- djm@cvs.openbsd.org 2005/11/04 05:15:59

     [kex.c kex.h kexdh.c kexdhc.c kexdhs.c kexgex.c kexgexc.c kexgexs.c]
     remove hardcoded hash lengths in key exchange code, allowing
     implementation of KEX methods with different hashes (e.g. SHA-256);
     ok markus@ dtucker@ stevesk@

1 files changed, 21 insertions, 15 deletions

diff --git a/kex.c b/kex.c
index 5dce335fe..cd71be9ca 100644
--- a/kex.c
+++ b/kex.c
@@ -23,7 +23,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: kex.c,v 1.64 2005/07/25 11:59:39 markus Exp $");
+RCSID("$OpenBSD: kex.c,v 1.65 2005/11/04 05:15:59 djm Exp $");
 
 #include <openssl/crypto.h>
 
@@ -294,13 +294,17 @@ choose_kex(Kex *k, char *client, char *server)
                 fatal("no kex alg");
         if (strcmp(k->name, KEX_DH1) == 0) {
                 k->kex_type = KEX_DH_GRP1_SHA1;
+                k->evp_md = EVP_sha1();
         } else if (strcmp(k->name, KEX_DH14) == 0) {
                 k->kex_type = KEX_DH_GRP14_SHA1;
-        } else if (strcmp(k->name, KEX_DHGEX) == 0) {
+                k->evp_md = EVP_sha1();
+        } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
                 k->kex_type = KEX_DH_GEX_SHA1;
+                k->evp_md = EVP_sha1();
         } else
                 fatal("bad kex alg %s", k->name);
 }
+
 static void
 choose_hostkeyalg(Kex *k, char *client, char *server)
 {
@@ -404,28 +408,28 @@ kex_choose_conf(Kex *kex)
 }
 
 static u_char *
-derive_key(Kex *kex, int id, u_int need, u_char *hash, BIGNUM *shared_secret)
+derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
+    BIGNUM *shared_secret)
 {
         Buffer b;
-        const EVP_MD *evp_md = EVP_sha1();
         EVP_MD_CTX md;
         char c = id;
         u_int have;
-        int mdsz = EVP_MD_size(evp_md);
+        int mdsz;
         u_char *digest;
 
-        if (mdsz < 0)
-                fatal("derive_key: mdsz < 0");
-        digest = xmalloc(roundup(need, mdsz));
+        if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
+                fatal("bad kex md size %d", mdsz);
+        digest = xmalloc(roundup(need, mdsz));
 
         buffer_init(&b);
         buffer_put_bignum2(&b, shared_secret);
 
         /* K1 = HASH(K || H || "A" || session_id) */
-        EVP_DigestInit(&md, evp_md);
+        EVP_DigestInit(&md, kex->evp_md);
         if (!(datafellows & SSH_BUG_DERIVEKEY))
                 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
-        EVP_DigestUpdate(&md, hash, mdsz);
+        EVP_DigestUpdate(&md, hash, hashlen);
         EVP_DigestUpdate(&md, &c, 1);
         EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
         EVP_DigestFinal(&md, digest, NULL);
@@ -436,10 +440,10 @@ derive_key(Kex *kex, int id, u_int need, u_char *hash, BIGNUM *shared_secret)
          * Key = K1 || K2 || ... || Kn
          */
         for (have = mdsz; need > have; have += mdsz) {
-                EVP_DigestInit(&md, evp_md);
+                EVP_DigestInit(&md, kex->evp_md);
                 if (!(datafellows & SSH_BUG_DERIVEKEY))
                         EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
-                EVP_DigestUpdate(&md, hash, mdsz);
+                EVP_DigestUpdate(&md, hash, hashlen);
                 EVP_DigestUpdate(&md, digest, have);
                 EVP_DigestFinal(&md, digest + have, NULL);
         }
@@ -455,13 +459,15 @@ Newkeys *current_keys[MODE_MAX];
 
 #define NKEYS   6
 void
-kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret)
+kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
 {
         u_char *keys[NKEYS];
         u_int i, mode, ctos;
 
-        for (i = 0; i < NKEYS; i++)
-                keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret);
+        for (i = 0; i < NKEYS; i++) {
+                keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
+                    shared_secret);
+        }
 
         debug2("kex_derive_keys");
         for (mode = 0; mode < MODE_MAX; mode++) {