proxmark3/common/mbedtls/ctr_drbg.c

/*
 *  CTR_DRBG implementation based on AES-256 (NIST SP 800-90)
 *
 *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
 *  SPDX-License-Identifier: GPL-2.0
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License along
 *  with this program; if not, write to the Free Software Foundation, Inc.,
 *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 *  This file is part of mbed TLS (https://tls.mbed.org)
 */
/*
 *  The NIST SP 800-90 DRBGs are described in the following publication.
 *
 *  http://csrc.nist.gov/publications/nistpubs/800-90/SP800-90revised_March2007.pdf
 */

#if !defined(MBEDTLS_CONFIG_FILE)
#include "mbedtls/config.h"
#else
#include MBEDTLS_CONFIG_FILE
#endif

#if defined(MBEDTLS_CTR_DRBG_C)

#include "mbedtls/ctr_drbg.h"
#include "mbedtls/platform_util.h"

#include <string.h>

#if defined(MBEDTLS_FS_IO)
#include <stdio.h>
#endif

#if defined(MBEDTLS_SELF_TEST)
#if defined(MBEDTLS_PLATFORM_C)
#include "mbedtls/platform.h"
#else
#include <stdio.h>
#define mbedtls_printf printf
#endif /* MBEDTLS_PLATFORM_C */
#endif /* MBEDTLS_SELF_TEST */

/*
 * CTR_DRBG context initialization
 */
void mbedtls_ctr_drbg_init(mbedtls_ctr_drbg_context *ctx) {
    memset(ctx, 0, sizeof(mbedtls_ctr_drbg_context));

#if defined(MBEDTLS_THREADING_C)
    mbedtls_mutex_init(&ctx->mutex);
#endif
}

/*
 * Non-public function wrapped by mbedtls_ctr_drbg_seed(). Necessary to allow
 * NIST tests to succeed (which require known length fixed entropy)
 */
int mbedtls_ctr_drbg_seed_entropy_len(
    mbedtls_ctr_drbg_context *ctx,
    int (*f_entropy)(void *, unsigned char *, size_t),
    void *p_entropy,
    const unsigned char *custom,
    size_t len,
    size_t entropy_len) {
    int ret;
    unsigned char key[MBEDTLS_CTR_DRBG_KEYSIZE];

    memset(key, 0, MBEDTLS_CTR_DRBG_KEYSIZE);

    mbedtls_aes_init(&ctx->aes_ctx);

    ctx->f_entropy = f_entropy;
    ctx->p_entropy = p_entropy;

    ctx->entropy_len = entropy_len;
    ctx->reseed_interval = MBEDTLS_CTR_DRBG_RESEED_INTERVAL;

    /*
     * Initialize with an empty key
     */
    if ((ret = mbedtls_aes_setkey_enc(&ctx->aes_ctx, key, MBEDTLS_CTR_DRBG_KEYBITS)) != 0) {
        return (ret);
    }

    if ((ret = mbedtls_ctr_drbg_reseed(ctx, custom, len)) != 0) {
        return (ret);
    }
    return (0);
}

int mbedtls_ctr_drbg_seed(mbedtls_ctr_drbg_context *ctx,
                          int (*f_entropy)(void *, unsigned char *, size_t),
                          void *p_entropy,
                          const unsigned char *custom,
                          size_t len) {
    return (mbedtls_ctr_drbg_seed_entropy_len(ctx, f_entropy, p_entropy, custom, len,
                                              MBEDTLS_CTR_DRBG_ENTROPY_LEN));
}

void mbedtls_ctr_drbg_free(mbedtls_ctr_drbg_context *ctx) {
    if (ctx == NULL)
        return;

