/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2011 The FreeBSD Project. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/* Based on:
 * SHA256-based Unix crypt implementation. Released into the Public Domain by
 * Ulrich Drepper <drepper@redhat.com>. */

#include <sys/cdefs.h>
#include <sys/endian.h>
#include <sys/param.h>

#include <errno.h>
#include <limits.h>
#include <sha256.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>

#include "crypt.h"

/* Define our magic string to mark salt for SHA256 "encryption" replacement. */
static const char sha256_salt_prefix[] = "$5$";

/* Prefix for optional rounds specification. */
static const char sha256_rounds_prefix[] = "rounds=";

/* Maximum salt string length. */
#define SALT_LEN_MAX 16
/* Default number of rounds if not explicitly specified. */
#define ROUNDS_DEFAULT 5000
/* Minimum number of rounds. */
#define ROUNDS_MIN 1000
/* Maximum number of rounds. */
#define ROUNDS_MAX 999999999

int
crypt_sha256(const char *key, const char *salt, char *buffer)
{
        u_long srounds;
        uint8_t alt_result[32], temp_result[32];
        SHA256_CTX ctx, alt_ctx;
        size_t salt_len, key_len, cnt, rounds;
        char *cp, *p_bytes, *s_bytes, *endp;
        const char *num;
        bool rounds_custom;

        /* Default number of rounds. */
        rounds = ROUNDS_DEFAULT;
        rounds_custom = false;

        /* Find beginning of salt string. The prefix should normally always
         * be present. Just in case it is not. */
        if (strncmp(sha256_salt_prefix, salt, sizeof(sha256_salt_prefix) - 1) == 0)
                /* Skip salt prefix. */
                salt += sizeof(sha256_salt_prefix) - 1;

        if (strncmp(salt, sha256_rounds_prefix, sizeof(sha256_rounds_prefix) - 1)
            == 0) {
                num = salt + sizeof(sha256_rounds_prefix) - 1;
                srounds = strtoul(num, &endp, 10);

                if (*endp == '$') {
                        salt = endp + 1;
                        rounds = MAX(ROUNDS_MIN, MIN(srounds, ROUNDS_MAX));
                        rounds_custom = true;
                }
        }

        salt_len = MIN(strcspn(salt, "$"), SALT_LEN_MAX);
        key_len = strlen(key);

        /* Prepare for the real work. */
        SHA256_Init(&ctx);

        /* Add the key string. */
        SHA256_Update(&ctx, key, key_len);

        /* The last part is the salt string. This must be at most 8
         * characters and it ends at the first `$' character (for
         * compatibility with existing implementations). */
        SHA256_Update(&ctx, salt, salt_len);

        /* Compute alternate SHA256 sum with input KEY, SALT, and KEY. The
         * final result will be added to the first context. */
        SHA256_Init(&alt_ctx);

        /* Add key. */
        SHA256_Update(&alt_ctx, key, key_len);

        /* Add salt. */
        SHA256_Update(&alt_ctx, salt, salt_len);

        /* Add key again. */
        SHA256_Update(&alt_ctx, key, key_len);

        /* Now get result of this (32 bytes) and add it to the other context. */
        SHA256_Final(alt_result, &alt_ctx);

        /* Add for any character in the key one byte of the alternate sum. */
        for (cnt = key_len; cnt > 32; cnt -= 32)
                SHA256_Update(&ctx, alt_result, 32);
        SHA256_Update(&ctx, alt_result, cnt);

        /* Take the binary representation of the length of the key and for
         * every 1 add the alternate sum, for every 0 the key. */
        for (cnt = key_len; cnt > 0; cnt >>= 1)
                if ((cnt & 1) != 0)
                        SHA256_Update(&ctx, alt_result, 32);
                else
                        SHA256_Update(&ctx, key, key_len);

        /* Create intermediate result. */
        SHA256_Final(alt_result, &ctx);

        /* Start computation of P byte sequence. */
        SHA256_Init(&alt_ctx);

        /* For every character in the password add the entire password. */
        for (cnt = 0; cnt < key_len; ++cnt)
                SHA256_Update(&alt_ctx, key, key_len);

