mod_ssl: Reference

mod_ssl |
Introduction | Compatibility
his chapter provides a reference to all configuration directives and additional user visible features mod_ssl provides. It's intended as the official resource when you want to know how a particilar mod_ssl functionality is actually configured or activated. Each directive is documented similar to the way standard Apache directives are documented in the official Apache documentation set, i.e. for each directive especially the syntax, default and context where applicable is given. Notice that there are three major classes of directives which are used by mod_ssl: Global Directives (i.e. directives with context ``server config''), Per-Server Directives (i.e. those with context ``server config, virtual host'') and Per-Directory Directives (i.e. those with context ``server config, virtual host, directory, .htaccess''). They are subsets of each other, i.e. directives from the per-directory class can also be used in the per-server and global context, and directives from the per-server class can also be used the in the global context. Additional directives and environment variables provided by mod_ssl (via on-the-fly mapping) for backward compatiblity to other Apache SSL solutions are documented in the Compatibility chapter. |  |
Table Of Contents
Configuration Directives Global Class Directives SSLMutex SSLPassPhraseDialog Per-Server Class Directives SSLEngine SSLCipherSuite SSLCertificateFile SSLCertificateKeyFile SSLCACertificatePath SSLCACertificateFile SSLCACertificateReqFile SSLVerifyClient SSLVerifyDepth SSLSessionCache SSLSessionCacheTimeout SSLLog SSLLogLevel Per-Directory Class Directives SSLOptions SSLRequireSSL SSLRequire Additional Features Environment Variables Custom Log Formats
# Configuration Directives The most visible and error-prone things of mod_ssl are the configuration directives it provides. So we document them in great detail here to assist you in as good as possible in configuring your SSL-aware webserver. ## Global Class Directives The first set of directives are those of the Global Class, i.e. which can occur inside the server config files but only outside of any sectioning commands like <VirtualHost>. ### SSLMutex
Name: | SSLMutex
Description: | Semaphore for internal mutual exclusion of operations
Syntax: | `SSLMutex` type
Default: | `SSLMutex none`
Context: | server config
Override: | Not applicable
Status: | Extension
Module: | mod_ssl
Compatibility: | mod_ssl 2.1
> 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. The following Mutex types are available: `none` 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 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. `file:/path/to/mutex` This is the portable and always provided Mutex variant where a physical (lock-)file is 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. `sem` This is the most elegant but also most non-portable Mutex variant where a SysV IPC Semaphore (under Unix) and a Windows Mutex (under Win32) is used when possible. It is only available when the underlaying platform supports it. Example:
>     SSLMutex file:/usr/local/apache/logs/ssl_mutex
### SSLPassPhraseDialog
Name: | SSLPassPhraseDialog
Description: | Type of pass phrase dialog for encrypted private keys
Syntax: | `SSLPassPhraseDialog` type
Default: | `SSLPassPhraseDialog builtin`
Context: | server config
Override: | Not applicable
Status: | Extension
Module: | mod_ssl
Compatibility: | mod_ssl 2.1
> 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 read 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). `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 an argument of ```servername:portnumber`'' for which 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 one could think about it. mod_ssl just defines the interface: an executable program which provides the Pass Phrase on `stdout`. Nothing more or less! So, when 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 or too 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
## Per-Server Class Directives The second set of directives are those of the Per-Server Class, i.e. which can occur inside the server config files outside (for the main/default server) and inside <VirtualHost> sections. ### SSLEngine
Name: | SSLEngine
Description: | SSL Engine Operation Switch
Syntax: | `SSLEngine` on|off
Default: | `SSLEngine off`
Context: | server config, virtual host
Override: | Not applicable
Status: | Extension
Module: | mod_ssl
Compatibility: | mod_ssl 2.1
> This directive toggles the usage of the SSL/TLS Protocol Engine. This is usually used inside a <VirtualHost> section to enable SSL/TLS for a particular virtual host. Per 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>
### SSLCipherSuite
Name: | SSLCipherSuite
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
Override: | Not applicable
Status: | Extension
Module: | mod_ssl
Compatibility: | mod_ssl 2.1
This complex directive uses a colon-separated cipher-spec string consisting of SSLeay cipher specifications to configure the Cipher Suite the client is permitted to negotiate in the SSL handshake phase. A 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. A SSL cipher can also be an export cipher and is either a SSLv2 or a SSLv3 cipher. 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).
Table 1: SSLeay Cipher Specification Tags
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
`EXP` | all export ciphers
`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, 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
- `+`: add ciphers to list and pull them to current location in list
- `-`: remove cipher from list (can be added later again)
- `!`: kill cipher from list and at all (can not be added later again)

