mod_ssl - Apache HTTP Server Version 2.2

Apache HTTP Server Version 2.2

Apache > HTTP Server > Documentation > Version 2.2 > Modules

# Apache Module mod_ssl

Available Languages: en

Description: | Strong cryptography using the Secure Sockets Layer (SSL) and Transport Layer Security (TLS) protocols
Status: | Extension
Module Identifier: | ssl_module
Source File: | mod_ssl.c

### Summary

This module provides SSL v2/v3 and TLS v1 support for the Apache HTTP Server. It was contributed by Ralf S. Engeschall based on his mod_ssl project and originally derived from work by Ben Laurie.

This module relies on OpenSSL to provide the cryptography engine.

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

### Directives

### Topics

- Environment Variables
- Custom Log Formats

- 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 (SSLv2, SSLv3, TLSv1, TLSv1.1, TLSv1.2)
`SSL_SESSION_ID` | string | The hex-encoded SSL session id
`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_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_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_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_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 an index to select a particular attribute. For example, where the server certificate subject DN included two OU fields, `SSL_SERVER_S_DN_OU_0` and `SSL_SERVER_S_DN_OU_1` could be used to reference each.

`SSL_CLIENT_V_REMAIN` is only available in version 2.1 and later.

## 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.

### Example

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

## 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`.

### Example

`SSLCACertificateFile /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.

### Example

`SSLCACertificatePath /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.

### Example

`SSLCADNRequestFile /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.

### Example

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

## 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`.

### Example

`SSLCARevocationFile /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.

### Example

`SSLCARevocationPath /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

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.

### Example

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

## SSLCertificateFile Directive

Description: | Server PEM-encoded X.509 Certificate file
Syntax: | `SSLCertificateFile file-path`
Context: | server config, virtual host
Status: | Extension
Module: | mod_ssl
Compatibility: | ECC support is available in Apache 2.2.26 and later

This directive points to the PEM-encoded Certificate file for the server and optionally also to the corresponding RSA or DSA Private Key file for it (contained in the same file). If the contained Private Key is encrypted the Pass Phrase dialog is forced at startup time. This directive can be used up to three times (referencing different filenames) when both a RSA, a DSA, and an ECC based server certificate is used in parallel.

### Example

`SSLCertificateFile /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
Compatibility: | ECC support is available in Apache 2.2.26 and later

This directive points to the PEM-encoded Private Key file for the server. If the Private Key is not combined with the Certificate in the `SSLCertificateFile`, use this additional directive to point to the file with the stand-alone Private Key. When `SSLCertificateFile` is used and the file contains both the Certificate and the Private Key this directive need not be used. But we strongly discourage this practice. Instead we recommend you to separate the Certificate and the Private Key. If the contained Private Key is encrypted, the Pass Phrase dialog is forced at startup time. This directive can be used up to three times (referencing different filenames) when both a RSA, a DSA, and an ECC based private key is used in parallel.

### Example

`SSLCertificateKeyFile /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 ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP`
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 or Diffie-Hellman variants.
- Authentication Algorithm:
  RSA, Diffie-Hellman, DSS or none.
- Cipher/Encryption Algorithm:
  DES, Triple-DES, RC4, RC2, IDEA or none.
- MAC Digest Algorithm:
  MD5, SHA or SHA1.

An SSL cipher can also be an export cipher and is either a SSLv2 or SSLv3/TLSv1 cipher (here TLSv1 is equivalent to SSLv3). 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).

