Apache Module mod_ssl

Summary

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

This module relies onOpenSSLto provide the cryptography engine.

Further details, discussion, and examples are provided in theSSL 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
• SSLOCSPNoverify
• SSLOCSPOverrideResponder
• SSLOCSPProxyURL
• SSLOCSPResponderCertificateFile
• 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 checklist

• httpd changelog
• Known issues
• Report a bug

See also

• Comments

Environment Variables

This module can be configured to provide several items of SSL informationas additional environment variables to the SSI and CGI namespace. Except forHTTPS andSSL_TLS_SNI which are always defined, thisinformation is not provided by default for performance reasons. (SeeSSLOptionsStdEnvVars, below)The generated variablesare listed in the table below. For backward compatibility the information canbe made available under different names, too. Look in theCompatibility chapter for details on thecompatibility variables.

x509 specifies a component of an X.509 DN; one ofC,ST,L,O,OU,CN,T,I,G,S,D,UID,Email. In httpd 2.2.0 andlater,x509 may also include a numeric_nsuffix. If the DN in question contains multiple attributes of thesame name, this suffix is used as a zero-based index to select aparticular attribute. For example, where the server certificatesubject DN included two OU attributes,SSL_SERVER_S_DN_OU_0andSSL_SERVER_S_DN_OU_1 could be used to reference each. Avariable name without a_n suffix is equivalent to thatname with a_0 suffix; the first (or only) attribute.When the environment table is populated usingtheStdEnvVars option oftheSSLOptions directive, thefirst (or only) attribute of any DN is added only under a non-suffixedname; i.e. no_0 suffixed entries are added.

In httpd 2.4.32 and later, an optional_RAW suffix may beadded tox509 in a DN component, to suppress conversion ofthe attribute value to UTF-8. This must be placed after the indexsuffix (if any). For example,SSL_SERVER_S_DN_OU_RAW orSSL_SERVER_S_DN_OU_0_RAW could be used.

The format of the*_DN variables has changed in Apache HTTPD2.3.11. See theLegacyDNStringFormat option forSSLOptions for details.

SSL_CLIENT_V_REMAIN is only available in version 2.1and later.

A number of additional environment variables can also be usedinSSLRequire expressions, or in custom logformats:

HTTP_USER_AGENT        PATH_INFO             AUTH_TYPEHTTP_REFERER           QUERY_STRING          SERVER_SOFTWAREHTTP_COOKIE            REMOTE_HOST           API_VERSIONHTTP_FORWARDED         REMOTE_IDENT          TIME_YEARHTTP_HOST              IS_SUBREQ             TIME_MONHTTP_PROXY_CONNECTION  DOCUMENT_ROOT         TIME_DAYHTTP_ACCEPT            SERVER_ADMIN          TIME_HOURTHE_REQUEST            SERVER_NAME           TIME_MINREQUEST_FILENAME       SERVER_PORT           TIME_SECREQUEST_METHOD         SERVER_PROTOCOL       TIME_WDAYREQUEST_SCHEME         REMOTE_ADDR           TIMEREQUEST_URI            REMOTE_USER

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

ENV:variablename

This will expand to the standard environment variablevariablename.

HTTP:headername

This will expand to the value of the request header with nameheadername.

Custom Log Formats

Whenmod_ssl is built into Apache or at leastloaded (under DSO situation) additional functions exist for theCustom Log Format ofmod_log_config. First there is anadditional ``%{varname}x''eXtension format function which can be used to expand any variablesprovided by any module, especially those provided by mod_ssl which canyou find in the above table.

For backward compatibility there is additionally a special``%{name}c'' cryptography format functionprovided. Information about this function is provided in theCompatibility chapter.

CustomLog "logs/ssl_request_log" "%t %h %{SSL_PROTOCOL}x %{SSL_CIPHER}x \"%r\" %b"

These formats even work without setting theStdEnvVarsoption of theSSLOptionsdirective.

Request Notes

mod_ssl sets "notes" for the request which can beused in logging with the%{name}n formatstring inmod_log_config.

The notes supported are as follows:

ssl-access-forbidden

This note is set to the value1 if access was denied due to anSSLRequire orSSLRequireSSL directive.

ssl-secure-reneg

Ifmod_ssl is built against a version of OpenSSL which supports the secure renegotiation extension, this note is set to the value1 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 value0. Ifmod_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

Whenmod_ssl is built into Apache or at leastloaded (under DSO situation) anyvariablesprovided bymod_ssl can be used in expressionsfor theap_expr Expression Parser.The variables can be referenced using the syntax``%{varname}''. Startingwith version 2.4.18 one can also use themod_rewrite style syntax``%{SSL:varname}'' orthe function style syntax``ssl(varname)''.