A simpler way to look at all of this is to use the ```ssleay 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 add all the export ciphers to the end. Then pull all SSLv2 and export ciphers to the end of the list.

>     $ ssleay 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
>     EDH-DSS-DES-CBC3-SHA    SSLv3 Kx=DH       Au=DSS  Enc=3DES(168) Mac=SHA1
>     DES-CBC3-SHA            SSLv3 Kx=RSA      Au=RSA  Enc=3DES(168) Mac=SHA1
>     IDEA-CBC-SHA            SSLv3 Kx=RSA      Au=RSA  Enc=IDEA(128) Mac=SHA1
>     RC4-SHA                 SSLv3 Kx=RSA      Au=RSA  Enc=RC4(128)  Mac=SHA1
>     RC4-MD5                 SSLv3 Kx=RSA      Au=RSA  Enc=RC4(128)  Mac=MD5
>     EDH-RSA-DES-CBC-SHA     SSLv3 Kx=DH       Au=RSA  Enc=DES(56)   Mac=SHA1
>     EDH-DSS-DES-CBC-SHA     SSLv3 Kx=DH       Au=DSS  Enc=DES(56)   Mac=SHA1
>     DES-CBC-SHA             SSLv3 Kx=RSA      Au=RSA  Enc=DES(56)   Mac=SHA1
>     DES-CBC3-MD5            SSLv2 Kx=RSA      Au=RSA  Enc=3DES(168) Mac=MD5
>     IDEA-CBC-MD5            SSLv2 Kx=RSA      Au=RSA  Enc=IDEA(128) Mac=MD5
>     RC2-CBC-MD5             SSLv2 Kx=RSA      Au=RSA  Enc=RC2(128)  Mac=MD5
>     RC4-MD5                 SSLv2 Kx=RSA      Au=RSA  Enc=RC4(128)  Mac=MD5
>     RC4-64-MD5              SSLv2 Kx=RSA      Au=RSA  Enc=RC4(64)   Mac=MD5
>     DES-CBC-MD5             SSLv2 Kx=RSA      Au=RSA  Enc=DES(56)   Mac=MD5
>     EXP-EDH-RSA-DES-CBC-SHA SSLv3 Kx=DH(512)  Au=RSA  Enc=DES(40)   Mac=SHA1 export
>     EXP-EDH-DSS-DES-CBC-SHA SSLv3 Kx=DH(512)  Au=DSS  Enc=DES(40)   Mac=SHA1 export
>     EXP-DES-CBC-SHA         SSLv3 Kx=RSA(512) Au=RSA  Enc=DES(40)   Mac=SHA1 export
>     EXP-RC2-CBC-MD5         SSLv3 Kx=RSA(512) Au=RSA  Enc=RC2(40)   Mac=MD5  export
>     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

Table 2: Particular SSL Ciphers
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

### SSLCertificateFile

Name: | SSLCertificateFile
Description: | Server PEM-encoded X.509 Certificate file
Syntax: | `SSLCertificateFile` filename
Default: | `SSLCertificateFile conf/ssl.crt/server.crt`
Context: | server config, virtual host
Override: | Not applicable
Status: | Extension
Module: | mod_ssl
Compatibility: | mod_ssl 2.0

This directive points to the PEM-encoded Certificate file for the server and optionally also to the corresponding RSA Private Key file for it (optionally contained in the same file). If the contained Private Key is encrypted the Pass Phrase dialog is forced at startup time.

