- dtucker@cvs.openbsd.org 2014/01/25 10:12:50

     [cipher.c cipher.h kex.c kex.h kexgexc.c]
     Add a special case for the DH group size for 3des-cbc, which has an
     effective strength much lower than the key size.  This causes problems
     with some cryptlib implementations, which don't support group sizes larger
     than 4k but also don't use the largest group size it does support as
     specified in the RFC.  Based on a patch from Petr Lautrbach at Redhat,
     reduced by me with input from Markus.  ok djm@ markus@

6 files changed, 32 insertions, 8 deletions

diff --git a/ChangeLog b/ChangeLog
index 44e56f4a6..64da7a475 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+20130126
+ - OpenBSD CVS Sync
+   - dtucker@cvs.openbsd.org 2014/01/25 10:12:50
+     [cipher.c cipher.h kex.c kex.h kexgexc.c]
+     Add a special case for the DH group size for 3des-cbc, which has an
+     effective strength much lower than the key size.  This causes problems
+     with some cryptlib implementations, which don't support group sizes larger
+     than 4k but also don't use the largest group size it does support as
+     specified in the RFC.  Based on a patch from Petr Lautrbach at Redhat,
+     reduced by me with input from Markus.  ok djm@ markus@
+
 20130125
  - (djm) [configure.ac] Fix detection of capsicum sandbox on FreeBSD
  - (djm) [configure.ac] Do not attempt to use capsicum sandbox unless
diff --git a/cipher.c b/cipher.c
index 76e6c5963..2476e6539 100644
--- a/cipher.c
+++ b/cipher.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: cipher.c,v 1.93 2013/12/06 13:34:54 markus Exp $ */
+/* $OpenBSD: cipher.c,v 1.94 2014/01/25 10:12:50 dtucker Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -142,6 +142,14 @@ cipher_keylen(const Cipher *c)
 }
 
 u_int
+cipher_seclen(const Cipher *c)
+{
+        if (strcmp("3des-cbc", c->name) == 0)
+                return 14;
+        return cipher_keylen(c);
+}
+
+u_int
 cipher_authlen(const Cipher *c)
 {
         return (c->auth_len);
diff --git a/cipher.h b/cipher.h
index d78245615..133d2e73d 100644
--- a/cipher.h
+++ b/cipher.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: cipher.h,v 1.43 2013/12/06 13:34:54 markus Exp $ */
+/* $OpenBSD: cipher.h,v 1.44 2014/01/25 10:12:50 dtucker Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -89,6 +89,7 @@ void	 cipher_cleanup(CipherContext *);
 void     cipher_set_key_string(CipherContext *, const Cipher *, const char *, int);
 u_int    cipher_blocksize(const Cipher *);
 u_int    cipher_keylen(const Cipher *);
+u_int    cipher_seclen(const Cipher *);
 u_int    cipher_authlen(const Cipher *);
 u_int    cipher_ivlen(const Cipher *);
 u_int    cipher_is_cbc(const Cipher *);
diff --git a/kex.c b/kex.c
index 7d054cdcb..39d16f8e3 100644
--- a/kex.c
+++ b/kex.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kex.c,v 1.95 2014/01/12 08:13:13 djm Exp $ */
+/* $OpenBSD: kex.c,v 1.96 2014/01/25 10:12:50 dtucker Exp $ */
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
  *
@@ -458,7 +458,7 @@ kex_choose_conf(Kex *kex)
         char **my, **peer;
         char **cprop, **sprop;
         int nenc, nmac, ncomp;
-        u_int mode, ctos, need, authlen;
+        u_int mode, ctos, need, dh_need, authlen;
         int first_kex_follows, type;
 
         my   = kex_buf2prop(&kex->my, NULL);
@@ -506,7 +506,7 @@ kex_choose_conf(Kex *kex)
         choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
         choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
             sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
-        need = 0;
+        need = dh_need = 0;
         for (mode = 0; mode < MODE_MAX; mode++) {
                 newkeys = kex->newkeys[mode];
                 if (need < newkeys->enc.key_len)
@@ -517,9 +517,12 @@ kex_choose_conf(Kex *kex)
                         need = newkeys->enc.iv_len;
                 if (need < newkeys->mac.key_len)
                         need = newkeys->mac.key_len;
+                if (dh_need < cipher_seclen(newkeys->enc.cipher))
+                        dh_need = cipher_seclen(newkeys->enc.cipher);
         }
         /* XXX need runden? */
         kex->we_need = need;
+        kex->dh_need = dh_need;
 
         /* ignore the next message if the proposals do not match */
         if (first_kex_follows && !proposals_match(my, peer) &&
diff --git a/kex.h b/kex.h
index 7e2878f70..1aa3ec26a 100644
--- a/kex.h
+++ b/kex.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: kex.h,v 1.60 2014/01/12 08:13:13 djm Exp $ */
+/* $OpenBSD: kex.h,v 1.61 2014/01/25 10:12:50 dtucker Exp $ */
 
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
@@ -124,6 +124,7 @@ struct Kex {
         u_int   session_id_len;
         Newkeys *newkeys[MODE_MAX];
         u_int   we_need;
+        u_int   dh_need;
         int     server;
         char    *name;
         int     hostkey_type;
diff --git a/kexgexc.c b/kexgexc.c
index a69ff2705..629b5fbbc 100644
--- a/kexgexc.c
+++ b/kexgexc.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kexgexc.c,v 1.15 2014/01/12 08:13:13 djm Exp $ */
+/* $OpenBSD: kexgexc.c,v 1.16 2014/01/25 10:12:50 dtucker Exp $ */
 /*
  * Copyright (c) 2000 Niels Provos.  All rights reserved.
  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
@@ -58,7 +58,7 @@ kexgex_client(Kex *kex)
         int min, max, nbits;
         DH *dh;
 
-        nbits = dh_estimate(kex->we_need * 8);
+        nbits = dh_estimate(kex->dh_need * 8);
 
         if (datafellows & SSH_OLD_DHGEX) {
                 /* Old GEX request */