- markus@cvs.openbsd.org 2001/02/28 09:57:07

     [packet.c packet.h sshconnect2.c]
     in ssh protocol v2 use ignore messages for padding (instead of
     trailing \0).

4 files changed, 69 insertions, 6 deletions

diff --git a/ChangeLog b/ChangeLog
index a30623c4a..b91677386 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -72,6 +72,10 @@
      [channels.c nchan.c nchan.h]
      make sure remote stderr does not get truncated.
      remove closed fd's from the select mask.
+   - markus@cvs.openbsd.org 2001/02/28 09:57:07
+     [packet.c packet.h sshconnect2.c]
+     in ssh protocol v2 use ignore messages for padding (instead of
+     trailing \0).
 
 20010304
  - (bal) Remove make-ssh-known-hosts.1 since it's no longer valid.
@@ -4264,4 +4268,4 @@
  - Wrote replacements for strlcpy and mkdtemp
  - Released 1.0pre1
 
-$Id: ChangeLog,v 1.872 2001/03/05 06:16:11 mouring Exp $
+$Id: ChangeLog,v 1.873 2001/03/05 06:17:49 mouring Exp $
diff --git a/packet.c b/packet.c
index 02f8ab1bb..26abf0e1a 100644
--- a/packet.c
+++ b/packet.c
@@ -37,7 +37,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: packet.c,v 1.52 2001/02/27 10:35:27 markus Exp $");
+RCSID("$OpenBSD: packet.c,v 1.53 2001/02/28 09:57:06 markus Exp $");
 
 #include "xmalloc.h"
 #include "buffer.h"
@@ -1305,3 +1305,57 @@ packet_set_maxsize(int s)
         max_packet_size = s;
         return s;
 }
+
+/*
+ * 9.2.  Ignored Data Message
+ * 
+ *   byte      SSH_MSG_IGNORE
+ *   string    data
+ * 
+ * All implementations MUST understand (and ignore) this message at any
+ * time (after receiving the protocol version). No implementation is
+ * required to send them. This message can be used as an additional
+ * protection measure against advanced traffic analysis techniques.
+ */
+/* size of current + ignore message should be n*sumlen bytes (w/o mac) */
+void
+packet_inject_ignore(int sumlen)
+{
+        u_int32_t rand = 0;
+        int i, blocksize, padlen, have, need, nb, mini, nbytes;
+        Enc *enc = NULL;
+
+        if (use_ssh2_packet_format == 0)
+                return;
+
+        have = buffer_len(&outgoing_packet);
+        debug2("packet_inject_ignore: current %d", have);
+        if (kex != NULL)
+        enc  = &kex->enc[MODE_OUT];
+        blocksize = enc ? enc->cipher->block_size : 8;
+        padlen = blocksize - (have % blocksize);
+        if (padlen < 4)
+                padlen += blocksize;
+        have += padlen;
+        have /= blocksize;      /* # of blocks for current message */
+
+        nb   = roundup(sumlen,  blocksize) / blocksize; /* blocks for both */
+        mini = roundup(5+1+4+4, blocksize) / blocksize; /* minsize ignore msg */
+        need = nb - (have % nb);                        /* blocks for ignore */
+        if (need <= mini)
+                need += nb;
+        nbytes = (need - mini) * blocksize;     /* size of ignore payload */
+        debug2("packet_inject_ignore: block %d have %d nb %d mini %d need %d",
+            blocksize, have, nb, mini, need);
+
+        /* enqueue current message and append a ignore message */
+        packet_send();
+        packet_start(SSH2_MSG_IGNORE);
+        packet_put_int(nbytes);
+        for(i = 0; i < nbytes; i++) {
+                if (i % 4 == 0)
+                        rand = arc4random();
+                packet_put_char(rand & 0xff);
+                rand >>= 8;
+        }
+}
diff --git a/packet.h b/packet.h
index 00f0c3778..059bb27a0 100644
--- a/packet.h
+++ b/packet.h
@@ -11,7 +11,7 @@
  * called by a name other than "ssh" or "Secure Shell".
  */
 
-/* RCSID("$OpenBSD: packet.h,v 1.19 2001/01/13 18:32:50 markus Exp $"); */
+/* RCSID("$OpenBSD: packet.h,v 1.20 2001/02/28 09:57:07 markus Exp $"); */
 
 #ifndef PACKET_H
 #define PACKET_H
@@ -214,4 +214,7 @@ void	packet_set_ssh2_format(void);
 /* returns remaining payload bytes */
 int     packet_remaining(void);
 
+/* append an ignore message */
+void    packet_inject_ignore(int sumlen);
+
 #endif                          /* PACKET_H */
diff --git a/sshconnect2.c b/sshconnect2.c
index 12335e80e..8b523232f 100644
--- a/sshconnect2.c
+++ b/sshconnect2.c
@@ -23,7 +23,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: sshconnect2.c,v 1.48 2001/02/15 23:19:59 markus Exp $");
+RCSID("$OpenBSD: sshconnect2.c,v 1.49 2001/02/28 09:57:07 markus Exp $");
 
 #include <openssl/bn.h>
 #include <openssl/md5.h>
@@ -658,9 +658,10 @@ userauth_passwd(Authctxt *authctxt)
         packet_put_cstring(authctxt->service);
         packet_put_cstring(authctxt->method->name);
         packet_put_char(0);
-        ssh_put_password(password);
+        packet_put_cstring(password);
         memset(password, 0, strlen(password));
         xfree(password);
+        packet_inject_ignore(64);
         packet_send();
         packet_write_wait();
         return 1;
@@ -928,13 +929,14 @@ input_userauth_info_req(int type, int plen, void *ctxt)
 
                 response = cli_prompt(prompt, echo);
 
-                ssh_put_password(response);
+                packet_put_cstring(response);
                 memset(response, 0, strlen(response));
                 xfree(response);
                 xfree(prompt);
         }
         packet_done(); /* done with parsing incoming message. */
 
+        packet_inject_ignore(64);
         packet_send();
         packet_write_wait();
 }