Proper use of PRF.

[tinc] / src / protocol_key.c

diff --git a/src/protocol_key.c b/src/protocol_key.c
index f52e896..4b2047a 100644 (file)
--- 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"
@@ -278,11 +279,8 @@ bool ans_key_h(connection_t *c, char *request) {
        from->outcompression = compression;
 
        /* ECDH or old-style key exchange? */
-       /* TODO: look at SSH and TLS to see how they derive cipher and HMAC keys from shared secret properly */
        
        if(!strncmp(key, "ECDH:", 5)) {
-               logger(LOG_DEBUG, "Got ECDH key from %s", from->name);
-
                keylen = (strlen(key) - 5) / 2;
 
                if(keylen != ECDH_SIZE) {
@@ -296,7 +294,6 @@ bool ans_key_h(connection_t *c, char *request) {
                }
 
                if(!from->ecdh) {
-                       logger(LOG_DEBUG, "Woops, we didn't generate our public key yet");
                        from->status.ecdh = true;
                        if(!send_ans_key(from))
                                return false;
@@ -311,31 +308,37 @@ 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;
-               }
+               size_t hiskeylen = cipher_keylength(&from->outcipher);
 
+               char *mykey;
+               char *hiskey;
+               char *seed;
+               
                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;
+                       hiskey = key + mykeylen * 2;
+                       xasprintf(&seed, "tinc UDP 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 + hiskeylen * 2;
+                       hiskey = key;
+                       xasprintf(&seed, "tinc UDP key expansion %s %s", from->name, myself->name);
                }
 
+               if(!prf(shared, ECDH_SHARED_SIZE, seed, strlen(seed), key, hiskeylen * 2 + mykeylen * 2))
+                       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;
 
                cipher_set_key(&from->incipher, mykey, true);
-               digest_set_key(&from->indigest, mykey, mykeylen);
+               digest_set_key(&from->indigest, mykey + mykeylen, mykeylen);
+
+               cipher_set_key(&from->outcipher, hiskey, false);
+               digest_set_key(&from->outdigest, hiskey + hiskeylen, hiskeylen);
 
                // Reset sequence number and late packet window
                mykeyused = true;
@@ -343,31 +346,22 @@ 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 * 2, hiskeylen * 2);
        } else {
                keylen = strlen(key) / 2;
                hex2bin(key, key, keylen);
-       }
 
-       /* Update our copy of the origin's packet key */
+               if(keylen != cipher_keylength(&from->outcipher)) {
+                       logger(LOG_ERR, "Node %s (%s) uses wrong keylength!", from->name, from->hostname);
+                       return false;
+               }
 
-       if(keylen != cipher_keylength(&from->outcipher)) {
-               logger(LOG_ERR, "Node %s (%s) uses wrong keylength!", from->name, from->hostname);
-               return false;
-       }
+               /* Update our copy of the origin's packet key */
 
-       cipher_set_key(&from->outcipher, key, false);
-       digest_set_key(&from->outdigest, key, keylen);
+               cipher_set_key(&from->outcipher, key, false);
+               digest_set_key(&from->outdigest, key, keylen);
+       }
 
        from->status.validkey = true;
        from->sent_seqno = 0;