#if defined(MBEDTLS_THREADING_C)
    mbedtls_mutex_free(&ctx->mutex);
#endif
    mbedtls_aes_free(&ctx->aes_ctx);
    mbedtls_platform_zeroize(ctx, sizeof(mbedtls_ctr_drbg_context));
}

void mbedtls_ctr_drbg_set_prediction_resistance(mbedtls_ctr_drbg_context *ctx, int resistance) {
    ctx->prediction_resistance = resistance;
}

void mbedtls_ctr_drbg_set_entropy_len(mbedtls_ctr_drbg_context *ctx, size_t len) {
    ctx->entropy_len = len;
}

void mbedtls_ctr_drbg_set_reseed_interval(mbedtls_ctr_drbg_context *ctx, int interval) {
    ctx->reseed_interval = interval;
}

static int block_cipher_df(unsigned char *output,
                           const unsigned char *data, size_t data_len) {
    unsigned char buf[MBEDTLS_CTR_DRBG_MAX_SEED_INPUT + MBEDTLS_CTR_DRBG_BLOCKSIZE + 16];
    unsigned char tmp[MBEDTLS_CTR_DRBG_SEEDLEN];
    unsigned char key[MBEDTLS_CTR_DRBG_KEYSIZE];
    unsigned char chain[MBEDTLS_CTR_DRBG_BLOCKSIZE];
    unsigned char *p, *iv;
    mbedtls_aes_context aes_ctx;
    int ret = 0;

    int i, j;
    size_t buf_len, use_len;

    if (data_len > MBEDTLS_CTR_DRBG_MAX_SEED_INPUT)
        return (MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG);

    memset(buf, 0, MBEDTLS_CTR_DRBG_MAX_SEED_INPUT + MBEDTLS_CTR_DRBG_BLOCKSIZE + 16);
    mbedtls_aes_init(&aes_ctx);

    /*
     * Construct IV (16 bytes) and S in buffer
     * IV = Counter (in 32-bits) padded to 16 with zeroes
     * S = Length input string (in 32-bits) || Length of output (in 32-bits) ||
     *     data || 0x80
     *     (Total is padded to a multiple of 16-bytes with zeroes)
     */
    p = buf + MBEDTLS_CTR_DRBG_BLOCKSIZE;
    *p++ = (data_len >> 24) & 0xff;
    *p++ = (data_len >> 16) & 0xff;
    *p++ = (data_len >> 8) & 0xff;
    *p++ = (data_len) & 0xff;
    p += 3;
    *p++ = MBEDTLS_CTR_DRBG_SEEDLEN;
    memcpy(p, data, data_len);
    p[data_len] = 0x80;

    buf_len = MBEDTLS_CTR_DRBG_BLOCKSIZE + 8 + data_len + 1;

    for (i = 0; i < MBEDTLS_CTR_DRBG_KEYSIZE; i++)
        key[i] = i;

    if ((ret = mbedtls_aes_setkey_enc(&aes_ctx, key, MBEDTLS_CTR_DRBG_KEYBITS)) != 0) {
        goto exit;
    }

    /*
     * Reduce data to MBEDTLS_CTR_DRBG_SEEDLEN bytes of data
     */
    for (j = 0; j < MBEDTLS_CTR_DRBG_SEEDLEN; j += MBEDTLS_CTR_DRBG_BLOCKSIZE) {
        p = buf;
        memset(chain, 0, MBEDTLS_CTR_DRBG_BLOCKSIZE);
        use_len = buf_len;

        while (use_len > 0) {
            for (i = 0; i < MBEDTLS_CTR_DRBG_BLOCKSIZE; i++)
                chain[i] ^= p[i];
            p += MBEDTLS_CTR_DRBG_BLOCKSIZE;
            use_len -= (use_len >= MBEDTLS_CTR_DRBG_BLOCKSIZE) ?
                       MBEDTLS_CTR_DRBG_BLOCKSIZE : use_len;

            if ((ret = mbedtls_aes_crypt_ecb(&aes_ctx, MBEDTLS_AES_ENCRYPT, chain, chain)) != 0) {
                goto exit;
            }
        }

        memcpy(tmp + j, chain, MBEDTLS_CTR_DRBG_BLOCKSIZE);

