/*

 * Copyright 1995-2024 The OpenSSL Project Authors. All Rights Reserved.

 *

 * Licensed under the Apache License 2.0 (the "License").  You may not use

 * this file except in compliance with the License.  You can obtain a copy

 * in the file LICENSE in the source distribution or at

 * https://www.openssl.org/source/license.html

 */

#include <stdio.h>

#include <time.h>

#include "internal/cryptlib.h"

#include "crypto/rand.h"

#include "bn_local.h"

#include <openssl/rand.h>

#include <openssl/sha.h>

#include <openssl/evp.h>

typedef enum bnrand_flag_e {

    NORMAL,

    TESTING,

    PRIVATE

} BNRAND_FLAG;

static int bnrand(BNRAND_FLAG flag, BIGNUM *rnd, int bits, int top, int bottom,

    unsigned int strength, BN_CTX *ctx)

{

    unsigned char *buf = NULL;

    int b, ret = 0, bit, bytes, mask;

    OSSL_LIB_CTX *libctx = ossl_bn_get_libctx(ctx);

    if (bits == 0) {

        if (top != BN_RAND_TOP_ANY || bottom != BN_RAND_BOTTOM_ANY)

            goto toosmall;

        BN_zero(rnd);

        return 1;

    }

    if (bits < 0 || (bits == 1 && top > 0))

        goto toosmall;

    bytes = (bits + 7) / 8;

    bit = (bits - 1) % 8;

    mask = 0xff << (bit + 1);

    buf = OPENSSL_malloc(bytes);

    if (buf == NULL)

        goto err;

    /* make a random number and set the top and bottom bits */

    b = flag == NORMAL ? RAND_bytes_ex(libctx, buf, bytes, strength)

                       : RAND_priv_bytes_ex(libctx, buf, bytes, strength);

    if (b <= 0)

        goto err;

    if (flag == TESTING) {

        /*

         * generate patterns that are more likely to trigger BN library bugs

         */

        int i;

        unsigned char c;

        for (i = 0; i < bytes; i++) {

            if (RAND_bytes_ex(libctx, &c, 1, strength) <= 0)

                goto err;

            if (c >= 128 && i > 0)

                buf[i] = buf[i - 1];

            else if (c < 42)

                buf[i] = 0;

            else if (c < 84)

                buf[i] = 255;

        }

    }

    if (top >= 0) {

        if (top) {

            if (bit == 0) {

                buf[0] = 1;

                buf[1] |= 0x80;

            } else {

                buf[0] |= (3 << (bit - 1));

            }

        } else {

            buf[0] |= (1 << bit);

        }

    }

    buf[0] &= ~mask;

    if (bottom) /* set bottom bit if requested */

        buf[bytes - 1] |= 1;

    if (!BN_bin2bn(buf, bytes, rnd))

        goto err;

    ret = 1;

err:

    OPENSSL_clear_free(buf, bytes);

    bn_check_top(rnd);

    return ret;

toosmall:

    ERR_raise(ERR_LIB_BN, BN_R_BITS_TOO_SMALL);

    return 0;

}

int BN_rand_ex(BIGNUM *rnd, int bits, int top, int bottom,

    unsigned int strength, BN_CTX *ctx)

{

    return bnrand(NORMAL, rnd, bits, top, bottom, strength, ctx);

}

#ifndef FIPS_MODULE

int BN_rand(BIGNUM *rnd, int bits, int top, int bottom)

{

    return bnrand(NORMAL, rnd, bits, top, bottom, 0, NULL);

}

int BN_bntest_rand(BIGNUM *rnd, int bits, int top, int bottom)

{

    return bnrand(TESTING, rnd, bits, top, bottom, 0, NULL);

}

#endif

int BN_priv_rand_ex(BIGNUM *rnd, int bits, int top, int bottom,

    unsigned int strength, BN_CTX *ctx)

{

    return bnrand(PRIVATE, rnd, bits, top, bottom, strength, ctx);

}

#ifndef FIPS_MODULE

int BN_priv_rand(BIGNUM *rnd, int bits, int top, int bottom)

{

    return bnrand(PRIVATE, rnd, bits, top, bottom, 0, NULL);

}

#endif

/* random number r:  0 <= r < range */

static int bnrand_range(BNRAND_FLAG flag, BIGNUM *r, const BIGNUM *range,

    unsigned int strength, BN_CTX *ctx)

{

    int n;

    int count = 100;

    if (r == NULL) {

        ERR_raise(ERR_LIB_BN, ERR_R_PASSED_NULL_PARAMETER);

        return 0;

    }

    if (range->neg || BN_is_zero(range)) {

        ERR_raise(ERR_LIB_BN, BN_R_INVALID_RANGE);

        return 0;

