/*	$OpenBSD: deattack.c,v 1.14 2001/06/23 15:12:18 itojun 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> *  * Modified for use in PuTTY by Simon Tatham */#include <assert.h>#include "misc.h"#include "ssh.h"typedef unsigned char uchar;typedef unsigned short uint16;/* SSH Constants */#define SSH_MAXBLOCKS	(32 * 1024)#define SSH_BLOCKSIZE	(8)/* Hashing constants */#define HASH_MINSIZE	(8 * 1024)#define HASH_ENTRYSIZE	(sizeof(uint16))#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)#define GET_32BIT_MSB_FIRST(cp) \  (((unsigned long)(unsigned char)(cp)[0] << 24) | \  ((unsigned long)(unsigned char)(cp)[1] << 16) | \  ((unsigned long)(unsigned char)(cp)[2] << 8) | \  ((unsigned long)(unsigned char)(cp)[3]))/* Hash function (Input keys are cipher results) */#define HASH(x)		GET_32BIT_MSB_FIRST(x)#define CMP(a, b)	(memcmp(a, b, SSH_BLOCKSIZE))const uchar ONE[4] = { 1, 0, 0, 0 };const uchar ZERO[4] = { 0, 0, 0, 0 };struct crcda_ctx {    uint16 *h;    uint32 n;};void *crcda_make_context(void){    struct crcda_ctx *ret = snew(struct crcda_ctx);    ret->h = NULL;    ret->n = HASH_MINSIZE / HASH_ENTRYSIZE;    return ret;}void crcda_free_context(void *handle){    struct crcda_ctx *ctx = (struct crcda_ctx *)handle;    if (ctx) {	sfree(ctx->h);	ctx->h = NULL;	sfree(ctx);    }}static void crc_update(uint32 *a, const void *b){    *a = crc32_update(*a, b, 4);}/* detect if a block is used in a particular pattern */static int check_crc(uchar *S, uchar *buf, uint32 len, uchar *IV){    uint32 crc;    uchar *c;    crc = 0;    if (IV && !CMP(S, IV)) {        crc_update(&crc, ONE);        crc_update(&crc, ZERO);    }    for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) {        if (!CMP(S, c)) {            crc_update(&crc, ONE);            crc_update(&crc, ZERO);        } else {            crc_update(&crc, ZERO);            crc_update(&crc, ZERO);        }    }    return (crc == 0);}/* Detect a crc32 compensation attack on a packet */int detect_attack(void *handle, uchar *buf, uint32 len, uchar *IV){    struct crcda_ctx *ctx = (struct crcda_ctx *)handle;    register uint32 i, j;    uint32 l;    register uchar *c;    uchar *d;    assert(!(len > (SSH_MAXBLOCKS * SSH_BLOCKSIZE) ||             len % SSH_BLOCKSIZE != 0));    for (l = ctx->n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2)        ;    if (ctx->h == NULL) {        ctx->n = l;        ctx->h = snewn(ctx->n, uint16);    } else {        if (l > ctx->n) {            ctx->n = l;            ctx->h = sresize(ctx->h, ctx->n, uint16);        }    }    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 1;          /* attack detected */                else                    break;            }            for (d = buf; d < c; d += SSH_BLOCKSIZE) {                if (!CMP(c, d)) {                    if ((check_crc(c, buf, len, IV)))                        return 1;      /* attack detected */                    else                        break;                }            }        }        return 0;                      /* ok */    }    memset(ctx->h, HASH_UNUSEDCHAR, ctx->n * HASH_ENTRYSIZE);    if (IV)        ctx->h[HASH(IV) & (ctx->n - 1)] = HASH_IV;    for (c = buf, j = 0; c < (buf + len); c += SSH_BLOCKSIZE, j++) {        for (i = HASH(c) & (ctx->n - 1); ctx->h[i] != HASH_UNUSED;             i = (i + 1) & (ctx->n - 1)) {            if (ctx->h[i] == HASH_IV) {                if (!CMP(c, IV)) {                    if (check_crc(c, buf, len, IV))                        return 1;      /* attack detected */                    else                        break;                }            } else if (!CMP(c, buf + ctx->h[i] * SSH_BLOCKSIZE)) {                if (check_crc(c, buf, len, IV))                    return 1;          /* attack detected */                else                    break;            }        }        ctx->h[i] = j;    }    return 0;                          /* ok */}