Implement RFC 5764 (DTLS-SRTP).

net/third_party/nss/ssl/sslsock.c

 /*
  * vtables (and methods that call through them) for the 4 types of 
  * SSLSockets supported.  Only one type is still supported.
  * Various other functions.
  *
  * ***** BEGIN LICENSE BLOCK *****
  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
  *
  * The contents of this file are subject to the Mozilla Public License Version
  * 1.1 (the "License"); you may not use this file except in compliance with
@@ skipping 207 matching lines @@
 PRBool                  locksEverDisabled;      /* implicitly PR_FALSE */
 PRBool                  ssl_force_locks;        /* implicitly PR_FALSE */
 int                     ssl_lock_readers        = 1;    /* default true. */
 char                    ssl_debug;
 char                    ssl_trace;
 FILE *                  ssl_trace_iob;
 FILE *                  ssl_keylog_iob;
 char lockStatus[] = "Locks are ENABLED.  ";
 #define LOCKSTATUS_OFFSET 10 /* offset of ENABLED */
 
+/* SRTP_NULL_HMAC_SHA1_80 and SRTP_NULL_HMAC_SHA1_32 are not implemented. */
+static const PRUint16 srtpCiphers[] = {
+    SRTP_AES128_CM_HMAC_SHA1_80,
+    SRTP_AES128_CM_HMAC_SHA1_32,
+    0
+};
+
 /* forward declarations. */
 static sslSocket *ssl_NewSocket(PRBool makeLocks, SSLProtocolVariant variant);
 static SECStatus  ssl_MakeLocks(sslSocket *ss);
 static void       ssl_SetDefaultsFromEnvironment(void);
 static PRStatus   ssl_PushIOLayer(sslSocket *ns, PRFileDesc *stack, 
                                   PRDescIdentity id);
 
 /************************************************************************/
 
 /*
@@ skipping 1351 matching lines @@
         }
         PORT_Memcpy(buf, ss->ssl3.nextProto.data, ss->ssl3.nextProto.len);
         *bufLen = ss->ssl3.nextProto.len;
     } else {
         *bufLen = 0;
     }
 
     return SECSuccess;
 }
 
+SECStatus SSL_SetSRTPCiphers(PRFileDesc *fd,
+                             const PRUint16 *ciphers,
+                             unsigned int numCiphers)
+{
+    sslSocket * ss;
+    int i;
+
+    ss = ssl_FindSocket(fd);
+    if (!ss || !IS_DTLS(ss)) {
+        SSL_DBG(("%d: SSL[%d]: bad socket in SSL_SetSRTPCiphers",
+                 SSL_GETPID(), fd));
+        PORT_SetError(SEC_ERROR_INVALID_ARGS);
+        return SECFailure;
+    }
+
+    for (i = 0; i < numCiphers; i++) {
+        const PRUint16 *srtpCipher = srtpCiphers;
+
+        while (*srtpCipher) {
+            if (ciphers[i] == *srtpCipher)
+                break;
+            srtpCipher++;
+        }
+        if (!*srtpCipher) {
+            SSL_DBG(("%d: SSL[%d]: invalid or unimplemented SRTP cipher "
+                     "suite specified: 0x%04hx", SSL_GETPID(), fd,
+                     ciphers[i]));
+            PORT_SetError(SEC_ERROR_INVALID_ARGS);

[Ryan Sleevi, 2012/05/10 19:43:11]

The NSS SSL/DTLS code accepts non-existant cipher suites without issue, simply
ignoring them. I think this works to our advantage. Does it make sense to do the
same here?

[wtc, 2012/05/12 01:00:59]

SSL_CipherPrefSet returns SECFailure with
SSL_ERROR_UNKNOWN_CIPHER_SUITE if the cipher suite is
nonexistent.  Perhaps I misunderstood your comment here?

[Ryan Sleevi, 2012/05/12 01:13:06]

Ah, you're right, sorry for not double-checking memory.

In the SSL/TLS case, we can enable/disable individual cipher suites via
SSL_CipherPrefSet, so we can safely ignore any errors with unrecognized suites (
see
http://code.google.com/searchframe#OAMlx_jo-ck/src/net/socket/ssl_server_sock...
)

With this code, because setting enabled suites is all-or-nothing, and because
even enabling SRTP is dependent on all-or-nothing suites, we couldn't do such an
approach if we wanted to.

This would be an issue if a cipher suite ever needed to be removed, as it would
break clients still supplying the old cipher suite. I think that would argue in
favour of separating the API?

[wtc, 2012/05/15 00:56:41]

I also came to the same conclusion that we probably should
enable SRTP cipher suites individually, in the same way we
enable TLS cipher suites.

Ekr: do you have time to implement an SSL_USE_SRTP socket
option and the SSL_SRTPCipherPrefSet and SSL_SRTPCipherPrefGet
functions, or do you want me to do that?

I think we can omit the global preferences and just support
a model socket.

+            return SECFailure;
+        }
+    }
+
+    if (numCiphers > MAX_DTLS_SRTP_CIPHER_SUITES) {
+        PORT_SetError(SEC_ERROR_INVALID_ARGS);
+        return SECFailure;
+    }
+    memcpy(ss->ssl3.dtlsSRTPCiphers, ciphers, sizeof(PRUint16) * numCiphers);
+    ss->ssl3.dtlsSRTPCipherCount = numCiphers;
+
+    return SECSuccess;
+}
+
+SECStatus
+SSL_GetSRTPCipher(PRFileDesc *fd, PRUint16 *cipher)
+{
+    sslSocket * ss;
+
+    ss = ssl_FindSocket(fd);
+    if (!ss) {
+        SSL_DBG(("%d: SSL[%d]: bad socket in SSL_GetSRTPCipher",
+                 SSL_GETPID(), fd));
+        PORT_SetError(SEC_ERROR_INVALID_ARGS);
+        return SECFailure;
+    }
+
+    if (!ss->ssl3.dtlsSRTPCipherSuite) {
+        PORT_SetError(SEC_ERROR_INVALID_ARGS);
+        return SECFailure;
+    }
+
+    *cipher = ss->ssl3.dtlsSRTPCipherSuite;
+    return SECSuccess;
+}
+
 PRFileDesc *
 SSL_ReconfigFD(PRFileDesc *model, PRFileDesc *fd)
 {
     PORT_SetError(PR_NOT_IMPLEMENTED_ERROR);
     PR_NOT_REACHED("not implemented");
     return NULL;
 
 #if 0

[Ryan Sleevi, 2012/05/10 19:43:11]

Does it make sense to update this function, even though it's not implemented?

Seems a subtle edge if it gets enabled but breaks.

[wtc, 2012/05/12 01:00:59]

I updated both this function and ssl_DupSocket (both of them
take a model socket as input).

     sslSocket * sm = NULL, *ss = NULL;
     int i;
     sslServerCerts * mc = NULL;
     sslServerCerts * sc = NULL;
 
     if (model == NULL) {
         PR_SetError(SEC_ERROR_INVALID_ARGS, 0);
         return NULL;
     }
     sm = ssl_FindSocket(model);
@@ skipping 1364 matching lines @@
             ssl_DestroySocketContents(ss);
             ssl_DestroyLocks(ss);
             PORT_Free(ss);
             ss = NULL;
         }
         ss->protocolVariant = protocolVariant;
     }
     return ss;
 }