Authentication.  Such a file is simply the concatenation of
the various PEM-encoded CRL files, in order of preference. This can be
used alternatively and/or additionally to SSLCARevocationPath.
ExampleSSLCARevocationFile "/usr/local/apache2/conf/ssl.crl/ca-bundle-client.crl"




SSLCARevocationPath Directive

Description:Directory of PEM-encoded CA CRLs for
Client Auth
Syntax:SSLCARevocationPath directory-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl


This directive sets the directory where you keep the Certificate Revocation
Lists (CRL) of Certification Authorities (CAs) whose clients you deal with.
These are used to revoke the client certificate on Client Authentication.

The files in this directory have to be PEM-encoded and are accessed through
hash filenames. So usually you have not only to place the CRL files there.
Additionally you have to create symbolic links named
hash-value.rN. And you should always make sure this directory
contains the appropriate symbolic links.
ExampleSSLCARevocationPath "/usr/local/apache2/conf/ssl.crl/"




SSLCertificateChainFile Directive

Description:File of PEM-encoded Server CA Certificates
Syntax:SSLCertificateChainFile file-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl

SSLCertificateChainFile is deprecated
SSLCertificateChainFile became obsolete with version 2.4.8,
when SSLCertificateFile
was extended to also load intermediate CA certificates from the server
certificate file.



This directive sets the optional all-in-one file where you can
assemble the certificates of Certification Authorities (CA) which form the
certificate chain of the server certificate. This starts with the issuing CA
certificate of the server certificate and can range up to the root CA
certificate. Such a file is simply the concatenation of the various
PEM-encoded CA Certificate files, usually in certificate chain order.

This should be used alternatively and/or additionally to SSLCACertificatePath for explicitly
constructing the server certificate chain which is sent to the browser
in addition to the server certificate. It is especially useful to
avoid conflicts with CA certificates when using client
authentication. Because although placing a CA certificate of the
server certificate chain into SSLCACertificatePath has the same effect
for the certificate chain construction, it has the side-effect that
client certificates issued by this same CA certificate are also
accepted on client authentication.

But be careful: Providing the certificate chain works only if you are using a
single RSA or DSA based server certificate. If you are
using a coupled RSA+DSA certificate pair, this will work only if actually both
certificates use the same certificate chain. Else the browsers will be
confused in this situation.
ExampleSSLCertificateChainFile "/usr/local/apache2/conf/ssl.crt/ca.crt"




SSLCertificateFile Directive

Description:Server PEM-encoded X.509 certificate data file
Syntax:SSLCertificateFile file-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl


This directive points to a file with certificate data in PEM format.
At a minimum, the file must include an end-entity (leaf) certificate.
The directive can be used multiple times (referencing different filenames)
to support multiple algorithms for server authentication - typically
RSA, DSA, and ECC. The number of supported algorithms depends on the
OpenSSL version being used for mod_ssl: with version 1.0.0 or later,
openssl list-public-key-algorithms will output a list
of supported algorithms, see also the note below about limitations
of OpenSSL versions prior to 1.0.2 and the ways to work around them.



The files may also include intermediate CA certificates, sorted from
leaf to root. This is supported with version 2.4.8 and later,
and obsoletes SSLCertificateChainFile.
When running with OpenSSL 1.0.2 or later, this allows
to configure the intermediate CA chain on a per-certificate basis.



Custom DH parameters and an EC curve name for ephemeral keys,
can also be added to end of the first file configured using
SSLCertificateFile.
This is supported in version 2.4.7 or later.
Such parameters can be generated using the commands
openssl dhparam and openssl ecparam.
The parameters can be added as-is to the end of the first
certificate file. Only the first file can be used for custom
parameters, as they are applied independently of the authentication
algorithm type.



Finally the end-entity certificate's private key can also be
added to the certificate file instead of using a separate
SSLCertificateKeyFile
directive. This practice is highly discouraged. If it is used,
the certificate files using such an embedded key must be configured
after the certificates using a separate key file. If the private
key is encrypted, the pass phrase dialog is forced at startup time.



DH parameter interoperability with primes > 1024 bit

Beginning with version 2.4.7, mod_ssl makes use of
standardized DH parameters with prime lengths of 2048, 3072 and 4096 bits
and with additional prime lengths of 6144 and 8192 bits beginning with
version 2.4.10
(from RFC 3526), and hands
them out to clients based on the length of the certificate's RSA/DSA key.
With Java-based clients in particular (Java 7 or earlier), this may lead
to handshake failures - see this
FAQ answer for working around
such issues.




Default DH parameters when using multiple certificates and OpenSSL
versions prior to 1.0.2

When using multiple certificates to support different authentication algorithms
(like RSA, DSA, but mainly ECC) and OpenSSL prior to 1.0.2, it is recommended
to either use custom DH parameters (preferably) by adding them to the
first certificate file (as described above), or to order the
SSLCertificateFile directives such that RSA/DSA
certificates are placed after the ECC one.


This is due to a limitation in older versions of OpenSSL which don't let the
Apache HTTP Server determine the currently selected certificate at handshake
time (when the DH parameters must be sent to the peer) but instead always
provide the last configured certificate. Consequently, the server may select
default DH parameters based on the length of the wrong certificate's key (ECC
keys are much smaller than RSA/DSA ones and their length is not relevant for
selecting DH primes).


Since custom DH parameters always take precedence over the default ones, this
issue can be avoided by creating and configuring them (as described above),
thus using a custom/suitable length.



ExampleSSLCertificateFile "/usr/local/apache2/conf/ssl.crt/server.crt"




SSLCertificateKeyFile Directive

Description:Server PEM-encoded private key file
Syntax:SSLCertificateKeyFile file-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl


This directive points to the PEM-encoded private key file for the
server. If the contained private key is encrypted, the pass phrase
dialog is forced at startup time.


The directive can be used multiple times (referencing different filenames)
to support multiple algorithms for server authentication. For each
SSLCertificateKeyFile
directive, there must be a matching SSLCertificateFile
directive.


The private key may also be combined with the certificate in the file given by
SSLCertificateFile, but this practice
is highly discouraged. If it is used, the certificate files using such
an embedded key must be configured after the certificates using a separate
key file.

ExampleSSLCertificateKeyFile "/usr/local/apache2/conf/ssl.key/server.key"




SSLCipherSuite Directive

Description:Cipher Suite available for negotiation in SSL
handshake
Syntax:SSLCipherSuite cipher-spec
Default:SSLCipherSuite DEFAULT (depends on OpenSSL version)
Context:server config, virtual host, directory, .htaccess
Override:AuthConfig
Status:Extension
Module:mod_ssl


This complex directive uses a colon-separated cipher-spec string
consisting of OpenSSL cipher specifications to configure the Cipher Suite the
client is permitted to negotiate in the SSL handshake phase. Notice that this
directive can be used both in per-server and per-directory context. In
per-server context it applies to the standard SSL handshake when a connection
is established. In per-directory context it forces a SSL renegotiation with the
reconfigured Cipher Suite after the HTTP request was read but before the HTTP
response is sent.

An SSL cipher specification in cipher-spec is composed of 4 major
attributes plus a few extra minor ones:

Key Exchange Algorithm:
    RSA, Diffie-Hellman, Elliptic Curve Diffie-Hellman, Secure Remote Password

Authentication Algorithm:
    RSA, Diffie-Hellman, DSS, ECDSA, or none.

Cipher/Encryption Algorithm:
    AES, DES, Triple-DES, RC4, RC2, IDEA, etc.

MAC Digest Algorithm:
    MD5, SHA or SHA1, SHA256, SHA384.


An SSL cipher can also be an export cipher. SSLv2 ciphers are no longer
supported. To specify which ciphers to use, one can either specify all the
Ciphers, one at a time, or use aliases to specify the preference and order
for the ciphers (see Table
1). The actually available ciphers and aliases depends on the used
openssl version. Newer openssl versions may include additional ciphers.



