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Apache HTTP Server Version 2.0

Apache > HTTP Server > Documentation > Version 2.0 > SSL/TLS

# SSL/TLS Strong Encryption: Compatibility

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> All PCs are compatible. But some of them are more compatible than others.

> -- Unknown

Here we talk about backward compatibility to other SSL solutions. As you perhaps know, mod_ssl is not the only existing SSL solution for Apache. Actually there are four additional major products available on the market: Ben Laurie's freely available Apache-SSL (from where mod_ssl were originally derived in 1998), Red Hat's commercial Secure Web Server (which is based on mod_ssl), Covalent's commercial Raven SSL Module (also based on mod_ssl) and finally C2Net's commercial product Stronghold (based on a different evolution branch named Sioux up to Stronghold 2.x and based on mod_ssl since Stronghold 3.x).

The idea in mod_ssl is mainly the following: because mod_ssl provides mostly a superset of the functionality of all other solutions we can easily provide backward compatibility for most of the cases. Actually there are three compatibility areas we currently address: configuration directives, environment variables and custom log functions.

## Configuration Directives

For backward compatibility to the configuration directives of other SSL solutions we do an on-the-fly mapping: directives which have a direct counterpart in mod_ssl are mapped silently while other directives lead to a warning message in the logfiles. The currently implemented directive mapping is listed in Table 1. Currently full backward compatibility is provided only for Apache-SSL 1.x and mod_ssl 2.0.x. Compatibility to Sioux 1.x and Stronghold 2.x is only partial because of special functionality in these interfaces which mod_ssl (still) doesn't provide.

### Table 1: Configuration Directive Mapping

Old Directive | mod_ssl Directive | Comment
--- | --- | ---
Apache-SSL 1.x & mod_ssl 2.0.x compatibility:
`SSLEnable` | `SSLEngine on` | compactified
`SSLDisable` | `SSLEngine off` | compactified
`SSLLogFile` file | `SSLLog` file | compactified
`SSLRequiredCiphers` spec | `SSLCipherSuite` spec | renamed
`SSLRequireCipher` c1 ... | `SSLRequire %{SSL_CIPHER} in {"`c1`", ...}` | generalized
`SSLBanCipher` c1 ... | `SSLRequire not (%{SSL_CIPHER} in {"`c1`", ...})` | generalized
`SSLFakeBasicAuth` | `SSLOptions +FakeBasicAuth` | merged
`SSLCacheServerPath` dir | - | functionality removed
`SSLCacheServerPort` integer | - | functionality removed
Apache-SSL 1.x compatibility:
`SSLExportClientCertificates` | `SSLOptions +ExportCertData` | merged
`SSLCacheServerRunDir` dir | - | functionality not supported
Sioux 1.x compatibility:
`SSL_CertFile` file | `SSLCertificateFile` file | renamed
`SSL_KeyFile` file | `SSLCertificateKeyFile` file | renamed
`SSL_CipherSuite` arg | `SSLCipherSuite` arg | renamed
`SSL_X509VerifyDir` arg | `SSLCACertificatePath` arg | renamed
`SSL_Log` file | `SSLLogFile` file | renamed
`SSL_Connect` flag | `SSLEngine` flag | renamed
`SSL_ClientAuth` arg | `SSLVerifyClient` arg | renamed
`SSL_X509VerifyDepth` arg | `SSLVerifyDepth` arg | renamed
`SSL_FetchKeyPhraseFrom` arg | - | not directly mappable; use SSLPassPhraseDialog
`SSL_SessionDir` dir | - | not directly mappable; use SSLSessionCache
`SSL_Require` expr | - | not directly mappable; use SSLRequire
`SSL_CertFileType` arg | - | functionality not supported
`SSL_KeyFileType` arg | - | functionality not supported
`SSL_X509VerifyPolicy` arg | - | functionality not supported
`SSL_LogX509Attributes` arg | - | functionality not supported
Stronghold 2.x compatibility:
`StrongholdAccelerator` dir | - | functionality not supported
`StrongholdKey` dir | - | functionality not supported
`StrongholdLicenseFile` dir | - | functionality not supported
`SSLFlag` flag | `SSLEngine` flag | renamed
`SSLSessionLockFile` file | `SSLMutex` file | renamed
`SSLCipherList` spec | `SSLCipherSuite` spec | renamed
`RequireSSL` | `SSLRequireSSL` | renamed
`SSLErrorFile` file | - | functionality not supported
`SSLRoot` dir | - | functionality not supported
`SSL_CertificateLogDir` dir | - | functionality not supported
`AuthCertDir` dir | - | functionality not supported
`SSL_Group` name | - | functionality not supported
`SSLProxyMachineCertPath` dir | - | functionality not supported
`SSLProxyMachineCertFile` file | - | functionality not supported
`SSLProxyCACertificatePath` dir | - | functionality not supported
`SSLProxyCACertificateFile` file | - | functionality not supported
`SSLProxyVerifyDepth` number | - | functionality not supported
`SSLProxyCipherList` spec | - | functionality not supported