Header set X-SSL-PROTOCOL "expr=%{SSL_PROTOCOL}"Header set X-SSL-CIPHER "expr=%{SSL:SSL_CIPHER}"

This feature even works without setting theStdEnvVarsoption of theSSLOptionsdirective.

Authorization providers for use with Require

mod_ssl provides a few authentication providers for use withmod_authz_core'sRequire directive.

Require ssl

Thessl provider denies access if a connection is not encrypted with SSL. This is similar to theSSLRequireSSL directive.

Require ssl

Require ssl-verify-client

Thessl provider allows access if the user is authenticated with a valid client certificate. This is only useful ifSSLVerifyClient 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-clientRequire valid-user

SSLCACertificateFileDirective

This directive sets theall-in-one file where you can assemble theCertificates of Certification Authorities (CA) whoseclients you dealwith. These are used for Client Authentication. Such a file is simply theconcatenation of the various PEM-encoded Certificate files, in order ofpreference. This can be used alternatively and/or additionally toSSLCACertificatePath.

SSLCACertificateFile "/usr/local/apache2/conf/ssl.crt/ca-bundle-client.crt"

SSLCACertificatePathDirective

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

The files in this directory have to be PEM-encoded and are accessed throughhash filenames. So usually you can't just place the Certificate filesthere: you also have to create symbolic links namedhash-value.N. And you should always make sure this directorycontains the appropriate symbolic links.

SSLCACertificatePath "/usr/local/apache2/conf/ssl.crt/"

SSLCADNRequestFileDirective

When a client certificate is requested by mod_ssl, a list ofacceptable Certificate Authority names is sent to the clientin the SSL handshake. These CA names can be used by the client toselect an appropriate client certificate out of those it hasavailable.

If neither of the directivesSSLCADNRequestPath orSSLCADNRequestFile are given, then theset of acceptable CA names sent to the client is the names of all theCA certificates given by theSSLCACertificateFile andSSLCACertificatePath directives; in otherwords, the names of the CAs which will actually be used to verify theclient certificate.

In some circumstances, it is useful to be able to send a set ofacceptable CA names which differs from the actual CAs used to verifythe client certificate - for example, if the client certificates aresigned by intermediate CAs. In such cases,SSLCADNRequestPath and/orSSLCADNRequestFile can be used; theacceptable CA names are then taken from the complete set ofcertificates in the directory and/or file specified by this pair ofdirectives.

SSLCADNRequestFile mustspecify anall-in-one file containing a concatenation ofPEM-encoded CA certificates.

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

SSLCADNRequestPathDirective

This optional directive can be used to specify the set ofacceptable CA names which will be sent to the client when aclient certificate is requested. See theSSLCADNRequestFile directive for moredetails.

The files in this directory have to be PEM-encoded and are accessedthrough hash filenames. So usually you can't just place theCertificate files there: you also have to create symbolic links namedhash-value.N. And you should always make surethis directory contains the appropriate symbolic links.

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

SSLCARevocationCheckDirective

Enables certificate revocation list (CRL) checking. At least one ofSSLCARevocationFileorSSLCARevocationPath must beconfigured. When set tochain (recommended setting),CRL checks are applied to all certificates in the chain, while setting it toleaf limits the checks to the end-entity cert.

The availableflags 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 withSSLCARevocationFile orSSLCARevocationPath.

  With the introduction ofSSLCARevocationFile, the behavior has been changed: by default withchain orleaf, CRLsmust be present for the validation to succeed - otherwise it will fail with an"unable to get certificate CRL" error.

  Theflagno_crl_for_cert_ok allows to restore previous behaviour.

SSLCARevocationCheck chain

SSLCARevocationCheck chain no_crl_for_cert_ok

SSLCARevocationFileDirective

This directive sets theall-in-one file where you canassemble the Certificate Revocation Lists (CRL) of CertificationAuthorities (CA) whoseclients you deal with. These are usedfor Client Authentication. Such a file is simply the concatenation ofthe various PEM-encoded CRL files, in order of preference. This can beused alternatively and/or additionally toSSLCARevocationPath.

SSLCARevocationFile "/usr/local/apache2/conf/ssl.crl/ca-bundle-client.crl"

SSLCARevocationPathDirective

This directive sets the directory where you keep the Certificate RevocationLists (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 throughhash filenames. So usually you have not only to place the CRL files there.Additionally you have to create symbolic links namedhash-value.rN. And you should always make sure this directorycontains the appropriate symbolic links.

SSLCARevocationPath "/usr/local/apache2/conf/ssl.crl/"

SSLCertificateChainFileDirective

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

This should be used alternatively and/or additionally toSSLCACertificatePath for explicitlyconstructing the server certificate chain which is sent to the browserin addition to the server certificate. It is especially useful toavoid conflicts with CA certificates when using clientauthentication. Because although placing a CA certificate of theserver certificate chain intoSSLCACertificatePath has the same effectfor the certificate chain construction, it has the side-effect thatclient certificates issued by this same CA certificate are alsoaccepted on client authentication.