    }

    n = BN_num_bits(range); /* n > 0 */

    /* BN_is_bit_set(range, n - 1) always holds */

    if (n == 1)

        BN_zero(r);

    else if (!BN_is_bit_set(range, n - 2) && !BN_is_bit_set(range, n - 3)) {

        /*

         * range = 100..._2, so 3*range (= 11..._2) is exactly one bit longer

         * than range

         */

        do {

            if (!bnrand(flag, r, n + 1, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY,

                    strength, ctx))

                return 0;

            /*

             * If r < 3*range, use r := r MOD range (which is either r, r -

             * range, or r - 2*range). Otherwise, iterate once more. Since

             * 3*range = 11..._2, each iteration succeeds with probability >=

             * .75.

             */

            if (BN_cmp(r, range) >= 0) {

                if (!BN_sub(r, r, range))

                    return 0;

                if (BN_cmp(r, range) >= 0)

                    if (!BN_sub(r, r, range))

                        return 0;

            }

            if (!--count) {

                ERR_raise(ERR_LIB_BN, BN_R_TOO_MANY_ITERATIONS);

                return 0;

            }

        } while (BN_cmp(r, range) >= 0);

    } else {

        do {

            /* range = 11..._2  or  range = 101..._2 */

            if (!bnrand(flag, r, n, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY,

                    strength, ctx))

                return 0;

            if (!--count) {

                ERR_raise(ERR_LIB_BN, BN_R_TOO_MANY_ITERATIONS);

                return 0;

            }

        } while (BN_cmp(r, range) >= 0);

    }

    bn_check_top(r);

    return 1;

}

int BN_rand_range_ex(BIGNUM *r, const BIGNUM *range, unsigned int strength,

    BN_CTX *ctx)

{

    return bnrand_range(NORMAL, r, range, strength, ctx);

}

#ifndef FIPS_MODULE

int BN_rand_range(BIGNUM *r, const BIGNUM *range)

{

    return bnrand_range(NORMAL, r, range, 0, NULL);

}

#endif

int BN_priv_rand_range_ex(BIGNUM *r, const BIGNUM *range, unsigned int strength,

    BN_CTX *ctx)

{

    return bnrand_range(PRIVATE, r, range, strength, ctx);

}

#ifndef FIPS_MODULE

int BN_priv_rand_range(BIGNUM *r, const BIGNUM *range)

{

    return bnrand_range(PRIVATE, r, range, 0, NULL);

}

#ifndef OPENSSL_NO_DEPRECATED_3_0

int BN_pseudo_rand(BIGNUM *rnd, int bits, int top, int bottom)

{

    return BN_rand(rnd, bits, top, bottom);

}

int BN_pseudo_rand_range(BIGNUM *r, const BIGNUM *range)

{

    return BN_rand_range(r, range);

}

#endif

#endif

int ossl_bn_priv_rand_range_fixed_top(BIGNUM *r, const BIGNUM *range,

    unsigned int strength, BN_CTX *ctx)

{

    int n;

    int count = 100;

    if (r == NULL) {

        ERR_raise(ERR_LIB_BN, ERR_R_PASSED_NULL_PARAMETER);

        return 0;

    }

    if (range->neg || BN_is_zero(range)) {

        ERR_raise(ERR_LIB_BN, BN_R_INVALID_RANGE);

        return 0;

    }

    n = BN_num_bits(range); /* n > 0 */

    /* BN_is_bit_set(range, n - 1) always holds */

    if (n == 1) {

        BN_zero(r);

    } else {

        BN_set_flags(r, BN_FLG_CONSTTIME);

        do {

            if (!bnrand(PRIVATE, r, n + 1, BN_RAND_TOP_ONE, BN_RAND_BOTTOM_ANY,

                    strength, ctx))

                return 0;

            if (!--count) {

                ERR_raise(ERR_LIB_BN, BN_R_TOO_MANY_ITERATIONS);

                return 0;

            }

            ossl_bn_mask_bits_fixed_top(r, n);

        } while (BN_ucmp(r, range) >= 0);

#ifdef BN_DEBUG

        /* With BN_DEBUG on a fixed top number cannot be returned */

        bn_correct_top(r);

#endif

    }

    return 1;

}

/*

 * ossl_bn_gen_dsa_nonce_fixed_top generates a random number 0 <= out < range.

 * Unlike BN_rand_range, it also includes the contents of |priv| and |message|

 * in the generation so that an RNG failure isn't fatal as long as |priv|

 * remains secret. This is intended for use in DSA and ECDSA where an RNG

 * weakness leads directly to private key exposure unless this function is

 * used.