Tag Description
Key Exchange Algorithm:
kRSA   RSA key exchange
kDHr   Diffie-Hellman key exchange with RSA key
kDHd   Diffie-Hellman key exchange with DSA key
kEDH   Ephemeral (temp.key) Diffie-Hellman key exchange (no cert)   
kSRP   Secure Remote Password (SRP) key exchange
Authentication Algorithm:
aNULL  No authentication
aRSA   RSA authentication
aDSS   DSS authentication 
aDH    Diffie-Hellman authentication
Cipher Encoding Algorithm:
eNULL  No encryption         
NULL   alias for eNULL         
AES    AES encryption        
DES    DES encryption        
3DES   Triple-DES encryption 
RC4    RC4 encryption       
RC2    RC2 encryption       
IDEA   IDEA encryption       
MAC Digest Algorithm:
MD5    MD5 hash function
SHA1   SHA1 hash function
SHA    alias for SHA1 
SHA256 SHA256 hash function 
SHA384 SHA384 hash function 
Aliases:
SSLv3  all SSL version 3.0 ciphers 
TLSv1  all TLS version 1.0 ciphers 
EXP    all export ciphers  
EXPORT40 all 40-bit export ciphers only  
EXPORT56 all 56-bit export ciphers only  
LOW    all low strength ciphers (no export, single DES)
MEDIUM all ciphers with 128 bit encryption 
HIGH   all ciphers using Triple-DES     
RSA    all ciphers using RSA key exchange 
DH     all ciphers using Diffie-Hellman key exchange 
EDH    all ciphers using Ephemeral Diffie-Hellman key exchange 
ECDH   Elliptic Curve Diffie-Hellman key exchange   
ADH    all ciphers using Anonymous Diffie-Hellman key exchange 
AECDH    all ciphers using Anonymous Elliptic Curve Diffie-Hellman key exchange 
SRP    all ciphers using Secure Remote Password (SRP) key exchange 
DSS    all ciphers using DSS authentication 
ECDSA    all ciphers using ECDSA authentication 
aNULL   all ciphers using no authentication 


Now where this becomes interesting is that these can be put together
to specify the order and ciphers you wish to use. To speed this up
there are also aliases (SSLv3, TLSv1, EXP, LOW, MEDIUM,
HIGH) for certain groups of ciphers. These tags can be joined
together with prefixes to form the cipher-spec. Available
prefixes are:

none: add cipher to list
+: move matching ciphers to the current location in list
-: remove cipher from list (can be added later again)
!: kill cipher from list completely (can not be added later again)



aNULL, eNULL and EXP
ciphers are always disabled
Beginning with version 2.4.7, null and export-grade
ciphers are always disabled, as mod_ssl unconditionally adds
!aNULL:!eNULL:!EXP to any cipher string at initialization.


A simpler way to look at all of this is to use the ``openssl ciphers
-v'' command which provides a nice way to successively create the
correct cipher-spec string. The default cipher-spec string
depends on the version of the OpenSSL libraries used. Let's suppose it is
``RC4-SHA:AES128-SHA:HIGH:MEDIUM:!aNULL:!MD5'' which
means the following: Put RC4-SHA and AES128-SHA at
the beginning. We do this, because these ciphers offer a good compromise
between speed and security. Next, include high and medium security ciphers.
Finally, remove all ciphers which do not authenticate, i.e. for SSL the
Anonymous Diffie-Hellman ciphers, as well as all ciphers which use
MD5 as hash algorithm, because it has been proven insufficient.
$ openssl ciphers -v 'RC4-SHA:AES128-SHA:HIGH:MEDIUM:!aNULL:!MD5'
RC4-SHA                 SSLv3 Kx=RSA      Au=RSA  Enc=RC4(128)  Mac=SHA1
AES128-SHA              SSLv3 Kx=RSA      Au=RSA  Enc=AES(128)  Mac=SHA1
DHE-RSA-AES256-SHA      SSLv3 Kx=DH       Au=RSA  Enc=AES(256)  Mac=SHA1
...                     ...               ...     ...           ...
SEED-SHA                SSLv3 Kx=RSA      Au=RSA  Enc=SEED(128) Mac=SHA1
PSK-RC4-SHA             SSLv3 Kx=PSK      Au=PSK  Enc=RC4(128)  Mac=SHA1
KRB5-RC4-SHA            SSLv3 Kx=KRB5     Au=KRB5 Enc=RC4(128)  Mac=SHA1
The complete list of particular RSA & DH ciphers for SSL is given in Table 2.
ExampleSSLCipherSuite RSA:!EXP:!NULL:+HIGH:+MEDIUM:-LOW



Cipher-Tag Protocol Key Ex. Auth. Enc. MAC Type 
RSA Ciphers:
DES-CBC3-SHA SSLv3 RSA RSA 3DES(168) SHA1  
IDEA-CBC-SHA SSLv3 RSA RSA IDEA(128) SHA1  
RC4-SHA SSLv3 RSA RSA RC4(128) SHA1  
RC4-MD5 SSLv3 RSA RSA RC4(128) MD5  
DES-CBC-SHA SSLv3 RSA RSA DES(56) SHA1  
EXP-DES-CBC-SHA SSLv3 RSA(512) RSA DES(40) SHA1  export 
EXP-RC2-CBC-MD5 SSLv3 RSA(512) RSA RC2(40) MD5   export 
EXP-RC4-MD5 SSLv3 RSA(512) RSA RC4(40) MD5   export 
NULL-SHA SSLv3 RSA RSA None SHA1  
NULL-MD5 SSLv3 RSA RSA None MD5  
Diffie-Hellman Ciphers:
ADH-DES-CBC3-SHA SSLv3 DH None 3DES(168) SHA1  
ADH-DES-CBC-SHA SSLv3 DH None DES(56) SHA1  
ADH-RC4-MD5 SSLv3 DH None RC4(128) MD5  
EDH-RSA-DES-CBC3-SHA SSLv3 DH RSA 3DES(168) SHA1  
EDH-DSS-DES-CBC3-SHA SSLv3 DH DSS 3DES(168) SHA1  
EDH-RSA-DES-CBC-SHA SSLv3 DH RSA DES(56) SHA1  
EDH-DSS-DES-CBC-SHA SSLv3 DH DSS DES(56) SHA1  
EXP-EDH-RSA-DES-CBC-SHA SSLv3 DH(512) RSA DES(40) SHA1  export 
EXP-EDH-DSS-DES-CBC-SHA SSLv3 DH(512) DSS DES(40) SHA1  export 
EXP-ADH-DES-CBC-SHA SSLv3 DH(512) None DES(40) SHA1  export 
EXP-ADH-RC4-MD5 SSLv3 DH(512) None RC4(40) MD5   export 




SSLCompression Directive

Description:Enable compression on the SSL level
Syntax:SSLCompression on|off
Default:SSLCompression off
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in httpd 2.4.3 and later, if using OpenSSL 0.9.8 or later;
virtual host scope available if using OpenSSL 1.0.0 or later.
The default used to be on in version 2.4.3.

This directive allows to enable compression on the SSL level.

Enabling compression causes security issues in most setups (the so called
CRIME attack).




SSLCryptoDevice Directive

Description:Enable use of a cryptographic hardware accelerator
Syntax:SSLCryptoDevice engine
Default:SSLCryptoDevice builtin
Context:server config
Status:Extension
Module:mod_ssl


This directive enables use of a cryptographic hardware accelerator
board to offload some of the SSL processing overhead.  This directive
can only be used if the SSL toolkit is built with "engine" support;
OpenSSL 0.9.7 and later releases have "engine" support by default, the
separate "-engine" releases of OpenSSL 0.9.6 must be used.

To discover which engine names are supported, run the command
"openssl engine".

Example# For a Broadcom accelerator:
SSLCryptoDevice ubsec




SSLEngine Directive

Description:SSL Engine Operation Switch
Syntax:SSLEngine on|off|optional
Default:SSLEngine off
Context:server config, virtual host
Status:Extension
Module:mod_ssl


This directive toggles the usage of the SSL/TLS Protocol Engine. This
is should be used inside a <VirtualHost> section to enable SSL/TLS for a
that virtual host. By default the SSL/TLS Protocol Engine is
disabled for both the main server and all configured virtual hosts.
Example<VirtualHost _default_:443>
SSLEngine on
#...
</VirtualHost>

In Apache 2.1 and later, SSLEngine can be set to
optional. This enables support for
RFC 2817, Upgrading to TLS
Within HTTP/1.1. At this time no web browsers support RFC 2817.



SSLFIPS Directive

Description:SSL FIPS mode Switch
Syntax:SSLFIPS on|off
Default:SSLFIPS off
Context:server config
Status:Extension
Module:mod_ssl


This directive toggles the usage of the SSL library FIPS_mode flag.
It must be set in the global server context and cannot be configured
with conflicting settings (SSLFIPS on followed by SSLFIPS off or
similar).  The mode applies to all SSL library operations.


If httpd was compiled against an SSL library which did not support
the FIPS_mode flag, SSLFIPS on will fail.  Refer to the
FIPS 140-2 Security Policy document of the SSL provider library for
specific requirements to use mod_ssl in a FIPS 140-2 approved mode
of operation; note that mod_ssl itself is not validated, but may be
described as using FIPS 140-2 validated cryptographic module, when
all components are assembled and operated under the guidelines imposed
by the applicable Security Policy.




