- djm@cvs.openbsd.org 2006/05/04 14:55:23

     [dh.c]
     tighter DH exponent checks here too; feedback and ok markus@

diff --git a/ChangeLog b/ChangeLog
index 04e60d0899f0db14e7584b2ca0e84ceb9b6916b8..580f7f8baf3507a4fc6b5e7b0c698f820d82a452 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -5,6 +5,9 @@
      Prevent ssh from trying to open private keys with bad permissions more than
      once or prompting for their passphrases (which it subsequently ignores
      anyway), similar to a previous change in ssh-add.  bz #1186, ok djm@
+   - djm@cvs.openbsd.org 2006/05/04 14:55:23
+     [dh.c]
+     tighter DH exponent checks here too; feedback and ok markus@
 
 20060504
  - (dtucker) [auth-pam.c groupaccess.c monitor.c monitor_wrap.c scard-opensc.c

diff --git a/dh.c b/dh.c
index b32a7efb556228c5623baa80b2f9f7787c8d2394..b3f4ceef1e8f3180f17d86b2d613780c2a643872 100644 (file)
--- a/dh.c
+++ b/dh.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: dh.c,v 1.35 2006/03/27 13:03:54 deraadt Exp $ */
+/* $OpenBSD: dh.c,v 1.36 2006/05/04 14:55:23 djm Exp $ */
 /*
  * Copyright (c) 2000 Niels Provos.  All rights reserved.
  *
@@ -181,19 +181,36 @@ dh_pub_is_valid(DH *dh, BIGNUM *dh_pub)
        int i;
        int n = BN_num_bits(dh_pub);
        int bits_set = 0;
+       BIGNUM *tmp;
 
        if (dh_pub->neg) {
                logit("invalid public DH value: negativ");
                return 0;
        }
+       if (BN_cmp(dh_pub, BN_value_one()) != 1) {      /* pub_exp <= 1 */
+               logit("invalid public DH value: <= 1");
+               return 0;
+       }
+
+       if ((tmp = BN_new()) == NULL)
+               return (-1);
+       if (!BN_sub(tmp, dh->p, BN_value_one()) ||
+           BN_cmp(dh_pub, tmp) != -1) {                /* pub_exp > p-2 */
+               BN_clear_free(tmp);
+               logit("invalid public DH value: >= p-1");
+               return 0;
+       }
+       BN_clear_free(tmp);
+
        for (i = 0; i <= n; i++)
                if (BN_is_bit_set(dh_pub, i))
                        bits_set++;
        debug2("bits set: %d/%d", bits_set, BN_num_bits(dh->p));
 
        /* if g==2 and bits_set==1 then computing log_g(dh_pub) is trivial */
-       if (bits_set > 1 && (BN_cmp(dh_pub, dh->p) == -1))
+       if (bits_set > 1)
                return 1;
+
        logit("invalid public DH value (%d/%d)", bits_set, BN_num_bits(dh->p));
        return 0;
 }