/* $OpenBSD: bcrypt_pbkdf.c,v 1.4 2013/07/29 00:55:53 tedu Exp $ */
/*
* Copyright (C) Ted Unangst <tedu@openbsd.org>
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*
* SPDX-License-Identifier: MIT
*/
#include "libssh2_priv.h"
#ifndef HAVE_BCRYPT_PBKDF
#include <stdlib.h>
#define LIBSSH2_BCRYPT_PBKDF_C
#include "blowfish.c"
/*
* pkcs #5 pbkdf2 implementation using the "bcrypt" hash
*
* The bcrypt hash function is derived from the bcrypt password hashing
* function with the following modifications:
* 1. The input password and salt are preprocessed with SHA512.
* 2. The output length is expanded to 256 bits.
* 3. Subsequently the magic string to be encrypted is lengthened and modified
* to "OxychromaticBlowfishSwatDynamite"
* 4. The hash function is defined to perform 64 rounds of initial state
* expansion. (More rounds are performed by iterating the hash.)
*
* Note that this implementation pulls the SHA512 operations into the caller
* as a performance optimization.
*
* One modification from official pbkdf2. Instead of outputting key material
* linearly, we mix it. pbkdf2 has a known weakness where if one uses it to
* generate (i.e.) 512 bits of key material for use as two 256 bit keys, an
* attacker can merely run once through the outer loop below, but the user
* always runs it twice. Shuffling output bytes requires computing the
* entirety of the key material to assemble any subkey. This is something a
* wise caller could do; we just do it for you.
*/
#define BCRYPT_BLOCKS 8
#define BCRYPT_HASHSIZE (BCRYPT_BLOCKS * 4)
static void
bcrypt_hash(uint8_t *sha2pass, uint8_t *sha2salt, uint8_t *out)
{
blf_ctx state;
uint8_t ciphertext[BCRYPT_HASHSIZE] = {
'O', 'x', 'y', 'c', 'h', 'r', 'o', 'm', 'a', 't', 'i', 'c',
'B', 'l', 'o', 'w', 'f', 'i', 's', 'h',
'S', 'w', 'a', 't',
'D', 'y', 'n', 'a', 'm', 'i', 't', 'e' };
uint32_t cdata[BCRYPT_BLOCKS];
int i;
uint16_t j;
uint16_t shalen = SHA512_DIGEST_LENGTH;
/* key expansion */
Blowfish_initstate(&state);
Blowfish_expandstate(&state, sha2salt, shalen, sha2pass, shalen);
for(i = 0; i < 64; i++) {
Blowfish_expand0state(&state, sha2salt, shalen);
Blowfish_expand0state(&state, sha2pass, shalen);
}
/* encryption */
j = 0;
for(i = 0; i < BCRYPT_BLOCKS; i++)
cdata[i] = Blowfish_stream2word(ciphertext, sizeof(ciphertext),
&j);
for(i = 0; i < 64; i++)
blf_enc(&state, cdata, BCRYPT_BLOCKS / 2);
/* copy out */
for(i = 0; i < BCRYPT_BLOCKS; i++) {
out[4 * i + 3] = (uint8_t)((cdata[i] >> 24) & 0xff);
out[4 * i + 2] = (cdata[i] >> 16) & 0xff;
out[4 * i + 1] = (cdata[i] >> 8) & 0xff;
out[4 * i + 0] = cdata[i] & 0xff;
}
/* zap */
_libssh2_explicit_zero(ciphertext, sizeof(ciphertext));
_libssh2_explicit_zero(cdata, sizeof(cdata));
_libssh2_explicit_zero(&state, sizeof(state));
}
static int
bcrypt_pbkdf(const char *pass, size_t passlen, const uint8_t *salt,
size_t saltlen,
uint8_t *key, size_t keylen, unsigned int rounds)
{
uint8_t sha2pass[SHA512_DIGEST_LENGTH];
uint8_t sha2salt[SHA512_DIGEST_LENGTH];
uint8_t out[BCRYPT_HASHSIZE];
uint8_t tmpout[BCRYPT_HASHSIZE];
uint8_t *countsalt;
size_t i, j, amt, stride;
uint32_t count;
size_t origkeylen = keylen;
libssh2_sha512_ctx ctx;
/* nothing crazy */
if(rounds < 1)
return -1;
if(passlen == 0 || saltlen == 0 || keylen == 0 ||
keylen > sizeof(out) * sizeof(out) || saltlen > 1<<20)
return -1;
countsalt = calloc(1, saltlen + 4);
if(!countsalt)
return -1;
stride = (keylen + sizeof(out) - 1) / sizeof(out);
amt = (keylen + stride - 1) / stride;
memcpy(countsalt, salt, saltlen);
/* collapse password */
if(!libssh2_sha512_init(&ctx) ||
!libssh2_sha512_update(ctx, pass, passlen) ||
!libssh2_sha512_final(ctx, sha2pass)) {
free(countsalt);
return -1;
}
/* generate key, sizeof(out) at a time */
for(count = 1; keylen > 0; count++) {
countsalt[saltlen + 0] = (uint8_t)((count >> 24) & 0xff);
countsalt[saltlen + 1] = (count >> 16) & 0xff;
countsalt[saltlen + 2] = (count >> 8) & 0xff;
countsalt[saltlen + 3] = count & 0xff;
/* first round, salt is salt */
if(!libssh2_sha512_init(&ctx) ||
!libssh2_sha512_update(ctx, countsalt, saltlen + 4) ||
!libssh2_sha512_final(ctx, sha2salt)) {
_libssh2_explicit_zero(out, sizeof(out));
free(countsalt);
return -1;
}
bcrypt_hash(sha2pass, sha2salt, tmpout);
memcpy(out, tmpout, sizeof(out));
for(i = 1; i < rounds; i++) {
/* subsequent rounds, salt is previous output */
if(!libssh2_sha512_init(&ctx) ||
!libssh2_sha512_update(ctx, tmpout, sizeof(tmpout)) ||
!libssh2_sha512_final(ctx, sha2salt)) {
_libssh2_explicit_zero(out, sizeof(out));
free(countsalt);
return -1;
}
bcrypt_hash(sha2pass, sha2salt, tmpout);
for(j = 0; j < sizeof(out); j++)
out[j] ^= tmpout[j];
}
/*
* pbkdf2 deviation: output the key material non-linearly.
*/
amt = LIBSSH2_MIN(amt, keylen);
for(i = 0; i < amt; i++) {
size_t dest = i * stride + (count - 1);
if(dest >= origkeylen) {
break;
}
key[dest] = out[i];
}
keylen -= i;
}
/* zap */
_libssh2_explicit_zero(out, sizeof(out));
free(countsalt);
return 0;
}
#endif /* HAVE_BCRYPT_PBKDF */
/* Wrapper */
int _libssh2_bcrypt_pbkdf(const char *pass,
size_t passlen,
const uint8_t *salt,
size_t saltlen,
uint8_t *key,
size_t keylen,
unsigned int rounds)
{
return bcrypt_pbkdf(pass,
passlen,
salt,
saltlen,
key,
keylen,
rounds);
}