        /* Finish the digest. */
        SHA256_Final(temp_result, &alt_ctx);

        /* Create byte sequence P. */
        cp = p_bytes = alloca(key_len);
        for (cnt = key_len; cnt >= 32; cnt -= 32) {
                memcpy(cp, temp_result, 32);
                cp += 32;
        }
        memcpy(cp, temp_result, cnt);

        /* Start computation of S byte sequence. */
        SHA256_Init(&alt_ctx);

        /* For every character in the password add the entire password. */
        for (cnt = 0; cnt < 16 + alt_result[0]; ++cnt)
                SHA256_Update(&alt_ctx, salt, salt_len);

        /* Finish the digest. */
        SHA256_Final(temp_result, &alt_ctx);

        /* Create byte sequence S. */
        cp = s_bytes = alloca(salt_len);
        for (cnt = salt_len; cnt >= 32; cnt -= 32) {
                memcpy(cp, temp_result, 32);
                cp += 32;
        }
        memcpy(cp, temp_result, cnt);

        /* Repeatedly run the collected hash value through SHA256 to burn CPU
         * cycles. */
        for (cnt = 0; cnt < rounds; ++cnt) {
                /* New context. */
                SHA256_Init(&ctx);

                /* Add key or last result. */
                if ((cnt & 1) != 0)
                        SHA256_Update(&ctx, p_bytes, key_len);
                else
                        SHA256_Update(&ctx, alt_result, 32);

                /* Add salt for numbers not divisible by 3. */
                if (cnt % 3 != 0)
                        SHA256_Update(&ctx, s_bytes, salt_len);

                /* Add key for numbers not divisible by 7. */
                if (cnt % 7 != 0)
                        SHA256_Update(&ctx, p_bytes, key_len);

                /* Add key or last result. */
                if ((cnt & 1) != 0)
                        SHA256_Update(&ctx, alt_result, 32);
                else
                        SHA256_Update(&ctx, p_bytes, key_len);

                /* Create intermediate result. */
                SHA256_Final(alt_result, &ctx);
        }

        /* Now we can construct the result string. It consists of three
         * parts. */
        cp = stpcpy(buffer, sha256_salt_prefix);

        if (rounds_custom)
                cp += sprintf(cp, "%s%zu$", sha256_rounds_prefix, rounds);

        cp = stpncpy(cp, salt, salt_len);

        *cp++ = '$';

        b64_from_24bit(alt_result[0], alt_result[10], alt_result[20], 4, &cp);
        b64_from_24bit(alt_result[21], alt_result[1], alt_result[11], 4, &cp);
        b64_from_24bit(alt_result[12], alt_result[22], alt_result[2], 4, &cp);
        b64_from_24bit(alt_result[3], alt_result[13], alt_result[23], 4, &cp);
        b64_from_24bit(alt_result[24], alt_result[4], alt_result[14], 4, &cp);
        b64_from_24bit(alt_result[15], alt_result[25], alt_result[5], 4, &cp);
        b64_from_24bit(alt_result[6], alt_result[16], alt_result[26], 4, &cp);
        b64_from_24bit(alt_result[27], alt_result[7], alt_result[17], 4, &cp);
        b64_from_24bit(alt_result[18], alt_result[28], alt_result[8], 4, &cp);
        b64_from_24bit(alt_result[9], alt_result[19], alt_result[29], 4, &cp);
        b64_from_24bit(0, alt_result[31], alt_result[30], 3, &cp);
        *cp = '\0';     /* Terminate the string. */

