Very primitive ECDSA signed ECDH key exchange for the meta protocol.

Nonces and hash of the ID requests should be included in the seed for the PRF.

diff --git a/src/protocol.h b/src/protocol.h
index 212afaf..191229a 100644 (file)
--- a/src/protocol.h
+++ b/src/protocol.h
@@ -24,7 +24,7 @@
 /* Protocol version. Different major versions are incompatible. */
 
 #define PROT_MAJOR 17
-#define PROT_MINOR 1
+#define PROT_MINOR 2
 
 /* Silly Windows */
 
@@ -83,6 +83,7 @@ extern bool seen_request(char *);
 
 extern bool send_id(struct connection_t *);
 extern bool send_metakey(struct connection_t *);
+extern bool send_metakey_ec(struct connection_t *);
 extern bool send_challenge(struct connection_t *);
 extern bool send_chal_reply(struct connection_t *);
 extern bool send_ack(struct connection_t *);

diff --git a/src/protocol_auth.c b/src/protocol_auth.c
index d98e5c4..d38814c 100644 (file)
--- a/src/protocol_auth.c
+++ b/src/protocol_auth.c
@@ -25,13 +25,16 @@
 #include "connection.h"
 #include "control.h"
 #include "control_common.h"
+#include "cipher.h"
 #include "crypto.h"
+#include "digest.h"
 #include "edge.h"
 #include "graph.h"
 #include "logger.h"
 #include "net.h"
 #include "netutl.h"
 #include "node.h"
+#include "prf.h"
 #include "protocol.h"
 #include "rsa.h"
 #include "utils.h"
@@ -109,13 +112,40 @@ bool id_h(connection_t *c, char *request) {
                }
        }
 
-       if(!read_rsa_public_key(c)) {
+       c->allow_request = METAKEY;
+
+       if(c->protocol_minor >= 2)
+               return send_metakey_ec(c);
+       else
+               return send_metakey(c);
+}
+
+bool send_metakey_ec(connection_t *c) {
+       if(!read_ecdsa_public_key(c))
                return false;
-       }
 
-       c->allow_request = METAKEY;
+       logger(LOG_DEBUG, "Sending ECDH metakey to %s", c->name);
+
+       size_t siglen = ecdsa_size(&myself->connection->ecdsa);
 
-       return send_metakey(c);
+       char key[ECDH_SIZE];
+       char sig[siglen];
+
+       // TODO: include nonce? Use relevant parts of SSH or TLS protocol
+
+       if(!ecdh_generate_public(&c->ecdh, key))
+               return false;
+
+       if(!ecdsa_sign(&myself->connection->ecdsa, key, ECDH_SIZE, sig))
+               return false;
+
+       char out[MAX_STRING_SIZE];
+
+       bin2hex(key, out, ECDH_SIZE);
+       bin2hex(sig, out + ECDH_SIZE * 2, siglen);
+       out[(ECDH_SIZE + siglen) * 2] = 0;
+       
+       bool result = send_request(c, "%d %s", METAKEY, out);
 }
 
 bool send_metakey(connection_t *c) {
@@ -124,6 +154,9 @@ bool send_metakey(connection_t *c) {
        char enckey[len];
        char hexkey[2 * len + 1];
 
+       if(!read_rsa_public_key(c))
+               return false;
+
        if(!cipher_open_blowfish_ofb(&c->outcipher))
                return false;
        
@@ -182,7 +215,91 @@ bool send_metakey(connection_t *c) {
        return result;
 }
 