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)
Authentication Algorithm:
`aNULL` | No authentication
`aRSA` | RSA authentication
`aDSS` | DSS authentication
`aDH` | Diffie-Hellman authentication
Cipher Encoding Algorithm:
`eNULL` | No encoding
`DES` | DES encoding
`3DES` | Triple-DES encoding
`RC4` | RC4 encoding
`RC2` | RC2 encoding
`IDEA` | IDEA encoding
MAC Digest Algorithm:
`MD5` | MD5 hash function
`SHA1` | SHA1 hash function
`SHA` | SHA hash function
Aliases:
`SSLv2` | all SSL version 2.0 ciphers
`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
`ADH` | all ciphers using Anonymous Diffie-Hellman key exchange
`DSS` | all ciphers using DSS authentication
`NULL` | all ciphers using no encryption

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 (`SSLv2, 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)

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 is ```ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP`'' which means the following: first, remove from consideration any ciphers that do not authenticate, i.e. for SSL only the Anonymous Diffie-Hellman ciphers. Next, use ciphers using RC4 and RSA. Next include the high, medium and then the low security ciphers. Finally pull all SSLv2 and export ciphers to the end of the list.

    $ openssl ciphers -v 'ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP'
    NULL-SHA                SSLv3 Kx=RSA      Au=RSA  Enc=None      Mac=SHA1
    NULL-MD5                SSLv3 Kx=RSA      Au=RSA  Enc=None      Mac=MD5
    EDH-RSA-DES-CBC3-SHA    SSLv3 Kx=DH       Au=RSA  Enc=3DES(168) Mac=SHA1
    ...                     ...               ...     ...           ...
    EXP-RC4-MD5             SSLv3 Kx=RSA(512) Au=RSA  Enc=RC4(40)   Mac=MD5  export
    EXP-RC2-CBC-MD5         SSLv2 Kx=RSA(512) Au=RSA  Enc=RC2(40)   Mac=MD5  export
    EXP-RC4-MD5             SSLv2 Kx=RSA(512) Au=RSA  Enc=RC4(40)   Mac=MD5  export

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

### Example

`SSLCipherSuite 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 |
`DES-CBC3-MD5` | SSLv2 | RSA | RSA | 3DES(168) | MD5 |
`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 |
`IDEA-CBC-MD5` | SSLv2 | RSA | RSA | IDEA(128) | MD5 |
`RC2-CBC-MD5` | SSLv2 | RSA | RSA | RC2(128) | MD5 |
`RC4-MD5` | SSLv2 | RSA | RSA | RC4(128) | MD5 |
`DES-CBC-SHA` | SSLv3 | RSA | RSA | DES(56) | SHA1 |
`RC4-64-MD5` | SSLv2 | RSA | RSA | RC4(64) | MD5 |
`DES-CBC-MD5` | SSLv2 | RSA | RSA | DES(56) | MD5 |
`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
`EXP-RC2-CBC-MD5` | SSLv2 | RSA(512) | RSA | RC2(40) | MD5 | export
`EXP-RC4-MD5` | SSLv2 | 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 2.2.24 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 versions 2.2.24 to 2.2.25.

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
Compatibility: | Available in Apache 2.1 and later, if using -engine flavor of OpenSSL 0.9.6, or OpenSSL 0.9.7 or later

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 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 flag`
Context: | server config, virtual host
Status: | Extension
Module: | mod_ssl
Compatibility: | Available in Apache 2.1 and later, if using OpenSSL 0.9.7 or later

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.

### Example

`SSLHonorCipherOrder on`

## SSLInsecureRenegotiation Directive

Description: | Option to enable support for insecure renegotiation
Syntax: | `SSLInsecureRenegotiation flag`
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.

### Example

`SSLInsecureRenegotiation 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.

## SSLMutex Directive

Description: | Semaphore for internal mutual exclusion of operations
Syntax: | `SSLMutex type`
Default: | `SSLMutex none`
Context: | server config
Status: | Extension
Module: | mod_ssl

This configures the SSL engine's semaphore (aka. lock) which is used for mutual exclusion of operations which have to be done in a synchronized way between the pre-forked Apache server processes. This directive can only be used in the global server context because it's only useful to have one global mutex. This directive is designed to closely match the `AcceptMutex` directive.

The following Mutex types are available:

- `none | no`

  This is the default where no Mutex is used at all. Use it at your own risk. But because currently the Mutex is mainly used for synchronizing write access to the SSL Session Cache you can live without it as long as you accept a sometimes garbled Session Cache. So it's not recommended to leave this the default. Instead configure a real Mutex.