But be careful: Providing the certificate chain works only if you are using asingle RSAor DSA based server certificate. If you areusing a coupled RSA+DSA certificate pair, this will work only if actually bothcertificates use thesame certificate chain. Else the browsers will beconfused in this situation.

SSLCertificateChainFile "/usr/local/apache2/conf/ssl.crt/ca.crt"

SSLCertificateFileDirective

This directive points to a file with certificate data in PEM format, or the certificate identifier through a configured cryptographic token.If using a PEM file, at 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 - typicallyRSA, DSA, and ECC. The number of supported algorithms depends on theOpenSSL version being used for mod_ssl: with version 1.0.0 or later,openssl list-public-key-algorithms will output a listof supported algorithms, see also the note below about limitationsof OpenSSL versions prior to 1.0.2 and the ways to work around them.

The files may also include intermediate CA certificates, sorted fromleaf to root. This is supported with version 2.4.8 and later,and obsoletesSSLCertificateChainFile.When running with OpenSSL 1.0.2 or later, this allowsto 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 usingSSLCertificateFile.This is supported in version 2.4.7 or later.Such parameters can be generated using the commandsopenssl dhparam andopenssl ecparam.The parameters can be added as-is to the end of the firstcertificate file. Only the first file can be used for customparameters, as they are applied independently of the authenticationalgorithm type.

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

As an alternative to storing certificates and private keys infiles, a certificate identifier can be used to identify a certificatestored in a token. Currently, onlyPKCS#11 URIs arerecognized as certificate identifiers, and can be used in conjunctionwith the OpenSSLpkcs11 engine or provider. IfSSLCertificateKeyFile is omitted, thecertificate and private key can be loaded through the singleidentifier specified withSSLCertificateFile.

# Example using a PEM-encoded file.SSLCertificateFile "/usr/local/apache2/conf/ssl.crt/server.crt"# Example use of a certificate and private key from a PKCS#11 token:SSLCertificateFile "pkcs11:token=My%20Token%20Name;id=45"

SSLCertificateKeyFileDirective

This directive points to the PEM-encoded private key file for theserver, or the key ID through a configured cryptographic token. If thecontained private key is encrypted, the pass phrase dialog is forcedat startup time.

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

The private key may also be combined with the certificate in the file given bySSLCertificateFile, but this practiceis highly discouraged. If it is used, the certificate files using suchan embedded key must be configured after the certificates using a separatekey file.

As an alternative to storing private keys in files, a keyidentifier can be used to identify a private key stored in atoken. Currently, onlyPKCS#11 URIs are recognized as private keyidentifiers, and can be used in conjunction with the OpenSSLpkcs11 engine or provider.

# To use a private key from a PEM-encoded file:SSLCertificateKeyFile "/usr/local/apache2/conf/ssl.key/server.key"# To use a private key from a PKCS#11 token:SSLCertificateKeyFile "pkcs11:token=My%20Token%20Name;id=45"

SSLCipherSuiteDirective

This complex directive uses a colon-separatedcipher-spec stringconsisting of OpenSSL cipher specifications to configure the Cipher Suite theclient is permitted to negotiate in the SSL handshake phase. The optional protocol specifier can configure the Cipher Suite for a specific SSL version.Possible values include "SSL" for all SSL Protocols up to and including TLSv1.2.

Notice that thisdirective can be used both in per-server and per-directory context. In per-server context it applies to the standard SSL handshake when a connectionis established. In per-directory context it forces a SSL renegotiation with thereconfigured Cipher Suite after the HTTP request was read but before the HTTPresponse is sent.

If the SSL library supports TLSv1.3 (OpenSSL 1.1.1 and later), the protocol specifier "TLSv1.3" can be used to configure the cipher suites for that protocol.Since TLSv1.3 does not offer renegotiations, specifying ciphers for it ina directory context is not allowed.

For a list of TLSv1.3 cipher names, seethe OpenSSLdocumentation.

An SSL cipher specification incipher-spec is composed of 4 majorattributes 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 longersupported. To specify which ciphers to use, one can either specify all theCiphers, one at a time, or use aliases to specify the preference and orderfor the ciphers (seeTable1). The actually available ciphers and aliases depends on the usedopenssl version. Newer openssl versions may include additional ciphers.