SSLHonorCipherOrder Directive

Description:Option to prefer the server's cipher preference order
Syntax:SSLHonorCipherOrder on|off
Default:SSLHonorCipherOrder off
Context:server config, virtual host
Status:Extension
Module:mod_ssl

When choosing a cipher during an SSLv3 or TLSv1 handshake, normally
the client's preference is used.  If this directive is enabled, the
server's preference will be used instead.
ExampleSSLHonorCipherOrder on




SSLInsecureRenegotiation Directive

Description:Option to enable support for insecure renegotiation
Syntax:SSLInsecureRenegotiation on|off
Default:SSLInsecureRenegotiation off
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in httpd 2.2.15 and later, if using OpenSSL 0.9.8m or later

As originally specified, all versions of the SSL and TLS protocols
(up to and including TLS/1.2) were vulnerable to a Man-in-the-Middle
attack
(CVE-2009-3555)
during a renegotiation.  This vulnerability allowed an attacker to
"prefix" a chosen plaintext to the HTTP request as seen by the web
server.  A protocol extension was developed which fixed this
vulnerability if supported by both client and server.

If mod_ssl is linked against OpenSSL version 0.9.8m
or later, by default renegotiation is only supported with
clients supporting the new protocol extension.  If this directive is
enabled, renegotiation will be allowed with old (unpatched) clients,
albeit insecurely.

Security warning
If this directive is enabled, SSL connections will be vulnerable to
the Man-in-the-Middle prefix attack as described
in CVE-2009-3555.


ExampleSSLInsecureRenegotiation on


The SSL_SECURE_RENEG environment variable can be used
from an SSI or CGI script to determine whether secure renegotiation is
supported for a given SSL connection.




SSLOCSPDefaultResponder Directive

Description:Set the default responder URI for OCSP validation
Syntax:SSLOCSDefaultResponder uri
Context:server config, virtual host
Status:Extension
Module:mod_ssl

This option sets the default OCSP responder to use.  If SSLOCSPOverrideResponder is not enabled,
the URI given will be used only if no responder URI is specified in
the certificate being verified.



SSLOCSPEnable Directive

Description:Enable OCSP validation of the client certificate chain
Syntax:SSLOCSPEnable on|off
Default:SSLOCSPEnable off
Context:server config, virtual host
Status:Extension
Module:mod_ssl

This option enables OCSP validation of the client certificate
chain.  If this option is enabled, certificates in the client's
certificate chain will be validated against an OCSP responder after
normal verification (including CRL checks) have taken place.

The OCSP responder used is either extracted from the certificate
itself, or derived by configuration; see the
SSLOCSPDefaultResponder and
SSLOCSPOverrideResponder
directives.

ExampleSSLVerifyClient on
SSLOCSPEnable on
SSLOCSPDefaultResponder "http://responder.example.com:8888/responder"
SSLOCSPOverrideResponder on




SSLOCSPOverrideResponder Directive

Description:Force use of the default responder URI for OCSP validation
Syntax:SSLOCSPOverrideResponder on|off
Default:SSLOCSPOverrideResponder off
Context:server config, virtual host
Status:Extension
Module:mod_ssl

This option forces the configured default OCSP responder to be used
during OCSP certificate validation, regardless of whether the
certificate being validated references an OCSP responder.



SSLOCSPProxyURL Directive

Description:Proxy URL to use for OCSP requests
Syntax:SSLOCSPProxyURL url
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in httpd 2.4.19 and later

This option allows to set the URL of a HTTP proxy that should be used for
all queries to OCSP responders.



SSLOCSPResponderTimeout Directive

Description:Timeout for OCSP queries
Syntax:SSLOCSPResponderTimeout seconds
Default:SSLOCSPResponderTimeout 10
Context:server config, virtual host
Status:Extension
Module:mod_ssl

This option sets the timeout for queries to OCSP responders, when
SSLOCSPEnable is turned on.



SSLOCSPResponseMaxAge Directive

Description:Maximum allowable age for OCSP responses
Syntax:SSLOCSPResponseMaxAge seconds
Default:SSLOCSPResponseMaxAge -1
Context:server config, virtual host
Status:Extension
Module:mod_ssl

This option sets the maximum allowable age ("freshness") for OCSP responses.
The default value (-1) does not enforce a maximum age,
which means that OCSP responses are considered valid as long as their
nextUpdate field is in the future.



SSLOCSPResponseTimeSkew Directive

Description:Maximum allowable time skew for OCSP response validation
Syntax:SSLOCSPResponseTimeSkew seconds
Default:SSLOCSPResponseTimeSkew 300
Context:server config, virtual host
Status:Extension
Module:mod_ssl

This option sets the maximum allowable time skew for OCSP responses
(when checking their thisUpdate and nextUpdate fields).



SSLOCSPUseRequestNonce Directive

Description:Use a nonce within OCSP queries
Syntax:SSLOCSPUseRequestNonce on|off
Default:SSLOCSPUseRequestNonce on
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in httpd 2.4.10 and later

This option determines whether queries to OCSP responders should contain
a nonce or not. By default, a query nonce is always used and checked against
the response's one. When the responder does not use nonces (e.g. Microsoft OCSP
Responder), this option should be turned off.



SSLOpenSSLConfCmd Directive

Description:Configure OpenSSL parameters through its SSL_CONF API
Syntax:SSLOpenSSLConfCmd command-name command-value
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in httpd 2.4.8 and later, if using OpenSSL 1.0.2 or later

This directive exposes OpenSSL's SSL_CONF API to mod_ssl,
allowing a flexible configuration of OpenSSL parameters without the need
of implementing additional mod_ssl directives when new
features are added to OpenSSL.

The set of available SSLOpenSSLConfCmd commands
depends on the OpenSSL version being used for mod_ssl
(at least version 1.0.2 is required). For a list of supported command
names, see the section Supported configuration file commands in the
SSL_CONF_cmd(3) manual page for OpenSSL.

Some of the SSLOpenSSLConfCmd commands can be used
as an alternative to existing directives (such as
SSLCipherSuite or
SSLProtocol),
though it should be noted that the syntax / allowable values for the parameters
may sometimes differ.

ExamplesSSLOpenSSLConfCmd Options -SessionTicket,ServerPreference
SSLOpenSSLConfCmd ECDHParameters brainpoolP256r1
SSLOpenSSLConfCmd ServerInfoFile "/usr/local/apache2/conf/server-info.pem"
SSLOpenSSLConfCmd Protocol "-ALL, TLSv1.2"
SSLOpenSSLConfCmd SignatureAlgorithms RSA+SHA384:ECDSA+SHA256




SSLOptions Directive

Description:Configure various SSL engine run-time options
Syntax:SSLOptions [+|-]option ...
Context:server config, virtual host, directory, .htaccess
Override:Options
Status:Extension
Module:mod_ssl


This directive can be used to control various run-time options on a
per-directory basis. Normally, if multiple SSLOptions
could apply to a directory, then the most specific one is taken
completely; the options are not merged. However if all the
options on the SSLOptions directive are preceded by a
plus (+) or minus (-) symbol, the options
are merged. Any options preceded by a + are added to the
options currently in force, and any options preceded by a
- are removed from the options currently in force.

The available options are:

StdEnvVars
    
    When this option is enabled, the standard set of SSL related CGI/SSI
    environment variables are created. This per default is disabled for
    performance reasons, because the information extraction step is a
    rather expensive operation. So one usually enables this option for
    CGI and SSI requests only.

ExportCertData
    
    When this option is enabled, additional CGI/SSI environment variables are
    created: SSL_SERVER_CERT, SSL_CLIENT_CERT and
    SSL_CLIENT_CERT_CHAIN_n (with n = 0,1,2,..).
    These contain the PEM-encoded X.509 Certificates of server and client for
    the current HTTPS connection and can be used by CGI scripts for deeper
    Certificate checking. Additionally all other certificates of the client
    certificate chain are provided, too. This bloats up the environment a
    little bit which is why you have to use this option to enable it on
    demand.

