First rough implementation of the diffie-hellman group exchange. The

client can ask the server for bigger groups to perform the diffie-hellman
in, thus increasing the attack complexity when using ciphers with longer
keys.  University of Windsor provided network, T the company.

1 files changed, 108 insertions, 27 deletions

diff --git a/usr.bin/ssh/kex.c b/usr.bin/ssh/kex.c
index 8a83db47e80..151dc1cffa4 100644
--- a/usr.bin/ssh/kex.c
+++ b/usr.bin/ssh/kex.c
@@ -23,7 +23,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: kex.c,v 1.10 2000/09/07 20:27:51 deraadt Exp $");
+RCSID("$OpenBSD: kex.c,v 1.11 2000/10/11 04:02:17 provos Exp $");
 
 #include "ssh.h"
 #include "ssh2.h"
@@ -123,11 +123,6 @@ dh_pub_is_valid(DH *dh, BIGNUM *dh_pub)
 	int n = BN_num_bits(dh_pub);
 	int bits_set = 0;
 
-	/* we only accept g==2 */
-	if (!BN_is_word(dh->g, 2)) {
-		log("invalid DH base != 2");
-		return 0;
-	}
 	if (dh_pub->neg) {
 		log("invalid public DH value: negativ");
 		return 0;
@@ -145,27 +140,10 @@ dh_pub_is_valid(DH *dh, BIGNUM *dh_pub)
 }
 
 DH *
-dh_new_group1()
+dh_gen_key(DH *dh)
 {
-	static char *group1 =
-	    "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1"
-	    "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD"
-	    "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245"
-	    "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED"
-	    "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE65381"
-	    "FFFFFFFF" "FFFFFFFF";
-	DH *dh;
-	int ret, tries = 0;
-	dh = DH_new();
-	if(dh == NULL)
-		fatal("DH_new");
-	ret = BN_hex2bn(&dh->p, group1);
-	if(ret<0)
-		fatal("BN_hex2bn");
-	dh->g = BN_new();
-	if(dh->g == NULL)
-		fatal("DH_new g");
-	BN_set_word(dh->g, 2);
+	int tries = 0;
+
 	do {
 		if (DH_generate_key(dh) == 0)
 			fatal("DH_generate_key");
@@ -175,6 +153,52 @@ dh_new_group1()
 	return dh;
 }
 
+DH *
+dh_new_group_asc(const char *gen, const char *modulus)
+{
+	DH *dh;
+	int ret;
+
+	dh = DH_new();
+	if (dh == NULL)
+		fatal("DH_new");
+
+	if ((ret = BN_hex2bn(&dh->p, modulus)) < 0)
+		fatal("BN_hex2bn p");
+	if ((ret = BN_hex2bn(&dh->g, gen)) < 0)
+		fatal("BN_hex2bn g");
+
+	return (dh_gen_key(dh));
+}
+
+DH *
+dh_new_group(BIGNUM *gen, BIGNUM *modulus)
+{
+	DH *dh;
+
+	dh = DH_new();
+	if (dh == NULL)
+		fatal("DH_new");
+	dh->p = modulus;
+	dh->g = gen;
+
+	return (dh_gen_key(dh));
+}
+
+DH *
+dh_new_group1()
+{
+	static char *gen = "2", *group1 =
+	    "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1"
+	    "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD"
+	    "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245"
+	    "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED"
+	    "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE65381"
+	    "FFFFFFFF" "FFFFFFFF";
+
+	return (dh_new_group_asc(gen, group1));
+}
+
 void
 dump_digest(unsigned char *digest, int len)
 {
@@ -237,6 +261,59 @@ kex_hash(
 }
 
 unsigned char *
+kex_hash_gex(
+    char *client_version_string,
+    char *server_version_string,
+    char *ckexinit, int ckexinitlen,
+    char *skexinit, int skexinitlen,
+    char *serverhostkeyblob, int sbloblen,
+    int minbits, BIGNUM *prime, BIGNUM *gen,
+    BIGNUM *client_dh_pub,
+    BIGNUM *server_dh_pub,
+    BIGNUM *shared_secret)
+{
+	Buffer b;
+	static unsigned char digest[EVP_MAX_MD_SIZE];
+	EVP_MD *evp_md = EVP_sha1();
+	EVP_MD_CTX md;
+
+	buffer_init(&b);
+	buffer_put_string(&b, client_version_string, strlen(client_version_string));
+	buffer_put_string(&b, server_version_string, strlen(server_version_string));
+
+	/* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
+	buffer_put_int(&b, ckexinitlen+1);
+	buffer_put_char(&b, SSH2_MSG_KEXINIT);
+	buffer_append(&b, ckexinit, ckexinitlen);
+	buffer_put_int(&b, skexinitlen+1);
+	buffer_put_char(&b, SSH2_MSG_KEXINIT);
+	buffer_append(&b, skexinit, skexinitlen);
+
+	buffer_put_string(&b, serverhostkeyblob, sbloblen);
+	buffer_put_int(&b, minbits);
+	buffer_put_bignum2(&b, prime);
+	buffer_put_bignum2(&b, gen);
+	buffer_put_bignum2(&b, client_dh_pub);
+	buffer_put_bignum2(&b, server_dh_pub);
+	buffer_put_bignum2(&b, shared_secret);
+	
+#ifdef DEBUG_KEX
+	buffer_dump(&b);
+#endif
+
+	EVP_DigestInit(&md, evp_md);
+	EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
+	EVP_DigestFinal(&md, digest, NULL);
+
+	buffer_free(&b);
+
+#ifdef DEBUG_KEX
+	dump_digest(digest, evp_md->md_size);
+#endif
+	return digest;
+}
+
+unsigned char *
 derive_key(int id, int need, char unsigned *hash, BIGNUM *shared_secret)
 {
 	Buffer b;
@@ -387,7 +464,11 @@ choose_kex(Kex *k, char *client, char *server)
 	k->name = get_match(client, server);
 	if (k->name == NULL)
 		fatal("no kex alg");
-	if (strcmp(k->name, KEX_DH1) != 0)
+	if (strcmp(k->name, KEX_DH1) == 0) {
+		k->kex_type = DH_GRP1_SHA1;
+	} else if (strcmp(k->name, KEX_DHGEX) == 0) {
+		k->kex_type = DH_GEX_SHA1;
+	} else
 		fatal("bad kex alg %s", k->name);
 }
 void