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Make the SSH2 traffic analysis defence robust in the face of Zlib

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compression. This involves introducing an option to disable Zlib
compression (that is, continue to work within the Zlib format but
output an uncompressed block) for the duration of a single packet.

[originally from svn r982]
This commit is contained in:
Simon Tatham
2001-03-05 16:38:42 +00:00
parent a1d5dab580
commit aaeecbb4ea
3 changed files with 177 additions and 46 deletions
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28
ssh.c
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@ -3224,15 +3224,29 @@ static void do_ssh2_authconn(unsigned char *in, int inlen, int ispkt)
* reason, we don't do this trick at all because we gain
* nothing by it.
*/
if (cscipher) {
int i, j;
if (cscipher) {
int stringlen, i;
stringlen = (256 - deferred_len);
stringlen += cscipher->blksize - 1;
stringlen -= (stringlen % cscipher->blksize);
if (cscomp) {
/*
* Temporarily disable actual compression,
* so we can guarantee to get this string
* exactly the length we want it. The
* compression-disabling routine should
* return an integer indicating how many
* bytes we should adjust our string length
* by.
*/
stringlen -= cscomp->disable_compression();
}
ssh2_pkt_init(SSH2_MSG_IGNORE);
ssh2_pkt_addstring_start();
for (i = deferred_len; i <= 256; i += cscipher->blksize) {
for (j = 0; j < cscipher->blksize; j++) {
char c = (char)random_byte();
ssh2_pkt_addstring_data(&c, 1);
}
for (i = 0; i < stringlen; i++) {
char c = (char)random_byte();
ssh2_pkt_addstring_data(&c, 1);
}
ssh2_pkt_defer();
}