- (djm) OpenBSD CVS Sync:

   - markus@cvs.openbsd.org  2001/01/29 12:47:32
     [rsa.c rsa.h ssh-agent.c sshconnect1.c sshd.c]
     handle rsa_private_decrypt failures; helps against the Bleichenbacher
     pkcs#1 attack

6 files changed, 63 insertions, 35 deletions

diff --git a/ChangeLog b/ChangeLog
index 250ab58af..9c97a1287 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -6,6 +6,10 @@
    - markus@cvs.openbsd.org  2001/01/29 12:42:35
      [canohost.c canohost.h channels.c clientloop.c]
      add get_peer_ipaddr(socket), x11-fwd in ssh2 requires ipaddr, not DNS
+   - markus@cvs.openbsd.org  2001/01/29 12:47:32
+     [rsa.c rsa.h ssh-agent.c sshconnect1.c sshd.c]
+     handle rsa_private_decrypt failures; helps against the Bleichenbacher
+     pkcs#1 attack
 
 20000129
  - (stevesk) sftp-server.c: use %lld vs. %qd
diff --git a/rsa.c b/rsa.c
index 04bb239e5..100524607 100644
--- a/rsa.c
+++ b/rsa.c
@@ -60,7 +60,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: rsa.c,v 1.19 2001/01/21 19:05:54 markus Exp $");
+RCSID("$OpenBSD: rsa.c,v 1.20 2001/01/29 19:47:30 markus Exp $");
 
 #include "rsa.h"
 #include "log.h"
@@ -94,7 +94,7 @@ rsa_public_encrypt(BIGNUM *out, BIGNUM *in, RSA *key)
         xfree(inbuf);
 }
 
-void
+int
 rsa_private_decrypt(BIGNUM *out, BIGNUM *in, RSA *key)
 {
         u_char *inbuf, *outbuf;
@@ -108,13 +108,14 @@ rsa_private_decrypt(BIGNUM *out, BIGNUM *in, RSA *key)
         BN_bn2bin(in, inbuf);
 
         if ((len = RSA_private_decrypt(ilen, inbuf, outbuf, key,
-            RSA_PKCS1_PADDING)) <= 0)
-                fatal("rsa_private_decrypt() failed");
-
-        BN_bin2bn(outbuf, len, out);
-
+            RSA_PKCS1_PADDING)) <= 0) {
+                error("rsa_private_decrypt() failed");
+        } else {
+                BN_bin2bn(outbuf, len, out);
+        }
         memset(outbuf, 0, olen);
         memset(inbuf, 0, ilen);
         xfree(outbuf);
         xfree(inbuf);
+        return len;
 }
diff --git a/rsa.h b/rsa.h
index 57d72cc78..713d31281 100644
--- a/rsa.h
+++ b/rsa.h
@@ -11,7 +11,7 @@
  * called by a name other than "ssh" or "Secure Shell".
  */
 
-/* RCSID("$OpenBSD: rsa.h,v 1.9 2000/11/12 19:50:38 markus Exp $"); */
+/* RCSID("$OpenBSD: rsa.h,v 1.10 2001/01/29 19:47:30 markus Exp $"); */
 
 #ifndef RSA_H
 #define RSA_H
@@ -20,6 +20,6 @@
 #include <openssl/rsa.h>
 
 void rsa_public_encrypt __P((BIGNUM * out, BIGNUM * in, RSA * prv));
-void rsa_private_decrypt __P((BIGNUM * out, BIGNUM * in, RSA * prv));
+int rsa_private_decrypt __P((BIGNUM * out, BIGNUM * in, RSA * prv));
 
 #endif                          /* RSA_H */
diff --git a/ssh-agent.c b/ssh-agent.c
index 539f8ce7d..deed3ecae 100644
--- a/ssh-agent.c
+++ b/ssh-agent.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: ssh-agent.c,v 1.48 2001/01/25 08:06:33 deraadt Exp $  */
+/*      $OpenBSD: ssh-agent.c,v 1.49 2001/01/29 19:47:31 markus Exp $   */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -37,7 +37,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: ssh-agent.c,v 1.48 2001/01/25 08:06:33 deraadt Exp $");
+RCSID("$OpenBSD: ssh-agent.c,v 1.49 2001/01/29 19:47:31 markus Exp $");
 
 #include <openssl/evp.h>
 #include <openssl/md5.h>
@@ -198,7 +198,8 @@ process_authentication_challenge1(SocketEntry *e)
         private = lookup_private_key(key, NULL, 1);
         if (private != NULL) {
                 /* Decrypt the challenge using the private key. */
-                rsa_private_decrypt(challenge, challenge, private->rsa);
+                if (rsa_private_decrypt(challenge, challenge, private->rsa) <= 0)
+                        goto failure;
 
                 /* The response is MD5 of decrypted challenge plus session id. */
                 len = BN_num_bytes(challenge);
diff --git a/sshconnect1.c b/sshconnect1.c
index 5a5a22227..e732806f3 100644
--- a/sshconnect1.c
+++ b/sshconnect1.c
@@ -13,7 +13,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: sshconnect1.c,v 1.20 2001/01/22 23:06:40 markus Exp $");
+RCSID("$OpenBSD: sshconnect1.c,v 1.21 2001/01/29 19:47:31 markus Exp $");
 
 #include <openssl/bn.h>
 #include <openssl/evp.h>
@@ -163,14 +163,17 @@ respond_to_rsa_challenge(BIGNUM * challenge, RSA * prv)
         int i, len;
 
