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.\" $OpenBSD: SSL_CTX_set_tlsext_use_srtp.3,v 1.4 2019/06/12 09:36:30 schwarze Exp $
.\" full merge up to: OpenSSL b0edda11 Mar 20 13:00:17 2018 +0000
.\"
.\" This file was written by Matt Caswell <matt@openssl.org>.
.\" 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. All advertising materials mentioning features or use of this
.\" software must display the following acknowledgment:
.\" "This product includes software developed by the OpenSSL Project
.\" for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
.\"
.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
.\" endorse or promote products derived from this software without
.\" prior written permission. For written permission, please contact
.\" openssl-core@openssl.org.
.\"
.\" 5. Products derived from this software may not be called "OpenSSL"
.\" nor may "OpenSSL" appear in their names without prior written
.\" permission of the OpenSSL Project.
.\"
.\" 6. Redistributions of any form whatsoever must retain the following
.\" acknowledgment:
.\" "This product includes software developed by the OpenSSL Project
.\" for use in the OpenSSL Toolkit (http://www.openssl.org/)"
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED. 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,
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
.\" OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd $Mdocdate: June 12 2019 $
.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 RFC5764.
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 RFC5763.
OpenSSL does not implement SRTP itself or RFC5763.
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 RFC5764.
.It Dv SRTP_AES128_CM_SHA1_32
This corresponds to SRTP_AES128_CM_HMAC_SHA1_32 defined in RFC5764.
.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 .
|