        /* Clear the buffer for the intermediate result so that people
         * attaching to processes or reading core dumps cannot get any
         * information. We do it in this way to clear correct_words[] inside
         * the SHA256 implementation as well. */
        SHA256_Init(&ctx);
        SHA256_Final(alt_result, &ctx);
        explicit_bzero(temp_result, sizeof(temp_result));
        explicit_bzero(p_bytes, key_len);
        explicit_bzero(s_bytes,  salt_len);

        return (0);
}

#ifdef TEST

static const struct {
        const char *input;
        const char result[32];
} tests[] =
{
        /* Test vectors from FIPS 180-2: appendix B.1. */
        {
                "abc",
                "\xba\x78\x16\xbf\x8f\x01\xcf\xea\x41\x41\x40\xde\x5d\xae\x22\x23"
                "\xb0\x03\x61\xa3\x96\x17\x7a\x9c\xb4\x10\xff\x61\xf2\x00\x15\xad"
        },
        /* Test vectors from FIPS 180-2: appendix B.2. */
        {
                "abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq",
                "\x24\x8d\x6a\x61\xd2\x06\x38\xb8\xe5\xc0\x26\x93\x0c\x3e\x60\x39"
                "\xa3\x3c\xe4\x59\x64\xff\x21\x67\xf6\xec\xed\xd4\x19\xdb\x06\xc1"
        },
        /* Test vectors from the NESSIE project. */
        {
                "",
                "\xe3\xb0\xc4\x42\x98\xfc\x1c\x14\x9a\xfb\xf4\xc8\x99\x6f\xb9\x24"
                "\x27\xae\x41\xe4\x64\x9b\x93\x4c\xa4\x95\x99\x1b\x78\x52\xb8\x55"
        },
        {
                "a",
                "\xca\x97\x81\x12\xca\x1b\xbd\xca\xfa\xc2\x31\xb3\x9a\x23\xdc\x4d"
                "\xa7\x86\xef\xf8\x14\x7c\x4e\x72\xb9\x80\x77\x85\xaf\xee\x48\xbb"
        },
        {
                "message digest",
                "\xf7\x84\x6f\x55\xcf\x23\xe1\x4e\xeb\xea\xb5\xb4\xe1\x55\x0c\xad"
                "\x5b\x50\x9e\x33\x48\xfb\xc4\xef\xa3\xa1\x41\x3d\x39\x3c\xb6\x50"
        },
        {
                "abcdefghijklmnopqrstuvwxyz",
                "\x71\xc4\x80\xdf\x93\xd6\xae\x2f\x1e\xfa\xd1\x44\x7c\x66\xc9\x52"
                "\x5e\x31\x62\x18\xcf\x51\xfc\x8d\x9e\xd8\x32\xf2\xda\xf1\x8b\x73"
        },
        {
                "abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq",
                "\x24\x8d\x6a\x61\xd2\x06\x38\xb8\xe5\xc0\x26\x93\x0c\x3e\x60\x39"
                "\xa3\x3c\xe4\x59\x64\xff\x21\x67\xf6\xec\xed\xd4\x19\xdb\x06\xc1"
        },
        {
                "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789",
                "\xdb\x4b\xfc\xbd\x4d\xa0\xcd\x85\xa6\x0c\x3c\x37\xd3\xfb\xd8\x80"
                "\x5c\x77\xf1\x5f\xc6\xb1\xfd\xfe\x61\x4e\xe0\xa7\xc8\xfd\xb4\xc0"
        },
        {
                "123456789012345678901234567890123456789012345678901234567890"
                "12345678901234567890",
                "\xf3\x71\xbc\x4a\x31\x1f\x2b\x00\x9e\xef\x95\x2d\xd8\x3c\xa8\x0e"
                "\x2b\x60\x02\x6c\x8e\x93\x55\x92\xd0\xf9\xc3\x08\x45\x3c\x81\x3e"
        }
};

#define ntests (sizeof (tests) / sizeof (tests[0]))