         /* Decrypt the challenge using the private key. */
-        rsa_private_decrypt(challenge, challenge, prv);
+        /* XXX think about Bleichenbacher, too */
+        if (rsa_private_decrypt(challenge, challenge, prv) <= 0)
+                packet_disconnect(
+                    "respond_to_rsa_challenge: rsa_private_decrypt failed");
 
         /* Compute the response. */
         /* The response is MD5 of decrypted challenge plus session id. */
         len = BN_num_bytes(challenge);
         if (len <= 0 || len > sizeof(buf))
-                packet_disconnect("respond_to_rsa_challenge: bad challenge length %d",
-                                  len);
+                packet_disconnect(
+                    "respond_to_rsa_challenge: bad challenge length %d", len);
 
         memset(buf, 0, sizeof(buf));
         BN_bn2bin(challenge, buf + sizeof(buf) - len);
diff --git a/sshd.c b/sshd.c
index d46e4aa8b..02fe2ec42 100644
--- a/sshd.c
+++ b/sshd.c
@@ -40,7 +40,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: sshd.c,v 1.158 2001/01/28 10:37:26 markus Exp $");
+RCSID("$OpenBSD: sshd.c,v 1.159 2001/01/29 19:47:31 markus Exp $");
 
 #include <openssl/dh.h>
 #include <openssl/bn.h>
@@ -1186,6 +1186,7 @@ do_ssh1_kex(void)
 {
         int i, len;
         int plen, slen;
+        int rsafail = 0;
         BIGNUM *session_key_int;
         u_char session_key[SSH_SESSION_KEY_LENGTH];
         u_char cookie[8];
@@ -1296,7 +1297,7 @@ do_ssh1_kex(void)
          * with larger modulus first).
          */
         if (BN_cmp(sensitive_data.server_key->rsa->n, sensitive_data.ssh1_host_key->rsa->n) > 0) {
-                /* Private key has bigger modulus. */
+                /* Server key has bigger modulus. */
                 if (BN_num_bits(sensitive_data.server_key->rsa->n) <
                     BN_num_bits(sensitive_data.ssh1_host_key->rsa->n) + SSH_KEY_BITS_RESERVED) {
                         fatal("do_connection: %s: server_key %d < host_key %d + SSH_KEY_BITS_RESERVED %d",
@@ -1305,10 +1306,12 @@ do_ssh1_kex(void)
                             BN_num_bits(sensitive_data.ssh1_host_key->rsa->n),
                             SSH_KEY_BITS_RESERVED);
                 }
-                rsa_private_decrypt(session_key_int, session_key_int,
-                    sensitive_data.server_key->rsa);
-                rsa_private_decrypt(session_key_int, session_key_int,
-                    sensitive_data.ssh1_host_key->rsa);
+                if (rsa_private_decrypt(session_key_int, session_key_int,
+                    sensitive_data.server_key->rsa) <= 0)
+                        rsafail++;
+                if (rsa_private_decrypt(session_key_int, session_key_int,
+                    sensitive_data.ssh1_host_key->rsa) <= 0)
+                        rsafail++;
         } else {
                 /* Host key has bigger modulus (or they are equal). */
                 if (BN_num_bits(sensitive_data.ssh1_host_key->rsa->n) <
@@ -1319,10 +1322,12 @@ do_ssh1_kex(void)
                             BN_num_bits(sensitive_data.server_key->rsa->n),
                             SSH_KEY_BITS_RESERVED);
                 }
-                rsa_private_decrypt(session_key_int, session_key_int,
-                    sensitive_data.ssh1_host_key->rsa);
-                rsa_private_decrypt(session_key_int, session_key_int,
-                    sensitive_data.server_key->rsa);
+                if (rsa_private_decrypt(session_key_int, session_key_int,
+                    sensitive_data.ssh1_host_key->rsa) < 0)
+                        rsafail++;
+                if (rsa_private_decrypt(session_key_int, session_key_int,
+                    sensitive_data.server_key->rsa) < 0)
+                        rsafail++;
         }
 
         compute_session_id(session_id, cookie,
@@ -1337,15 +1342,29 @@ do_ssh1_kex(void)
          * least significant 256 bits of the integer; the first byte of the
          * key is in the highest bits.
          */
-        BN_mask_bits(session_key_int, sizeof(session_key) * 8);
-        len = BN_num_bytes(session_key_int);
-        if (len < 0 || len > sizeof(session_key))
-                fatal("do_connection: bad len from %s: session_key_int %d > sizeof(session_key) %d",
-                    get_remote_ipaddr(),
-                    len, sizeof(session_key));
-        memset(session_key, 0, sizeof(session_key));
-        BN_bn2bin(session_key_int, session_key + sizeof(session_key) - len);
-
+        if (!rsafail) {
+                BN_mask_bits(session_key_int, sizeof(session_key) * 8);
+                len = BN_num_bytes(session_key_int);
+                if (len < 0 || len > sizeof(session_key)) {
+                        error("do_connection: bad session key len from %s: "
+                            "session_key_int %d > sizeof(session_key) %d",
+                            get_remote_ipaddr(), len, sizeof(session_key));
+                        rsafail++;
+                } else {
+                        memset(session_key, 0, sizeof(session_key));
+                        BN_bn2bin(session_key_int,
+                            session_key + sizeof(session_key) - len);
+                }
+        }
+        if (rsafail) {
+                log("do_connection: generating a fake encryption key");
+                for (i = 0; i < SSH_SESSION_KEY_LENGTH; i++) {
+                        if (i % 4 == 0)
+                                rand = arc4random();
+                        session_key[i] = rand & 0xff;
+                        rand >>= 8;
+                }
+        }
         /* Destroy the decrypted integer.  It is no longer needed. */
         BN_clear_free(session_key_int);