Now where this becomes interesting is that these can be put togetherto specify the order and ciphers you wish to use. To speed this upthere are also aliases (SSLv3, TLSv1, EXP, LOW, MEDIUM,HIGH) for certain groups of ciphers. These tags can be joinedtogether with prefixes to form thecipher-spec. Availableprefixes 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 (cannot be added later again)

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 thecorrectcipher-spec string. The defaultcipher-spec stringdepends on the version of the OpenSSL libraries used. Let's suppose it is``RC4-SHA:AES128-SHA:HIGH:MEDIUM:!aNULL:!MD5'' whichmeans the following: PutRC4-SHA andAES128-SHA atthe beginning. We do this, because these ciphers offer a good compromisebetween speed and security. Next, include high and medium security ciphers.Finally, remove all ciphers which do not authenticate, i.e. for SSL theAnonymous Diffie-Hellman ciphers, as well as all ciphers which useMD5 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=SHA1AES128-SHA              SSLv3 Kx=RSA      Au=RSA  Enc=AES(128)  Mac=SHA1DHE-RSA-AES256-SHA      SSLv3 Kx=DH       Au=RSA  Enc=AES(256)  Mac=SHA1...                     ...               ...     ...           ...SEED-SHA                SSLv3 Kx=RSA      Au=RSA  Enc=SEED(128) Mac=SHA1PSK-RC4-SHA             SSLv3 Kx=PSK      Au=PSK  Enc=RC4(128)  Mac=SHA1KRB5-RC4-SHA            SSLv3 Kx=KRB5     Au=KRB5 Enc=RC4(128)  Mac=SHA1

The complete list of particular RSA & DH ciphers for SSL is given inTable 2.

SSLCipherSuite RSA:!EXP:!NULL:+HIGH:+MEDIUM:-LOW

SSLCompressionDirective

This directive allows to enable compression on the SSL level.

SSLCryptoDeviceDirective

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

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

# For a Broadcom accelerator:SSLCryptoDevice ubsec

With OpenSSL 3.0 or later, if no engine is specified but the key or certificateis specified using aPKCS#11 URIsthen it is tried to load the key and certificate from an OpenSSL provider.The OpenSSL provider to use must be defined and configured in the OpenSSL config file,and it must support theSTORE methodforPKCS#11 URIs.

SSLEngineDirective

This directive toggles the usage of the SSL/TLS Protocol Engine. Thisis should be used inside a<VirtualHost> section to enable SSL/TLS for athat virtual host. By default the SSL/TLS Protocol Engine isdisabled for both the main server and all configured virtual hosts.

<VirtualHost _default_:443>SSLEngine on#...</VirtualHost>

SSLFIPSDirective

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

If httpd was compiled against an SSL library which did not supportthe FIPS_mode flag,SSLFIPS on will fail. Refer to theFIPS 140-2 Security Policy document of the SSL provider library forspecific requirements to use mod_ssl in a FIPS 140-2 approved modeof operation; note that mod_ssl itself is not validated, but may bedescribed as using FIPS 140-2 validated cryptographic module, whenall components are assembled and operated under the guidelines imposedby the applicable Security Policy.

SSLHonorCipherOrderDirective

When choosing a cipher during an SSLv3 or TLSv1 handshake, normallythe client's preference is used. If this directive is enabled, theserver's preference will be used instead.

SSLHonorCipherOrder on

SSLInsecureRenegotiationDirective

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-Middleattack(CVE-2009-3555)during a renegotiation. This vulnerability allowed an attacker to"prefix" a chosen plaintext to the HTTP request as seen by the webserver. A protocol extension was developed which fixed thisvulnerability if supported by both client and server.

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

SSLInsecureRenegotiation on

TheSSL_SECURE_RENEG environment variable can be usedfrom an SSI or CGI script to determine whether secure renegotiation issupported for a given SSL connection.

SSLOCSPDefaultResponderDirective

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

SSLOCSPEnableDirective

This option enables OCSP validation of the client certificatechain. If this option is enabled, certificates in the client'scertificate chain will be validated against an OCSP responder afternormal verification (including CRL checks) have taken place. In mode 'leaf', only the client certificate itself will be validated.

The OCSP responder used is either extracted from the certificateitself, or derived by configuration; see theSSLOCSPDefaultResponder andSSLOCSPOverrideResponderdirectives.

SSLVerifyClient onSSLOCSPEnable onSSLOCSPDefaultResponder "http://responder.example.com:8888/responder"SSLOCSPOverrideResponder on

SSLOCSPNoverifyDirective

Skip the OCSP responder certificates verification, mostly useful whentesting an OCSP server.

SSLOCSPOverrideResponderDirective

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

SSLOCSPProxyURLDirective

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

SSLOCSPResponderCertificateFileDirective

This supplies a list of trusted OCSP responder certificates to be usedduring OCSP responder certificate validation. The supplied certificates areimplicitly trusted without any further validation. This is typically usedwhere the OCSP responder certificate is self signed or omitted from the OCSPresponse.

