Apache Module mod_ssl

For a Broadcom accelerator: SSLCryptoDevice ubsec

This module relies on OpenSSL to provide the cryptography engine.

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

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.

if secure renegotiation is supported, else false

if cipher is an export cipherSSLCIPHERUSEKEYSIZE

x509 specifies a component of an X.509 DN; one of C,ST,L,O,OU,CN,T,I,G,S,D,UID,Email

suffix. If the DN in question contains multiple attributes of the same name, this suffix is used as a zero-based index to select a particular attribute. For example, where the server certificate subject DN included two OU attributes, SSLSERVERSDNOU_0

could be used to reference each. A variable name without a _n

directive, the first (or only) attribute of any DN is added only under a non-suffixed name; i.e. no SSLOptions_0

The format of the *_DN variables has changed in Apache HTTPD 2.3.11. See the LegacyDNStringFormat

HTTPUSERAGENT PATHINFO AUTHTYPE HTTPREFERER QUERYSTRING SERVERSOFTWARE HTTPCOOKIE REMOTEHOST APIVERSION HTTPFORWARDED REMOTEIDENT TIMEYEAR HTTPHOST ISSUBREQ TIMEMON HTTPPROXYCONNECTION DOCUMENTROOT TIMEDAY HTTPACCEPT SERVERADMIN TIMEHOUR THEREQUEST SERVERNAME TIMEMIN REQUESTFILENAME SERVERPORT TIMESEC REQUESTMETHOD SERVERPROTOCOL TIMEWDAY REQUESTSCHEME REMOTEADDR TIME REQUESTURI REMOTEUSER

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

'' 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.

CustomLog logs/sslrequestlog "%t %h %{SSLPROTOCOL}x %{SSLCIPHER}x \"%r\" %b"

is built against a version of OpenSSL which supports the secure renegotiation extension, this note is set to the value 1

provider denies access if a connection is not encrypted with SSL. This is similar to the SSLRequireSSL

provider allows access if the user is authenticated with a valid client certificate. This is only useful if SSLVerifyClient optional

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

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

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.

directives; in other words, the names of the CAs which will actually be used to verify the client certificate.SSLCACertificatePath

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,

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

, CRLs Prior to version 2.3.15, CRL checking in mod_ssl also succeeded when no CRL(s) were found in any of the locations configured with

. With the introduction of this directive, the behavior has been changed: when checking is enabled, CRLs SSLCARevocationPathmust be present for the validation to succeed - otherwise it will fail with an "unable to get certificate CRL"

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.

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.SSLCACertificatePath

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.

Additional optional elements are DH parameters and/or an EC curve name for ephemeral keys, as generated by openssl dhparam

, respectively (supported in version 2.4.7 or later) and finally, the end-entity certificate's private key. If the private key is encrypted, the pass phrase dialog is forced at startup time.

This directive can be used multiple times (referencing different filenames) to support multiple algorithms for server authentication - typically RSA, DSA, and ECC. The number of supported algorithms depends on the OpenSSL version being used for mod_ssl: with version 1.0.0 or later, openssl list-public-key-algorithms

When running with OpenSSL 1.0.2 or later, this directive allows to configure the intermediate CA chain on a per-certificate basis, which removes a limitation of the (now obsolete)

directive. DH and ECDH parameters, however, are only read from the first SSLCertificateChainFileSSLCertificateFile

directive, as they are applied independently of the authentication algorithm type.

Beginning with version 2.4.7, mod_ssl makes use of standardized DH parameters with prime lengths of 2048, 3072 and 4096 bits and with additional prime lengths of 6144 and 8192 bits beginning with version 2.4.10 (from RFC 3526), and hands them out to clients based on the length of the certificate's RSA/DSA key. With Java-based clients in particular (Java 7 or earlier), this may lead to handshake failures - see this FAQ answer for working around such issues.

directive, there must be a matching SSLCertificateKeyFileSSLCertificateFile

An SSL cipher specification in cipher-spec is composed of 4 major attributes plus a few extra minor ones:

An SSL cipher can also be an export cipher. SSLv2 ciphers are no longer supported. 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). The actually available ciphers and aliases depends on the used openssl version. Newer openssl versions may include additional ciphers.

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 ( 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:

: remove cipher from list (can be added later again)!

