From 8132be8fbd6c45be309c63a117f418ad12ced094 Mon Sep 17 00:00:00 2001
From: Guus Sliepen <guus@tinc-vpn.org>
Date: Thu, 7 Jul 2011 22:30:55 +0200
Subject: [PATCH] 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.
---
src/protocol.h | 3 +-
src/protocol_auth.c | 131 +++++++++++++++++++++++++++++++++++++++++---
2 files changed, 126 insertions(+), 8 deletions(-)
diff --git a/src/protocol.h b/src/protocol.h
index 212afaf3..191229ad 100644
--- 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 d98e5c4b..d38814c6 100644
--- 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;
}
--
2.39.5