Add BUG_SSH2_DERIVEKEY, present (according to OpenSSH) in ssh.com

versions 2.0.*, and causing the shared secret not to be included in
key derivation hashes. (This doesn't quite cause a blatant security
hole because the session ID - _derived_ from the shared secret - is
still included.)

git-svn-id: svn://svn.tartarus.org/sgt/putty@1853 cda61777-01e9-0310-a592-d414129be87e

diff --git a/ssh.c b/ssh.c
index acc4598..19c93df 100644 (file)
--- a/ssh.c
+++ b/ssh.c
@@ -182,6 +182,7 @@ static const char *const ssh2_disconnect_reasons[] = {
 #define BUG_NEEDS_SSH1_PLAIN_PASSWORD            4
 #define BUG_CHOKES_ON_RSA                        8
 #define BUG_SSH2_RSA_PADDING                    16
+#define BUG_SSH2_DERIVEKEY                       32
 
 static int ssh_pkt_ctx = 0;
 
@@ -1701,6 +1702,16 @@ static void ssh_detect_bugs(char *vstring)
        logevent("We believe remote version has SSH2 HMAC bug");
     }
 
+    if (!strncmp(imp, "2.0.", 4)) {
+       /*
+        * These versions have the key-derivation bug (failing to
+        * include the literal shared secret in the hashes that
+        * generate the keys).
+        */
+       ssh_remote_bugs |= BUG_SSH2_DERIVEKEY;
+       logevent("We believe remote version has SSH2 key-derivation bug");
+    }
+
     if ((!strncmp(imp, "OpenSSH_2.", 10) && imp[10]>='5' && imp[10]<='9') ||
        (!strncmp(imp, "OpenSSH_3.", 10) && imp[10]>='0' && imp[10]<='2')) {
        /*
@@ -3497,14 +3508,16 @@ static void ssh2_mkkey(Bignum K, char *H, char *sessid, char chr,
     SHA_State s;
     /* First 20 bytes. */
     SHA_Init(&s);
-    sha_mpint(&s, K);
+    if (!(ssh_remote_bugs & BUG_SSH2_DERIVEKEY))
+       sha_mpint(&s, K);
     SHA_Bytes(&s, H, 20);
     SHA_Bytes(&s, &chr, 1);
     SHA_Bytes(&s, sessid, 20);
     SHA_Final(&s, keyspace);
     /* Next 20 bytes. */
     SHA_Init(&s);
-    sha_mpint(&s, K);
+    if (!(ssh_remote_bugs & BUG_SSH2_DERIVEKEY))
+       sha_mpint(&s, K);
     SHA_Bytes(&s, H, 20);
     SHA_Bytes(&s, keyspace, 20);
     SHA_Final(&s, keyspace + 20);