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/* $OpenBSD: bcrypt_pbkdf.c,v 1.4 2013/07/29 00:55:53 tedu Exp $ */
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/*
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* Copyright (c) 2013 Ted Unangst <tedu@openbsd.org>
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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#include <sys/types.h>
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#include <sys/param.h>
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#include <stdlib.h>
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#include <blf.h>
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#include <sha2.h>
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#include <string.h>
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#include <util.h>
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/*
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* pkcs #5 pbkdf2 implementation using the "bcrypt" hash
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*
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* The bcrypt hash function is derived from the bcrypt password hashing
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* function with the following modifications:
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* 1. The input password and salt are preprocessed with SHA512.
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* 2. The output length is expanded to 256 bits.
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* 3. Subsequently the magic string to be encrypted is lengthened and modifed
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* to "OxychromaticBlowfishSwatDynamite"
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* 4. The hash function is defined to perform 64 rounds of initial state
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* expansion. (More rounds are performed by iterating the hash.)
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*
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* Note that this implementation pulls the SHA512 operations into the caller
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* as a performance optimization.
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*
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* One modification from official pbkdf2. Instead of outputting key material
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* linearly, we mix it. pbkdf2 has a known weakness where if one uses it to
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* generate (i.e.) 512 bits of key material for use as two 256 bit keys, an
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* attacker can merely run once through the outer loop below, but the user
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* always runs it twice. Shuffling output bytes requires computing the
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* entirety of the key material to assemble any subkey. This is something a
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* wise caller could do; we just do it for you.
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*/
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#define BCRYPT_BLOCKS 8
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#define BCRYPT_HASHSIZE (BCRYPT_BLOCKS * 4)
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static void
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bcrypt_hash(uint8_t *sha2pass, uint8_t *sha2salt, uint8_t *out)
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{
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blf_ctx state;
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uint8_t ciphertext[BCRYPT_HASHSIZE] =
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"OxychromaticBlowfishSwatDynamite";
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uint32_t cdata[BCRYPT_BLOCKS];
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int i;
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uint16_t j;
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size_t shalen = SHA512_DIGEST_LENGTH;
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/* key expansion */
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Blowfish_initstate(&state);
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Blowfish_expandstate(&state, sha2salt, shalen, sha2pass, shalen);
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for (i = 0; i < 64; i++) {
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Blowfish_expand0state(&state, sha2salt, shalen);
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Blowfish_expand0state(&state, sha2pass, shalen);
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}
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/* encryption */
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j = 0;
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for (i = 0; i < BCRYPT_BLOCKS; i++)
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cdata[i] = Blowfish_stream2word(ciphertext, sizeof(ciphertext),
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&j);
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for (i = 0; i < 64; i++)
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blf_enc(&state, cdata, sizeof(cdata) / sizeof(uint64_t));
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/* copy out */
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for (i = 0; i < BCRYPT_BLOCKS; i++) {
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out[4 * i + 3] = (cdata[i] >> 24) & 0xff;
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out[4 * i + 2] = (cdata[i] >> 16) & 0xff;
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out[4 * i + 1] = (cdata[i] >> 8) & 0xff;
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out[4 * i + 0] = cdata[i] & 0xff;
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}
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/* zap */
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memset(ciphertext, 0, sizeof(ciphertext));
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memset(cdata, 0, sizeof(cdata));
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memset(&state, 0, sizeof(state));
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}
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int
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bcrypt_pbkdf(const char *pass, size_t passlen, const uint8_t *salt, size_t saltlen,
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uint8_t *key, size_t keylen, unsigned int rounds)
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{
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SHA2_CTX ctx;
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uint8_t sha2pass[SHA512_DIGEST_LENGTH];
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uint8_t sha2salt[SHA512_DIGEST_LENGTH];
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uint8_t out[BCRYPT_HASHSIZE];
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uint8_t tmpout[BCRYPT_HASHSIZE];
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uint8_t countsalt[4];
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size_t i, j, amt, stride;
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uint32_t count;
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/* nothing crazy */
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if (rounds < 1)
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return -1;
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if (passlen == 0 || saltlen == 0 || keylen == 0 ||
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keylen > sizeof(out) * sizeof(out))
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return -1;
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stride = (keylen + sizeof(out) - 1) / sizeof(out);
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amt = (keylen + stride - 1) / stride;
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/* collapse password */
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SHA512Init(&ctx);
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SHA512Update(&ctx, pass, passlen);
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SHA512Final(sha2pass, &ctx);
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/* generate key, sizeof(out) at a time */
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for (count = 1; keylen > 0; count++) {
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countsalt[0] = (count >> 24) & 0xff;
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countsalt[1] = (count >> 16) & 0xff;
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countsalt[2] = (count >> 8) & 0xff;
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countsalt[3] = count & 0xff;
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/* first round, salt is salt */
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SHA512Init(&ctx);
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SHA512Update(&ctx, salt, saltlen);
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SHA512Update(&ctx, countsalt, sizeof(countsalt));
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SHA512Final(sha2salt, &ctx);
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bcrypt_hash(sha2pass, sha2salt, tmpout);
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memcpy(out, tmpout, sizeof(out));
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for (i = 1; i < rounds; i++) {
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/* subsequent rounds, salt is previous output */
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SHA512Init(&ctx);
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SHA512Update(&ctx, tmpout, sizeof(tmpout));
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SHA512Final(sha2salt, &ctx);
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bcrypt_hash(sha2pass, sha2salt, tmpout);
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for (j = 0; j < sizeof(out); j++)
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out[j] ^= tmpout[j];
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}
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/*
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* pbkdf2 deviation: ouput the key material non-linearly.
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*/
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amt = MIN(amt, keylen);
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for (i = 0; i < amt; i++)
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key[i * stride + (count - 1)] = out[i];
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keylen -= amt;
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}
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/* zap */
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memset(&ctx, 0, sizeof(ctx));
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memset(out, 0, sizeof(out));
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return 0;
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}
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