/* $OpenBSD: bcrypt_pbkdf.c,v 1.3 2021/03/12 10:22:46 jsg 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 <lib/libsa/stand.h>
#include <sys/param.h>
 
#include "bcrypt_pbkdf.h"
#include "blowfish.h"
#include "sha2.h"

#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 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 (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)
{
        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;
        size_t origkeylen = keylen;

        /* 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, 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: 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 */
        explicit_bzero(&ctx, sizeof(ctx));
        explicit_bzero(out, sizeof(out));

        return 0;
}