libsxmp/sxt/bcrypt.c

/*
 * 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.
 */

#ifndef HAVE_BCRYPT_PBKDF

#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <sys/types.h>

#include <sys/param.h>
#ifndef MIN
#define MIN(a,b) (((a)<(b))?(a):(b))
#endif

#include <sxt/blowfish.h>
#include <sxt/ciphers.h>
#include <sxt/lcrypt.h>

#ifndef SHA512_DIGEST_LENGTH
#define SHA512_DIGEST_LENGTH SHA512_DIGEST_LEN
#endif

/*
 * 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 (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] =
    "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 */
  memset(ciphertext, 0, sizeof(ciphertext));
  memset(cdata, 0, sizeof(cdata));
  memset(&state, 0, sizeof(blf_ctx));
}

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;
  SHA512CTX 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;
  if ((countsalt = calloc(1, saltlen + 4)) == NULL)
    return -1;
  stride = (keylen + sizeof(out) - 1) / sizeof(out);
  amt = (keylen + stride - 1) / stride;

  memcpy(countsalt, salt, saltlen);

  /* collapse password */
  ctx = sha512_init();
  sha512_update(ctx, pass, passlen);
  sha512_final(sha2pass, ctx);

  /* generate key, sizeof(out) at a time */
  for (count = 1; keylen > 0; count++) {
    countsalt[saltlen + 0] = (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 */
    ctx = sha512_init();
    sha512_update(ctx, countsalt, saltlen + 4);
    sha512_final(sha2salt, ctx);

    bcrypt_hash(sha2pass, sha2salt, tmpout);
    memcpy(out, tmpout, sizeof(out));

    for (i = 1; i < rounds; i++) {
      /* subsequent rounds, salt is previous output */
      ctx = sha512_init();
      sha512_update(ctx, tmpout, sizeof(tmpout));
      sha512_final(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++) {
      size_t dest = i * stride + (count - 1);
      if (dest >= origkeylen) {
        break;
      }
      key[dest] = out[i];
    }
    keylen -= i;
  }

  /* zap */
  memset(out, 0, sizeof(out));
  free(countsalt);

  return 0;
}
#endif /* HAVE_BCRYPT_PBKDF */