% `mod_gnutls` Manual * * * * * `mod_gnutls` is a module for the Apache web server that provides HTTPS (HTTP over Transport Layer Security (TLS)) using the GnuTLS library. More information about the module can be found at [the project's website](https://mod.gnutls.org/). * * * * * Compilation & Installation ========================== `mod_gnutls` uses the `./configure && make && make install` mechanism common to many Open Source programs. Most of the dirty work is handled by either `./configure` or Apache's `apxs` utility. If you have built Apache modules before, there shouldn't be any surprises for you. The interesting options you can pass to configure are: `--with-apxs=PATH` : This option is used to specify the location of the apxs utility that was installed as part of apache. Specify the location of the binary, not the directory it is located in. `--with-apu-config=PATH` : Path to APR Utility Library config tool (`apu-1-config`) `--help` : Provides a list of all available configure options. It is recommended to run `make check` before installation. If your system doesn't have a loopback device with IPv6 and IPv4 support or `localhost` does not resolve to at least one of `[::1]` and `127.0.0.1`, you may have to set the `TEST_HOST` or `TEST_IP` environment variables when running `./configure` to make the test suite work correctly. * * * * * Integration =========== To activate `mod_gnutls` just add the following line to your httpd.conf and restart Apache: LoadModule gnutls_module modules/mod_gnutls.so * * * * * Configuration Directives ======================== General Options --------------- ### GnuTLSEnable Enable GnuTLS for this virtual host GnuTLSEnable [on|off] Default: *off*\ Context: virtual host This directive enables SSL/TLS Encryption for a Virtual Host. ### GnuTLSCache Configure TLS Session Cache GnuTLSCache (shmcb|dbm|memcache|...|none)[:PARAMETERS] Default: `GnuTLSCache none`\ Context: server config This directive configures the TLS Session Cache for `mod_gnutls`. This could be shared between machines of different architectures. If the selected cache implementation is not thread-safe, access is serialized using the `gnutls-cache` mutex. Which cache implementations are available depends on your Apache installation and configuration, `mod_gnutls` can use any socache provider. In general you will need to load a `mod_socache_PROVIDER` module. Common options are described below, please check the Apache HTTPD documentation for details on available providers and their configuration. `shmcb` : Uses a shared memory segment. This is a high performance local cache. The parameter is a relative or absolute path to be used if the local shared memory implementation requires one, followed by the cache size in bytes enclosed in parentheses. Example: `shmcb:cache/gnutls_cache(65536)` `dbm` : Uses a DBM cache file. The parameter is a relative or absolute path to be used as the DBM cache file. Example: `dbm:cache/gnutls_cache` `memcache` : Uses memcached server(s) to cache TLS session data. The parameter is a comma separated list of servers (host:port). This can be used to share a session cache between all servers in a cluster. Example: `memcache:memcache.example.com:12345,memcache2.example.com:12345` `none` : Turns off all caching of TLS sessions. This can significantly reduce the performance of `mod_gnutls` since even followup connections by a client must renegotiate parameters instead of reusing old ones. This is the default, since it requires no configuration. Session tickets are an alternative to using a session cache, please see `GnuTLSSessionTickets`. Note that for TLS 1.3 GnuTLS supports resumption using session tickets only as of version 3.6.4. ### GnuTLSCacheTimeout Timeout for TLS Session Cache expiration GnuTLSCacheTimeout SECONDS Default: `GnuTLSCacheTimeout 300`\ Context: server config, virtual host Sets the expiration timeout for cached TLS sessions. ### GnuTLSSessionTickets Enable Session Tickets for the server GnuTLSSessionTickets [on|off] Default: `on` with GnuTLS 3.6.4 and newer, `off` otherwise\ Context: server config, virtual host Session tickets allow TLS session resumption without session state stored on the server, using encrypted tickets provided to the clients instead. Tickets are an alternative to using a session cache, and currently the only session resumption mechanism in TLS 1.3. For a pool of servers this option is not recommended since the tickets are bound to the issuing server only. If this option is set in the global configuration, virtual hosts without a `GnuTLSSessionTickets` setting will use the global setting. *Warning:* With GnuTLS version before 3.6.4 the master key that protects the tickets is generated only on server start, and there is no mechanism to roll over the key. If session tickets are enabled it is highly recommended to restart the server regularly to protect past sessions in case an attacker gains access to server memory. GnuTLS 3.6.4 introduced an automatic TOTP-based key rollover, so this warning does not apply any more and tickets are enabled by default. ### GnuTLSClientVerify Enable Client Certificate Verification GnuTLSClientVerify [ignore|request|require] Default: `ignore`\ Context: server config, virtual host, directory, .htaccess This directive controls the use of TLS Client Certificate Authentication. If used in the .htaccess context, it can force TLS re-negotiation. `ignore` : `mod_gnutls` will ignore the contents of any TLS Client Certificates sent. It will not request that the client sends a certificate. `request` : The client certificate will be requested, but not required. The Certificate will be validated if sent. The output of the validation status will be stored in the `SSL_CLIENT_VERIFY` environment variable and can be `SUCCESS`, `FAILED` or `NONE`. `require` : A Client certificate will be required. Any requests without a valid client certificate will be denied. The `SSL_CLIENT_VERIFY` environment variable will only be set to `SUCCESS`. ### GnuTLSDHFile Use the provided PKCS \#3 encoded Diffie-Hellman parameters GnuTLSDHFile FILEPATH Default: *none*\ Context: server config, virtual host By default, `mod_gnutls` uses the DH parameters included with GnuTLS corresponding to the security level of the configured private keys if compiled with GnuTLS 3.5.6 or newer, and the ffdhe2048 DH group as defined in RFC 7919, Appendix A.1 otherwise. If you need to use different DH parameters, you can provide a PEM file containing them in PKCS \#3 encoding using this option. Please see the "[Parameter generation](https://gnutls.org/manual/html_node/Parameter-generation.html)" section of the GnuTLS documentation for a short discussion of the security implications. ### GnuTLSPriorities Set the allowed protocol versions, ciphers, key exchange algorithms, MACs and compression methods GnuTLSPriorities NORMAL:+CIPHER_0:+CIPHER_1:...:+CIPHER_N Default: `NORMAL`\ Context: server config, virtual host Sets the allowed protocol version(s), ciphers, key exchange methods, message authentication codes, and other TLS parameters for the server. The parameter is a GnuTLS priority string as described in the [the GnuTLS documentation](https://gnutls.org/manual/html_node/Priority-Strings.html). For example, to disable TLS 1.0 use `NORMAL:-VERS-TLS1.0`. ### GnuTLSP11Module Load this PKCS #11 module. GnuTLSP11Module PATH_TO_LIBRARY Default: *none*\ Context: server config Load this PKCS #11 provider module, instead of the system defaults. May occur multiple times to load multiple modules. ### GnuTLSPIN Set the PIN to be used to access encrypted key files or PKCS #11 objects. GnuTLSPIN XXXXXX Default: *none*\ Context: server config, virtual host Takes a string to be used as a PIN for the protected objects in a security module, or as a key to be used to decrypt PKCS #8, PKCS #12, or openssl encrypted keys. ### GnuTLSSRKPIN Set the SRK PIN to be used to access the TPM. GnuTLSSRKPIN XXXXXX Default: *none*\ Context: server config, virtual host Takes a string to be used as a PIN for the protected objects in the TPM module. ### GnuTLSExportCertificates Export the PEM encoded