static const struct {
        const char *salt;
        const char *input;
        const char *expected;
} tests2[] =
{
        {
                "$5$saltstring", "Hello world!",
                "$5$saltstring$5B8vYYiY.CVt1RlTTf8KbXBH3hsxY/GNooZaBBGWEc5"
        },
        {
                "$5$rounds=10000$saltstringsaltstring", "Hello world!",
                "$5$rounds=10000$saltstringsaltst$3xv.VbSHBb41AL9AvLeujZkZRBAwqFMz2."
                "opqey6IcA"
        },
        {
                "$5$rounds=5000$toolongsaltstring", "This is just a test",
                "$5$rounds=5000$toolongsaltstrin$Un/5jzAHMgOGZ5.mWJpuVolil07guHPvOW8"
                "mGRcvxa5"
        },
        {
                "$5$rounds=1400$anotherlongsaltstring",
                "a very much longer text to encrypt.  This one even stretches over more"
                "than one line.",
                "$5$rounds=1400$anotherlongsalts$Rx.j8H.h8HjEDGomFU8bDkXm3XIUnzyxf12"
                "oP84Bnq1"
        },
        {
                "$5$rounds=77777$short",
                "we have a short salt string but not a short password",
                "$5$rounds=77777$short$JiO1O3ZpDAxGJeaDIuqCoEFysAe1mZNJRs3pw0KQRd/"
        },
        {
                "$5$rounds=123456$asaltof16chars..", "a short string",
                "$5$rounds=123456$asaltof16chars..$gP3VQ/6X7UUEW3HkBn2w1/Ptq2jxPyzV/"
                "cZKmF/wJvD"
        },
        {
                "$5$rounds=10$roundstoolow", "the minimum number is still observed",
                "$5$rounds=1000$roundstoolow$yfvwcWrQ8l/K0DAWyuPMDNHpIVlTQebY9l/gL97"
                "2bIC"
        },
};

#define ntests2 (sizeof (tests2) / sizeof (tests2[0]))

int
main(void)
{
        SHA256_CTX ctx;
        uint8_t sum[32];
        int result = 0;
        int i, cnt;

        for (cnt = 0; cnt < (int)ntests; ++cnt) {
                SHA256_Init(&ctx);
                SHA256_Update(&ctx, tests[cnt].input, strlen(tests[cnt].input));
                SHA256_Final(sum, &ctx);
                if (memcmp(tests[cnt].result, sum, 32) != 0) {
                        for (i = 0; i < 32; i++)
                                printf("%02X", tests[cnt].result[i]);
                        printf("\n");
                        for (i = 0; i < 32; i++)
                                printf("%02X", sum[i]);
                        printf("\n");
                        printf("test %d run %d failed\n", cnt, 1);
                        result = 1;
                }

                SHA256_Init(&ctx);
                for (i = 0; tests[cnt].input[i] != '\0'; ++i)
                        SHA256_Update(&ctx, &tests[cnt].input[i], 1);
                SHA256_Final(sum, &ctx);
                if (memcmp(tests[cnt].result, sum, 32) != 0) {
                        for (i = 0; i < 32; i++)
                                printf("%02X", tests[cnt].result[i]);
                        printf("\n");
                        for (i = 0; i < 32; i++)
                                printf("%02X", sum[i]);
                        printf("\n");
                        printf("test %d run %d failed\n", cnt, 2);
                        result = 1;
                }
        }

        /* Test vector from FIPS 180-2: appendix B.3. */
        char buf[1000];

        memset(buf, 'a', sizeof(buf));
        SHA256_Init(&ctx);
        for (i = 0; i < 1000; ++i)
                SHA256_Update(&ctx, buf, sizeof(buf));
        SHA256_Final(sum, &ctx);
        static const char expected[32] =
        "\xcd\xc7\x6e\x5c\x99\x14\xfb\x92\x81\xa1\xc7\xe2\x84\xd7\x3e\x67"
        "\xf1\x80\x9a\x48\xa4\x97\x20\x0e\x04\x6d\x39\xcc\xc7\x11\x2c\xd0";

        if (memcmp(expected, sum, 32) != 0) {
                printf("test %d failed\n", cnt);
                result = 1;
        }

        for (cnt = 0; cnt < ntests2; ++cnt) {
                char *cp = crypt_sha256(tests2[cnt].input, tests2[cnt].salt);

                if (strcmp(cp, tests2[cnt].expected) != 0) {
                        printf("test %d: expected \"%s\", got \"%s\"\n",
                               cnt, tests2[cnt].expected, cp);
                        result = 1;
                }
        }

        if (result == 0)
                puts("all tests OK");

        return result;
}

#endif /* TEST */