## Environment Variables

When you use ```SSLOptions +CompatEnvVars`'' additional environment variables are generated. They all correspond to existing official mod_ssl variables. The currently implemented variable derivation is listed in Table 2.

### Table 2: Environment Variable Derivation

Old Variable | mod_ssl Variable | Comment
--- | --- | ---
`SSL_PROTOCOL_VERSION` | `SSL_PROTOCOL` | renamed
`SSLEAY_VERSION` | `SSL_VERSION_LIBRARY` | renamed
`HTTPS_SECRETKEYSIZE` | `SSL_CIPHER_USEKEYSIZE` | renamed
`HTTPS_KEYSIZE` | `SSL_CIPHER_ALGKEYSIZE` | renamed
`HTTPS_CIPHER` | `SSL_CIPHER` | renamed
`HTTPS_EXPORT` | `SSL_CIPHER_EXPORT` | renamed
`SSL_SERVER_KEY_SIZE` | `SSL_CIPHER_ALGKEYSIZE` | renamed
`SSL_SERVER_CERTIFICATE` | `SSL_SERVER_CERT` | renamed
`SSL_SERVER_CERT_START` | `SSL_SERVER_V_START` | renamed
`SSL_SERVER_CERT_END` | `SSL_SERVER_V_END` | renamed
`SSL_SERVER_CERT_SERIAL` | `SSL_SERVER_M_SERIAL` | renamed
`SSL_SERVER_SIGNATURE_ALGORITHM` | `SSL_SERVER_A_SIG` | renamed
`SSL_SERVER_DN` | `SSL_SERVER_S_DN` | renamed
`SSL_SERVER_CN` | `SSL_SERVER_S_DN_CN` | renamed
`SSL_SERVER_EMAIL` | `SSL_SERVER_S_DN_Email` | renamed
`SSL_SERVER_O` | `SSL_SERVER_S_DN_O` | renamed
`SSL_SERVER_OU` | `SSL_SERVER_S_DN_OU` | renamed
`SSL_SERVER_C` | `SSL_SERVER_S_DN_C` | renamed
`SSL_SERVER_SP` | `SSL_SERVER_S_DN_SP` | renamed
`SSL_SERVER_L` | `SSL_SERVER_S_DN_L` | renamed
`SSL_SERVER_IDN` | `SSL_SERVER_I_DN` | renamed
`SSL_SERVER_ICN` | `SSL_SERVER_I_DN_CN` | renamed
`SSL_SERVER_IEMAIL` | `SSL_SERVER_I_DN_Email` | renamed
`SSL_SERVER_IO` | `SSL_SERVER_I_DN_O` | renamed
`SSL_SERVER_IOU` | `SSL_SERVER_I_DN_OU` | renamed
`SSL_SERVER_IC` | `SSL_SERVER_I_DN_C` | renamed
`SSL_SERVER_ISP` | `SSL_SERVER_I_DN_SP` | renamed
`SSL_SERVER_IL` | `SSL_SERVER_I_DN_L` | renamed
`SSL_CLIENT_CERTIFICATE` | `SSL_CLIENT_CERT` | renamed
`SSL_CLIENT_CERT_START` | `SSL_CLIENT_V_START` | renamed
`SSL_CLIENT_CERT_END` | `SSL_CLIENT_V_END` | renamed
`SSL_CLIENT_CERT_SERIAL` | `SSL_CLIENT_M_SERIAL` | renamed
`SSL_CLIENT_SIGNATURE_ALGORITHM` | `SSL_CLIENT_A_SIG` | renamed
`SSL_CLIENT_DN` | `SSL_CLIENT_S_DN` | renamed
`SSL_CLIENT_CN` | `SSL_CLIENT_S_DN_CN` | renamed
`SSL_CLIENT_EMAIL` | `SSL_CLIENT_S_DN_Email` | renamed
`SSL_CLIENT_O` | `SSL_CLIENT_S_DN_O` | renamed
`SSL_CLIENT_OU` | `SSL_CLIENT_S_DN_OU` | renamed