certificates to CGIs GnuTLSExportCertificates [off|on|SIZE] Default: `off`\ Context: server config, virtual host This directive configures exporting the full certificates of the server and the client to CGI scripts via the `SSL_SERVER_CERT` and `SSL_CLIENT_CERT` environment variables. The exported certificates will be PEM-encoded, limited to the given size. The type of the certificate will be exported in `SSL_SERVER_CERT_TYPE` and `SSL_CLIENT_CERT_TYPE`. SIZE should be an integer number of bytes, or may be written with a trailing `K` to indicate kibibytes. `off` means the same thing as `0`, in which case the certificates will not be exported to the environment. `on` is an alias for `16K`. If a non-zero size is specified for this directive, but a certificate is too large to fit in the buffer, then the corresponding environment variable will contain the fixed string `GNUTLS_CERTIFICATE_SIZE_LIMIT_EXCEEDED`. With GnuTLSExportCertificates enabled, `mod_gnutls` exports the same environment variables to the CGI process as `mod_ssl`. X.509 Certificate Authentication -------------------------------- ### GnuTLSCertificateFile Set the PEM encoded server certificate or certificate chain GnuTLSCertificateFile FILEPATH Default: *none*\ Context: server config, virtual host FILEPATH is an absolute or relative path to a file containing the PEM-encoded X.509 certificate to use as this Server's End Entity (EE) certificate, and optionally those of the issuing Certificate Authorities (CAs). If the file contains multiple certificates they should be ordered from EE to the CA closest to the root CA (or the root CA itself). Including at least the immediately issuing CA is highly recommended because it is required for OCSP stapling. Since version 0.7 this can be a PKCS #11 URL instead of a file. On Linux and other Unix-like systems you can create the file with a command like this (assuming "CA 1" issued the server certificate and has been issued by "Root CA" itself): $ cat server.pem ca-1.pem root-ca.pem >server-chain.pem ### GnuTLSKeyFile Set to the PEM Encoded Server Private Key GnuTLSKeyFile FILEPATH Default: *none*\ Context: server config, virtual host Takes an absolute or relative path to the Server Private Key. Set `GnuTLSPIN` if the key file is encrypted. Since version 0.7 this can be a PKCS #11 URL. **Security Warning:**\ This private key must be protected. It is read while Apache is still running as root, and does not need to be readable by the nobody or apache user. ### GnuTLSClientCAFile Set the PEM encoded Certificate Authority list to use for X.509 base client authentication GnuTLSClientCAFile FILEPATH Default: *none* Context: server config, virtual host Takes an absolute or relative path to a PEM Encoded Certificate to use as a Certificate Authority with Client Certificate Authentication. This file may contain a list of trusted authorities. SRP Authentication ------------------ ### GnuTLSSRPPasswdFile Set to the SRP password file for SRP ciphersuites GnuTLSSRPPasswdFile FILEPATH Default: *none*\ Context: server config, virtual host Takes an absolute or relative path to an SRP password file. This is the same format as used in libsrp. You can generate such file using the command `srptool --passwd /etc/tpasswd --passwd-conf /etc/tpasswd.conf -u test` to set a password for user test. This password file holds the username, a password verifier and the dependency to the SRP parameters. ### GnuTLSSRPPasswdConfFile Set to the SRP password.conf file for SRP ciphersuites GnuTLSSRPPasswdConfFile FILEPATH Default: *none*\ Context: server config, virtual host Takes an absolute or relative path to an SRP password.conf file. This is the same format as used in `libsrp`. You can generate such file using the command `srptool --create-conf /etc/tpasswd.conf`. This file holds the SRP parameters and is associate with the password file (the verifiers depends on these parameters). TLS Proxy Configuration ----------------------- ### GnuTLSProxyEngine Enable TLS proxy connections for this virtual host GnuTLSProxyEngine [on|off] Default: *off*\ Context: virtual host This directive enables support for TLS proxy connections for a virtual host. ### GnuTLSProxyCAFile Set to the PEM encoded Certificate Authority Certificate GnuTLSProxyCAFile FILEPATH Default: *none*\ Context: server config, virtual host Takes an absolute or relative path to a PEM encoded certificate to use as a Certificate Authority when verifying certificates provided by proxy back end servers. This file may contain a list of trusted authorities. If not set, verification of TLS back end servers will always fail due to lack of a trusted CA. ### GnuTLSProxyCRLFile Set to the PEM encoded Certificate Revocation List GnuTLSProxyCRLFile FILEPATH Default: *none*\ Context: server config, virtual host Takes an absolute or relative path to a PEM encoded Certificate Revocation List to use when verifying certificates provided by proxy back end servers. The file may contain a list of CRLs. ### GnuTLSProxyCertificateFile Set to the PEM encoded Client Certificate GnuTLSProxyCertificateFile FILEPATH Default: *none*\ Context: server config, virtual host Takes an absolute or relative path to a PEM encoded X.509 certificate to use as this Server's End Entity (EE) client certificate for TLS client authentication in proxy TLS connections. If you need to supply certificates for intermediate Certificate Authorities (iCAs), they should be listed in sequence in the file, from EE to the iCA closest to the root CA. Optionally, you can also include the root CA's certificate as the last certificate in the list. If not set, TLS client authentication will be disabled for TLS proxy connections. If set, `GnuTLSProxyKeyFile` must be set as well to provide the matching private key. ### GnuTLSProxyKeyFile Set to the PEM encoded Private Key GnuTLSProxyKeyFile FILEPATH Default: *none*\ Context: server config, virtual host Takes an absolute or relative path to the Private Key matching the certificate configured using the `GnuTLSProxyCertificateFile` directive. This key cannot currently be password protected. **Security Warning:**\ This private key must be protected. It is read while Apache is still running as root, and does not need to be readable by the nobody or apache user. ### GnuTLSProxyPriorities Set the allowed ciphers, key exchange algorithms, MACs and compression methods for proxy connections GnuTLSProxyPriorities NORMAL:+CIPHER_0:+CIPHER_1:...:+CIPHER_N Default: `NORMAL`\ Context: server config, virtual host Sets the allowed protocol version(s), ciphers, key exchange methods, message authentication codes, and other TLS parameters for TLS proxy connections. Like for `GnuTLSPriorities` the parameter is a GnuTLS priority string as described in the [the GnuTLS documentation](https://gnutls.org/manual/html_node/Priority-Strings.html). OCSP Stapling Configuration --------------------------- ### GnuTLSOCSPStapling Enable OCSP stapling for this (virtual) host. GnuTLSOCSPStapling [On|Off] Default: *on* if requirements are met, *off* otherwise\ Context: server config, virtual host OCSP stapling, formally known as the TLS Certificate Status Request extension, allows the server to provide the client with a cached OCSP response for its certificate during the handshake. With OCSP stapling the client does not have to send an OCSP request to the issuer CA to check the certificate status, which offers privacy and performance advantages, and avoids the security issue of how to handle errors that prevent the client from getting a response. Using OCSP stapling has a few requirements: * `GnuTLSCertificateFile` must contain the issuer CA certificate in addition to the server certificate so responses can be verified. * The server certificate must either contain an OCSP access URI using HTTP, or `GnuTLSOCSPResponseFile` must be set. * Caching OCSP responses requires a cache to store responses. If `mod_socache_shmcb` is loaded `mod_gnutls` can set up the cache automatically without additional configuration, see `GnuTLSOCSPCache`. Stapling is activated by default if these requirements are met. If `GnuTLSOCSPStapling` is explicitly set to `on` unmet requirements are an error. OCSP cache updates are serialized using the `gnutls-ocsp` mutex. ### GnuTLSOCSPCache OCSP stapling cache configuration GnuTLSOCSPCache (shmcb|memcache|...