FakeBasicAuth
    
    When this option is enabled, the Subject Distinguished Name (DN) of the
    Client X509 Certificate is translated into a HTTP Basic Authorization
    username. This means that the standard Apache authentication methods can
    be used for access control. The user name is just the Subject of the
    Client's X509 Certificate (can be determined by running OpenSSL's
    openssl x509 command: openssl x509 -noout -subject -in
    certificate.crt). Note that no password is
    obtained from the user. Every entry in the user file needs this password:
    ``xxj31ZMTZzkVA'', which is the DES-encrypted version of the
    word `password''. Those who live under MD5-based encryption
    (for instance under FreeBSD or BSD/OS, etc.) should use the following MD5
    hash of the same word: ``$1$OXLyS...$Owx8s2/m9/gfkcRVXzgoE/''.

    Note that the AuthBasicFake
    directive within mod_auth_basic can be used as a more
    general mechanism for faking basic authentication, giving control over the
    structure of both the username and password.

StrictRequire
    
    This forces forbidden access when SSLRequireSSL or
    SSLRequire successfully decided that access should be
    forbidden. Usually the default is that in the case where a ``Satisfy
    any'' directive is used, and other access restrictions are passed,
    denial of access due to SSLRequireSSL or
    SSLRequire is overridden (because that's how the Apache
    Satisfy mechanism should work.) But for strict access restriction
    you can use SSLRequireSSL and/or SSLRequire in
    combination with an ``SSLOptions +StrictRequire''. Then an
    additional ``Satisfy Any'' has no chance once mod_ssl has
    decided to deny access.

OptRenegotiate
    
    This enables optimized SSL connection renegotiation handling when SSL
    directives are used in per-directory context. By default a strict
    scheme is enabled where every per-directory reconfiguration of
    SSL parameters causes a full SSL renegotiation handshake. When this
    option is used mod_ssl tries to avoid unnecessary handshakes by doing more
    granular (but still safe) parameter checks. Nevertheless these granular
    checks sometimes may not be what the user expects, so enable this on a
    per-directory basis only, please.

LegacyDNStringFormat
    
    This option influences how values of the
    SSL_{CLIENT,SERVER}_{I,S}_DN variables are formatted. Since
    version 2.3.11, Apache HTTPD uses a RFC 2253 compatible format by
    default. This uses commas as delimiters between the attributes, allows the
    use of non-ASCII characters (which are converted to UTF8), escapes
    various special characters with backslashes, and sorts the attributes
    with the "C" attribute last.

    If LegacyDNStringFormat is set, the old format will be
    used which sorts the "C" attribute first, uses slashes as separators, and
    does not handle non-ASCII and special characters in any consistent way.
    


ExampleSSLOptions +FakeBasicAuth -StrictRequire
<Files ~ "\.(cgi|shtml)$">
    SSLOptions +StdEnvVars -ExportCertData
</Files>




SSLPassPhraseDialog Directive

Description:Type of pass phrase dialog for encrypted private
keys
Syntax:SSLPassPhraseDialog type
Default:SSLPassPhraseDialog builtin
Context:server config
Status:Extension
Module:mod_ssl


When Apache starts up it has to read the various Certificate (see
SSLCertificateFile) and
Private Key (see SSLCertificateKeyFile) files of the
SSL-enabled virtual servers. Because for security reasons the Private
Key files are usually encrypted, mod_ssl needs to query the
administrator for a Pass Phrase in order to decrypt those files. This
query can be done in two ways which can be configured by
type:

builtin
    
    This is the default where an interactive terminal dialog occurs at startup
    time just before Apache detaches from the terminal. Here the administrator
    has to manually enter the Pass Phrase for each encrypted Private Key file.
    Because a lot of SSL-enabled virtual hosts can be configured, the
    following reuse-scheme is used to minimize the dialog: When a Private Key
    file is encrypted, all known Pass Phrases (at the beginning there are
    none, of course) are tried. If one of those known Pass Phrases succeeds no
    dialog pops up for this particular Private Key file. If none succeeded,
    another Pass Phrase is queried on the terminal and remembered for the next
    round (where it perhaps can be reused).
    
    This scheme allows mod_ssl to be maximally flexible (because for N encrypted
    Private Key files you can use N different Pass Phrases - but then
    you have to enter all of them, of course) while minimizing the terminal
    dialog (i.e. when you use a single Pass Phrase for all N Private Key files
    this Pass Phrase is queried only once).

|/path/to/program [args...]

   This mode allows an external program to be used which acts as a
   pipe to a particular input device; the program is sent the standard
   prompt text used for the builtin mode on
   stdin, and is expected to write password strings on
   stdout.  If several passwords are needed (or an
   incorrect password is entered), additional prompt text will be
   written subsequent to the first password being returned, and more
   passwords must then be written back.

exec:/path/to/program
    
    Here an external program is configured which is called at startup for each
    encrypted Private Key file. It is called with two arguments (the first is
    of the form ``servername:portnumber'', the second is either
    ``RSA'', ``DSA'', ``ECC'' or an
    integer index starting at 3 if more than three keys are configured), which
    indicate for which server and algorithm it has to print the corresponding
    Pass Phrase to stdout. In versions 2.4.8 (unreleased)
    and 2.4.9, it is called with one argument, a string of the
    form ``servername:portnumber:index'' (with index
    being a zero-based integer number), which indicate the server, TCP port
    and certificate number.  The intent is that this external
    program first runs security checks to make sure that the system is not
    compromised by an attacker, and only when these checks were passed
    successfully it provides the Pass Phrase.
    
    Both these security checks, and the way the Pass Phrase is determined, can
    be as complex as you like. Mod_ssl just defines the interface: an
    executable program which provides the Pass Phrase on stdout.
    Nothing more or less! So, if you're really paranoid about security, here
    is your interface. Anything else has to be left as an exercise to the
    administrator, because local security requirements are so different.
    
    The reuse-algorithm above is used here, too. In other words: The external
    program is called only once per unique Pass Phrase.

ExampleSSLPassPhraseDialog "exec:/usr/local/apache/sbin/pp-filter"




SSLProtocol Directive

Description:Configure usable SSL/TLS protocol versions
Syntax:SSLProtocol [+|-]protocol ...
Default:SSLProtocol all -SSLv3 (up to 2.4.16: all)
Context:server config, virtual host
Status:Extension
Module:mod_ssl


This directive can be used to control which versions of the SSL/TLS protocol
will be accepted in new connections.

The available (case-insensitive) protocols are:

SSLv3
    
    This is the Secure Sockets Layer (SSL) protocol, version 3.0, from
    the Netscape Corporation.
    It is the successor to SSLv2 and the predecessor to TLSv1, but is
    deprecated in RFC 7568.

TLSv1
    
    This is the Transport Layer Security (TLS) protocol, version 1.0.
    It is the successor to SSLv3 and is defined in
    RFC 2246.
    It is supported by nearly every client.

TLSv1.1 (when using OpenSSL 1.0.1 and later)
    
    A revision of the TLS 1.0 protocol, as defined in
    RFC 4346.

TLSv1.2 (when using OpenSSL 1.0.1 and later)
    
    A revision of the TLS 1.1 protocol, as defined in
    RFC 5246.

all
    
    This is a shortcut for ``+SSLv3 +TLSv1'' or
    - when using OpenSSL 1.0.1 and later -
    ``+SSLv3 +TLSv1 +TLSv1.1 +TLSv1.2'', respectively
    (except for OpenSSL versions compiled with the ``no-ssl3'' configuration
    option, where all does not include +SSLv3).

ExampleSSLProtocol TLSv1




SSLProxyCACertificateFile Directive

Description:File of concatenated PEM-encoded CA Certificates
for Remote Server Auth
Syntax:SSLProxyCACertificateFile file-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl


This directive sets the all-in-one file where you can assemble the
Certificates of Certification Authorities (CA) whose remote servers you deal
with. These are used for Remote Server Authentication. Such a file is simply the
concatenation of the various PEM-encoded Certificate files, in order of
preference. This can be used alternatively and/or additionally to
SSLProxyCACertificatePath.
ExampleSSLProxyCACertificateFile "/usr/local/apache2/conf/ssl.crt/ca-bundle-remote-server.crt"




SSLProxyCACertificatePath Directive

Description:Directory of PEM-encoded CA Certificates for
Remote Server Auth
Syntax:SSLProxyCACertificatePath directory-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl


This directive sets the directory where you keep the Certificates of
Certification Authorities (CAs) whose remote servers you deal with. These are used to
verify the remote server certificate on Remote Server Authentication.