        /*
         * Update IV
         */
        buf[3]++;
    }

    /*
     * Do final encryption with reduced data
     */
    if ((ret = mbedtls_aes_setkey_enc(&aes_ctx, tmp, MBEDTLS_CTR_DRBG_KEYBITS)) != 0) {
        goto exit;
    }
    iv = tmp + MBEDTLS_CTR_DRBG_KEYSIZE;
    p = output;

    for (j = 0; j < MBEDTLS_CTR_DRBG_SEEDLEN; j += MBEDTLS_CTR_DRBG_BLOCKSIZE) {
        if ((ret = mbedtls_aes_crypt_ecb(&aes_ctx, MBEDTLS_AES_ENCRYPT, iv, iv)) != 0) {
            goto exit;
        }
        memcpy(p, iv, MBEDTLS_CTR_DRBG_BLOCKSIZE);
        p += MBEDTLS_CTR_DRBG_BLOCKSIZE;
    }
exit:
    mbedtls_aes_free(&aes_ctx);
    /*
    * tidy up the stack
    */
    mbedtls_platform_zeroize(buf, sizeof(buf));
    mbedtls_platform_zeroize(tmp, sizeof(tmp));
    mbedtls_platform_zeroize(key, sizeof(key));
    mbedtls_platform_zeroize(chain, sizeof(chain));
    if (0 != ret) {
        /*
        * wipe partial seed from memory
        */
        mbedtls_platform_zeroize(output, MBEDTLS_CTR_DRBG_SEEDLEN);
    }

    return (ret);
}

static int ctr_drbg_update_internal(mbedtls_ctr_drbg_context *ctx,
                                    const unsigned char data[MBEDTLS_CTR_DRBG_SEEDLEN]) {
    unsigned char tmp[MBEDTLS_CTR_DRBG_SEEDLEN];
    unsigned char *p = tmp;
    int i, j;
    int ret = 0;

    memset(tmp, 0, MBEDTLS_CTR_DRBG_SEEDLEN);

    for (j = 0; j < MBEDTLS_CTR_DRBG_SEEDLEN; j += MBEDTLS_CTR_DRBG_BLOCKSIZE) {
        /*
         * Increase counter
         */
        for (i = MBEDTLS_CTR_DRBG_BLOCKSIZE; i > 0; i--)
            if (++ctx->counter[i - 1] != 0)
                break;

        /*
         * Crypt counter block
         */
        if ((ret = mbedtls_aes_crypt_ecb(&ctx->aes_ctx, MBEDTLS_AES_ENCRYPT, ctx->counter, p)) != 0) {
            return (ret);
        }

        p += MBEDTLS_CTR_DRBG_BLOCKSIZE;
    }

    for (i = 0; i < MBEDTLS_CTR_DRBG_SEEDLEN; i++)
        tmp[i] ^= data[i];

    /*
     * Update key and counter
     */
    if ((ret = mbedtls_aes_setkey_enc(&ctx->aes_ctx, tmp, MBEDTLS_CTR_DRBG_KEYBITS)) != 0) {
        return (ret);
    }
    memcpy(ctx->counter, tmp + MBEDTLS_CTR_DRBG_KEYSIZE, MBEDTLS_CTR_DRBG_BLOCKSIZE);

    return (0);
}

void mbedtls_ctr_drbg_update(mbedtls_ctr_drbg_context *ctx,
                             const unsigned char *additional, size_t add_len) {
    unsigned char add_input[MBEDTLS_CTR_DRBG_SEEDLEN];

    if (add_len > 0) {
        /* MAX_INPUT would be more logical here, but we have to match
         * block_cipher_df()'s limits since we can't propagate errors */
        if (add_len > MBEDTLS_CTR_DRBG_MAX_SEED_INPUT)
            add_len = MBEDTLS_CTR_DRBG_MAX_SEED_INPUT;

        block_cipher_df(add_input, additional, add_len);
        ctr_drbg_update_internal(ctx, add_input);
    }
}

int mbedtls_ctr_drbg_reseed(mbedtls_ctr_drbg_context *ctx,
                            const unsigned char *additional, size_t len) {
    unsigned char seed[MBEDTLS_CTR_DRBG_MAX_SEED_INPUT];
    size_t seedlen = 0;
    int ret;

    if (ctx->entropy_len > MBEDTLS_CTR_DRBG_MAX_SEED_INPUT ||
            len > MBEDTLS_CTR_DRBG_MAX_SEED_INPUT - ctx->entropy_len)
        return (MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG);

    memset(seed, 0, MBEDTLS_CTR_DRBG_MAX_SEED_INPUT);

