/*      $OpenBSD: pkcs5_pbkdf2.c,v 1.12 2024/09/20 02:00:46 jsg Exp $   */

/*-
 * Copyright (c) 2008 Damien Bergamini <damien.bergamini@free.fr>
 *
 * 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 <string.h>
#include <stdint.h>
#include <stdlib.h>
#include <util.h>

#include <sha1.h>

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

/*
 * HMAC-SHA-1 (from RFC 2202).
 */
static void
hmac_sha1(const u_int8_t *text, size_t text_len, const u_int8_t *key,
    size_t key_len, u_int8_t digest[SHA1_DIGEST_LENGTH])
{
        SHA1_CTX ctx;
        u_int8_t k_pad[SHA1_BLOCK_LENGTH];
        u_int8_t tk[SHA1_DIGEST_LENGTH];
        int i;

        if (key_len > SHA1_BLOCK_LENGTH) {
                SHA1Init(&ctx);
                SHA1Update(&ctx, key, key_len);
                SHA1Final(tk, &ctx);

                key = tk;
                key_len = SHA1_DIGEST_LENGTH;
        }

        bzero(k_pad, sizeof k_pad);
        bcopy(key, k_pad, key_len);
        for (i = 0; i < SHA1_BLOCK_LENGTH; i++)
                k_pad[i] ^= 0x36;

        SHA1Init(&ctx);
        SHA1Update(&ctx, k_pad, SHA1_BLOCK_LENGTH);
        SHA1Update(&ctx, text, text_len);
        SHA1Final(digest, &ctx);

        bzero(k_pad, sizeof k_pad);
        bcopy(key, k_pad, key_len);
        for (i = 0; i < SHA1_BLOCK_LENGTH; i++)
                k_pad[i] ^= 0x5c;

        SHA1Init(&ctx);
        SHA1Update(&ctx, k_pad, SHA1_BLOCK_LENGTH);
        SHA1Update(&ctx, digest, SHA1_DIGEST_LENGTH);
        SHA1Final(digest, &ctx);
}

/*
 * Password-Based Key Derivation Function 2 (PKCS #5 v2.0).
 * Code based on IEEE Std 802.11-2007, Annex H.4.2.
 */
int
pkcs5_pbkdf2(const char *pass, size_t pass_len, const uint8_t *salt,
    size_t salt_len, uint8_t *key, size_t key_len, unsigned int rounds)
{
        uint8_t *asalt, obuf[SHA1_DIGEST_LENGTH];
        uint8_t d1[SHA1_DIGEST_LENGTH], d2[SHA1_DIGEST_LENGTH];
        unsigned int i, j;
        unsigned int count;
        size_t r;

        if (rounds < 1 || key_len == 0)
                goto bad;
        if (salt_len == 0 || salt_len > SIZE_MAX - 4)
                goto bad;
        if ((asalt = malloc(salt_len + 4)) == NULL)
                goto bad;

        memcpy(asalt, salt, salt_len);

        for (count = 1; key_len > 0; count++) {
                asalt[salt_len + 0] = (count >> 24) & 0xff;
                asalt[salt_len + 1] = (count >> 16) & 0xff;
                asalt[salt_len + 2] = (count >> 8) & 0xff;
                asalt[salt_len + 3] = count & 0xff;
                hmac_sha1(asalt, salt_len + 4, pass, pass_len, d1);
                memcpy(obuf, d1, sizeof(obuf));

                for (i = 1; i < rounds; i++) {
                        hmac_sha1(d1, sizeof(d1), pass, pass_len, d2);
                        memcpy(d1, d2, sizeof(d1));
                        for (j = 0; j < sizeof(obuf); j++)
                                obuf[j] ^= d1[j];
                }

                r = MINIMUM(key_len, SHA1_DIGEST_LENGTH);
                memcpy(key, obuf, r);
                key += r;
                key_len -= r;
        }
        freezero(asalt, salt_len + 4);
        explicit_bzero(d1, sizeof(d1));
        explicit_bzero(d2, sizeof(d2));
        explicit_bzero(obuf, sizeof(obuf));

        return 0;

bad:
        /* overwrite with random in case caller doesn't check return code */
        arc4random_buf(key, key_len);
        return -1;
}