`SSL_CLIENT_C` | `SSL_CLIENT_S_DN_C` | renamed
`SSL_CLIENT_SP` | `SSL_CLIENT_S_DN_SP` | renamed
`SSL_CLIENT_L` | `SSL_CLIENT_S_DN_L` | renamed
`SSL_CLIENT_IDN` | `SSL_CLIENT_I_DN` | renamed
`SSL_CLIENT_ICN` | `SSL_CLIENT_I_DN_CN` | renamed
`SSL_CLIENT_IEMAIL` | `SSL_CLIENT_I_DN_Email` | renamed
`SSL_CLIENT_IO` | `SSL_CLIENT_I_DN_O` | renamed
`SSL_CLIENT_IOU` | `SSL_CLIENT_I_DN_OU` | renamed
`SSL_CLIENT_IC` | `SSL_CLIENT_I_DN_C` | renamed
`SSL_CLIENT_ISP` | `SSL_CLIENT_I_DN_SP` | renamed
`SSL_CLIENT_IL` | `SSL_CLIENT_I_DN_L` | renamed
`SSL_EXPORT` | `SSL_CIPHER_EXPORT` | renamed
`SSL_KEYSIZE` | `SSL_CIPHER_ALGKEYSIZE` | renamed
`SSL_SECKEYSIZE` | `SSL_CIPHER_USEKEYSIZE` | renamed
`SSL_SSLEAY_VERSION` | `SSL_VERSION_LIBRARY` | renamed
`SSL_STRONG_CRYPTO` | `-` | Not supported by mod_ssl
`SSL_SERVER_KEY_EXP` | `-` | Not supported by mod_ssl
`SSL_SERVER_KEY_ALGORITHM` | `-` | Not supported by mod_ssl
`SSL_SERVER_KEY_SIZE` | `-` | Not supported by mod_ssl
`SSL_SERVER_SESSIONDIR` | `-` | Not supported by mod_ssl
`SSL_SERVER_CERTIFICATELOGDIR` | `-` | Not supported by mod_ssl
`SSL_SERVER_CERTFILE` | `-` | Not supported by mod_ssl
`SSL_SERVER_KEYFILE` | `-` | Not supported by mod_ssl
`SSL_SERVER_KEYFILETYPE` | `-` | Not supported by mod_ssl
`SSL_CLIENT_KEY_EXP` | `-` | Not supported by mod_ssl
`SSL_CLIENT_KEY_ALGORITHM` | `-` | Not supported by mod_ssl
`SSL_CLIENT_KEY_SIZE` | `-` | Not supported by mod_ssl

## Custom Log Functions

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` as documented in the Reference Chapter. Beside the ```%{`varname`}x`'' eXtension format function which can be used to expand any variables provided by any module, an additional Cryptography ```%{`name`}c`'' cryptography format function exists for backward compatibility. The currently implemented function calls are listed in Table 3.

### Table 3: Custom Log Cryptography Function

Function Call | Description
--- | ---
`%...{version}c` | SSL protocol version
`%...{cipher}c` | SSL cipher
`%...{subjectdn}c` | Client Certificate Subject Distinguished Name
`%...{issuerdn}c` | Client Certificate Issuer Distinguished Name
`%...{errcode}c` | Certificate Verification Error (numerical)
`%...{errstr}c` | Certificate Verification Error (string)

Available Languages: en