SSLOCSPResponderTimeoutDirective

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

SSLOCSPResponseMaxAgeDirective

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 theirnextUpdate field is in the future.

SSLOCSPResponseTimeSkewDirective

This option sets the maximum allowable time skew for OCSP responses(when checking theirthisUpdate andnextUpdate fields).

SSLOCSPUseRequestNonceDirective

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

SSLOpenSSLConfCmdDirective

This directive exposes OpenSSL'sSSL_CONF API to mod_ssl,allowing a flexible configuration of OpenSSL parameters without the needof implementing additionalmod_ssl directives when newfeatures are added to OpenSSL.

The set of availableSSLOpenSSLConfCmd commandsdepends on the OpenSSL version being used formod_ssl(at least version 1.0.2 is required). For a list of supported commandnames, see the sectionSupported configuration file commands in theSSL_CONF_cmd(3) manual page for OpenSSL.

Some of theSSLOpenSSLConfCmd commands can be usedas an alternative to existing directives (such asSSLCipherSuite orSSLProtocol),though it should be noted that the syntax / allowable values for the parametersmay sometimes differ.

SSLOpenSSLConfCmd Options -SessionTicket,ServerPreferenceSSLOpenSSLConfCmd ECDHParameters brainpoolP256r1SSLOpenSSLConfCmd ServerInfoFile "/usr/local/apache2/conf/server-info.pem"SSLOpenSSLConfCmd Protocol "-ALL, TLSv1.2"SSLOpenSSLConfCmd SignatureAlgorithms RSA+SHA384:ECDSA+SHA256

SSLOptionsDirective

This directive can be used to control various run-time options on aper-directory basis. Normally, if multipleSSLOptionscould apply to a directory, then the most specific one is takencompletely; the options are not merged. However ifall theoptions on theSSLOptions directive are preceded by aplus (+) or minus (-) symbol, the optionsare merged. Any options preceded by a+ are added to theoptions currently in force, and any options preceded by a- are removed from the options currently in force.

The availableoptions 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 andSSL_CLIENT_CERT_CHAIN_n (withn = 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'sopenssl x509 command:openssl x509 -noout -subject -incertificate.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 theAuthBasicFake directive withinmod_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

  Thisforces forbidden access whenSSLRequireSSL orSSLRequire 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 toSSLRequireSSL orSSLRequire is overridden (because that's how the ApacheSatisfy mechanism should work.) But for strict access restriction you can useSSLRequireSSL and/orSSLRequire 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 whereevery per-directory reconfiguration of SSL parameters causes afull 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 theSSL_{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.

  IfLegacyDNStringFormat 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.

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

SSLPassPhraseDialogDirective

When Apache starts up it has to read the various Certificate (seeSSLCertificateFile) andPrivate Key (seeSSLCertificateKeyFile) files of theSSL-enabled virtual servers. Because for security reasons the PrivateKey files are usually encrypted, mod_ssl needs to query theadministrator for a Pass Phrase in order to decrypt those files. Thisquery can be done in two ways which can be configured bytype:

• 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 youcan 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 thebuiltin mode onstdin, and is expected to write password strings onstdout. 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 tostdout. In versions 2.4.8 (unreleased) and 2.4.9, it is called with one argument, a string of the form ``servername:portnumber:index'' (withindex 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 onstdout. 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.

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

SSLProtocolDirective

This directive can be used to control which versions of the SSL/TLS protocolwill 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 inRFC 7568.

• TLSv1

  This is the Transport Layer Security (TLS) protocol, version 1.0. It is the successor to SSLv3 and is defined inRFC 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 inRFC 4346.

• TLSv1.2 (when using OpenSSL 1.0.1 and later)

  A revision of the TLS 1.1 protocol, as defined inRFC 5246.

• TLSv1.3 (when using OpenSSL 1.1.1 and later)

  A new version of the TLS protocol, as defined inRFC 8446.

• 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, whereall does not include+SSLv3).

SSLProtocol TLSv1

SSLProxyCACertificateFileDirective

This directive sets theall-in-one file where you can assemble theCertificates of Certification Authorities (CA) whoseremote servers you dealwith. These are used for Remote Server Authentication. Such a file is simply theconcatenation of the various PEM-encoded Certificate files, in order ofpreference. This can be used alternatively and/or additionally toSSLProxyCACertificatePath.

SSLProxyCACertificateFile "/usr/local/apache2/conf/ssl.crt/ca-bundle-remote-server.crt"

SSLProxyCACertificatePathDirective

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

The files in this directory have to be PEM-encoded and are accessed throughhash filenames. So usually you can't just place the Certificate filesthere: you also have to create symbolic links namedhash-value.N. And you should always make sure this directorycontains the appropriate symbolic links.