 */

int ossl_bn_gen_dsa_nonce_fixed_top(BIGNUM *out, const BIGNUM *range,

    const BIGNUM *priv,

    const unsigned char *message,

    size_t message_len, BN_CTX *ctx)

{

    EVP_MD_CTX *mdctx = EVP_MD_CTX_new();

    /*

     * We use 512 bits of random data per iteration to ensure that we have at

     * least |range| bits of randomness.

     */

    unsigned char random_bytes[64];

    unsigned char digest[SHA512_DIGEST_LENGTH];

    unsigned done, todo;

    /* We generate |range|+1 bytes of random output. */

    const unsigned num_k_bytes = BN_num_bytes(range) + 1;

    unsigned char private_bytes[96];

    unsigned char *k_bytes = NULL;

    const int max_n = 64; /* Pr(failure to generate) < 2^max_n */

    int n;

    int ret = 0;

    EVP_MD *md = NULL;

    OSSL_LIB_CTX *libctx = ossl_bn_get_libctx(ctx);

    if (mdctx == NULL)

        goto end;

    k_bytes = OPENSSL_malloc(num_k_bytes);

    if (k_bytes == NULL)

        goto end;

    /* Ensure top byte is set to avoid non-constant time in bin2bn */

    k_bytes[0] = 0xff;

    /* We copy |priv| into a local buffer to avoid exposing its length. */

    if (BN_bn2binpad(priv, private_bytes, sizeof(private_bytes)) < 0) {

        /*

         * No reasonable DSA or ECDSA key should have a private key this

         * large and we don't handle this case in order to avoid leaking the

         * length of the private key.

         */

        ERR_raise(ERR_LIB_BN, BN_R_PRIVATE_KEY_TOO_LARGE);

        goto end;

    }

    md = EVP_MD_fetch(libctx, "SHA512", NULL);

    if (md == NULL) {

        ERR_raise(ERR_LIB_BN, BN_R_NO_SUITABLE_DIGEST);

        goto end;

    }

    for (n = 0; n < max_n; n++) {

        unsigned char i = 0;

        for (done = 1; done < num_k_bytes;) {

            if (RAND_priv_bytes_ex(libctx, random_bytes, sizeof(random_bytes),

                    0)

                <= 0)

                goto end;

            if (!EVP_DigestInit_ex(mdctx, md, NULL)

                || !EVP_DigestUpdate(mdctx, &i, sizeof(i))

                || !EVP_DigestUpdate(mdctx, private_bytes,

                    sizeof(private_bytes))

                || !EVP_DigestUpdate(mdctx, message, message_len)

                || !EVP_DigestUpdate(mdctx, random_bytes,

                    sizeof(random_bytes))

                || !EVP_DigestFinal_ex(mdctx, digest, NULL))

                goto end;

            todo = num_k_bytes - done;

            if (todo > SHA512_DIGEST_LENGTH)

                todo = SHA512_DIGEST_LENGTH;

            memcpy(k_bytes + done, digest, todo);

            done += todo;

            ++i;

        }

        if (!BN_bin2bn(k_bytes, num_k_bytes, out))

            goto end;

        /* Clear out the top bits and rejection filter into range */

        BN_set_flags(out, BN_FLG_CONSTTIME);

        ossl_bn_mask_bits_fixed_top(out, BN_num_bits(range));

        if (BN_ucmp(out, range) < 0) {

            ret = 1;

#ifdef BN_DEBUG

            /* With BN_DEBUG on a fixed top number cannot be returned */

            bn_correct_top(out);

#endif

            goto end;

        }

    }

    /* Failed to generate anything */

    ERR_raise(ERR_LIB_BN, ERR_R_INTERNAL_ERROR);

end:

    EVP_MD_CTX_free(mdctx);

    EVP_MD_free(md);

    OPENSSL_clear_free(k_bytes, num_k_bytes);

    OPENSSL_cleanse(digest, sizeof(digest));

    OPENSSL_cleanse(random_bytes, sizeof(random_bytes));

    OPENSSL_cleanse(private_bytes, sizeof(private_bytes));

    return ret;

}

int BN_generate_dsa_nonce(BIGNUM *out, const BIGNUM *range,

    const BIGNUM *priv, const unsigned char *message,

    size_t message_len, BN_CTX *ctx)

{

    int ret;

    ret = ossl_bn_gen_dsa_nonce_fixed_top(out, range, priv, message,

        message_len, ctx);

    /*

     * This call makes the BN_generate_dsa_nonce non-const-time, thus we

     * do not use it internally. But fixed_top BNs currently cannot be returned

     * from public API calls.

     */

    bn_correct_top(out);

    return ret;

}