/* $OpenBSD: bcrypt_pbkdf.c,v 1.16 2020/08/02 18:35:48 tb 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.

 */

/* OPENBSD ORIGINAL: lib/libutil/bcrypt_pbkdf.c */

/* This version has been modified to use SHA512 from SUPERCOP */

#include "includes.h"

#ifndef HAVE_BCRYPT_PBKDF

#include <sys/types.h>

#ifdef HAVE_STDLIB_H

# include <stdlib.h>

#endif

#include <string.h>

#ifdef HAVE_BLF_H

# include <blf.h>

#endif

#include "crypto_api.h"

#ifdef SHA512_DIGEST_LENGTH

# undef SHA512_DIGEST_LENGTH

#endif

#define SHA512_DIGEST_LENGTH crypto_hash_sha512_BYTES

#define MINIMUM(a,b) (((a) < (b)) ? (a) : (b))

/*

 * 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_WORDS 8

#define BCRYPT_HASHSIZE (BCRYPT_WORDS * 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_WORDS];

  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_WORDS; i++)

    cdata[i] = Blowfish_stream2word(ciphertext, sizeof(ciphertext),

        &j);

  for (i = 0; i < 64; i++)

    blf_enc(&state, cdata, BCRYPT_WORDS / 2);

  /* copy out */

  for (i = 0; i < BCRYPT_WORDS; 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)

{

  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;

  /* nothing crazy */

  if (rounds < 1)

    goto bad;

  if (passlen == 0 || saltlen == 0 || keylen == 0 ||

      keylen > sizeof(out) * sizeof(out) || saltlen > 1<<20)

    goto bad;

  if ((countsalt = calloc(1, saltlen + 4)) == NULL)

    goto bad;

  stride = (keylen + sizeof(out) - 1) / sizeof(out);

  amt = (keylen + stride - 1) / stride;

  memcpy(countsalt, salt, saltlen);

  /* collapse password */

  crypto_hash_sha512(sha2pass, pass, passlen);

  /* 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 */

    crypto_hash_sha512(sha2salt, countsalt, saltlen + 4);

    bcrypt_hash(sha2pass, sha2salt, tmpout);

    memcpy(out, tmpout, sizeof(out));

    for (i = 1; i < rounds; i++) {

      /* subsequent rounds, salt is previous output */

      crypto_hash_sha512(sha2salt, tmpout, sizeof(tmpout));

      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 = MINIMUM(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 */

  freezero(countsalt, saltlen + 4);

  explicit_bzero(out, sizeof(out));

  explicit_bzero(tmpout, sizeof(tmpout));

  return 0;

bad:

  /* overwrite with random in case caller doesn't check return code */

  arc4random_buf(key, keylen);

  return -1;

}

#endif /* HAVE_BCRYPT_PBKDF */