The files in this directory have to be PEM-encoded and are accessed through
hash filenames. So usually you can't just place the Certificate files
there: you also have to create symbolic links named
hash-value.N. And you should always make sure this directory
contains the appropriate symbolic links.
ExampleSSLProxyCACertificatePath "/usr/local/apache2/conf/ssl.crt/"




SSLProxyCARevocationCheck Directive

Description:Enable CRL-based revocation checking for Remote Server Auth
Syntax:SSLProxyCARevocationCheck chain|leaf|none
Default:SSLProxyCARevocationCheck none
Context:server config, virtual host
Status:Extension
Module:mod_ssl


Enables certificate revocation list (CRL) checking for the
remote servers you deal with. At least one of
SSLProxyCARevocationFile
or SSLProxyCARevocationPath must be
configured. When set to chain (recommended setting),
CRL checks are applied to all certificates in the chain, while setting it to
leaf limits the checks to the end-entity cert.


When set to chain or leaf,
CRLs must be available for successful validation

Prior to version 2.3.15, CRL checking in mod_ssl also succeeded when
no CRL(s) were found in any of the locations configured with
SSLProxyCARevocationFile
or SSLProxyCARevocationPath.
With the introduction of this directive, the behavior has been changed:
when checking is enabled, CRLs must be present for the validation
to succeed - otherwise it will fail with an
"unable to get certificate CRL" error.


ExampleSSLProxyCARevocationCheck chain




SSLProxyCARevocationFile Directive

Description:File of concatenated PEM-encoded CA CRLs for
Remote Server Auth
Syntax:SSLProxyCARevocationFile file-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl


This directive sets the all-in-one file where you can
assemble the Certificate Revocation Lists (CRL) of Certification
Authorities (CA) whose remote servers you deal with. These are used
for Remote Server Authentication.  Such a file is simply the concatenation of
the various PEM-encoded CRL files, in order of preference. This can be
used alternatively and/or additionally to SSLProxyCARevocationPath.
ExampleSSLProxyCARevocationFile "/usr/local/apache2/conf/ssl.crl/ca-bundle-remote-server.crl"




SSLProxyCARevocationPath Directive

Description:Directory of PEM-encoded CA CRLs for
Remote Server Auth
Syntax:SSLProxyCARevocationPath directory-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl


This directive sets the directory where you keep the Certificate Revocation
Lists (CRL) of Certification Authorities (CAs) whose remote servers you deal with.
These are used to revoke the remote server certificate on Remote Server Authentication.

The files in this directory have to be PEM-encoded and are accessed through
hash filenames. So usually you have not only to place the CRL files there.
Additionally you have to create symbolic links named
hash-value.rN. And you should always make sure this directory
contains the appropriate symbolic links.
ExampleSSLProxyCARevocationPath "/usr/local/apache2/conf/ssl.crl/"




SSLProxyCheckPeerCN Directive

Description:Whether to check the remote server certificate's CN field

Syntax:SSLProxyCheckPeerCN on|off
Default:SSLProxyCheckPeerCN on
Context:server config, virtual host
Status:Extension
Module:mod_ssl


This directive sets whether the remote server certificate's CN field is
compared against the hostname of the request URL. If both are not equal
a 502 status code (Bad Gateway) is sent. SSLProxyCheckPeerCN is
superseded by SSLProxyCheckPeerName
in release 2.4.5 and later. 


In all releases 2.4.5 through 2.4.20, setting
SSLProxyCheckPeerName off was sufficient to enable this behavior
(as the SSLProxyCheckPeerCN default was on.) In 
these releases, both directives must be set to off to completely
avoid remote server certificate name validation. Many users reported this
to be very confusing.


As of release 2.4.21, all configurations which enable either one of the
SSLProxyCheckPeerName or SSLProxyCheckPeerCN options
will use the new SSLProxyCheckPeerName
behavior, and all configurations which disable either one of the 
SSLProxyCheckPeerName or SSLProxyCheckPeerCN options
will supress all remote server certificate name validation. Only the following
configuration will trigger the legacy certificate CN comparison in 2.4.21 and
later releases;

ExampleSSLProxyCheckPeerCN on
SSLProxyCheckPeerName off




SSLProxyCheckPeerExpire Directive

Description:Whether to check if remote server certificate is expired

Syntax:SSLProxyCheckPeerExpire on|off
Default:SSLProxyCheckPeerExpire on
Context:server config, virtual host
Status:Extension
Module:mod_ssl


This directive sets whether it is checked if the remote server certificate
is expired or not. If the check fails a 502 status code (Bad Gateway) is
sent.

ExampleSSLProxyCheckPeerExpire on




SSLProxyCheckPeerName Directive

Description:Configure host name checking for remote server certificates

Syntax:SSLProxyCheckPeerName on|off
Default:SSLProxyCheckPeerName on
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Apache HTTP Server 2.4.5 and later


This directive configures host name checking for server certificates when 
mod_ssl is acting as an SSL client. The check will succeed if the host name 
from the request URI matches one of the CN attribute(s) of the certificate's 
subject, or matches the subjectAltName extension. If the check fails, the SSL 
request is aborted and a 502 status code (Bad Gateway) is returned.


Wildcard matching is supported for specific cases: an subjectAltName entry
of type dNSName, or CN attributes starting with *. will match
with any host name of the same number of name elements and the same suffix.
E.g. *.example.org will match foo.example.org,
but will not match foo.bar.example.org, because the number of
elements in the respective host names differs.


This feature was introduced in 2.4.5 and superseded the behavior of the 
SSLProxyCheckPeerCN directive, which 
only tested the exact value in the first CN attribute against the host name.
However, many users were confused by the behavior of using these directives
individually, so the mutual behavior of SSLProxyCheckPeerName 
and SSLProxyCheckPeerCN directives were improved in release 
2.4.21. See the SSLProxyCheckPeerCN 
directive description for the original behavior and details of these 
improvements.




SSLProxyCipherSuite Directive

Description:Cipher Suite available for negotiation in SSL
proxy handshake
Syntax:SSLProxyCipherSuite cipher-spec
Default:SSLProxyCipherSuite ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+EXP
Context:server config, virtual host, directory, .htaccess
Override:AuthConfig
Status:Extension
Module:mod_ssl

Equivalent to SSLCipherSuite, but
for the proxy connection.
Please refer to SSLCipherSuite
for additional information.



SSLProxyEngine Directive

Description:SSL Proxy Engine Operation Switch
Syntax:SSLProxyEngine on|off
Default:SSLProxyEngine off
Context:server config, virtual host
Status:Extension
Module:mod_ssl


This directive toggles the usage of the SSL/TLS Protocol Engine for proxy. This
is usually used inside a <VirtualHost> section to enable SSL/TLS for proxy
usage in a particular virtual host. By default the SSL/TLS Protocol Engine is
disabled for proxy both for the main server and all configured virtual hosts.

Note that the SSLProxyEngine directive should not, in
general, be included in a virtual host that will be acting as a
forward proxy (using <Proxy>
or ProxyRequests directives).
SSLProxyEngine is not required to enable a forward proxy
server to proxy SSL/TLS requests.

Example<VirtualHost _default_:443>
    SSLProxyEngine on
    #...
</VirtualHost>




SSLProxyMachineCertificateChainFile Directive

Description:File of concatenated PEM-encoded CA certificates to be used by the proxy for choosing a certificate
Syntax:SSLProxyMachineCertificateChainFile filename
Context:server config
Override:Not applicable
Status:Extension
Module:mod_ssl


This directive sets the all-in-one file where you keep the certificate chain
for all of the client certs in use. This directive will be needed if the
remote server presents a list of CA certificates that are not direct signers
of one of the configured client certificates.


This referenced file is simply the concatenation of the various PEM-encoded
certificate files. Upon startup, each client certificate configured will
be examined and a chain of trust will be constructed.

Security warning
If this directive is enabled, all of the certificates in the file will be
trusted as if they were also in 
SSLProxyCACertificateFile.

ExampleSSLProxyMachineCertificateChainFile "/usr/local/apache2/conf/ssl.crt/proxyCA.pem"




SSLProxyMachineCertificateFile Directive

Description:File of concatenated PEM-encoded client certificates and keys to be used by the proxy
Syntax:SSLProxyMachineCertificateFile filename
Context:server config
Override:Not applicable
Status:Extension
Module:mod_ssl


This directive sets the all-in-one file where you keep the certificates and
keys used for authentication of the proxy server to remote servers.


This referenced file is simply the concatenation of the various PEM-encoded
certificate files, in order of preference. Use this directive alternatively
or additionally to SSLProxyMachineCertificatePath.


Currently there is no support for encrypted private keys

ExampleSSLProxyMachineCertificateFile "/usr/local/apache2/conf/ssl.crt/proxy.pem"




SSLProxyMachineCertificatePath Directive

Description:Directory of PEM-encoded client certificates and keys to be used by the proxy
Syntax:SSLProxyMachineCertificatePath directory
Context:server config
Override:Not applicable
Status:Extension
Module:mod_ssl


This directive sets the directory where you keep the certificates and
keys used for authentication of the proxy server to remote servers.