SSLProxyCACertificatePath "/usr/local/apache2/conf/ssl.crt/"

SSLProxyCARevocationCheckDirective

Enables certificate revocation list (CRL) checking for theremote servers you deal with. At least one ofSSLProxyCARevocationFileorSSLProxyCARevocationPath must beconfigured. When set tochain (recommended setting),CRL checks are applied to all certificates in the chain, while setting it toleaf limits the checks to the end-entity cert.

SSLProxyCARevocationCheck chain

SSLProxyCARevocationFileDirective

This directive sets theall-in-one file where you canassemble the Certificate Revocation Lists (CRL) of CertificationAuthorities (CA) whoseremote servers you deal with. These are usedfor Remote Server Authentication. Such a file is simply the concatenation ofthe various PEM-encoded CRL files, in order of preference. This can beused alternatively and/or additionally toSSLProxyCARevocationPath.

SSLProxyCARevocationFile "/usr/local/apache2/conf/ssl.crl/ca-bundle-remote-server.crl"

SSLProxyCARevocationPathDirective

This directive sets the directory where you keep the Certificate RevocationLists (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 throughhash filenames. So usually you have not only to place the CRL files there.Additionally you have to create symbolic links namedhash-value.rN. And you should always make sure this directorycontains the appropriate symbolic links.

SSLProxyCARevocationPath "/usr/local/apache2/conf/ssl.crl/"

SSLProxyCheckPeerCNDirective

This directive sets whether the remote server certificate's CN field iscompared against the hostname of the request URL. If both are not equala 502 status code (Bad Gateway) is sent.SSLProxyCheckPeerCN issuperseded bySSLProxyCheckPeerNamein release 2.4.5 and later.

In all releases 2.4.5 through 2.4.20, settingSSLProxyCheckPeerName off was sufficient to enable this behavior(as theSSLProxyCheckPeerCN default wason.) In these releases, both directives must be set tooff to completelyavoid remote server certificate name validation. Many users reported thisto be very confusing.

As of release 2.4.21, all configurations which enable either one of theSSLProxyCheckPeerName orSSLProxyCheckPeerCN optionswill use the newSSLProxyCheckPeerNamebehavior, and all configurations which disable either one of theSSLProxyCheckPeerName orSSLProxyCheckPeerCN optionswill suppress all remote server certificate name validation. Only the followingconfiguration will trigger the legacy certificate CN comparison in 2.4.21 andlater releases;

SSLProxyCheckPeerCN onSSLProxyCheckPeerName off

SSLProxyCheckPeerExpireDirective

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

SSLProxyCheckPeerExpire on

SSLProxyCheckPeerNameDirective

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 entryof type dNSName, or CN attributes starting with*. will matchwith any host name of the same number of name elements and the same suffix.E.g.*.example.org will matchfoo.example.org,but will not matchfoo.bar.example.org, because the number ofelements in the respective host names differs.

This feature was introduced in 2.4.5 and superseded the behavior of theSSLProxyCheckPeerCN 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 directivesindividually, so the mutual behavior ofSSLProxyCheckPeerName andSSLProxyCheckPeerCN directives were improved in release 2.4.21. See theSSLProxyCheckPeerCN directive description for the original behavior and details of these improvements.

SSLProxyCipherSuiteDirective

Equivalent toSSLCipherSuite, butfor the proxy connection.Please refer toSSLCipherSuitefor additional information.

SSLProxyEngineDirective

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

Note that theSSLProxyEngine directive should not, ingeneral, be included in a virtual host that will be acting as aforward proxy (using<Proxy>orProxyRequests directives).SSLProxyEngine is not required to enable a forward proxyserver to proxy SSL/TLS requests.

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

SSLProxyMachineCertificateChainFileDirective

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

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

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

SSLProxyMachineCertificateFileDirective

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

This referenced file is simply the concatenation of the variousPEM-encoded certificate files. Use this directive alternatively oradditionally toSSLProxyMachineCertificatePath. The referenced file can contain any number of pairs of clientcertificate and associated private key. Each pair can be specified ineither (certificate, key) or (key, certificate) order. Non-leaf (CA) certificates canalso be included in the file, and are treated as if configured withSSLProxyMachineCertificateChainFile.

When challenged to provide a client certificate by a remote server,the server should provide a list ofacceptable certificateauthority names in the challenge. If such a list isnotprovided,mod_ssl will use the first configuredclient cert/key. If a list of CA namesis provided,mod_ssl will iterate through that list, and attemptto find a configured client cert which was issued either directly bythat CA, or indirectly via any number of intermediary CA certificates.The chain of intermediate CA certificates can be built from thoseincluded in the file, or configured withSSLProxyMachineCertificateChainFile. Thefirst configured matching certificate will then be supplied inresponse to the challenge.