|none)[:PARAMETERS] Default: `shmcb:gnutls_ocsp_cache`\ Context: server config This directive configures the OCSP stapling cache, and uses the same syntax as `GnuTLSOCSPCache`. Please check there for details. The default should be reasonable for most servers and requires `mod_socache_shmcb` to be loaded. Servers with very many virtual hosts may need to increase the default cache size via the parameters string, those with few virtual hosts and constrains could save a few KB by reducing it. Note that `mod_socache_dbm` has a size constraint for entries that is generally too small for OCSP responses. If the selected cache implementation is not thread-safe, access is serialized using the `gnutls-ocsp-cache` mutex. ### GnuTLSOCSPAutoRefresh Regularly refresh cached OCSP response independent of TLS handshakes? GnuTLSOCSPAutoRefresh [On|Off] Default: *on*\ Context: server config, virtual host By default `mod_gnutls` will regularly refresh the cached OCSP response for hosts that have OCSP stapling enabled, regardless of whether it is used. This has advantages over updating the OCSP response only if a TLS handshake needs it: * Updating the cached response before it expires can hide short unavailability of the OCSP responder, if a repeated request is successful before the cache expires (see below). * Handshakes are not slowed down by fetching responses. The interval to the next request is determined as follows: After a successful OCSP request the next one is scheduled for a random period between `GnuTLSOCSPFuzzTime` and half of it before `GnuTLSOCSPCacheTimeout` expires. For example, if the cache timeout is 3600 seconds and the fuzz time 600 seconds, the next request will be sent after 3000 to 3300 seconds. If the validity period of the response expires before then, the selected interval is halved until it is smaller than the time until expiry. If an OCSP request fails, it is retried after `GnuTLSOCSPFailureTimeout`. Regularly updating the OCSP cache requires `mod_watchdog`, `mod_gnutls` will fall back to updating the OCSP cache during handshakes if `mod_watchdog` is not available or this option is set to `Off`. ### GnuTLSOCSPCheckNonce Check the nonce in OCSP responses? GnuTLSOCSPCheckNonce [On|Off] Default: *on*\ Context: server config, virtual host Some CAs refuse to send nonces in their OCSP responses, probably because that way they can cache responses. If your CA is one of them you can use this flag to disable nonce verification. Note that `mod_gnutls` will _send_ a nonce either way. ### GnuTLSOCSPResponseFile Read the OCSP response for stapling from this file instead of sending a request over HTTP. GnuTLSOCSPResponseFile /path/to/response.der Default: *empty*\ Context: server config, virtual host The response file must be updated externally, for example using a cron job. This option is an alternative to the server fetching OCSP responses over HTTP. Reasons to use this option include: * Performing OCSP requests separate from the web server, to prevent slow responses from stalling handshakes. * The issuer CA uses an access method other than HTTP. * Testing You can use a GnuTLS `ocsptool` command like the following to create and update the response file: ocsptool --ask --nonce --load-issuer ca_cert.pem \ --load-cert server_cert.pem --outfile ocsp_response.der Additional error checking is highly recommended. You may have to remove the `--nonce` option if the OCSP responder of your CA does not support nonces. ### GnuTLSOCSPCacheTimeout Cache timeout for OCSP responses GnuTLSOCSPCacheTimeout SECONDS Default: *3600*\ Context: server config, virtual host Cached OCSP responses will be refreshed after the configured number of seconds. How long this timeout should reasonably be depends on your CA, namely how often its OCSP responder is updated and how long responses are valid. Note that a response will not be