The files in this directory must be PEM-encoded and are accessed through
hash filenames. Additionally, you must create symbolic links named
hash-value.N. And you should always make sure this
directory contains the appropriate symbolic links.

Currently there is no support for encrypted private keys

ExampleSSLProxyMachineCertificatePath "/usr/local/apache2/conf/proxy.crt/"




SSLProxyProtocol Directive

Description:Configure usable SSL protocol flavors for proxy usage
Syntax:SSLProxyProtocol [+|-]protocol ...
Default:SSLProxyProtocol all -SSLv3 (up to 2.4.16: all)
Context:server config, virtual host
Override:Options
Status:Extension
Module:mod_ssl



This directive can be used to control the SSL protocol flavors mod_ssl should
use when establishing its server environment for proxy . It will only connect
to servers using one of the provided protocols.
Please refer to SSLProtocol
for additional information.




SSLProxyVerify Directive

Description:Type of remote server Certificate verification
Syntax:SSLProxyVerify level
Default:SSLProxyVerify none
Context:server config, virtual host
Status:Extension
Module:mod_ssl


When a proxy is configured to forward requests to a remote SSL
server, this directive can be used to configure certificate
verification of the remote server. 

The following levels are available for level:

none:
     no remote server Certificate is required at all
optional:
     the remote server may present a valid Certificate
require:
     the remote server has to present a valid Certificate
optional_no_ca:
     the remote server may present a valid Certificate
     but it need not to be (successfully) verifiable.

In practice only levels none and
require are really interesting, because level
optional doesn't work with all servers and level
optional_no_ca is actually against the idea of
authentication (but can be used to establish SSL test pages, etc.)
ExampleSSLProxyVerify require




SSLProxyVerifyDepth Directive

Description:Maximum depth of CA Certificates in Remote Server
Certificate verification
Syntax:SSLProxyVerifyDepth number
Default:SSLProxyVerifyDepth 1
Context:server config, virtual host
Status:Extension
Module:mod_ssl


This directive sets how deeply mod_ssl should verify before deciding that the
remote server does not have a valid certificate. 

The depth actually is the maximum number of intermediate certificate issuers,
i.e. the number of CA certificates which are max allowed to be followed while
verifying the remote server certificate. A depth of 0 means that self-signed
remote server certificates are accepted only, the default depth of 1 means
the remote server certificate can be self-signed or has to be signed by a CA
which is directly known to the server (i.e. the CA's certificate is under
SSLProxyCACertificatePath), etc.
ExampleSSLProxyVerifyDepth 10




SSLRandomSeed Directive

Description:Pseudo Random Number Generator (PRNG) seeding
source
Syntax:SSLRandomSeed context source
[bytes]
Context:server config
Status:Extension
Module:mod_ssl


This configures one or more sources for seeding the Pseudo Random Number
Generator (PRNG) in OpenSSL at startup time (context is
startup) and/or just before a new SSL connection is established
(context is connect). This directive can only be used
in the global server context because the PRNG is a global facility.

The following source variants are available:

builtin
     This is the always available builtin seeding source. Its usage
    consumes minimum CPU cycles under runtime and hence can be always used
    without drawbacks. The source used for seeding the PRNG contains of the
    current time, the current process id and (when applicable) a randomly
    chosen 1KB extract of the inter-process scoreboard structure of Apache.
    The drawback is that this is not really a strong source and at startup
    time (where the scoreboard is still not available) this source just
    produces a few bytes of entropy. So you should always, at least for the
    startup, use an additional seeding source.
file:/path/to/source
    
    This variant uses an external file /path/to/source as the
    source for seeding the PRNG. When bytes is specified, only the
    first bytes number of bytes of the file form the entropy (and
    bytes is given to /path/to/source as the first
    argument). When bytes is not specified the whole file forms the
    entropy (and 0 is given to /path/to/source as
    the first argument). Use this especially at startup time, for instance
    with an available /dev/random and/or
    /dev/urandom devices (which usually exist on modern Unix
    derivatives like FreeBSD and Linux).
    
    But be careful: Usually /dev/random provides only as
    much entropy data as it actually has, i.e. when you request 512 bytes of
    entropy, but the device currently has only 100 bytes available two things
    can happen: On some platforms you receive only the 100 bytes while on
    other platforms the read blocks until enough bytes are available (which
    can take a long time). Here using an existing /dev/urandom is
    better, because it never blocks and actually gives the amount of requested
    data. The drawback is just that the quality of the received data may not
    be the best.

exec:/path/to/program
    
    This variant uses an external executable
    /path/to/program as the source for seeding the
    PRNG. When bytes is specified, only the first
    bytes number of bytes of its stdout contents
    form the entropy. When bytes is not specified, the
    entirety of the data produced on stdout form the
    entropy. Use this only at startup time when you need a very strong
    seeding with the help of an external program (for instance as in
    the example above with the truerand utility you can
    find in the mod_ssl distribution which is based on the AT&T
    truerand library). Using this in the connection context
    slows down the server too dramatically, of course.  So usually you
    should avoid using external programs in that context.
egd:/path/to/egd-socket (Unix only)
    
    This variant uses the Unix domain socket of the
    external Entropy Gathering Daemon (EGD) (see http://www.lothar.com/tech
    /crypto/) to seed the PRNG. Use this if no random device exists
    on your platform.

ExampleSSLRandomSeed startup builtin
SSLRandomSeed startup "file:/dev/random"
SSLRandomSeed startup "file:/dev/urandom" 1024
SSLRandomSeed startup "exec:/usr/local/bin/truerand" 16
SSLRandomSeed connect builtin
SSLRandomSeed connect "file:/dev/random"
SSLRandomSeed connect "file:/dev/urandom" 1024




SSLRenegBufferSize Directive

Description:Set the size for the SSL renegotiation buffer
Syntax:SSLRenegBufferSize bytes
Default:SSLRenegBufferSize 131072
Context:directory, .htaccess
Override:AuthConfig
Status:Extension
Module:mod_ssl


If an SSL renegotiation is required in per-location context, for
example, any use of SSLVerifyClient in a Directory or
Location block, then mod_ssl must buffer any HTTP
request body into memory until the new SSL handshake can be performed.
This directive can be used to set the amount of memory that will be
used for this buffer. 


Note that in many configurations, the client sending the request body
will be untrusted so a denial of service attack by consumption of
memory must be considered when changing this configuration setting.


ExampleSSLRenegBufferSize 262144




SSLRequire Directive

Description:Allow access only when an arbitrarily complex
boolean expression is true
Syntax:SSLRequire expression
Context:directory, .htaccess
Override:AuthConfig
Status:Extension
Module:mod_ssl


SSLRequire is deprecated
SSLRequire is deprecated and should in general be replaced
by Require expr. The so called
ap_expr syntax of Require expr is
a superset of the syntax of SSLRequire, with the following
exception:

In SSLRequire, the comparison operators <,
<=, ... are completely equivalent to the operators
lt, le, ... and work in a somewhat peculiar way that
first compares the length of two strings and then the lexical order.
On the other hand, ap_expr has two sets of
comparison operators: The operators <,
<=, ... do lexical string comparison, while the operators
-lt, -le, ... do integer comparison.
For the latter, there are also aliases without the leading dashes:
lt, le, ...





This directive specifies a general access requirement which has to be
fulfilled in order to allow access. It is a very powerful directive because the
requirement specification is an arbitrarily complex boolean expression
containing any number of access checks.

The expression must match the following syntax (given as a BNF
grammar notation):

expr     ::= "true" | "false"
           | "!" expr
           | expr "&&" expr
           | expr "||" expr
           | "(" expr ")"
           | comp

comp     ::= word "==" word | word "eq" word
           | word "!=" word | word "ne" word
           | word "<"  word | word "lt" word
           | word "<=" word | word "le" word
           | word ">"  word | word "gt" word
           | word ">=" word | word "ge" word
           | word "in" "{" wordlist "}"
           | word "in" "PeerExtList(" word ")"
           | word "=~" regex
           | word "!~" regex

wordlist ::= word
           | wordlist "," word

word     ::= digit
           | cstring
           | variable
           | function

digit    ::= [0-9]+
cstring  ::= "..."
variable ::= "%{" varname "}"
function ::= funcname "(" funcargs ")"

For varname any of the variables described in Environment Variables can be used.  For
funcname the available functions are listed in
the ap_expr documentation.