If the list of CA namesis provided by the remote server,andno matching client certificate can be found, no clientcertificate will be provided bymod_ssl, which willlikely fail the SSL/TLS handshake (depending on the remote serverconfiguration).

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

SSLProxyMachineCertificatePathDirective

This directive sets the directory where you keep the clientcertificates and keys used for authentication of the proxy server toremote servers.

mod_ssl will attempt to load every file inside the specified directoryas if it was configured individually withSSLProxyMachineCertificateFile.

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

SSLProxyProtocolDirective

This directive can be used to control the SSL protocol flavors mod_ssl shoulduse when establishing its server environment for proxy . It will only connectto servers using one of the provided protocols.

Please refer toSSLProtocolfor additional information.

SSLProxyVerifyDirective

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

The following levels are available forlevel:

• none: no remote server Certificate is required at all
• optional: the remote servermay present a valid Certificate
• require: the remote serverhas 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 levelsnone andrequire are really interesting, because leveloptional doesn't work with all servers and leveloptional_no_ca is actually against the idea ofauthentication (but can be used to establish SSL test pages, etc.)

SSLProxyVerify require

SSLProxyVerifyDepthDirective

This directive sets how deeply mod_ssl should verify before deciding that theremote 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 whileverifying the remote server certificate. A depth of 0 means that self-signedremote server certificates are accepted only, the default depth of 1 meansthe remote server certificate can be self-signed or has to be signed by a CAwhich is directly known to the server (i.e. the CA's certificate is underSSLProxyCACertificatePath), etc.

SSLProxyVerifyDepth 10

SSLRandomSeedDirective

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

The followingsource 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 a randomly chosen 128 bytes extract of the stack. 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. Whenbytes is specified, only the firstbytes number of bytes of the file form the entropy (andbytes is given to/path/to/source as the first argument). Whenbytes is not specified the whole file forms the entropy (and0 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. Whenbytes is specified, only the firstbytes number of bytes of itsstdout contents form the entropy. Whenbytes is not specified, the entirety of the data produced onstdout 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 thetruerand utility you can find in the mod_ssl distribution which is based on the AT&Ttruerand 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) (seehttp://www.lothar.com/tech /crypto/) to seed the PRNG. Use this if no random device exists on your platform.

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

SSLRenegBufferSizeDirective

If an SSL renegotiation is required in per-location context, forexample, any use ofSSLVerifyClient in a Directory orLocation block, thenmod_ssl must buffer any HTTPrequest body into memory until the new SSL handshake can be performed.This directive can be used to set the amount of memory that will beused for this buffer.

SSLRenegBufferSize 262144

SSLRequireDirective

This directive specifies a general access requirement which has to befulfilled in order to allow access. It is a very powerful directive because therequirement specification is an arbitrarily complex boolean expressioncontaining any number of access checks.

Theexpression must match the following syntax (given as a BNFgrammar notation):

expr     ::= "true" | "false"           | "!" expr           | expr "&&" expr           | expr "||" expr           | "(" expr ")"           | compcomp     ::= 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 "!~" regexwordlist ::= word           | wordlist "," wordword     ::= digit           | cstring           | variable           | functiondigit    ::= [0-9]+cstring  ::= "..."variable ::= "%{" varname "}"function ::= funcname "(" funcargs ")"

Forvarname any of the variables described inEnvironment Variables can be used. Forfuncname the available functions are listed intheap_expr documentation.

Theexpression is parsed into an internal machinerepresentation when the configuration is loaded, and then evaluatedduring request processing. In .htaccess context, theexpression isboth parsed and executed each time the .htaccess file is encountered duringrequest processing.

SSLRequire (    %{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]+$/

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

SSLRequire "foobar" in PeerExtList("1.2.3.4.5.6")

See also

• Environment Variables in Apache HTTP Server,for additional examples.
• Require expr
• Generic expression syntax in Apache HTTP Server

SSLRequireSSLDirective

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

SSLRequireSSL

SSLSessionCacheDirective

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

The following five storagetypes 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 thatmod_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 thatmod_socache_shmcb is loaded.

• dc:UNIX:/path/to/socket

  This makes use of thedistcache 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 thatmod_socache_dc is loaded.

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

Thessl-cache mutex is used to serialize access tothe session cache to prevent corruption. This mutex can be configuredusing theMutex directive.

SSLSessionCacheTimeoutDirective

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

SSLSessionCacheTimeout 600

SSLSessionTicketKeyFileDirective

Optionally configures a secret key for encrypting and decryptingTLS session tickets, as defined inRFC 5077.Primarily suitable for clustered environments where TLS sessions informationshould be shared between multiple nodes. For single-instance httpd setups,it is recommended tonot configure a ticket key file, but torely on (random) keys generated by mod_ssl at startup, instead.

