#include <openssl/ssl.h> int SSL_CONF_cmd(SSL_CONF_CTX *cctx, const char *cmd, const char *value); int SSL_CONF_cmd_value_type(SSL_CONF_CTX *cctx, const char *cmd);
SSL_CONF_cmd_value_type() returns the type of value that cmd refers to.
The value argument should be a colon separated list of signature algorithms in order of decreasing preference of the form algorithm+hash or signature_scheme. algorithm is one of RSA, DSA or ECDSA and hash is a supported algorithm OID short name such as SHA1, SHA224, SHA256, SHA384 of SHA512. Note: algorithm and hash names are case sensitive. signature_scheme is one of the signature schemes defined in TLSv1.3, specified using the IETF name, e.g., ecdsa_secp256r1_sha256, ed25519, or rsa_pss_pss_sha256.
If this option is not set then all signature algorithms supported by the OpenSSL library are permissible.
Note: algorithms which specify a PKCS#1 v1.5 signature scheme (either by using RSA as the algorithm or by using one of the rsa_pkcs1_* identifiers) are ignored in TLSv1.3 and will not be negotiated.
The syntax of value is identical to -sigalgs. If not set then the value set for -sigalgs will be used instead.
The value argument is a colon separated list of groups. The group can be either the NIST name (e.g. P-256), some other commonly used name where applicable (e.g. X25519) or an OpenSSL OID name (e.g. prime256v1). Group names are case sensitive. The list should be in order of preference with the most preferred group first.
The value argument is a curve name or the special value auto which picks an appropriate curve based on client and server preferences. The curve can be either the NIST name (e.g. P-256) or an OpenSSL OID name (e.g. prime256v1). Curve names are case sensitive.
Note: the command prefix (if set) alters the recognised cmd values.
The value argument should be a colon separated list of signature algorithms in order of decreasing preference of the form algorithm+hash or signature_scheme. algorithm is one of RSA, DSA or ECDSA and hash is a supported algorithm OID short name such as SHA1, SHA224, SHA256, SHA384 of SHA512. Note: algorithm and hash names are case sensitive. signature_scheme is one of the signature schemes defined in TLSv1.3, specified using the IETF name, e.g., ecdsa_secp256r1_sha256, ed25519, or rsa_pss_pss_sha256.
If this option is not set then all signature algorithms supported by the OpenSSL library are permissible.
Note: algorithms which specify a PKCS#1 v1.5 signature scheme (either by using RSA as the algorithm or by using one of the rsa_pkcs1_* identifiers) are ignored in TLSv1.3 and will not be negotiated.
The syntax of value is identical to SignatureAlgorithms. If not set then the value set for SignatureAlgorithms will be used instead.
The value argument is a colon separated list of groups. The group can be either the NIST name (e.g. P-256), some other commonly used name where applicable (e.g. X25519) or an OpenSSL OID name (e.g. prime256v1). Group names are case sensitive. The list should be in order of preference with the most preferred group first.
Currently supported protocol values are SSLv3, TLSv1, TLSv1.1, TLSv1.2, TLSv1.3, DTLSv1 and DTLSv1.2. The SSL and TLS bounds apply only to TLS-based contexts, while the DTLS bounds apply only to DTLS-based contexts. The command can be repeated with one instance setting a TLS bound, and the other setting a DTLS bound. The value None applies to both types of contexts and disables the limits.
Currently supported protocol values are SSLv3, TLSv1, TLSv1.1, TLSv1.2, TLSv1.3, DTLSv1 and DTLSv1.2. The SSL and TLS bounds apply only to TLS-based contexts, while the DTLS bounds apply only to DTLS-based contexts. The command can be repeated with one instance setting a TLS bound, and the other setting a DTLS bound. The value None applies to both types of contexts and disables the limits.
The value argument is a comma separated list of supported protocols to enable or disable. If a protocol is preceded by - that version is disabled.
All protocol versions are enabled by default. You need to disable at least one protocol version for this setting have any effect. Only enabling some protocol versions does not disable the other protocol versions.
Currently supported protocol values are SSLv3, TLSv1, TLSv1.1, TLSv1.2, TLSv1.3, DTLSv1 and DTLSv1.2. The special value ALL refers to all supported versions.