The expression is parsed into an internal machine
representation when the configuration is loaded, and then evaluated 
during request processing.  In .htaccess context, the expression is 
both parsed and executed each time the .htaccess file is encountered during 
request processing.

ExampleSSLRequire (    %{SSL_CIPHER} !~ m/^(EXP|NULL)-/                   \
            and %{SSL_CLIENT_S_DN_O} eq "Snake Oil, Ltd."          \
            and %{SSL_CLIENT_S_DN_OU} in {"Staff", "CA", "Dev"}    \
            and %{TIME_WDAY} -ge 1 and %{TIME_WDAY} -le 5          \
            and %{TIME_HOUR} -ge 8 and %{TIME_HOUR} -le 20       ) \
           or %{REMOTE_ADDR} =~ m/^192\.76\.162\.[0-9]+$/


The PeerExtList(object-ID) function expects
to find zero or more instances of the X.509 certificate extension
identified by the given object ID (OID) in the client certificate.
The expression evaluates to true if the left-hand side string matches
exactly against the value of an extension identified with this OID.
(If multiple extensions with the same OID are present, at least one
extension must match).

ExampleSSLRequire "foobar" in PeerExtList("1.2.3.4.5.6")


Notes on the PeerExtList function



The object ID can be specified either as a descriptive
name recognized by the SSL library, such as "nsComment",
or as a numeric OID, such as "1.2.3.4.5.6".

Expressions with types known to the SSL library are rendered to
a string before comparison.  For an extension with a type not
recognized by the SSL library, mod_ssl will parse the value if it is
one of the primitive ASN.1 types UTF8String, IA5String, VisibleString,
or BMPString.  For an extension of one of these types, the string
value will be converted to UTF-8 if necessary, then compared against
the left-hand-side expression.





See also

Environment Variables in Apache HTTP Server,
for additional examples.

Require expr
Generic expression syntax in Apache HTTP Server




SSLRequireSSL Directive

Description:Deny access when SSL is not used for the
HTTP request
Syntax:SSLRequireSSL
Context:directory, .htaccess
Override:AuthConfig
Status:Extension
Module:mod_ssl


This directive forbids access unless HTTP over SSL (i.e. HTTPS) is enabled for
the current connection. This is very handy inside the SSL-enabled virtual
host or directories for defending against configuration errors that expose
stuff that should be protected. When this directive is present all requests
are denied which are not using SSL.
ExampleSSLRequireSSL




SSLSessionCache Directive

Description:Type of the global/inter-process SSL Session
Cache
Syntax:SSLSessionCache type
Default:SSLSessionCache none
Context:server config
Status:Extension
Module:mod_ssl


This configures the storage type of the global/inter-process SSL Session
Cache. This cache is an optional facility which speeds up parallel request
processing. For requests to the same server process (via HTTP keep-alive),
OpenSSL already caches the SSL session information locally. But because modern
clients request inlined images and other data via parallel requests (usually
up to four parallel requests are common) those requests are served by
different pre-forked server processes. Here an inter-process cache
helps to avoid unnecessary session handshakes.

The following five storage types are currently supported:

none

    This disables the global/inter-process Session Cache.  This
    will incur a noticeable speed penalty and may cause problems if
    using certain browsers, particularly if client certificates are
    enabled.  This setting is not recommended.

nonenotnull

    This disables any global/inter-process Session Cache.  However
    it does force OpenSSL to send a non-null session ID to
    accommodate buggy clients that require one.

dbm:/path/to/datafile

    This makes use of a DBM hashfile on the local disk to
    synchronize the local OpenSSL memory caches of the server
    processes. This session cache may suffer reliability issues under
    high load. To use this, ensure that
    mod_socache_dbm is loaded.

shmcb:/path/to/datafile[(size)]

    This makes use of a high-performance cyclic buffer
    (approx. size bytes in size) inside a shared memory
    segment in RAM (established via /path/to/datafile) to
    synchronize the local OpenSSL memory caches of the server
    processes.  This is the recommended session cache. To use this,
    ensure that mod_socache_shmcb is loaded.

dc:UNIX:/path/to/socket

    This makes use of the distcache distributed session
    caching libraries.  The argument should specify the location of
    the server or proxy to be used using the distcache address syntax;
    for example, UNIX:/path/to/socket specifies a UNIX
    domain socket (typically a local dc_client proxy);
    IP:server.example.com:9001 specifies an IP
    address. To use this, ensure that
    mod_socache_dc is loaded.



ExamplesSSLSessionCache "dbm:/usr/local/apache/logs/ssl_gcache_data"
SSLSessionCache "shmcb:/usr/local/apache/logs/ssl_gcache_data(512000)"


The ssl-cache mutex is used to serialize access to
the session cache to prevent corruption.  This mutex can be configured
using the Mutex directive.



SSLSessionCacheTimeout Directive

Description:Number of seconds before an SSL session expires
in the Session Cache
Syntax:SSLSessionCacheTimeout seconds
Default:SSLSessionCacheTimeout 300
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Applies also to RFC 5077 TLS session resumption in Apache 2.4.10 and later


This directive sets the timeout in seconds for the information stored in the
global/inter-process SSL Session Cache, the OpenSSL internal memory cache and
for sessions resumed by TLS session resumption (RFC 5077).
It can be set as low as 15 for testing, but should be set to higher
values like 300 in real life.
ExampleSSLSessionCacheTimeout 600




SSLSessionTicketKeyFile Directive

Description:Persistent encryption/decryption key for TLS session tickets
Syntax:SSLSessionTicketKeyFile file-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in httpd 2.4.0 and later, if using OpenSSL 0.9.8h or later

Optionally configures a secret key for encrypting and decrypting
TLS session tickets, as defined in
RFC 5077.
Primarily suitable for clustered environments where TLS sessions information
should be shared between multiple nodes. For single-instance httpd setups,
it is recommended to not configure a ticket key file, but to
rely on (random) keys generated by mod_ssl at startup, instead.
The ticket key file must contain 48 bytes of random data,
preferrably created from a high-entropy source. On a Unix-based system,
a ticket key file can be created as follows:


dd if=/dev/random of=/path/to/file.tkey bs=1 count=48


Ticket keys should be rotated (replaced) on a frequent basis,
as this is the only way to invalidate an existing session ticket -
OpenSSL currently doesn't allow to specify a limit for ticket lifetimes.
A new ticket key only gets used after restarting the web server.
All existing session tickets become invalid after a restart.


The ticket key file contains sensitive keying material and should
be protected with file permissions similar to those used for
SSLCertificateKeyFile.




SSLSessionTickets Directive

Description:Enable or disable use of TLS session tickets
Syntax:SSLSessionTickets on|off
Default:SSLSessionTickets on
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in httpd 2.4.11 and later, if using OpenSSL 0.9.8f
or later.

This directive allows to enable or disable the use of TLS session tickets
(RFC 5077).

TLS session tickets are enabled by default. Using them without restarting
the web server with an appropriate frequency (e.g. daily) compromises perfect
forward secrecy.




SSLSRPUnknownUserSeed Directive

Description:SRP unknown user seed
Syntax:SSLSRPUnknownUserSeed secret-string
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in httpd 2.4.4 and later, if using OpenSSL 1.0.1 or
later


This directive sets the seed used to fake SRP user parameters for unknown
users, to avoid leaking whether a given user exists. Specify a secret
string. If this directive is not used, then Apache will return the
UNKNOWN_PSK_IDENTITY alert to clients who specify an unknown username.

Example
SSLSRPUnknownUserSeed "secret"




SSLSRPVerifierFile Directive

Description:Path to SRP verifier file
Syntax:SSLSRPVerifierFile file-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in httpd 2.4.4 and later, if using OpenSSL 1.0.1 or
later


This directive enables TLS-SRP and sets the path to the OpenSSL SRP (Secure
Remote Password) verifier file containing TLS-SRP usernames, verifiers, salts,
and group parameters.
Example
SSLSRPVerifierFile "/path/to/file.srpv"


The verifier file can be created with the openssl command line
utility:
Creating the SRP verifier file
openssl srp -srpvfile passwd.srpv -userinfo "some info" -add username

 The value given with the optional -userinfo parameter is
avalable in the SSL_SRP_USERINFO request environment variable.




SSLStaplingCache Directive

Description:Configures the OCSP stapling cache
Syntax:SSLStaplingCache type
Context:server config
Status:Extension
Module:mod_ssl
Compatibility:Available if using OpenSSL 0.9.8h or later

Configures the cache used to store OCSP responses which get included
in the TLS handshake if SSLUseStapling
is enabled. Configuration of a cache is mandatory for OCSP stapling.
With the exception of none and nonenotnull,
the same storage types are supported as with
SSLSessionCache.



