Configure and query SRTP
*ctx, const char *profiles);
*ssl, const char *profiles);
SRTP is the Secure Real-Time Transport Protocol. OpenSSL implements support for the "use_srtp" DTLS extension defined in RFC 5764. This provides a mechanism for establishing SRTP keying material, algorithms and parameters using DTLS. This capability may be used as part of an implementation that conforms to RFC 5763. OpenSSL does not implement SRTP itself or RFC 5763. Note that OpenSSL does not support the use of SRTP Master Key Identifiers (MKIs). Also note that this extension is only supported in DTLS. Any SRTP configuration is ignored if a TLS connection is attempted.
An OpenSSL client wishing to send
the "use_srtp" extension should call
to set its use for all SSL objects subsequently
created from ctx. Alternatively a client may call
to set its use for an individual SSL object. The
profiles parameter should point to a NUL-terminated,
colon delimited list of SRTP protection profile names.
The currently supported protection profile names are:
- This corresponds to SRTP_AES128_CM_HMAC_SHA1_80 defined in RFC 5764.
- This corresponds to SRTP_AES128_CM_HMAC_SHA1_32 defined in RFC 5764.
- This corresponds to SRTP_AEAD_AES_128_GCM defined in RFC 7714.
- This corresponds to SRTP_AEAD_AES_256_GCM defined in RFC 7714.
Supplying an unrecognised protection profile name results in an error.
An OpenSSL server wishing to
support the "use_srtp" extension should also call
to indicate the protection profiles that it is willing to negotiate.
The currently configured list of
protection profiles for either a client or a server can be obtained by
This returns a stack of SRTP_PROTECTION_PROFILE
objects. The memory pointed to in the return value of this function should
not be freed by the caller.
After a handshake has been
completed, the negotiated SRTP protection profile (if any) can be obtained
(on the client or the server) by calling
This function returns
NULL if no SRTP protection
profile was negotiated. The memory returned from this function should not be
freed by the caller.
If an SRTP protection profile has been successfully negotiated,
then the SRTP keying material (on both the client and server) should be
obtained by calling
SSL_export_keying_material(3) with a
label of "EXTRACTOR-dtls_srtp", a
NULL, and a
use_context argument of 0. The total length of keying
material obtained should be equal to two times the sum of the master key
length and the salt length as defined for the protection profile in use.
This provides the client write master key, the server write master key, the
client write master salt and the server write master salt in that order.
Contrary to OpenSSL conventions,
SSL_set_tlsext_use_srtp() return 0 on success or 1
SSL_get_srtp_profiles() returns a stack of
SRTP_PROTECTION_PROFILE objects on success or
NULL on error or if no protection profiles have been
SSL_get_selected_srtp_profile() returns a
pointer to an SRTP_PROTECTION_PROFILE object if one
has been negotiated or
These functions first appeared in OpenSSL 1.0.1 and have been available since OpenBSD 5.3.