157 lines
3.6 KiB
C
157 lines
3.6 KiB
C
/* $OpenBSD: deattack.c,v 1.9 2000/09/07 20:27:51 deraadt Exp $ */
|
|
|
|
/*
|
|
* Cryptographic attack detector for ssh - source code
|
|
*
|
|
* Copyright (c) 1998 CORE SDI S.A., Buenos Aires, Argentina.
|
|
*
|
|
* All rights reserved. Redistribution and use in source and binary
|
|
* forms, with or without modification, are permitted provided that
|
|
* this copyright notice is retained.
|
|
*
|
|
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
|
|
* WARRANTIES ARE DISCLAIMED. IN NO EVENT SHALL CORE SDI S.A. BE
|
|
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY OR
|
|
* CONSEQUENTIAL DAMAGES RESULTING FROM THE USE OR MISUSE OF THIS
|
|
* SOFTWARE.
|
|
*
|
|
* Ariel Futoransky <futo@core-sdi.com>
|
|
* <http://www.core-sdi.com>
|
|
*/
|
|
|
|
#include "includes.h"
|
|
#include "deattack.h"
|
|
#include "ssh.h"
|
|
#include "crc32.h"
|
|
#include "getput.h"
|
|
#include "xmalloc.h"
|
|
|
|
/* SSH Constants */
|
|
#define SSH_MAXBLOCKS (32 * 1024)
|
|
#define SSH_BLOCKSIZE (8)
|
|
|
|
/* Hashing constants */
|
|
#define HASH_MINSIZE (8 * 1024)
|
|
#define HASH_ENTRYSIZE (2)
|
|
#define HASH_FACTOR(x) ((x)*3/2)
|
|
#define HASH_UNUSEDCHAR (0xff)
|
|
#define HASH_UNUSED (0xffff)
|
|
#define HASH_IV (0xfffe)
|
|
|
|
#define HASH_MINBLOCKS (7*SSH_BLOCKSIZE)
|
|
|
|
|
|
/* Hash function (Input keys are cipher results) */
|
|
#define HASH(x) GET_32BIT(x)
|
|
|
|
#define CMP(a,b) (memcmp(a, b, SSH_BLOCKSIZE))
|
|
|
|
|
|
void
|
|
crc_update(u_int32_t *a, u_int32_t b)
|
|
{
|
|
b ^= *a;
|
|
*a = ssh_crc32((unsigned char *) &b, sizeof(b));
|
|
}
|
|
|
|
/* detect if a block is used in a particular pattern */
|
|
int
|
|
check_crc(unsigned char *S, unsigned char *buf, u_int32_t len,
|
|
unsigned char *IV)
|
|
{
|
|
u_int32_t crc;
|
|
unsigned char *c;
|
|
|
|
crc = 0;
|
|
if (IV && !CMP(S, IV)) {
|
|
crc_update(&crc, 1);
|
|
crc_update(&crc, 0);
|
|
}
|
|
for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) {
|
|
if (!CMP(S, c)) {
|
|
crc_update(&crc, 1);
|
|
crc_update(&crc, 0);
|
|
} else {
|
|
crc_update(&crc, 0);
|
|
crc_update(&crc, 0);
|
|
}
|
|
}
|
|
return (crc == 0);
|
|
}
|
|
|
|
|
|
/* Detect a crc32 compensation attack on a packet */
|
|
int
|
|
detect_attack(unsigned char *buf, u_int32_t len, unsigned char *IV)
|
|
{
|
|
static u_int16_t *h = (u_int16_t *) NULL;
|
|
static u_int16_t n = HASH_MINSIZE / HASH_ENTRYSIZE;
|
|
register u_int32_t i, j;
|
|
u_int32_t l;
|
|
register unsigned char *c;
|
|
unsigned char *d;
|
|
|
|
if (len > (SSH_MAXBLOCKS * SSH_BLOCKSIZE) ||
|
|
len % SSH_BLOCKSIZE != 0) {
|
|
fatal("detect_attack: bad length %d", len);
|
|
}
|
|
for (l = n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2)
|
|
;
|
|
|
|
if (h == NULL) {
|
|
debug("Installing crc compensation attack detector.");
|
|
n = l;
|
|
h = (u_int16_t *) xmalloc(n * HASH_ENTRYSIZE);
|
|
} else {
|
|
if (l > n) {
|
|
n = l;
|
|
h = (u_int16_t *) xrealloc(h, n * HASH_ENTRYSIZE);
|
|
}
|
|
}
|
|
|
|
if (len <= HASH_MINBLOCKS) {
|
|
for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) {
|
|
if (IV && (!CMP(c, IV))) {
|
|
if ((check_crc(c, buf, len, IV)))
|
|
return (DEATTACK_DETECTED);
|
|
else
|
|
break;
|
|
}
|
|
for (d = buf; d < c; d += SSH_BLOCKSIZE) {
|
|
if (!CMP(c, d)) {
|
|
if ((check_crc(c, buf, len, IV)))
|
|
return (DEATTACK_DETECTED);
|
|
else
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
return (DEATTACK_OK);
|
|
}
|
|
memset(h, HASH_UNUSEDCHAR, n * HASH_ENTRYSIZE);
|
|
|
|
if (IV)
|
|
h[HASH(IV) & (n - 1)] = HASH_IV;
|
|
|
|
for (c = buf, j = 0; c < (buf + len); c += SSH_BLOCKSIZE, j++) {
|
|
for (i = HASH(c) & (n - 1); h[i] != HASH_UNUSED;
|
|
i = (i + 1) & (n - 1)) {
|
|
if (h[i] == HASH_IV) {
|
|
if (!CMP(c, IV)) {
|
|
if (check_crc(c, buf, len, IV))
|
|
return (DEATTACK_DETECTED);
|
|
else
|
|
break;
|
|
}
|
|
} else if (!CMP(c, buf + h[i] * SSH_BLOCKSIZE)) {
|
|
if (check_crc(c, buf, len, IV))
|
|
return (DEATTACK_DETECTED);
|
|
else
|
|
break;
|
|
}
|
|
}
|
|
h[i] = j;
|
|
}
|
|
return (DEATTACK_OK);
|
|
}
|