SSLStaplingErrorCacheTimeout Directive

Description:Number of seconds before expiring invalid responses in the OCSP stapling cache
Syntax:SSLStaplingErrorCacheTimeout seconds
Default:SSLStaplingErrorCacheTimeout 600
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available if using OpenSSL 0.9.8h or later

Sets the timeout in seconds before invalid responses
in the OCSP stapling cache (configured through SSLStaplingCache) will expire.
To set the cache timeout for valid responses, see
SSLStaplingStandardCacheTimeout.



SSLStaplingFakeTryLater Directive

Description:Synthesize "tryLater" responses for failed OCSP stapling queries
Syntax:SSLStaplingFakeTryLater on|off
Default:SSLStaplingFakeTryLater on
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available if using OpenSSL 0.9.8h or later

When enabled and a query to an OCSP responder for stapling
purposes fails, mod_ssl will synthesize a "tryLater" response for the
client. Only effective if SSLStaplingReturnResponderErrors
is also enabled.



SSLStaplingForceURL Directive

Description:Override the OCSP responder URI specified in the certificate's AIA extension
Syntax:SSLStaplingForceURL uri
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available if using OpenSSL 0.9.8h or later

This directive overrides the URI of an OCSP responder as obtained from
the authorityInfoAccess (AIA) extension of the certificate.
One potential use is when a proxy is used for retrieving OCSP queries.



SSLStaplingResponderTimeout Directive

Description:Timeout for OCSP stapling queries
Syntax:SSLStaplingResponderTimeout seconds
Default:SSLStaplingResponderTimeout 10
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available if using OpenSSL 0.9.8h or later

This option sets the timeout for queries to OCSP responders when
SSLUseStapling is enabled
and mod_ssl is querying a responder for OCSP stapling purposes.



SSLStaplingResponseMaxAge Directive

Description:Maximum allowable age for OCSP stapling responses
Syntax:SSLStaplingResponseMaxAge seconds
Default:SSLStaplingResponseMaxAge -1
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available if using OpenSSL 0.9.8h or later

This option sets the maximum allowable age ("freshness") when
considering OCSP responses for stapling purposes, i.e. when
SSLUseStapling is turned on.
The default value (-1) does not enforce a maximum age,
which means that OCSP responses are considered valid as long as their
nextUpdate field is in the future.



SSLStaplingResponseTimeSkew Directive

Description:Maximum allowable time skew for OCSP stapling response validation
Syntax:SSLStaplingResponseTimeSkew seconds
Default:SSLStaplingResponseTimeSkew 300
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available if using OpenSSL 0.9.8h or later

This option sets the maximum allowable time skew when mod_ssl checks the
thisUpdate and nextUpdate fields of OCSP responses
which get included in the TLS handshake (OCSP stapling). Only applicable
if SSLUseStapling is turned on.



SSLStaplingReturnResponderErrors Directive

Description:Pass stapling related OCSP errors on to client
Syntax:SSLStaplingReturnResponderErrors on|off
Default:SSLStaplingReturnResponderErrors on
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available if using OpenSSL 0.9.8h or later

When enabled, mod_ssl will pass responses from unsuccessful
stapling related OCSP queries (such as responses with an overall status
other than "successful", responses with a certificate status other than
"good", expired responses etc.) on to the client.
If set to off, only responses indicating a certificate status
of "good" will be included in the TLS handshake.



SSLStaplingStandardCacheTimeout Directive

Description:Number of seconds before expiring responses in the OCSP stapling cache
Syntax:SSLStaplingStandardCacheTimeout seconds
Default:SSLStaplingStandardCacheTimeout 3600
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available if using OpenSSL 0.9.8h or later

Sets the timeout in seconds before responses in the OCSP stapling cache
(configured through SSLStaplingCache)
will expire. This directive applies to valid responses, while
SSLStaplingErrorCacheTimeout is
used for controlling the timeout for invalid/unavailable responses.




SSLStrictSNIVHostCheck Directive

Description:Whether to allow non-SNI clients to access a name-based virtual
host.

Syntax:SSLStrictSNIVHostCheck on|off
Default:SSLStrictSNIVHostCheck off
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in Apache 2.2.12 and later


This directive sets whether a non-SNI client is allowed to access a name-based
virtual host. If set to on in the default name-based virtual
host, clients that are SNI unaware will not be allowed to access any
virtual host, belonging to this particular IP / port combination.
If set to on in any other virtual host, SNI unaware clients
are not allowed to access this particular virtual host.



This option is only available if httpd was compiled against an SNI capable
version of OpenSSL.


ExampleSSLStrictSNIVHostCheck on




SSLUserName Directive

Description:Variable name to determine user name
Syntax:SSLUserName varname
Context:server config, directory, .htaccess
Override:AuthConfig
Status:Extension
Module:mod_ssl


This directive sets the "user" field in the Apache request object.
This is used by lower modules to identify the user with a character
string. In particular, this may cause the environment variable
REMOTE_USER to be set.  The varname can be
any of the SSL environment variables.

Note that this directive has no effect if the
FakeBasicAuth option is used (see SSLOptions).

ExampleSSLUserName SSL_CLIENT_S_DN_CN




SSLUseStapling Directive

Description:Enable stapling of OCSP responses in the TLS handshake
Syntax:SSLUseStapling on|off
Default:SSLUseStapling off
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available if using OpenSSL 0.9.8h or later

This option enables OCSP stapling, as defined by the "Certificate
Status Request" TLS extension specified in RFC 6066. If enabled (and
requested by the client), mod_ssl will include an OCSP response
for its own certificate in the TLS handshake. Configuring an
SSLStaplingCache is a
prerequisite for enabling OCSP stapling.

OCSP stapling relieves the client of querying the OCSP responder
on its own, but it should be noted that with the RFC 6066 specification,
the server's CertificateStatus reply may only include an
OCSP response for a single cert. For server certificates with intermediate
CA certificates in their chain (the typical case nowadays),
stapling in its current implementation therefore only partially achieves the
stated goal of "saving roundtrips and resources" - see also
RFC 6961
(TLS Multiple Certificate Status Extension).


When OCSP stapling is enabled, the ssl-stapling mutex is used
to control access to the OCSP stapling cache in order to prevent corruption,
and the sss-stapling-refresh mutex is used to control refreshes
of OCSP responses.  These mutexes can be configured using the
Mutex directive.





SSLVerifyClient Directive

Description:Type of Client Certificate verification
Syntax:SSLVerifyClient level
Default:SSLVerifyClient none
Context:server config, virtual host, directory, .htaccess
Override:AuthConfig
Status:Extension
Module:mod_ssl


This directive sets the Certificate verification level for the Client
Authentication. Notice that this directive can be used both in per-server and
per-directory context. In per-server context it applies to the client
authentication process used in the standard SSL handshake when a connection is
established. In per-directory context it forces a SSL renegotiation with the
reconfigured client verification level after the HTTP request was read but
before the HTTP response is sent.

The following levels are available for level:

none:
     no client Certificate is required at all
optional:
     the client may present a valid Certificate
require:
     the client has to present a valid Certificate
optional_no_ca:
     the client may present a valid Certificate
     but it need not to be (successfully) verifiable. This option
     cannot be relied upon for client authentication.  

ExampleSSLVerifyClient require




SSLVerifyDepth Directive

Description:Maximum depth of CA Certificates in Client
Certificate verification
Syntax:SSLVerifyDepth number
Default:SSLVerifyDepth 1
Context:server config, virtual host, directory, .htaccess
Override:AuthConfig
Status:Extension
Module:mod_ssl


This directive sets how deeply mod_ssl should verify before deciding that the
clients don't have a valid certificate. Notice that this directive can be
used both in per-server and per-directory context. In per-server context it
applies to the client authentication process used in the standard SSL
handshake when a connection is established. In per-directory context it forces
a SSL renegotiation with the reconfigured client verification depth after the
HTTP request was read but before the HTTP response is sent.

The depth actually is the maximum number of intermediate certificate issuers,
i.e. the number of CA certificates which are max allowed to be followed while
verifying the client certificate. A depth of 0 means that self-signed client
certificates are accepted only, the default depth of 1 means the client
certificate can be self-signed or has to be signed by a CA which is directly
known to the server (i.e. the CA's certificate is under
SSLCACertificatePath), etc.
ExampleSSLVerifyDepth 10





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