The ticket key file must contain 48 bytes of random data,preferably created from a high-entropy source. On a Unix-based system,a ticket key file can be created as follows:

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.

SSLSessionTicketsDirective

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

SSLSRPUnknownUserSeedDirective

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

SSLSRPVerifierFileDirective

This directive enables TLS-SRP and sets the path to the OpenSSL SRP (SecureRemote Password) verifier file containing TLS-SRP usernames, verifiers, salts,and group parameters.

The verifier file can be created with theopenssl command lineutility:

The value given with the optional-userinfo parameter isavailable in theSSL_SRP_USERINFO request environment variable.

SSLStaplingCacheDirective

Configures the cache used to store OCSP responses which get includedin the TLS handshake ifSSLUseStaplingis enabled. Configuration of a cache is mandatory for OCSP stapling.With the exception ofnone andnonenotnull,the same storage types are supported as withSSLSessionCache.

SSLStaplingErrorCacheTimeoutDirective

Sets the timeout in seconds beforeinvalid responsesin the OCSP stapling cache (configured throughSSLStaplingCache) will expire.To set the cache timeout for valid responses, seeSSLStaplingStandardCacheTimeout.

SSLStaplingFakeTryLaterDirective

When enabled and a query to an OCSP responder for staplingpurposes fails, mod_ssl will synthesize a "tryLater" response for theclient. Only effective ifSSLStaplingReturnResponderErrorsis also enabled.

SSLStaplingForceURLDirective

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

SSLStaplingResponderTimeoutDirective

This option sets the timeout for queries to OCSP responders whenSSLUseStapling is enabledand mod_ssl is querying a responder for OCSP stapling purposes.

SSLStaplingResponseMaxAgeDirective

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

SSLStaplingResponseTimeSkewDirective

This option sets the maximum allowable time skew when mod_ssl checks thethisUpdate andnextUpdate fields of OCSP responseswhich get included in the TLS handshake (OCSP stapling). Only applicableifSSLUseStapling is turned on.

SSLStaplingReturnResponderErrorsDirective

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

SSLStaplingStandardCacheTimeoutDirective

Sets the timeout in seconds before responses in the OCSP stapling cache(configured throughSSLStaplingCache)will expire. This directive applies tovalid responses, whileSSLStaplingErrorCacheTimeout isused for controlling the timeout for invalid/unavailable responses.

SSLStrictSNIVHostCheckDirective

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

SSLStrictSNIVHostCheck on

SSLUserNameDirective

This directive sets the "user" field in the Apache request object.This is used by lower modules to identify the user with a characterstring. In particular, this may cause the environment variableREMOTE_USER to be set. Thevarname can beany of theSSL environment variables.

Note that this directive has no effect if theFakeBasicAuth option is used (seeSSLOptions).

SSLUserName SSL_CLIENT_S_DN_CN

SSLUseStaplingDirective

This option enables OCSP stapling, as defined by the "CertificateStatus Request" TLS extension specified in RFC 6066. If enabled (andrequested by the client), mod_ssl will include an OCSP responsefor its own certificate in the TLS handshake. Configuring anSSLStaplingCache is aprerequisite for enabling OCSP stapling.

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

When OCSP stapling is enabled, thessl-stapling mutex is usedto control access to the OCSP stapling cache in order to prevent corruption,and thesss-stapling-refresh mutex is used to control refreshesof OCSP responses. These mutexes can be configured using theMutex directive.

SSLVerifyClientDirective

This directive sets the Certificate verification level for the ClientAuthentication. Notice that this directive can be used both in per-server andper-directory context. In per-server context it applies to the clientauthentication process used in the standard SSL handshake when a connection isestablished. In per-directory context it forces a SSL renegotiation with thereconfigured client verification level after the HTTP request was read butbefore the HTTP response is sent.

The following levels are available forlevel:

• none: no client Certificate is required at all
• optional: the clientmay present a valid Certificate
• require: the clienthas 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.

SSLVerifyClient require

SSLVerifyDepthDirective

This directive sets how deeply mod_ssl should verify before deciding that theclients don't have a valid certificate. Notice that this directive can beused both in per-server and per-directory context. In per-server context itapplies to the client authentication process used in the standard SSLhandshake when a connection is established. In per-directory context it forcesa SSL renegotiation with the reconfigured client verification depth after theHTTP 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 whileverifying the client certificate. A depth of 0 means that self-signed clientcertificates are accepted only, the default depth of 1 means the clientcertificate can be self-signed or has to be signed by a CA which is directlyknown to the server (i.e. the CA's certificate is underSSLCACertificatePath), etc.

SSLVerifyDepth 10