Add documentation for SRTP functions

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4205)

doc/man3/SSL_CTX_set_tlsext_use_srtp.pod

@@ -0,0 +1,111 @@
+=pod
+
+=head1 NAME
+
+SSL_CTX_set_tlsext_use_srtp,
+SSL_set_tlsext_use_srtp,
+SSL_get_srtp_profiles,
+SSL_get_selected_srtp_profile
+- Configure and query SRTP support
+
+=head1 SYNOPSIS
+
+ #include <openssl/srtp.h>
+
+ int SSL_CTX_set_tlsext_use_srtp(SSL_CTX *ctx, const char *profiles);
+ int SSL_set_tlsext_use_srtp(SSL *ssl, const char *profiles);
+
+ STACK_OF(SRTP_PROTECTION_PROFILE) *SSL_get_srtp_profiles(SSL *ssl);
+ SRTP_PROTECTION_PROFILE *SSL_get_selected_srtp_profile(SSL *s);
+
+=head1 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 will be ignored if a
+TLS connection is attempted.
+
+An OpenSSL client wishing to send the "use_srtp" extension should call
+SSL_CTX_set_tlsext_use_srtp() to set its use for all SSL objects subsequently
+created from an SSL_CTX. Alternatively a client may call
+SSL_set_tlsext_use_srtp() to set its use for an individual SSL object. The
+B<profiles> parameters should point to a NUL-terminated, colon delimited list of
+SRTP protection profile names.
+
+The currently supported protection profile names are:
+
+=over 4
+
+=item SRTP_AES128_CM_SHA1_80
+
+This corresponds to SRTP_AES128_CM_HMAC_SHA1_80 defined in RFC5764.
+
+=item SRTP_AES128_CM_SHA1_32
+
+This corresponds to SRTP_AES128_CM_HMAC_SHA1_32 defined in RFC5764.
+
+=item SRTP_AEAD_AES_128_GCM
+
+This corresponds to the profile of the same name defined in RFC7714.
+
+=item SRTP_AEAD_AES_256_GCM
+
+This corresponds to the profile of the same name defined in RFC7714.
+
+=back
+
+Supplying an unrecognised protection profile name will result in an error.
+
+An OpenSSL server wishing to support the "use_srtp" extension should also call
+SSL_CTX_set_tlsext_use_srtp() or SSL_set_tlsext_use_srtp() 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 calling SSL_get_srtp_profiles(). 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
+SSL_get_selected_srtp_profile(). This function will return 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 sucessfully negotiated then the SRTP
+keying material (on both the client and server) should be obtained via a call to
+L<SSL_export_keying_material(3)>. This call should provide a label value of
+"EXTRACTOR-dtls_srtp" and a NULL context value (use_context is 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.
+
+=head1 RETURN VALUES
+
+SSL_CTX_set_tlsext_use_srtp() and SSL_set_tlsext_use_srtp() return 0 on success
+or 1 on error.
+
+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 configured.
+
+SSL_get_selected_srtp_profile() returns a pointer to an SRTP_PROTECTION_PROFILE
+object if one has been negotiated or NULL otherwise.
+
+=head1 SEE ALSO
+
+L<SSL_export_keying_material(3)>
+
+=head1 COPYRIGHT
+
+Copyright 2017 The OpenSSL Project Authors. All Rights Reserved.
+
+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
+L<https://www.openssl.org/source/license.html>.
+
+=cut

include/openssl/srtp.h

@@ -36,7 +36,7 @@ extern "C" {
 # ifndef OPENSSL_NO_SRTP
 
 __owur int SSL_CTX_set_tlsext_use_srtp(SSL_CTX *ctx, const char *profiles);
-__owur int SSL_set_tlsext_use_srtp(SSL *ctx, const char *profiles);
+__owur int SSL_set_tlsext_use_srtp(SSL *ssl, const char *profiles);
 
 __owur STACK_OF(SRTP_PROTECTION_PROFILE) *SSL_get_srtp_profiles(SSL *ssl);
 __owur SRTP_PROTECTION_PROFILE *SSL_get_selected_srtp_profile(SSL *s);