This can't enable protocols that are disabled using MinProtocol or MaxProtocol, but can disable protocols that are still allowed by them.
The Protocol command is fragile and deprecated; do not use it. Use MinProtocol and MaxProtocol instead. If you do use Protocol, make sure that the resulting range of enabled protocols has no ``holes'', e.g. if TLS 1.0 and TLS 1.2 are both enabled, make sure to also leave TLS 1.1 enabled.
Each option is listed below. Where an operation is enabled by default the -flag syntax is needed to disable it.
SessionTicket: session ticket support, enabled by default. Inverse of SSL_OP_NO_TICKET: that is -SessionTicket is the same as setting SSL_OP_NO_TICKET.
Compression: SSL/TLS compression support, enabled by default. Inverse of SSL_OP_NO_COMPRESSION.
EmptyFragments: use empty fragments as a countermeasure against a SSL 3.0/TLS 1.0 protocol vulnerability affecting CBC ciphers. It is set by default. Inverse of SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS.
Bugs: enable various bug workarounds. Same as SSL_OP_ALL.
DHSingle: enable single use DH keys, set by default. Inverse of SSL_OP_DH_SINGLE. Only used by servers.
ECDHSingle: enable single use ECDH keys, set by default. Inverse of SSL_OP_ECDH_SINGLE. Only used by servers.
ServerPreference: use server and not client preference order when determining which cipher suite, signature algorithm or elliptic curve to use for an incoming connection. Equivalent to SSL_OP_CIPHER_SERVER_PREFERENCE. Only used by servers.
PrioritizeChaCha: prioritizes ChaCha ciphers when the client has a ChaCha20 cipher at the top of its preference list. This usually indicates a mobile client is in use. Equivalent to SSL_OP_PRIORITIZE_CHACHA. Only used by servers.
NoResumptionOnRenegotiation: set SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION flag. Only used by servers.
NoRenegotiation: disables all attempts at renegotiation in TLSv1.2 and earlier, same as setting SSL_OP_NO_RENEGOTIATION.
UnsafeLegacyRenegotiation: permits the use of unsafe legacy renegotiation. Equivalent to SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION.
UnsafeLegacyServerConnect: permits the use of unsafe legacy renegotiation for OpenSSL clients only. Equivalent to SSL_OP_LEGACY_SERVER_CONNECT. Set by default.
EncryptThenMac: use encrypt-then-mac extension, enabled by default. Inverse of SSL_OP_NO_ENCRYPT_THEN_MAC: that is, -EncryptThenMac is the same as setting SSL_OP_NO_ENCRYPT_THEN_MAC.
AllowNoDHEKEX: In TLSv1.3 allow a non-(ec)dhe based key exchange mode on resumption. This means that there will be no forward secrecy for the resumed session. Equivalent to SSL_OP_ALLOW_NO_DHE_KEX.
MiddleboxCompat: If set then dummy Change Cipher Spec (CCS) messages are sent in TLSv1.3. This has the effect of making TLSv1.3 look more like TLSv1.2 so that middleboxes that do not understand TLSv1.3 will not drop the connection. This option is set by default. A future version of OpenSSL may not set this by default. Equivalent to SSL_OP_ENABLE_MIDDLEBOX_COMPAT.
AntiReplay: If set then OpenSSL will automatically detect if a session ticket has been used more than once, TLSv1.3 has been negotiated, and early data is enabled on the server. A full handshake is forced if a session ticket is used a second or subsequent time. This option is set by default and is only used by servers. Anti-replay measures are required to comply with the TLSv1.3 specification. Some applications may be able to mitigate the replay risks in other ways and in such cases the built-in OpenSSL functionality is not required. Disabling anti-replay is equivalent to setting SSL_OP_NO_ANTI_REPLAY.
Peer enables peer verification: for clients only.
Request requests but does not require a certificate from the client. Servers only.
Require requests and requires a certificate from the client: an error occurs if the client does not present a certificate. Servers only.
Once requests a certificate from a client only on the initial connection: not when renegotiating. Servers only.