    /*
     * Gather entropy_len bytes of entropy to seed state
     */
    if (0 != ctx->f_entropy(ctx->p_entropy, seed,
                            ctx->entropy_len)) {
        return (MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED);
    }

    seedlen += ctx->entropy_len;

    /*
     * Add additional data
     */
    if (additional && len) {
        memcpy(seed + seedlen, additional, len);
        seedlen += len;
    }

    /*
     * Reduce to 384 bits
     */
    if ((ret = block_cipher_df(seed, seed, seedlen)) != 0) {
        return (ret);
    }

    /*
     * Update state
     */
    if ((ret = ctr_drbg_update_internal(ctx, seed)) != 0) {
        return (ret);
    }
    ctx->reseed_counter = 1;

    return (0);
}

int mbedtls_ctr_drbg_random_with_add(void *p_rng,
                                     unsigned char *output, size_t output_len,
                                     const unsigned char *additional, size_t add_len) {
    int ret = 0;
    mbedtls_ctr_drbg_context *ctx = (mbedtls_ctr_drbg_context *) p_rng;
    unsigned char add_input[MBEDTLS_CTR_DRBG_SEEDLEN];
    unsigned char *p = output;
    unsigned char tmp[MBEDTLS_CTR_DRBG_BLOCKSIZE];
    int i;
    size_t use_len;

    if (output_len > MBEDTLS_CTR_DRBG_MAX_REQUEST)
        return (MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG);

    if (add_len > MBEDTLS_CTR_DRBG_MAX_INPUT)
        return (MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG);

    memset(add_input, 0, MBEDTLS_CTR_DRBG_SEEDLEN);

    if (ctx->reseed_counter > ctx->reseed_interval ||
            ctx->prediction_resistance) {
        if ((ret = mbedtls_ctr_drbg_reseed(ctx, additional, add_len)) != 0) {
            return (ret);
        }
        add_len = 0;
    }

    if (add_len > 0) {
        if ((ret = block_cipher_df(add_input, additional, add_len)) != 0) {
            return (ret);
        }
        if ((ret = ctr_drbg_update_internal(ctx, add_input)) != 0) {
            return (ret);
        }
    }

    while (output_len > 0) {
        /*
         * Increase counter
         */
        for (i = MBEDTLS_CTR_DRBG_BLOCKSIZE; i > 0; i--)
            if (++ctx->counter[i - 1] != 0)
                break;

        /*
         * Crypt counter block
         */
        if ((ret = mbedtls_aes_crypt_ecb(&ctx->aes_ctx, MBEDTLS_AES_ENCRYPT, ctx->counter, tmp)) != 0) {
            return (ret);
        }

        use_len = (output_len > MBEDTLS_CTR_DRBG_BLOCKSIZE) ? MBEDTLS_CTR_DRBG_BLOCKSIZE :
                  output_len;
        /*
         * Copy random block to destination
         */
        memcpy(p, tmp, use_len);
        p += use_len;
        output_len -= use_len;
    }

    if ((ret = ctr_drbg_update_internal(ctx, add_input)) != 0) {
        return (ret);
    }

    ctx->reseed_counter++;

    return (0);
}

int mbedtls_ctr_drbg_random(void *p_rng, unsigned char *output, size_t output_len) {
    int ret;
    mbedtls_ctr_drbg_context *ctx = (mbedtls_ctr_drbg_context *) p_rng;

#if defined(MBEDTLS_THREADING_C)
    if ((ret = mbedtls_mutex_lock(&ctx->mutex)) != 0)
        return (ret);
#endif

    ret = mbedtls_ctr_drbg_random_with_add(ctx, output, output_len, NULL, 0);

