nhyatt/putty-source
1
0
Fork 0
mirror of https://git.tartarus.org/simon/putty.git synced 2025-03-12 18:13:50 -05:00
Code Issues Projects Releases Wiki Activity

In SSH2, rather than sending an SSH_MSG_IGNORE after every password, just

Browse Source 
pad the packet out to 256 bytes.  Much simpler.

This leavs ssh2_pkt_defer() unused, so ifdef it out.

[originally from svn r5122]
This commit is contained in:
Ben Harris 2005-01-17 00:50:35 +00:00
parent 214e11a7fe
commit 8a20515844
1 changed files with 16 additions and 45 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

61
ssh.c
View File

@ -533,6 +533,7 @@ struct ssh_portfwd {
struct Packet {
long length;
long forcepad; /* Force padding to at least this length */
int type;
unsigned long sequence;
unsigned char *data;
@ -1572,6 +1573,7 @@ static struct Packet *ssh2_pkt_init(int pkt_type)
{
struct Packet *pkt = ssh_new_packet();
pkt->length = 5;
pkt->forcepad = 0;
ssh2_pkt_addbyte(pkt, (unsigned char) pkt_type);
return pkt;
}
@ -1668,12 +1670,17 @@ static int ssh2_pkt_construct(Ssh ssh, struct Packet *pkt)
/*
* Add padding. At least four bytes, and must also bring total
* length (minus MAC) up to a multiple of the block size.
* If pkt->forcepad is set, make sure the packet is at least that size
* after padding.
*/
cipherblk = ssh->cscipher ? ssh->cscipher->blksize : 8; /* block size */
cipherblk = cipherblk < 8 ? 8 : cipherblk; /* or 8 if blksize < 8 */
padding = 4;
if (pkt->length + padding < pkt->forcepad)
padding = pkt->forcepad - pkt->length;
padding +=
(cipherblk - (pkt->length + padding) % cipherblk) % cipherblk;
assert(padding <= 255);
maclen = ssh->csmac ? ssh->csmac->len : 0;
ssh2_pkt_ensure(pkt, pkt->length + padding + maclen);
pkt->data[4] = padding;
@ -1791,6 +1798,7 @@ static void ssh2_pkt_send(Ssh ssh, struct Packet *pkt)
ssh2_pkt_send_noqueue(ssh, pkt);
}
#if 0 /* disused */
/*
* Either queue or defer a packet, depending on whether queueing is
* set.
@ -1802,6 +1810,7 @@ static void ssh2_pkt_defer(Ssh ssh, struct Packet *pkt)
else
ssh2_pkt_defer_noqueue(ssh, pkt);
}
#endif
/*
* Send the whole deferred data block constructed by
@ -6756,20 +6765,16 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
}
} else if (s->method == AUTH_PASSWORD) {
/*
* We send the password packet lumped tightly together with
* an SSH_MSG_IGNORE packet. The IGNORE packet contains a
* string long enough to make the total length of the two
* packets constant. This should ensure that a passive
* listener doing traffic analyis can't work out the length
* of the password.
* We pad out the password packet to 256 bytes to make
* it harder for an attacker to find the length of the
* user's password.
*
* For this to work, we need an assumption about the
* maximum length of the password packet. I think 256 is
* pretty conservative. Anyone using a password longer than
* that probably doesn't have much to worry about from
* Anyone using a password longer than 256 bytes
* probably doesn't have much to worry about from
* people who find out how long their password is!
*/
s->pktout = ssh2_pkt_init(SSH2_MSG_USERAUTH_REQUEST);
s->pktout->forcepad = 256;
ssh2_pkt_addstring(s->pktout, s->username);
ssh2_pkt_addstring(s->pktout, "ssh-connection"); /* service requested */
ssh2_pkt_addstring(s->pktout, "password");
@ -6778,41 +6783,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
ssh2_pkt_addstring(s->pktout, s->password);
memset(s->password, 0, sizeof(s->password));
end_log_omission(ssh, s->pktout);
ssh2_pkt_defer(ssh, s->pktout);
/*
* We'll include a string that's an exact multiple of the
* cipher block size. If the cipher is NULL for some
* reason, we don't do this trick at all because we gain
* nothing by it.
*/
if (ssh->cscipher) {
int stringlen, i;
stringlen = (256 - ssh->deferred_len);
stringlen += ssh->cscipher->blksize - 1;
stringlen -= (stringlen % ssh->cscipher->blksize);
if (ssh->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 -=
ssh->cscomp->disable_compression(ssh->cs_comp_ctx);
}
s->pktout = ssh2_pkt_init(SSH2_MSG_IGNORE);
ssh2_pkt_addstring_start(s->pktout);
for (i = 0; i < stringlen; i++) {
char c = (char) random_byte();
ssh2_pkt_addstring_data(s->pktout, &c, 1);
}
ssh2_pkt_defer(ssh, s->pktout);
}
ssh_pkt_defersend(ssh);
ssh2_pkt_send(ssh, s->pktout);
logevent("Sent password");
s->type = AUTH_TYPE_PASSWORD;
} else if (s->method == AUTH_KEYBOARD_INTERACTIVE) {