RequestPostHandshake configures the connection to support requests but does not require a certificate from the client post-handshake. A certificate will not be requested during the initial handshake. The server application must provide a mechanism to request a certificate post-handshake. Servers only. TLSv1.3 only.
RequiresPostHandshake configures the connection to support requests and requires a certificate from the client post-handshake: an error occurs if the client does not present a certificate. A certificate will not be requested during the initial handshake. The server application must provide a mechanism to request a certificate post-handshake. Servers only. TLSv1.3 only.
SSL_CONF_cmd(ctx, "Protocol", "-SSLv3"); SSL_CONF_cmd(ctx, userparam, uservalue);
it will disable SSLv3 support by default but the user can override it. If however the call sequence is:
SSL_CONF_cmd(ctx, userparam, uservalue); SSL_CONF_cmd(ctx, "Protocol", "-SSLv3");
SSLv3 is always disabled and attempt to override this by the user are ignored.
By checking the return code of SSL_CONF_cmd() it is possible to query if a given cmd is recognised, this is useful if SSL_CONF_cmd() values are mixed with additional application specific operations.
For example an application might call SSL_CONF_cmd() and if it returns -2 (unrecognised command) continue with processing of application specific commands.
Applications can also use SSL_CONF_cmd() to process command lines though the utility function SSL_CONF_cmd_argv() is normally used instead. One way to do this is to set the prefix to an appropriate value using SSL_CONF_CTX_set1_prefix(), pass the current argument to cmd and the following argument to value (which may be NULL).
In this case if the return value is positive then it is used to skip that number of arguments as they have been processed by SSL_CONF_cmd(). If -2 is returned then cmd is not recognised and application specific arguments can be checked instead. If -3 is returned a required argument is missing and an error is indicated. If 0 is returned some other error occurred and this can be reported back to the user.
The function SSL_CONF_cmd_value_type() can be used by applications to check for the existence of a command or to perform additional syntax checking or translation of the command value. For example if the return value is SSL_CONF_TYPE_FILE an application could translate a relative pathname to an absolute pathname.
A return value of -2 means cmd is not recognised.
A return value of -3 means cmd is recognised and the command requires a value but value is NULL.
A return code of 0 indicates that both cmd and value are valid but an error occurred attempting to perform the operation: for example due to an error in the syntax of value in this case the error queue may provide additional information.
SSL_CONF_cmd(ctx, "SignatureAlgorithms", "ECDSA+SHA256:RSA+SHA256:DSA+SHA256");
There are various ways to select the supported protocols.
This set the minimum protocol version to TLSv1, and so disables SSLv3. This is the recommended way to disable protocols.
SSL_CONF_cmd(ctx, "MinProtocol", "TLSv1");
The following also disables SSLv3:
SSL_CONF_cmd(ctx, "Protocol", "-SSLv3");
The following will first enable all protocols, and then disable SSLv3. If no protocol versions were disabled before this has the same effect as ``-SSLv3'', but if some versions were disables this will re-enable them before disabling SSLv3.
SSL_CONF_cmd(ctx, "Protocol", "ALL,-SSLv3");
Only enable TLSv1.2:
SSL_CONF_cmd(ctx, "MinProtocol", "TLSv1.2"); SSL_CONF_cmd(ctx, "MaxProtocol", "TLSv1.2");
This also only enables TLSv1.2:
SSL_CONF_cmd(ctx, "Protocol", "-ALL,TLSv1.2");
Disable TLS session tickets:
SSL_CONF_cmd(ctx, "Options", "-SessionTicket");
Enable compression:
SSL_CONF_cmd(ctx, "Options", "Compression");
Set supported curves to P-256, P-384:
SSL_CONF_cmd(ctx, "Curves", "P-256:P-384");
The SSL_OP_NO_SSL2 option doesn't have effect since 1.1.0, but the macro is retained for backwards compatibility.
The SSL_CONF_TYPE_NONE was added in OpenSSL 1.1.0. In earlier versions of OpenSSL passing a command which didn't take an argument would return SSL_CONF_TYPE_UNKNOWN.
MinProtocol and MaxProtocol where added in OpenSSL 1.1.0.
AllowNoDHEKEX and PrioritizeChaCha were added in OpenSSL 1.1.1.
Licensed under the OpenSSL license (the ``License''). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.