: kill cipher from list completely (can aNULL

ciphers are always disabledBeginning with version 2.4.7, null and export-grade ciphers are always disabled, as mod_ssl unconditionally prepends any supplied cipher suite string with !aNULL:!eNULL:!EXP:

'' command which provides a nice way to successively create the correct cipher-spec string. The default cipher-spec string depends on the version of the OpenSSL libraries used. Let's suppose it is RC4-SHA:AES128-SHA:HIGH:MEDIUM:!aNULL:!MD5

at the beginning. We do this, because these ciphers offer a good compromise between speed and security. Next, include high and medium security ciphers. Finally, remove all ciphers which do not authenticate, i.e. for SSL the Anonymous Diffie-Hellman ciphers, as well as all ciphers which use MD5

as hash algorithm, because it has been proven insufficient.

$ openssl ciphers -v 'RC4-SHA:AES128-SHA:HIGH:MEDIUM:!aNULL:!MD5' RC4-SHA SSLv3 Kx=RSA Au=RSA Enc=RC4(128) Mac=SHA1 AES128-SHA SSLv3 Kx=RSA Au=RSA Enc=AES(128) Mac=SHA1 DHE-RSA-AES256-SHA SSLv3 Kx=DH Au=RSA Enc=AES(256) Mac=SHA1 ... ... ... ... ... SEED-SHA SSLv3 Kx=RSA Au=RSA Enc=SEED(128) Mac=SHA1 PSK-RC4-SHA SSLv3 Kx=PSK Au=PSK Enc=RC4(128) Mac=SHA1 KRB5-RC4-SHA SSLv3 Kx=KRB5 Au=KRB5 Enc=RC4(128) Mac=SHA1

EXP-DES-CBC-SHA

ADH-DES-CBC3-SHA

EDH-DSS-DES-CBC3-SHA

Enabling compression causes security issues in most setups (the so called CRIME attack).

. This enables support for RFC 2817, Upgrading to TLS Within HTTP/1.1. At this time no web browsers support RFC 2817.

will fail. Refer to the FIPS 140-2 Security Policy document of the SSL provider library for specific requirements to use modssl in a FIPS 140-2 approved mode of operation; note that modssl 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.

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.

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.mod_ssl

environment variable can be used from an SSI or CGI script to determine whether secure renegotiation is supported for a given SSL connection.

The OCSP responder used is either extracted from the certificate itself, or derived by configuration; see the

(at least version 1.0.2 is required). For a list of supported command names, see the section modsslSupported configuration file commands in the SSLCONF_cmd(3) manual page for OpenSSL.

commands can be used as an alternative to existing directives (such as

), though it should be noted that the syntax / allowable values for the parameters may sometimes differ.SSLProtocol

SSLOpenSSLConfCmd Options -SessionTicket,ServerPreference SSLOpenSSLConfCmd ECDHParameters brainpoolP256r1 SSLOpenSSLConfCmd ServerInfoFile /usr/local/apache2/conf/server-info.pem SSLOpenSSLConfCmd Protocol "-ALL, TLSv1.2" SSLOpenSSLConfCmd SignatureAlgorithms RSA+SHA384:ECDSA+SHA256

are added to the options currently in force, and any options preceded by a -

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.

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.

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

). Note that no password is obtained from the user. Every entry in the user file needs this password: xxj31ZMTZzkVA

''. 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/

can be used as a more general mechanism for faking basic authentication, giving control over the structure of both the username and password.modauthbasic

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

mechanism should work.) But for strict access restriction you can use SSLRequireSSL

'' has no chance once mod_ssl has decided to deny access.

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

variables are formatted. Since version 2.3.11, Apache HTTPD uses a RFC 2253 compatible format by default. This uses commas as delimiters between the attributes, allows the use of non-ASCII characters (which are converted to UTF8), escapes various special characters with backslashes, and sorts the attributes with the "C" attribute last.

is set, the old format will be used which sorts the "C" attribute first, uses slashes as separators, and does not handle non-ASCII and special characters in any consistent way.

SSLOptions +FakeBasicAuth -StrictRequire SSLOptions +StdEnvVars -ExportCertData

) 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 SSLCertificateKeyFiletype:

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

, 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.

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

'' or an integer index starting at 3 if more than three keys are configured), which indicate for which server and algorithm it has to print the corresponding Pass Phrase to stdout

. In versions 2.4.8 (unreleased) and 2.4.9, it is called with one argument, a string of the form servername:portnumber:index

being a zero-based integer number), which indicate the server, TCP port and certificate number. The intent is that this external program first runs security checks to make sure that the system is not compromised by an attacker, and only when these checks were passed successfully it provides the Pass Phrase.