#if defined(MBEDTLS_THREADING_C)
    if (mbedtls_mutex_unlock(&ctx->mutex) != 0)
        return (MBEDTLS_ERR_THREADING_MUTEX_ERROR);
#endif

    return (ret);
}

#if defined(MBEDTLS_FS_IO)
int mbedtls_ctr_drbg_write_seed_file(mbedtls_ctr_drbg_context *ctx, const char *path) {
    int ret = MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR;
    FILE *f;
    unsigned char buf[ MBEDTLS_CTR_DRBG_MAX_INPUT ];

    if ((f = fopen(path, "wb")) == NULL)
        return (MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR);

    if ((ret = mbedtls_ctr_drbg_random(ctx, buf, MBEDTLS_CTR_DRBG_MAX_INPUT)) != 0)
        goto exit;

    if (fwrite(buf, 1, MBEDTLS_CTR_DRBG_MAX_INPUT, f) != MBEDTLS_CTR_DRBG_MAX_INPUT)
        ret = MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR;
    else
        ret = 0;

exit:
    mbedtls_platform_zeroize(buf, sizeof(buf));

    fclose(f);
    return (ret);
}

int mbedtls_ctr_drbg_update_seed_file(mbedtls_ctr_drbg_context *ctx, const char *path) {
    int ret = 0;
    FILE *f;
    size_t n;
    unsigned char buf[ MBEDTLS_CTR_DRBG_MAX_INPUT ];

    if ((f = fopen(path, "rb")) == NULL)
        return (MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR);

    fseek(f, 0, SEEK_END);
    n = (size_t) ftell(f);
    fseek(f, 0, SEEK_SET);

    if (n > MBEDTLS_CTR_DRBG_MAX_INPUT) {
        fclose(f);
        return (MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG);
    }

    if (fread(buf, 1, n, f) != n)
        ret = MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR;
    else
        mbedtls_ctr_drbg_update(ctx, buf, n);

    fclose(f);

    mbedtls_platform_zeroize(buf, sizeof(buf));

    if (ret != 0)
        return (ret);

    return (mbedtls_ctr_drbg_write_seed_file(ctx, path));
}
#endif /* MBEDTLS_FS_IO */

#if defined(MBEDTLS_SELF_TEST)

static const unsigned char entropy_source_pr[96] = {
    0xc1, 0x80, 0x81, 0xa6, 0x5d, 0x44, 0x02, 0x16,
    0x19, 0xb3, 0xf1, 0x80, 0xb1, 0xc9, 0x20, 0x02,
    0x6a, 0x54, 0x6f, 0x0c, 0x70, 0x81, 0x49, 0x8b,
    0x6e, 0xa6, 0x62, 0x52, 0x6d, 0x51, 0xb1, 0xcb,
    0x58, 0x3b, 0xfa, 0xd5, 0x37, 0x5f, 0xfb, 0xc9,
    0xff, 0x46, 0xd2, 0x19, 0xc7, 0x22, 0x3e, 0x95,
    0x45, 0x9d, 0x82, 0xe1, 0xe7, 0x22, 0x9f, 0x63,
    0x31, 0x69, 0xd2, 0x6b, 0x57, 0x47, 0x4f, 0xa3,
    0x37, 0xc9, 0x98, 0x1c, 0x0b, 0xfb, 0x91, 0x31,
    0x4d, 0x55, 0xb9, 0xe9, 0x1c, 0x5a, 0x5e, 0xe4,
    0x93, 0x92, 0xcf, 0xc5, 0x23, 0x12, 0xd5, 0x56,
    0x2c, 0x4a, 0x6e, 0xff, 0xdc, 0x10, 0xd0, 0x68
};

static const unsigned char entropy_source_nopr[64] = {
    0x5a, 0x19, 0x4d, 0x5e, 0x2b, 0x31, 0x58, 0x14,
    0x54, 0xde, 0xf6, 0x75, 0xfb, 0x79, 0x58, 0xfe,
    0xc7, 0xdb, 0x87, 0x3e, 0x56, 0x89, 0xfc, 0x9d,
    0x03, 0x21, 0x7c, 0x68, 0xd8, 0x03, 0x38, 0x20,
    0xf9, 0xe6, 0x5e, 0x04, 0xd8, 0x56, 0xf3, 0xa9,
    0xc4, 0x4a, 0x4c, 0xbd, 0xc1, 0xd0, 0x08, 0x46,
    0xf5, 0x98, 0x3d, 0x77, 0x1c, 0x1b, 0x13, 0x7e,
    0x4e, 0x0f, 0x9d, 0x8e, 0xf4, 0x09, 0xf9, 0x2e
};

