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/* $OpenBSD: bcrypt_pbkdf.c,v 1.6 2014/01/31 16:56:32 tedu Exp $ */
/*
* Copyright (c) 2013 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.
*/
#include <sys/types.h>
#include <sys/param.h>
#include <stdlib.h>
#include <blf.h>
#include <sha2.h>
#include <string.h>
#include <util.h>
/*
* 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 modifed
* 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 (e.g.) 512 bits of key material for use as two 256 bit keys, an
* attacker can merely run once through the outer loop, 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] =
"OxychromaticBlowfishSwatDynamite";
uint32_t cdata[BCRYPT_BLOCKS];
int i;
uint16_t j;
size_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, sizeof(cdata) / sizeof(uint64_t));
/* copy out */
for (i = 0; i < BCRYPT_BLOCKS; i++) {
out[4 * i + 3] = (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 */
explicit_bzero(ciphertext, sizeof(ciphertext));
explicit_bzero(cdata, sizeof(cdata));
explicit_bzero(&state, sizeof(state));
}
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)
{
SHA2_CTX ctx;
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[4];
size_t i, j, amt, stride;
uint32_t count;
/* nothing crazy */
if (rounds < 1)
return -1;
if (passlen == 0 || saltlen == 0 || keylen == 0 ||
keylen > sizeof(out) * sizeof(out))
return -1;
stride = (keylen + sizeof(out) - 1) / sizeof(out);
amt = (keylen + stride - 1) / stride;
/* collapse password */
SHA512Init(&ctx);
SHA512Update(&ctx, (uint8_t*)pass, passlen);
SHA512Final(sha2pass, &ctx);
/* generate key, sizeof(out) at a time */
for (count = 1; keylen > 0; count++) {
countsalt[0] = (count >> 24) & 0xff;
countsalt[1] = (count >> 16) & 0xff;
countsalt[2] = (count >> 8) & 0xff;
countsalt[3] = count & 0xff;
/* first round, salt is salt */
SHA512Init(&ctx);
SHA512Update(&ctx, salt, saltlen);
SHA512Update(&ctx, countsalt, sizeof(countsalt));
SHA512Final(sha2salt, &ctx);
bcrypt_hash(sha2pass, sha2salt, tmpout);
memcpy(out, tmpout, sizeof(out));
for (i = 1; i < rounds; i++) {
/* subsequent rounds, salt is previous output */
SHA512Init(&ctx);
SHA512Update(&ctx, tmpout, sizeof(tmpout));
SHA512Final(sha2salt, &ctx);
bcrypt_hash(sha2pass, sha2salt, tmpout);
for (j = 0; j < sizeof(out); j++)
out[j] ^= tmpout[j];
}
/*
* pbkdf2 deviation: ouput the key material non-linearly.
*/
amt = MIN(amt, keylen);
for (i = 0; i < amt; i++)
key[i * stride + (count - 1)] = out[i];
keylen -= amt;
}
/* zap */
explicit_bzero(&ctx, sizeof(ctx));
explicit_bzero(out, sizeof(out));
return 0;
}
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