Apache SSL Directives
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Apache HTTP Server Version 2.0
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Apache Module mod_ssl
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Description:Strong cryptography using the Secure Sockets Layer (SSL) and Transport Layer Security (TLS) protocols Status:Extension 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
[*] SSLCACertificateFile
[*] SSLCACertificatePath
[*] SSLCARevocationFile
[*] SSLCARevocationPath
[*] SSLCertificateChainFile
[*] SSLCertificateFile
[*] SSLCertificateKeyFile
[*] SSLCipherSuite
[*] SSLEngine
[*] SSLMutex
[*] SSLOptions
[*] SSLPassPhraseDialog
[*] SSLProtocol
[*] SSLProxyCACertificateFile
[*] SSLProxyCACertificatePath
[*] SSLProxyCARevocationFile
[*] SSLProxyCARevocationPath
[*] SSLProxyCipherSuite
[*] SSLProxyEngine
[*] SSLProxyMachineCertificateFile
[*] SSLProxyMachineCertificatePath
[*] SSLProxyProtocol
[*] SSLProxyVerify
[*] SSLProxyVerifyDepth
[*] SSLRandomSeed
[*] SSLRequire
[*] SSLRequireSSL
[*] SSLSessionCache
[*] SSLSessionCacheTimeout
[*] SSLUserName
[*] SSLVerifyClient
[*] SSLVerifyDepth
Topics
[*] Environment Variables
[*] Custom Log Formats
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 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) 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_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_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_CHAINn 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 [ where x509 is a component of a X.509 DN: C,ST,L,O,OU,CN,T,I,G,S,D,UID,Email ]
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 ofmod_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 Certificatesfor 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 toSSLCACertificatePath.
Example
SSLCACertificateFile /usr/local/apache2/conf/ssl.crt/ca-bundle-client.crt
SSLCACertificatePath Directive
Description:Directory of PEM-encoded CA Certificates forClient 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/
SSLCARevocationFile Directive
Description:File of concatenated PEM-encoded CA CRLs forClient 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 forClient 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 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. That's usually not one expect.
But be careful: Providing the certificate chain works only if you are using a single (either 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 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 two times (referencing different filenames) when both a RSA and a DSA 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 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 two times (referencing different filenames) when both a RSA and a DSA 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 SSLhandshake 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 renegotation 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: aNULLNo authentication aRSA RSA authentication aDSS DSS authentication aDH Diffie-Hellman authentication Cipher Encoding Algorithm: eNULLNo 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: SSLv2all SSL version 2.0 ciphers SSLv3all SSL version 3.0 ciphers TLSv1all 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
[*]+: 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 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=RSAEnc=None Mac=SHA1
NULL-MD5 SSLv3 Kx=RSA Au=RSAEnc=None Mac=MD5
EDH-RSA-DES-CBC3-SHA SSLv3 Kx=DH Au=RSAEnc=3DES(168) Mac=SHA1
... ... ... ... ...
EXP-RC4-MD5 SSLv3 Kx=RSA(512) Au=RSAEnc=RC4(40) Mac=MD5export
EXP-RC2-CBC-MD5 SSLv2 Kx=RSA(512) Au=RSAEnc=RC2(40) Mac=MD5export
EXP-RC4-MD5 SSLv2 Kx=RSA(512) Au=RSAEnc=RC4(40) Mac=MD5export
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
SSLEngine Directive
Description:SSL Engine Operation Switch Syntax:SSLEngine on|off Default:SSLEngine off Context:server config, virtual host Status:Extension Module:mod_ssl This directive toggles the usage of the SSL/TLS Protocol Engine. This is usually used inside asection to enable SSL/TLS for a particular virtual host. By default the SSL/TLS Protocol Engine is disabled for both the main server and all configured virtual hosts.
Example
SSLEngine on
...
SSLMutex Directive
Description:Semaphore for internal mutual exclusion ofoperations 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() fucntion 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.
[*]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 particular variables generated.
[*]ExportCertData When this option is enabled, additional CGI/SSI environment variables are created: SSL_SERVER_CERT, SSL_CLIENT_CERT and SSL_CLIENT_CERT_CHAINn (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
SSLOptions +StdEnvVars +CompatEnvVars -ExportCertData
SSLPassPhraseDialog Directive
Description:Type of pass phrase dialog for encrypted privatekeys 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).
[*]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'' or ``DSA''), 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.
[*]SSLv3 This is the Secure Sockets Layer (SSL) protocol, version 3.0. It is the successor to SSLv2 and the currently (as of February 1999) de-facto standardized SSL protocol from Netscape Corporation. 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 currently (as of February 1999) still under construction by the Internet Engineering Task Force (IETF). It's still not supported by any popular browsers.
[*]All This is a shortcut for ``+SSLv2 +SSLv3 +TLSv1'' and a convinient way for enabling all protocols except one when used in combination with the minus sign on a protocol as the example above shows.
Example
# enable SSLv3 and TLSv1, but not SSLv2
SSLProtocol all -SSLv2
SSLProxyCACertificateFile Directive
Description:File of concatenated PEM-encoded CA Certificatesfor 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 toSSLProxyCACertificatePath.
Example
SSLProxyCACertificateFile /usr/local/apache2/conf/ssl.crt/ca-bundle-remote-server.crt
SSLProxyCACertificatePath Directive
Description:Directory of PEM-encoded CA Certificates forRemote 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. Use the Makefile which comes with mod_ssl to accomplish this task.
Example
SSLProxyCACertificatePath /usr/local/apache2/conf/ssl.crt/
SSLProxyCARevocationFile Directive
Description:File of concatenated PEM-encoded CA CRLs forRemote 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 forRemote 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. Use the Makefile which comes with mod_ssl to accomplish this task.
Example
SSLProxyCARevocationPath /usr/local/apache2/conf/ssl.crl/
SSLProxyCipherSuite Directive
Description:Cipher Suite available for negotiation in SSLproxy 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 asection to enable SSL/TLS for proxy usage in a particular virtual host. By default the SSL/TLS Protocol Engine is disabled for proxy image both for the main server and all configured virtual hosts.
Example
SSLProxyEngine on
...
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. Use the Makefile which comes with mod_ssl to accomplish this task.
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, directory, .htaccess Override:AuthConfig Status:Extension Module:mod_ssl This directive sets the Certificate verification level for the remote server Authentication. Notice that this directive can be used both in per-server and per-directory context. In per-server context it applies to the remote server authentication process used in the standard SSL handshake when a connection is established. In per-directory context it forces a SSL renegotation with the reconfigured remote server verification level after the HTTP request was read but before the HTTP response is sent.
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, directory, .htaccess 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. 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 renegotation with the reconfigured remote server 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 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) seedingsource 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. It's 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 choosen 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 derivates 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 tool like EGD (Entropy Gathering Daemon) and run it's 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
SSLRequire Directive
Description:Allow access only when an arbitrarily complexboolean 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's a very powerful directive because the requirement specification is an arbitrarily complex boolean expression containing any number of access checks.
The expression must match the following syntax (given as a BNF grammar notation):
expr ::= "true" | "false"
| "!" expr
| expr "&&" expr
| expr "||" expr
| "(" expr ")"
| comp
comp ::= word "==" word | word "eq" word
| word "!=" word | word "ne" word
| word "=" word | word "ge" word
| word "in" "{" wordlist "}"
| word "=~" regex
| word "!~" regex
wordlist ::= word
| wordlist "," word
word ::= digit
| cstring
| variable
| function
digit ::= +
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 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} = 8 and %{TIME_HOUR}
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