+static bool metakey_ec_h(connection_t *c, const char *request) {
+       size_t siglen = ecdsa_size(&c->ecdsa);
+       char in[MAX_STRING_SIZE];
+       char key[MAX_STRING_SIZE];
+       char sig[siglen];
+
+       logger(LOG_DEBUG, "Got ECDH metakey from %s", c->name);
+
+       if(sscanf(request, "%*d " MAX_STRING, in) != 1) {
+               logger(LOG_ERR, "Got bad %s from %s (%s)", "METAKEY", c->name, c->hostname);
+               return false;
+       }
+
+       if(strlen(in) != (ECDH_SIZE + siglen) * 2) {
+               logger(LOG_ERR, "Possible intruder %s (%s): %s %d != %d", c->name, c->hostname, "wrong keylength", strlen(in) / 2, (ECDH_SIZE + siglen));
+               return false;
+       }
+
+       hex2bin(in, key, ECDH_SIZE);
+       hex2bin(in + ECDH_SIZE * 2, sig, siglen);
+
+       if(!ecdsa_verify(&c->ecdsa, key, ECDH_SIZE, sig)) {
+               logger(LOG_ERR, "Possible intruder %s (%s): %s", c->name, c->hostname, "invalid ECDSA signature");
+               return false;
+       }
+
+       char shared[ECDH_SHARED_SIZE * 2 + 1];
+
+       if(!ecdh_compute_shared(&c->ecdh, key, shared))
+               return false;
+
+       /* Update our crypto end */
+
+       if(!cipher_open_by_name(&c->incipher, "aes-256-ofb"))
+               return false;
+       if(!digest_open_by_name(&c->indigest, "sha512", -1))
+               return false;
+       if(!cipher_open_by_name(&c->outcipher, "aes-256-ofb"))
+               return false;
+       if(!digest_open_by_name(&c->outdigest, "sha512", -1))
+               return false;
+
+       size_t mykeylen = cipher_keylength(&c->incipher);
+       size_t hiskeylen = cipher_keylength(&c->outcipher);
+
+       char *mykey;
+       char *hiskey;
+       char *seed;
+       
+       if(strcmp(myself->name, c->name) < 0) {
+               mykey = key;
+               hiskey = key + mykeylen * 2;
+               xasprintf(&seed, "tinc TCP key expansion %s %s", myself->name, c->name);
+       } else {
+               mykey = key + hiskeylen * 2;
+               hiskey = key;
+               xasprintf(&seed, "tinc TCP key expansion %s %s", c->name, myself->name);
+       }
+
+       if(!prf(shared, ECDH_SHARED_SIZE, seed, strlen(seed), key, hiskeylen * 2 + mykeylen * 2))
+               return false;
+
+       free(seed);
+
+       bin2hex(shared, shared, ECDH_SHARED_SIZE);
+       shared[ECDH_SHARED_SIZE * 2] = 0;
+       logger(LOG_DEBUG, "Shared secret is %s", shared);
+
+       cipher_set_key(&c->incipher, mykey, true);
+       digest_set_key(&c->indigest, mykey + mykeylen, mykeylen);
+
+       cipher_set_key(&c->outcipher, hiskey, false);
+       digest_set_key(&c->outdigest, hiskey + hiskeylen, hiskeylen);
+
+       c->status.decryptin = true;
+       c->status.encryptout = true;
+       c->allow_request = CHALLENGE;
+
+       return send_challenge(c);
+}
+
 bool metakey_h(connection_t *c, char *request) {
+       if(c->protocol_minor >= 2)
+               return metakey_ec_h(c, request);
+
        char hexkey[MAX_STRING_SIZE];
        int cipher, digest, maclength, compression;
        size_t len = rsa_size(&myself->connection->rsa);
@@ -238,7 +355,7 @@ bool metakey_h(connection_t *c, char *request) {
 }
 
 bool send_challenge(connection_t *c) {
-       size_t len = rsa_size(&c->rsa);
+       size_t len = c->protocol_minor >= 2 ? ECDH_SIZE : rsa_size(&c->rsa);
        char buffer[len * 2 + 1];
 
        if(!c->hischallenge)
@@ -260,7 +377,7 @@ bool send_challenge(connection_t *c) {
 
 bool challenge_h(connection_t *c, char *request) {
        char buffer[MAX_STRING_SIZE];
-       size_t len = rsa_size(&myself->connection->rsa);
+       size_t len = c->protocol_minor >= 2 ? ECDH_SIZE : rsa_size(&myself->connection->rsa);
        size_t digestlen = digest_length(&c->indigest);
        char digest[digestlen];
 
@@ -318,7 +435,7 @@ bool chal_reply_h(connection_t *c, char *request) {
 
        /* Verify the hash */
 
-       if(!digest_verify(&c->outdigest, c->hischallenge, rsa_size(&c->rsa), hishash)) {
+       if(!digest_verify(&c->outdigest, c->hischallenge, c->protocol_minor >= 2 ? ECDH_SIZE : rsa_size(&c->rsa), hishash)) {
                logger(LOG_ERR, "Possible intruder %s (%s): %s", c->name, c->hostname, "wrong challenge reply");
                return false;
        }