From 82f00ea07bffc10985ccb1a15723e6daa0ab4969 Mon Sep 17 00:00:00 2001
From: Guus Sliepen <guus@tinc-vpn.org>
Date: Sun, 3 Jul 2011 15:59:49 +0200
Subject: [PATCH] Use PRF.

---
 src/openssl/prf.c  |  4 ++--
 src/protocol_key.c | 36 +++++++++++++++---------------------
 2 files changed, 17 insertions(+), 23 deletions(-)

diff --git a/src/openssl/prf.c b/src/openssl/prf.c
index 2830d609..59e8a3aa 100644
--- a/src/openssl/prf.c
+++ b/src/openssl/prf.c
@@ -22,14 +22,14 @@
 #include "digest.h"
 #include "prf.h"
 
-/* Generate key material from a master secret and a seed, based on RFC 2246.
+/* Generate key material from a master secret and a seed, based on RFC 4346 section 5.
    We use SHA512 and Whirlpool instead of MD5 and SHA1.
  */
 
 static bool prf_xor(int nid, char *secret, size_t secretlen, char *seed, size_t seedlen, char *out, ssize_t outlen) {
 	digest_t digest;
 	
-	if(!digest_open_by_nid(&digest, nid, 0))
+	if(!digest_open_by_nid(&digest, nid, -1))
 		return false;
 
 	if(!digest_set_key(&digest, secret, secretlen))
diff --git a/src/protocol_key.c b/src/protocol_key.c
index f52e8961..8bbb6ad4 100644
--- a/src/protocol_key.c
+++ b/src/protocol_key.c
@@ -29,6 +29,7 @@
 #include "net.h"
 #include "netutl.h"
 #include "node.h"
+#include "prf.h"
 #include "protocol.h"
 #include "utils.h"
 #include "xalloc.h"
@@ -311,25 +312,27 @@ bool ans_key_h(connection_t *c, char *request) {
 
 		/* Update our crypto end */
 
-		char *mykey;
 		size_t mykeylen = cipher_keylength(&myself->incipher);
 		keylen = cipher_keylength(&from->outcipher);
 
-		if(ECDH_SHARED_SIZE < mykeylen) {
-			logger(LOG_ERR, "ECDH key too short for cipher of MYSELF!");
-			return false;
-		}
-
+		char *mykey;
+		char *seed = NULL;
+		
 		if(strcmp(myself->name, from->name) < 0) {
 			logger(LOG_DEBUG, "Using left half of shared secret");
-			mykey = shared;
-			memcpy(key, shared + ECDH_SHARED_SIZE - keylen, keylen);
+			mykey = key;
+			xasprintf(&seed, "tinc key expansion %s %s", myself->name, from->name);
 		} else {
 			logger(LOG_DEBUG, "Using right half of shared secret");
-			mykey = shared + ECDH_SHARED_SIZE - mykeylen;
-			memcpy(key, shared, keylen);
+			mykey = key + keylen;
+			xasprintf(&seed, "tinc key expansion %s %s", from->name, myself->name);
 		}
 
+		if(!prf(shared, ECDH_SHARED_SIZE, seed, strlen(seed), key, keylen + mykeylen))
+			return false;
+
+		free(seed);
+
 		cipher_open_by_nid(&from->incipher, cipher_get_nid(&myself->incipher));
 		digest_open_by_nid(&from->indigest, digest_get_nid(&myself->indigest), digest_length(&myself->indigest));
 		from->incompression = myself->incompression;
@@ -343,17 +346,8 @@ bool ans_key_h(connection_t *c, char *request) {
 		if(replaywin)
 			memset(from->late, 0, replaywin);
 
-		bin2hex(shared, hex, ECDH_SHARED_SIZE);
-		hex[ECDH_SHARED_SIZE * 2] = 0;
-		logger(LOG_DEBUG, "Shared secret was %s", hex);
-
-		bin2hex(mykey, hex, mykeylen);
-		hex[mykeylen * 2] = 0;
-		logger(LOG_DEBUG, "My part is: %s (%d)", hex, mykeylen);
-
-		bin2hex(key, hex, keylen);
-		hex[keylen * 2] = 0;
-		logger(LOG_DEBUG, "His part is: %s (%d)", hex, keylen);
+		if(strcmp(myself->name, from->name) < 0)
+			memmove(key, key + mykeylen, keylen);
 	} else {
 		keylen = strlen(key) / 2;
 		hex2bin(key, key, keylen);
-- 
2.39.5