- `posixsem`

  This is an elegant Mutex variant where a Posix Semaphore is used when possible. It is only available when the underlying platform and APR supports it.

- `sysvsem`

  This is a somewhat elegant Mutex variant where a SystemV IPC Semaphore is used when possible. It is possible to "leak" SysV semaphores if processes crash before the semaphore is removed. It is only available when the underlying platform and APR supports it.

- `sem`

  This directive tells the SSL Module to pick the "best" semaphore implementation available to it, choosing between Posix and SystemV IPC, in that order. It is only available when the underlying platform and APR supports at least one of the 2.

- `pthread`

  This directive tells the SSL Module to use Posix thread mutexes. It is only available if the underlying platform and APR supports it.

- `fcntl:/path/to/mutex`

  This is a portable Mutex variant where a physical (lock-)file and the `fcntl()` function are used as the Mutex. Always use a local disk filesystem for `/path/to/mutex` and never a file residing on a NFS- or AFS-filesystem. It is only available when the underlying platform and APR supports it. Note: Internally, the Process ID (PID) of the Apache parent process is automatically appended to `/path/to/mutex` to make it unique, so you don't have to worry about conflicts yourself. Notice that this type of mutex is not available under the Win32 environment. There you have to use the semaphore mutex.

- `flock:/path/to/mutex`

  This is similar to the `fcntl:/path/to/mutex` method with the exception that the `flock()` function is used to provide file locking. It is only available when the underlying platform and APR supports it.

- `file:/path/to/mutex`

  This directive tells the SSL Module to pick the "best" file locking implementation available to it, choosing between `fcntl` and `flock`, in that order. It is only available when the underlying platform and APR supports at least one of the 2.

- `default | yes`

  This directive tells the SSL Module to pick the default locking implementation as determined by the platform and APR.

### Example

`SSLMutex file:/usr/local/apache/logs/ssl_mutex`

## 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/`''.

- `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 maybe not what the user expects, so enable this on a per-directory basis only, please.

### Example

`SSLOptions +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`'', or ```ECC`''), which indicate for which server and algorithm it has to print the corresponding Pass Phrase to `stdout`. 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.

### Example

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

## SSLProtocol Directive

Description: | Configure usable SSL protocol flavors
Syntax: | `SSLProtocol [+|-]protocol ...`
Default: | `SSLProtocol 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. Clients then can only connect with one of the provided protocols.

The available (case-insensitive) protocols are:

- `SSLv2`

  This is the Secure Sockets Layer (SSL) protocol, version 2.0. It is the original SSL protocol as designed by Netscape Corporation. Though its use has been deprecated, because of weaknesses in the security of the protocol.

- `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. It's supported by almost all popular browsers.

- `TLSv1`

  This is the Transport Layer Security (TLS) protocol, version 1.0. It is the successor to SSLv3 and is defined in RFC 2246.

- `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 ```+SSLv2 +SSLv3 +TLSv1`'' or - when using OpenSSL 1.0.1 and later - ```+SSLv2 +SSLv3 +TLSv1 +TLSv1.1 +TLSv1.2`'', respectively.

### Example

`# enable SSLv3 and all available TLSv1 flavors, but not SSLv2
SSLProtocol All -SSLv2`

## 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`.

### Example

`SSLProxyCACertificateFile /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.

### Example

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

## 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`.

### Example

`SSLProxyCARevocationFile /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.

### Example

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

## SSLProxyCheckPeerCN Directive

Description: | Whether to check the remote server certificates CN field
Syntax: | `SSLProxyCheckPeerCN on|off`
Default: | `SSLProxyCheckPeerCN off`
Context: | server config, virtual host
Status: | Extension
Module: | mod_ssl

This directive sets whether the remote server certificates CN field is compared against the hostname of the request URL. If both are not equal a 502 status code (Bad Gateway) is sent.

### Example

`SSLProxyCheckPeerCN on`

## SSLProxyCheckPeerExpire Directive

Description: | Whether to check if remote server certificate is expired
Syntax: | `SSLProxyCheckPeerExpire on|off`
Default: | `SSLProxyCheckPeerExpire off`
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.

