.\" $OpenBSD: SSL_CTX_set_tlsext_use_srtp.3,v 1.6 2021/06/11 19:41:39 jmc Exp $ .\" full merge up to: OpenSSL b0edda11 Mar 20 13:00:17 2018 +0000 .\" .\" This file was written by Matt Caswell . .\" Copyright (c) 2017 The OpenSSL Project. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in .\" the documentation and/or other materials provided with the .\" distribution. .\" .\" 3. 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IN NO EVENT SHALL THE OpenSSL PROJECT OR .\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, .\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; .\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, .\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED .\" OF THE POSSIBILITY OF SUCH DAMAGE. .\" .Dd $Mdocdate: June 11 2021 $ .Dt SSL_CTX_SET_TLSEXT_USE_SRTP 3 .Os .Sh NAME .Nm SSL_CTX_set_tlsext_use_srtp , .Nm SSL_set_tlsext_use_srtp , .Nm SSL_get_srtp_profiles , .Nm SSL_get_selected_srtp_profile .Nd Configure and query SRTP support .Sh SYNOPSIS .In openssl/srtp.h .Ft int .Fo SSL_CTX_set_tlsext_use_srtp .Fa "SSL_CTX *ctx" .Fa "const char *profiles" .Fc .Ft int .Fo SSL_set_tlsext_use_srtp .Fa "SSL *ssl" .Fa "const char *profiles" .Fc .Ft STACK_OF(SRTP_PROTECTION_PROFILE) * .Fo SSL_get_srtp_profiles .Fa "SSL *ssl" .Fc .Ft SRTP_PROTECTION_PROFILE * .Fo SSL_get_selected_srtp_profile .Fa "SSL *ssl" .Fc .Sh DESCRIPTION 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. .Pp An OpenSSL client wishing to send the "use_srtp" extension should call .Fn SSL_CTX_set_tlsext_use_srtp to set its use for all .Vt SSL objects subsequently created from .Fa ctx . Alternatively a client may call .Fn SSL_set_tlsext_use_srtp to set its use for an individual .Vt SSL object. The .Fa profiles parameter should point to a NUL-terminated, colon delimited list of SRTP protection profile names. .Pp The currently supported protection profile names are: .Bl -tag -width Ds .It Dv SRTP_AES128_CM_SHA1_80 This corresponds to SRTP_AES128_CM_HMAC_SHA1_80 defined in RFC 5764. .It Dv SRTP_AES128_CM_SHA1_32 This corresponds to SRTP_AES128_CM_HMAC_SHA1_32 defined in RFC 5764. .It Dv SRTP_AEAD_AES_128_GCM This corresponds to SRTP_AEAD_AES_128_GCM defined in RFC 7714. .It Dv SRTP_AEAD_AES_256_GCM This corresponds to SRTP_AEAD_AES_256_GCM defined in RFC 7714. .El .Pp Supplying an unrecognised protection profile name results in an error. .Pp An OpenSSL server wishing to support the "use_srtp" extension should also call .Fn SSL_CTX_set_tlsext_use_srtp or .Fn SSL_set_tlsext_use_srtp to indicate the protection profiles that it is willing to negotiate. .Pp The currently configured list of protection profiles for either a client or a server can be obtained by calling .Fn SSL_get_srtp_profiles . This returns a stack of .Vt SRTP_PROTECTION_PROFILE objects. The memory pointed to in the return value of this function should not be freed by the caller. .Pp After a handshake has been completed, the negotiated SRTP protection profile (if any) can be obtained (on the client or the server) by calling .Fn SSL_get_selected_srtp_profile . This function returns .Dv NULL if no SRTP protection profile was negotiated. The memory returned from this function should not be freed by the caller. .Pp 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 .Xr SSL_export_keying_material 3 with a .Fa label of .Qq EXTRACTOR-dtls_srtp , a .Fa context of .Dv NULL , and a .Fa 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. .Sh RETURN VALUES Contrary to OpenSSL conventions, .Fn SSL_CTX_set_tlsext_use_srtp and .Fn SSL_set_tlsext_use_srtp return 0 on success or 1 on error. .Pp .Fn SSL_get_srtp_profiles returns a stack of .Vt SRTP_PROTECTION_PROFILE objects on success or .Dv NULL on error or if no protection profiles have been configured. .Pp .Fn SSL_get_selected_srtp_profile returns a pointer to an .Vt SRTP_PROTECTION_PROFILE object if one has been negotiated or .Dv NULL otherwise. .Sh SEE ALSO .Xr ssl 3 , .Xr SSL_export_keying_material 3 .Sh HISTORY These functions first appeared in OpenSSL 1.0.1 and have been available since .Ox 5.3 .