- 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).
diff --git a/packet.c b/packet.c
index 02f8ab1..26abf0e 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 @@
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;
+ }
+}