static const unsigned char nonce_pers_pr[16] = {
    0xd2, 0x54, 0xfc, 0xff, 0x02, 0x1e, 0x69, 0xd2,
    0x29, 0xc9, 0xcf, 0xad, 0x85, 0xfa, 0x48, 0x6c
};

static const unsigned char nonce_pers_nopr[16] = {
    0x1b, 0x54, 0xb8, 0xff, 0x06, 0x42, 0xbf, 0xf5,
    0x21, 0xf1, 0x5c, 0x1c, 0x0b, 0x66, 0x5f, 0x3f
};

static const unsigned char result_pr[16] = {
    0x34, 0x01, 0x16, 0x56, 0xb4, 0x29, 0x00, 0x8f,
    0x35, 0x63, 0xec, 0xb5, 0xf2, 0x59, 0x07, 0x23
};

static const unsigned char result_nopr[16] = {
    0xa0, 0x54, 0x30, 0x3d, 0x8a, 0x7e, 0xa9, 0x88,
    0x9d, 0x90, 0x3e, 0x07, 0x7c, 0x6f, 0x21, 0x8f
};

static size_t test_offset;
static int ctr_drbg_self_test_entropy(void *data, unsigned char *buf,
                                      size_t len) {
    const unsigned char *p = data;
    memcpy(buf, p + test_offset, len);
    test_offset += len;
    return (0);
}

#define CHK( c )    if( (c) != 0 )                          \
    {                                       \
        if( verbose != 0 )                  \
            mbedtls_printf( "failed\n" );  \
        return( 1 );                        \
    }

/*
 * Checkup routine
 */
int mbedtls_ctr_drbg_self_test(int verbose) {
    mbedtls_ctr_drbg_context ctx;
    unsigned char buf[16];

    mbedtls_ctr_drbg_init(&ctx);

    /*
     * Based on a NIST CTR_DRBG test vector (PR = True)
     */
    if (verbose != 0)
        mbedtls_printf("  CTR_DRBG (PR = TRUE) : ");

    test_offset = 0;
    CHK(mbedtls_ctr_drbg_seed_entropy_len(&ctx, ctr_drbg_self_test_entropy,
                                          (void *) entropy_source_pr, nonce_pers_pr, 16, 32));
    mbedtls_ctr_drbg_set_prediction_resistance(&ctx, MBEDTLS_CTR_DRBG_PR_ON);
    CHK(mbedtls_ctr_drbg_random(&ctx, buf, MBEDTLS_CTR_DRBG_BLOCKSIZE));
    CHK(mbedtls_ctr_drbg_random(&ctx, buf, MBEDTLS_CTR_DRBG_BLOCKSIZE));
    CHK(memcmp(buf, result_pr, MBEDTLS_CTR_DRBG_BLOCKSIZE));

    mbedtls_ctr_drbg_free(&ctx);

    if (verbose != 0)
        mbedtls_printf("passed\n");

    /*
     * Based on a NIST CTR_DRBG test vector (PR = FALSE)
     */
    if (verbose != 0)
        mbedtls_printf("  CTR_DRBG (PR = FALSE): ");

    mbedtls_ctr_drbg_init(&ctx);

    test_offset = 0;
    CHK(mbedtls_ctr_drbg_seed_entropy_len(&ctx, ctr_drbg_self_test_entropy,
                                          (void *) entropy_source_nopr, nonce_pers_nopr, 16, 32));
    CHK(mbedtls_ctr_drbg_random(&ctx, buf, 16));
    CHK(mbedtls_ctr_drbg_reseed(&ctx, NULL, 0));
    CHK(mbedtls_ctr_drbg_random(&ctx, buf, 16));
    CHK(memcmp(buf, result_nopr, 16));

    mbedtls_ctr_drbg_free(&ctx);

    if (verbose != 0)
        mbedtls_printf("passed\n");

    if (verbose != 0)
        mbedtls_printf("\n");

    return (0);
}
#endif /* MBEDTLS_SELF_TEST */

#endif /* MBEDTLS_CTR_DRBG_C */