cached beyond its lifetime as denoted in the `nextUpdate` field of the response. ### GnuTLSOCSPFailureTimeout Wait this many seconds before retrying a failed OCSP request. GnuTLSOCSPFailureTimeout SECONDS Default: *300*\ Context: server config, virtual host Retries of failed OCSP requests must be rate limited to avoid overloading both the server using mod_gnutls and the CA's OCSP responder. A shorter value increases the load on both sides, a longer one means that stapling will remain disabled for longer after a failed request. ### GnuTLSOCSPFuzzTime Update the cached OCSP response up to this time before the cache expires GnuTLSOCSPFuzzTime SECONDS Default: *larger of GnuTLSOCSPCacheTimeout / 8 and GnuTLSOCSPFailureTimeout \* 2*\ Context: server config, virtual host Refreshing the cached response before it expires hides short OCSP responder unavailability. See `GnuTLSOCSPAutoRefresh` for how this value is used, using at least twice `GnuTLSOCSPFailureTimeout` is recommended. ### GnuTLSOCSPSocketTimeout Timeout for TCP sockets used to send OCSP requests GnuTLSOCSPFailureTimeout SECONDS Default: *6*\ Context: server config, virtual host Stalled OCSP requests must time out after a while to prevent stalling the server too much. However, if the timeout is too short requests may fail with a slow OCSP responder or high latency network connection. This parameter allows you to adjust the timeout if necessary. Note that this is not an upper limit for the completion of an OCSP request but a socket timeout. The connection will time out if there is no activity (successful send or receive) at all for the configured time. * * * * * Configuration Examples ====================== Simple Standard TLS Example --------------------------- The following is an example of simple TLS hosting, using one IP Addresses for each virtual host. # Load the module into Apache. LoadModule gnutls_module modules/mod_gnutls.so GnuTLSCache dbm:/var/cache/www-tls-cache GnuTLSCacheTimeout 500 # Without SNI you need one IP Address per-site. Listen 192.0.2.1:443 Listen 192.0.2.2:443 Listen 192.0.2.3:443 Listen 192.0.2.4:443 GnuTLSEnable on GnuTLSPriorities SECURE128 DocumentRoot /www/site1.example.com/html ServerName site1.example.com:443 GnuTLSCertificateFile conf/tls/site1.crt GnuTLSKeyFile conf/tls/site1.key # This virtual host enables SRP authentication GnuTLSEnable on GnuTLSPriorities NORMAL:+SRP DocumentRoot /www/site2.example.com/html ServerName site2.example.com:443 GnuTLSSRPPasswdFile conf/tls/tpasswd.site2 GnuTLSSRPPasswdConfFile conf/tls/tpasswd.site2.conf # This server enables SRP and X.509 authentication. GnuTLSEnable on GnuTLSPriorities NORMAL:+SRP:+SRP-RSA:+SRP-DSS DocumentRoot /www/site3.example.com/html ServerName site3.example.com:443 GnuTLSCertificateFile conf/tls/site3.crt GnuTLSKeyFile conf/tls/site3.key GnuTLSClientVerify ignore GnuTLSSRPPasswdFile conf/tls/tpasswd.site3 GnuTLSSRPPasswdConfFile conf/tls/tpasswd.site3.conf GnuTLSEnable on # %COMPAT disables some security features to enable maximum # compatibility with clients. Don't use this if you need strong # security. GnuTLSPriorities NORMAL:%COMPAT DocumentRoot /www/site4.example.com/html ServerName site4.example.com:443 GnuTLSCertificateFile conf/tls/site4.crt GnuTLSKeyFile conf/tls/site4.key Server Name Indication Example ------------------------------ `mod_gnutls` supports "Server Name Indication", as specified in [RFC 6066, Section 3](https://tools.ietf.org/html/rfc6066#section-3). This allows hosting many TLS websites with a single IP address. All recent browsers support this standard. Here is an example using SNI: # Load the module into Apache. LoadModule gnutls_module modules/mod_gnutls.so # SNI allows hosting multiple sites using one IP address. This # could also be 'Listen *:443', just like '*:80' is common for # non-HTTPS Listen 198.51.100.1:443 GnuTLSEnable on GnuTLSSessionTickets on DocumentRoot /www/site1.example.com/html ServerName site1.example.com:443 GnuTLSCertificateFile conf/tls/site1.crt GnuTLSKeyFile conf/tls/site1.key GnuTLSEnable on DocumentRoot /www/site2.example.com/html ServerName site2.example.com:443 GnuTLSCertificateFile conf/tls/site2.crt GnuTLSKeyFile conf/tls/site2.key GnuTLSEnable on DocumentRoot /www/site3.example.com/html ServerName site3.example.com:443 GnuTLSCertificateFile conf/tls/site3.crt GnuTLSKeyFile conf/tls/site3.key GnuTLSEnable on DocumentRoot /www/site4.example.com/html ServerName site4.example.com:443 GnuTLSCertificateFile conf/tls/site4.crt GnuTLSKeyFile conf/tls/site4.key OCSP Stapling Example --------------------- This example uses an X.509 server certificate. The server will fetch OCSP responses from the responder listed in the certificate and store them im a memcached cache shared with another server. # Load the module into Apache. LoadModule gnutls_module modules/mod_gnutls.so GnuTLSCache memcache:192.0.2.1:11211,192.0.2.2:11211 GnuTLSCacheTimeout 600 Listen 192.0.2.1:443 GnuTLSEnable On DocumentRoot /www/site1.example.com/html ServerName site1.example.com:443 GnuTLSCertificateFile conf/tls/site1.crt GnuTLSKeyFile conf/tls/site1.key GnuTLSOCSPStapling On * * * * * Environment Variables ===================== `mod_gnutls` exports the following environment variables to scripts. These are compatible with `mod_ssl`. `HTTPS` ------- Can be `on` or `off` `SSL_VERSION_LIBRARY` --------------------- The version of the GnuTLS library `SSL_VERSION_INTERFACE` ----------------------- The version of this module `SSL_PROTOCOL` -------------- The SSL or TLS protocol name (such as `TLS 1.0` etc.) `SSL_CIPHER` ------------ The SSL or TLS cipher suite name `SSL_COMPRESS_METHOD` --------------------- The negotiated compression method (`NULL` or `DEFLATE`) `SSL_SRP_USER` -------------- The SRP username used for authentication (only set when `GnuTLSSRPPasswdFile` and `GnuTLSSRPPasswdConfFile` are configured). `SSL_CIPHER_USEKEYSIZE` & `SSL_CIPHER_ALGKEYSIZE` ------------------------------------------------- The number if bits used in the used cipher algorithm. This does not fully reflect the security level since the size of RSA or DHE key exchange parameters affect the security level too. `SSL_DH_PRIME_BITS` ------------------- The number if bits in the modulus for the DH group, if DHE or static DH is used. This will not be set if DH is not used. `SSL_CIPHER_EXPORT` ------------------- `True` or `False`. Whether the cipher suite negotiated is an export one. `SSL_SESSION_ID` ---------------- The session ID negotiated in this session. Can be the same during client reloads. `SSL_CLIENT_V_REMAIN` --------------------- The number of days until the client's certificate is expired. `SSL_CLIENT_V_START` -------------------- The activation time of client's certificate. `SSL_CLIENT_V_END` ------------------ The expiration time of client's certificate. `SSL_CLIENT_S_DN` ----------------- The distinguished name of client's certificate in RFC2253 format. `SSL_CLIENT_I_DN` ----------------- The distinguished name of the issuer of the client's certificate in RFC2253 format. `SSL_CLIENT_S_AN%` ------------------ These will contain the alternative names of the client certificate (`%` is a number starting from zero). The values will be prepended by `DNSNAME:`, `RFC822NAME:` or `URI:` depending on the type. If it is not supported the value `UNSUPPORTED` will be set. `SSL_SERVER_M_SERIAL` --------------------- The serial number of the server's certificate. `SSL_SERVER_M_VERSION` ---------------------- The version of the server's certificate. `SSL_SERVER_A_SIG` ------------------ The algorithm used for the signature in server's certificate. `SSL_SERVER_A_KEY` ------------------ The public key algorithm in server's certificate. `SSL_SERVER_CERT` ------------------ The PEM-encoded (X.509) server certificate (see the `GnuTLSExportCertificates` directive). `SSL_SERVER_CERT_TYPE` ---------------------- The certificate type will be `X.509`. `SSL_CLIENT_CERT` ------------------ PEM-encoded (X.509) client certificate, if any (see the `GnuTLSExportCertificates` directive). `SSL_CLIENT_CERT_TYPE` ---------------------- The certificate type will be `X.509`, if any.