### Example

`SSLProxyCheckPeerExpire on`

## 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:+SSLv2:+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 <ProxyRequest> 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
Compatibility: | Available in Apache 2.2.23 and later

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`.

### Example

`SSLProxyMachineCertificateChainFile /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

### Example

`SSLProxyMachineCertificateFile /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

### Example

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

## SSLProxyProtocol Directive

Description: | Configure usable SSL protocol flavors for proxy usage
Syntax: | `SSLProxyProtocol [+|-]protocol ...`
Default: | `SSLProxyProtocol 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.

Note that even when certificate verification is enabled, `mod_ssl` does not check whether the `commonName` (hostname) attribute of the server certificate matches the hostname used to connect to the server. In other words, the proxy does not guarantee that the SSL connection to the backend server is "secure" beyond the fact that the certificate is signed by one of the CAs configured using the `SSLProxyCACertificatePath` and/or `SSLProxyCACertificateFile` directives. In order to get this check done please have a look at `SSLProxyCheckPeerCN` and `SSLProxyCheckPeerExpire` directives which are off by default.

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.)

### Example

`SSLProxyVerify 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
Override: | AuthConfig
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.

### Example

`SSLProxyVerifyDepth 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.

  On some platforms like FreeBSD one can even control how the entropy is actually generated, i.e. by which system interrupts. More details one can find under rndcontrol(8) on those platforms. Alternatively, when your system lacks such a random device, you can use a tool like EGD (Entropy Gathering Daemon) and run its client program with the `exec:/path/to/program/` variant (see below) or use `egd:/path/to/egd-socket` (see below).

- `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.

### Example

`SSLRandomSeed 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.

### Example

`SSLRenegBufferSize 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

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 implementation of `SSLRequire` is not thread safe. Using `SSLRequire` inside `.htaccess` files on a threaded MPM may cause random crashes.

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" "OID(" word ")"
>                | word "=~" regex
>                | word "!~" regex

>     wordlist ::= word
>                | wordlist "," word

>     word     ::= digit
>                | cstring
>                | variable
>                | function

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

while for `varname` any variable from Table 3 can be used. Finally for `funcname` the following functions are available:

- `file(`filename`)`

  This function takes one string argument and expands to the contents of the file. This is especially useful for matching this contents against a regular expression, etc.

Notice that expression is first parsed into an internal machine representation and then evaluated in a second step. Actually, in Global and Per-Server Class context expression is parsed at startup time and at runtime only the machine representation is executed. For Per-Directory context, specifically in a .htaccess context, this is different: here expression has to be parsed and immediately executed for every request.

### Example

`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} >= 1 and %{TIME_WDAY} <= 5 \
and %{TIME_HOUR} >= 8 and %{TIME_HOUR} <= 20 ) \
or %{REMOTE_ADDR} =~ m/^192\.76\.162\.[0-9]+$/`

The `OID()` function expects to find zero or more instances of the given OID in the client certificate, and compares the left-hand side string against the value of matching OID attributes. Every matching OID is checked, until a match is found.

Standard CGI/1.0 and Apache variables:

    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
    HTTP:headername        SERVER_NAME           TIME_MIN
    THE_REQUEST            SERVER_PORT           TIME_SEC
    REQUEST_METHOD         SERVER_PROTOCOL       TIME_WDAY
    REQUEST_SCHEME         REMOTE_ADDR           TIME
    REQUEST_URI            REMOTE_USER           ENV:variablename
    REQUEST_FILENAME

SSL-related variables:

