upstream: factor out kex_dh_compute_key() - it's shared between

plain DH KEX and DH GEX in both the client and server implementations

from markus@ ok djm@

OpenBSD-Commit-ID: 12186e18791fffcd4642c82e7e0cfdd7ea37e2ec

1 files changed, 14 insertions, 44 deletions

diff --git a/kexgexs.c b/kexgexs.c
index 4ffbb1918..f8eb36545 100644
--- a/kexgexs.c
+++ b/kexgexs.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kexgexs.c,v 1.39 2019/01/21 09:55:52 djm Exp $ */
+/* $OpenBSD: kexgexs.c,v 1.40 2019/01/21 10:03:37 djm Exp $ */
 /*
  * Copyright (c) 2000 Niels Provos.  All rights reserved.
  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
@@ -126,14 +126,15 @@ static int
 input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh)
 {
         struct kex *kex = ssh->kex;
-        BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
+        BIGNUM *dh_client_pub = NULL;
         const BIGNUM *pub_key, *dh_p, *dh_g;
+        struct sshbuf *shared_secret = NULL;
         struct sshkey *server_host_public, *server_host_private;
-        u_char *kbuf = NULL, *signature = NULL, *server_host_key_blob = NULL;
+        u_char *signature = NULL, *server_host_key_blob = NULL;
         u_char hash[SSH_DIGEST_MAX_LENGTH];
         size_t sbloblen, slen;
-        size_t klen = 0, hashlen;
-        int kout, r;
+        size_t hashlen;
+        int r;
 
         if (kex->load_host_public_key == NULL ||
             kex->load_host_private_key == NULL) {
@@ -153,44 +154,19 @@ input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh)
         if ((r = sshpkt_get_bignum2(ssh, &dh_client_pub)) != 0 ||
             (r = sshpkt_get_end(ssh)) != 0)
                 goto out;
-
-        DH_get0_key(kex->dh, &pub_key, NULL);
-        DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
-
-#ifdef DEBUG_KEXDH
-        fprintf(stderr, "dh_client_pub= ");
-        BN_print_fp(stderr, dh_client_pub);
-        fprintf(stderr, "\n");
-        debug("bits %d", BN_num_bits(dh_client_pub));
-        DHparams_print_fp(stderr, kex->dh);
-        fprintf(stderr, "pub= ");
-        BN_print_fp(stderr, pub_key);
-        fprintf(stderr, "\n");
-#endif
-        if (!dh_pub_is_valid(kex->dh, dh_client_pub)) {
-                sshpkt_disconnect(ssh, "bad client public DH value");
-                r = SSH_ERR_MESSAGE_INCOMPLETE;
-                goto out;
-        }
-
-        klen = DH_size(kex->dh);
-        if ((kbuf = malloc(klen)) == NULL ||
-            (shared_secret = BN_new()) == NULL) {
+        if ((shared_secret = sshbuf_new()) == NULL) {
                 r = SSH_ERR_ALLOC_FAIL;
                 goto out;
         }
-        if ((kout = DH_compute_key(kbuf, dh_client_pub, kex->dh)) < 0 ||
-            BN_bin2bn(kbuf, kout, shared_secret) == NULL) {
-                r = SSH_ERR_LIBCRYPTO_ERROR;
+        if ((r = kex_dh_compute_key(kex, dh_client_pub, shared_secret)) != 0)
                 goto out;
-        }
-#ifdef DEBUG_KEXDH
-        dump_digest("shared secret", kbuf, kout);
-#endif
         if ((r = sshkey_to_blob(server_host_public, &server_host_key_blob,
             &sbloblen)) != 0)
                 goto out;
+
         /* calc H */
+        DH_get0_key(kex->dh, &pub_key, NULL);
+        DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
         hashlen = sizeof(hash);
         if ((r = kexgex_hash(
             kex->hash_alg,
@@ -203,7 +179,7 @@ input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh)
             dh_p, dh_g,
             dh_client_pub,
             pub_key,
-            shared_secret,
+            sshbuf_ptr(shared_secret), sshbuf_len(shared_secret),
             hash, &hashlen)) != 0)
                 goto out;
 
@@ -212,8 +188,6 @@ input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh)
             &signature, &slen, hash, hashlen, kex->hostkey_alg)) < 0)
                 goto out;
 
-        /* destroy_sensitive_data(); */
-
         /* send server hostkey, DH pubkey 'f' and signed H */
         if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REPLY)) != 0 ||
             (r = sshpkt_put_string(ssh, server_host_key_blob, sbloblen)) != 0 ||
@@ -222,18 +196,14 @@ input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh)
             (r = sshpkt_send(ssh)) != 0)
                 goto out;
 
-        if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0)
+        if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0)
                 r = kex_send_newkeys(ssh);
  out:
         explicit_bzero(hash, sizeof(hash));
         DH_free(kex->dh);
         kex->dh = NULL;
         BN_clear_free(dh_client_pub);
-        if (kbuf) {
-                explicit_bzero(kbuf, klen);
-                free(kbuf);
-        }
-        BN_clear_free(shared_secret);
+        sshbuf_free(shared_secret);
         free(server_host_key_blob);
         free(signature);
         return r;