Both these security checks, and the way the Pass Phrase is determined, can be as complex as you like. Mod_ssl just defines the interface: an executable program which provides the Pass Phrase 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.

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

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.

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

, and its setting is only taken into account when SSLProxyCheckPeerNameSSLProxyCheckPeerName off

This directive configures host name checking for server certificates when mod_ssl is acting as an SSL client. The check will succeed if the host name from the request URI is found in either the subjectAltName extension or (one of) the CN attribute(s) in the certificate's subject. If the check fails, the SSL request is aborted and a 502 status code (Bad Gateway) is returned. The directive supersedes

Wildcard matching is supported in one specific flavor: subjectAltName entries of type dNSName or CN attributes starting with *.

will match for any DNS name with the same number of labels and the same suffix (i.e., *.example.org

matches for foo.example.org

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.

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

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

SSLRandomSeed context source [bytes]

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.

as the first argument). When bytes is not specified the whole file forms the entropy (and 0

and/or /dev/urandom

devices (which usually exist on modern Unix derivatives like FreeBSD and Linux).

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.

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.

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.

, ... and work in a somewhat peculiar way that first compares the length of two strings and then the lexical order. On the other hand, ap_expr has two sets of comparison operators: The operators <

, ... do integer comparison. For the latter, there are also aliases without the leading dashes: lt

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 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" "PeerExtList(" word ")" | word "=~" regex | word "!~" regex wordlist ::= word | wordlist "," word word ::= digit | cstring | variable | function digit ::= [0-9]+ cstring ::= "..." variable ::= "%{" varname "}" function ::= funcname "(" funcargs ")"

The expression is parsed into an internal machine representation when the configuration is loaded, and then evaluated during request processing. In .htaccess context, the expression is both parsed and executed each time the .htaccess file is encountered during request processing.

SSLRequire ( %{SSLCIPHER} !~ m/^(EXP|NULL)-/ \ and %{SSLCLIENTSDNO} eq "Snake Oil, Ltd." \ and %{SSLCLIENTSDNOU} in {"Staff", "CA", "Dev"} \ and %{TIMEWDAY} -ge 1 and %{TIMEWDAY} -le 5 \ and %{TIMEHOUR} -ge 8 and %{TIMEHOUR} -le 20 ) \ or %{REMOTEADDR} =~ m/^192\.76\.162\.[0-9]+$/

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

The object ID can be specified either as a descriptive name recognized by the SSL library, such as "nsComment"

Expressions with types known to the SSL library are rendered to a string before comparison. For an extension with a type not recognized by the SSL library, mod_ssl will parse the value if it is one of the primitive ASN.1 types UTF8String, IA5String, VisibleString, or BMPString. For an extension of one of these types, the string value will be converted to UTF-8 if necessary, then compared against the left-hand-side expression.

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.

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.

This disables any global/inter-process Session Cache. However it does force OpenSSL to send a non-null session ID to accommodate buggy clients that require one.

dbm:/path/to/datafile

This makes use of a DBM hashfile on the local disk to synchronize the local OpenSSL memory caches of the server processes. This session cache may suffer reliability issues under high load. To use this, ensure that

] 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

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

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

mutex is used to serialize access to the session cache to prevent corruption. This mutex can be configured using the

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.

Optionally configures a secret key for encrypting and decrypting TLS session tickets, as defined in RFC 5077. Primarily suitable for clustered environments where TLS sessions information should be shared between multiple nodes. For single-instance httpd setups, it is recommended to not configure a ticket key file, but to rely on (random) keys generated by mod_ssl at startup, instead.

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

dd if=/dev/random of=/path/to/file.tkey bs=1 count=48

Ticket keys should be rotated (replaced) on a frequent basis, as this is the only way to invalidate an existing session ticket - OpenSSL currently doesn't allow to specify a limit for ticket lifetimes.

The ticket key file contains sensitive keying material and should be protected with file permissions similar to those used for

openssl srp -srpvfile passwd.srpv -userinfo "some info" -add username

parameter is avalable in the SSLSRPUSERINFO

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

OCSP stapling relieves the client of querying the OCSP responder on its own, but it should be noted that with the RFC 6066 specification, the server's CertificateStatus

reply may only include an OCSP response for a single cert. For server certificates with intermediate CA certificates in their chain (the typical case nowadays), stapling in its current implementation therefore only partially achieves the stated goal of "saving roundtrips and resources" - see also RFC 6961 (TLS Multiple Certificate Status Extension).

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