Example:

>     SSLCertificateFile /usr/local/apache/conf/ssl.crt/server.crt

### SSLCertificateKeyFile

Name: | SSLCertificateKeyFile
Description: | Server PEM-encoded RSA Private Key file
Syntax: | `SSLCertificateKeyFile` filename
Default: | None
Context: | server config, virtual host
Override: | Not applicable
Status: | Extension
Module: | mod_ssl
Compatibility: | mod_ssl 2.0

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 dissuade from this practice. Instead it is recommended to separate the Certificate and the Private Key. If the contained Private Key is encrypted the Pass Phrase dialog is forced at startup time.

Example:

>     SSLCertificateKeyFile /usr/local/apache/conf/ssl.key/server.key

### SSLCACertificatePath

Name: | SSLCACertificatePath
Description: | Directory of PEM-encoded CA Certificates for Client Auth.
Syntax: | `SSLCACertificatePath` directory
Default: | None
Context: | server config, virtual host
Override: | Not applicable
Status: | Extension
Module: | mod_ssl
Compatibility: | mod_ssl 2.0

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 have not only to place the Certificate files there. Additionally you have to create symbolic links named hash-value`.N`. And you should always make sure this directory contains the appropriate symbolic links. Use the `Makefile` which comes with mod_ssl to accomplish this task.

Example:

>     SSLCACertificatePath /usr/local/apache/conf/ssl.crt/

### SSLCACertificateFile

Name: | SSLCACertificateFile
Description: | File of concatenated PEM-encoded CA Certificates for Client Auth.
Syntax: | `SSLCACertificateFile` filename
Default: | None
Context: | server config, virtual host
Override: | Not applicable
Status: | Extension
Module: | mod_ssl
Compatibility: | mod_ssl 2.0

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/apache/conf/ssl.crt/ca-bundle-client.crt

### SSLCACertificateReqFile

Name: | SSLCACertificateReqFile
Description: | File of concatenated PEM-encoded CA Certificates for Cert. Chain Loading
Syntax: | `SSLCACertificateReqFile` filename
Default: | None
Context: | server config, virtual host
Override: | Not applicable
Status: | Extension
Module: | mod_ssl
Compatibility: | mod_ssl 2.1

This directive sets the all-in-one file where you can assemble the Certificates of Certification Authorities (CA) whose CAs you deal with. This is optionally used by the clients for SSLv3 Server Authentication to speedup processing the verification of the server certificate. The file is requested by the client via the ``SSLv3 write Certificate request A'' for loading intermediate CA Certificates in a possible Certificate chain (only SSLv3). It's simply the concatenation of the various PEM-encoded Certificate files, in order of preference. Per default this is the same as `SSLCACertificateFile`.

Example:

>     SSLCACertificateReqFile /usr/local/apache/conf/ssl.crt/ca-bundle-server.crt

### SSLVerifyClient

Name: | SSLVerifyClient
Description: | Type of Client Certificate verification
Syntax: | `SSLVerifyClient` level
Default: | `SSLVerifyClient none`
Context: | server config, virtual host
Override: | Not applicable
Status: | Extension
Module: | mod_ssl
Compatibility: | mod_ssl 2.0

This directive sets the Certificate verification level for the Client Authentication. 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 has not to be (successfully) verifyable.

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

Name: | SSLVerifyDepth
Description: | Maximum depth of CA Certificates in Client Certificate verification
Syntax: | `SSLVerifyDepth` number
Default: | `SSLVerifyDepth 1`
Context: | server config, virtual host
Override: | Not applicable
Status: | Extension
Module: | mod_ssl
Compatibility: | mod_ssl 2.0

This directive sets how deeply mod_ssl should verify before deciding the clients don't have a valid certificate. The depth actually is the number of max 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 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

### SSLSessionCache

Name: | SSLSessionCache
Description: | Type of the global/inter-process SSL Session Cache
Syntax: | `SSLSessionCache` type
Default: | `SSLSessionCache none`
Context: | server config, virtual host
Override: | Not applicable
Status: | Extension
Module: | mod_ssl
Compatibility: | mod_ssl 2.1

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. Because for requests to the same server process (via HTTP keep-alive) SSLeay 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 unneccessary session handshakes.