    HTTPS                  SSL_CLIENT_M_VERSION   SSL_SERVER_M_VERSION
                           SSL_CLIENT_M_SERIAL    SSL_SERVER_M_SERIAL
    SSL_PROTOCOL           SSL_CLIENT_V_START     SSL_SERVER_V_START
    SSL_SESSION_ID         SSL_CLIENT_V_END       SSL_SERVER_V_END
    SSL_CIPHER             SSL_CLIENT_S_DN        SSL_SERVER_S_DN
    SSL_CIPHER_EXPORT      SSL_CLIENT_S_DN_C      SSL_SERVER_S_DN_C
    SSL_CIPHER_ALGKEYSIZE  SSL_CLIENT_S_DN_ST     SSL_SERVER_S_DN_ST
    SSL_CIPHER_USEKEYSIZE  SSL_CLIENT_S_DN_L      SSL_SERVER_S_DN_L
    SSL_VERSION_LIBRARY    SSL_CLIENT_S_DN_O      SSL_SERVER_S_DN_O
    SSL_VERSION_INTERFACE  SSL_CLIENT_S_DN_OU     SSL_SERVER_S_DN_OU
                           SSL_CLIENT_S_DN_CN     SSL_SERVER_S_DN_CN
                           SSL_CLIENT_S_DN_T      SSL_SERVER_S_DN_T
                           SSL_CLIENT_S_DN_I      SSL_SERVER_S_DN_I
                           SSL_CLIENT_S_DN_G      SSL_SERVER_S_DN_G
                           SSL_CLIENT_S_DN_S      SSL_SERVER_S_DN_S
                           SSL_CLIENT_S_DN_D      SSL_SERVER_S_DN_D
                           SSL_CLIENT_S_DN_UID    SSL_SERVER_S_DN_UID
                           SSL_CLIENT_S_DN_Email  SSL_SERVER_S_DN_Email
                           SSL_CLIENT_I_DN        SSL_SERVER_I_DN
                           SSL_CLIENT_I_DN_C      SSL_SERVER_I_DN_C
                           SSL_CLIENT_I_DN_ST     SSL_SERVER_I_DN_ST
                           SSL_CLIENT_I_DN_L      SSL_SERVER_I_DN_L
                           SSL_CLIENT_I_DN_O      SSL_SERVER_I_DN_O
                           SSL_CLIENT_I_DN_OU     SSL_SERVER_I_DN_OU
                           SSL_CLIENT_I_DN_CN     SSL_SERVER_I_DN_CN
                           SSL_CLIENT_I_DN_T      SSL_SERVER_I_DN_T
                           SSL_CLIENT_I_DN_I      SSL_SERVER_I_DN_I
                           SSL_CLIENT_I_DN_G      SSL_SERVER_I_DN_G
                           SSL_CLIENT_I_DN_S      SSL_SERVER_I_DN_S
                           SSL_CLIENT_I_DN_D      SSL_SERVER_I_DN_D
                           SSL_CLIENT_I_DN_UID    SSL_SERVER_I_DN_UID
                           SSL_CLIENT_I_DN_Email  SSL_SERVER_I_DN_Email
                           SSL_CLIENT_A_SIG       SSL_SERVER_A_SIG
                           SSL_CLIENT_A_KEY       SSL_SERVER_A_KEY
                           SSL_CLIENT_CERT        SSL_SERVER_CERT
                           SSL_CLIENT_CERT_CHAIN_n
                           SSL_CLIENT_VERIFY      SSL_TLS_SNI

## 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.

### Example

`SSLRequireSSL`

## 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 four 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.

- `shm:/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.

- `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.

### Examples

`SSLSessionCache dbm:/usr/local/apache/logs/ssl_gcache_data
SSLSessionCache shm:/usr/local/apache/logs/ssl_gcache_data(512000)`

## 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 2.2.28 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.

### Example

`SSLSessionCacheTimeout 600`

## 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 non default name based virtual host, non SNI clients are not allowed to access this particular virtual host. If set to `on` in the default name based virtual host, non SNI clients are not allowed to access any name based virtual host belonging to this IP / port combination.

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

### Example

`SSLStrictSNIVHostCheck 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
Compatibility: | Available in Apache 2.0.51 and later

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).

### Example

`SSLUserName SSL_CLIENT_S_DN_CN`

## 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.

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

### Example

`SSLVerifyClient 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.

### Example

`SSLVerifyDepth 10`

Available Languages: en

## Comments

Notice:
This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our mailing lists.