The following two storage types are currently supported:

- `none`

  This is the default and just disables the global/inter-process Session Cache. There is no drawback in functionality, but a noticeable speed penalty can be observed.

- `dbm:/path/to/datafile`

  This makes use of a DBM hashfile on the local disk to synchronize the local SSLeay memory caches of the server processes. The little more amount of I/O on the server results in a visible request speedup for your clients. So it's recommended to use this storage.

Example:

>     SSLSessionCache dbm:/usr/local/apache/logs/ssl_gcache_data

### SSLSessionCacheTimeout

Name: | SSLSessionCacheTimeout
Description: | Number of seconds before a SSL session expires in the Session Cache
Syntax: | `SSLSessionCacheTimeout` seconds
Default: | `SSLSessionCacheTimeout 300`
Context: | server config, virtual host
Override: | Not applicable
Status: | Extension
Module: | mod_ssl
Compatibility: | mod_ssl 2.0

This directive sets the timeout in seconds for the information stored in the global/inter-process SSL Session Cache and the SSLeay internal memory cache. 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

### SSLLog

Name: | SSLLog
Description: | Where to write the dedicated SSL engine logfile
Syntax: | `SSLLog` filename
Default: | None
Context: | server config, virtual host
Override: | Not applicable
Status: | Extension
Module: | mod_ssl
Compatibility: | mod_ssl 2.1

This directive sets the name of the dedicated SSL protocol engine logfile. Error type messages are additionally duplicated to the general Apache error log file (directive `ErrorLog`). Put this somewhere where it cannot be used for symlink attacks on a real server (i.e. somewhere where only root can write). If the filename does not begin with a slash ('`/`') then it is assumed to be relative to the Server Root. If filename begins with a bar ('`|`') then the following string is assumed to be a path to an executable program to which a reliable pipe can be established. The directive should occur only once per virtual server config.

Example:

>     SSLLog /usr/local/apache/logs/ssl_engine_log

### SSLLogLevel

Name: | SSLLogLevel
Description: | Logging level for the dedicated SSL engine logfile
Syntax: | `SSLLogLevel` level
Default: | `SSLLogLevel none`
Context: | server config, virtual host
Override: | Not applicable
Status: | Extension
Module: | mod_ssl
Compatibility: | mod_ssl 2.1

This directive sets the verbosity degree of the dedicated SSL protocol engine logfile. The level is one of the following (in ascending order where higher levels include lower levels):

- `none`
  no dedicated SSL logging is done, but errors are still duplicated to the general Apache error logfile.

- `error`
  log messages of error type only, but duplicate them to the general Apache error logfile, too.

- `warn`
  log also messages of warning type

- `info`
  log also messages of information type

- `debug`
  log also messages of debugging type

Example:

>     SSLLogLevel warn

## Per-Directory Class Directives

The third set of directives are those of the Per-Directory Class, i.e. which can occur mostly everywhere. Especially both inside the server config files and the per-directory `.htaccess` files.

### SSLOptions

Name: | SSLOptions
Description: | Configure various SSL engine run-time options
Syntax: | `SSLOptions` [+-]option ...
Default: | None
Context: | server config, virtual host, directory, .htaccess
Override: | Options
Status: | Extension
Module: | mod_ssl
Compatibility: | mod_ssl 2.1

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 complete; 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:

- `CompatEnvVars`

  When this option is enabled additional CGI/SSI environment variables are created for backward compatibility to other Apache SSL solutions. Look in the Compatibility chapter for details on the actually generated variables.

- `ExportCertData`

  When this option is enabled two additional CGI/SSI environment variables are created: `SSL_CLIENT_CERT` and `SSL_SERVER_CERT`. These contain the PEM-encoded X.509 Certificates of client and server for the current HTTPS connection and can be used by CGI scripts for deeper Certificate checking. 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 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 SSLeay's `ssleay x509` command: `ssleay 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 encrypted version of the word ```password`''.

Example:

>     SSLOptions +FakeBasicAuth -CompatEnvVars

### SSLRequireSSL

Name: | SSLRequireSSL
Description: | Deny access when SSL is not used for the HTTP request
Syntax: | `SSLRequireSSL`
Default: | None
Context: | server config, virtual host, directory, .htaccess
Override: | AuthConfig
Status: | Extension
Module: | mod_ssl
Compatibility: | mod_ssl 2.0

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

### SSLRequire

Name: | SSLRequire
Description: | Allow access only when an arbitrary complex boolean expression is true
Syntax: | `SSLRequire` expression
Default: | None
Context: | server config, virtual host, directory, .htaccess
Override: | AuthConfig
Status: | Extension
Module: | mod_ssl
Compatibility: | mod_ssl 2.1

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

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

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

>     comp     ::= word "==" word | word "eq" word
>                | word "!=" word | word "ne" word
>                | word "<"  word | word "lt" word
>                | word "<=" word | word "le" word
>                | word ">"  word | word "gt" word
>                | word ">=" word | word "ge" word
>                | word "in" "{" wordlist "}"
>                | word "=~" 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 the machine representation is executed only. For Per-Directory 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]+$/

Table 3: Available Variables for SSLRequire
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_URI            REMOTE_ADDR           TIME
    REQUEST_FILENAME       REMOTE_USER           ENV:variablename
SSL-related variables:
    HTTPS                  SSL_CLIENT_M_VERSION  SSL_SERVER_M_VERSION
                           SSL_CLIENT_M_SERIAL   SSL_SERVER_M_SERIAL
    SSL_VERSION_LIBRARY    SSL_CLIENT_V_START    SSL_SERVER_V_START
    SSL_VERSION_INTERFACE  SSL_CLIENT_V_END      SSL_SERVER_V_END
    SSL_CIPHER             SSL_CLIENT_S_DN       SSL_SERVER_S_DN
    SSL_CIPHER_USEKEYSIZE  SSL_CLIENT_S_DN_C     SSL_SERVER_S_DN_C
    SSL_CIPHER_ALGKEYSIZE  SSL_CLIENT_S_DN_SP    SSL_SERVER_S_DN_SP
                           SSL_CLIENT_S_DN_L     SSL_SERVER_S_DN_L
                           SSL_CLIENT_S_DN_O     SSL_SERVER_S_DN_O
                           SSL_CLIENT_S_DN_OU    SSL_SERVER_S_DN_OU
                           SSL_CLIENT_S_DN_CN    SSL_SERVER_S_DN_CN
                           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_SP    SSL_SERVER_I_DN_SP
                           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_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

# Additional Features

## Environment Variables

This module provides a lot of SSL information as additional environment variables to the SSI and CGI namespace. The generated variables are listed in Table 4. For backward compatibility the information can be made available under different names, too. Look in the Compatibility chapter for details on the compatibility variables.

Table 4: SSI/CGI Environment Variables
Variable Name: | Value Type: | Description:
`HTTPS` | flag | HTTPS is being used.
`SSL_PROTOCOL` | string | The SSL protocol version (SSLv2, SSLv3, TLSv1)
`SSL_CIPHER` | string | The cipher specification name
`SSL_CIPHER_USEKEYSIZE` | number | Number of cipher bits (actually used)
`SSL_CIPHER_ALGKEYSIZE` | number | Number of cipher bits (possible)
`SSL_VERSION_INTERFACE` | string | The mod_ssl program version
`SSL_VERSION_LIBRARY` | string | The SSLeay 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_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_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
[ where x509 is a component of a X.509 DN: `C, SP, L, O, OU, CN, Email` ]

## Custom Log Formats

When mod_ssl is build into Apache or at least loaded (under DSO situation) additional functions exists 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 Table 4.

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_req_log \
>               "%t %h %{SSL_PROTOCOL}x %{SSL_CIPHER}x \"%r\" %b"

Introduction | Compatibility
mod_ssl 2.1, User Manual The Apache Interface to SSLeay | Copyright © 1998 Ralf S. Engelschall All Rights Reserved