/*

 * Copyright 1995-2021 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 <openssl/opensslconf.h>

#include "crypto/rand.h"

#include <openssl/engine.h>

#include "internal/thread_once.h"

#include "crypto/rand_pool.h"

/*

 * Allocate memory and initialize a new random pool

 */

RAND_POOL *ossl_rand_pool_new(int entropy_requested, int secure,

                              size_t min_len, size_t max_len)

{

    RAND_POOL *pool = OPENSSL_zalloc(sizeof(*pool));

    size_t min_alloc_size = RAND_POOL_MIN_ALLOCATION(secure);

    if (pool == NULL)

        return NULL;

    pool->min_len = min_len;

    pool->max_len = (max_len > RAND_POOL_MAX_LENGTH) ?

        RAND_POOL_MAX_LENGTH : max_len;

    pool->alloc_len = min_len < min_alloc_size ? min_alloc_size : min_len;

    if (pool->alloc_len > pool->max_len)

        pool->alloc_len = pool->max_len;

    if (secure)

        pool->buffer = OPENSSL_secure_zalloc(pool->alloc_len);

    else

        pool->buffer = OPENSSL_zalloc(pool->alloc_len);

    if (pool->buffer == NULL)

        goto err;

    pool->entropy_requested = entropy_requested;

    pool->secure = secure;

    return pool;

err:

    OPENSSL_free(pool);

    return NULL;

}

/*

 * Attach new random pool to the given buffer

 *

 * This function is intended to be used only for feeding random data

 * provided by RAND_add() and RAND_seed() into the <master> DRBG.

 */

RAND_POOL *ossl_rand_pool_attach(const unsigned char *buffer, size_t len,

                                 size_t entropy)

{

    RAND_POOL *pool = OPENSSL_zalloc(sizeof(*pool));

    if (pool == NULL)

        return NULL;

    /*

     * The const needs to be cast away, but attached buffers will not be

     * modified (in contrary to allocated buffers which are zeroed and

     * freed in the end).

     */

    pool->buffer = (unsigned char *) buffer;

    pool->len = len;

    pool->attached = 1;

    pool->min_len = pool->max_len = pool->alloc_len = pool->len;

    pool->entropy = entropy;

    return pool;

}

/*

 * Free |pool|, securely erasing its buffer.

 */

void ossl_rand_pool_free(RAND_POOL *pool)

{

    if (pool == NULL)

        return;

    /*

     * Although it would be advisable from a cryptographical viewpoint,

     * we are not allowed to clear attached buffers, since they are passed

     * to ossl_rand_pool_attach() as `const unsigned char*`.

     * (see corresponding comment in ossl_rand_pool_attach()).

     */

    if (!pool->attached) {

        if (pool->secure)

            OPENSSL_secure_clear_free(pool->buffer, pool->alloc_len);

        else

            OPENSSL_clear_free(pool->buffer, pool->alloc_len);

    }

    OPENSSL_free(pool);

}

/*

 * Return the |pool|'s buffer to the caller (readonly).

 */

const unsigned char *ossl_rand_pool_buffer(RAND_POOL *pool)

{

    return pool->buffer;

}

/*

 * Return the |pool|'s entropy to the caller.

 */

size_t ossl_rand_pool_entropy(RAND_POOL *pool)

{

    return pool->entropy;

}

/*

 * Return the |pool|'s buffer length to the caller.

 */

size_t ossl_rand_pool_length(RAND_POOL *pool)

{

    return pool->len;

}

/*

 * Detach the |pool| buffer and return it to the caller.

 * It's the responsibility of the caller to free the buffer

 * using OPENSSL_secure_clear_free() or to re-attach it

 * again to the pool using ossl_rand_pool_reattach().

 */

unsigned char *ossl_rand_pool_detach(RAND_POOL *pool)

{

    unsigned char *ret = pool->buffer;

    pool->buffer = NULL;

    pool->entropy = 0;

    return ret;

}

/*

 * Re-attach the |pool| buffer. It is only allowed to pass

 * the |buffer| which was previously detached from the same pool.

 */

void ossl_rand_pool_reattach(RAND_POOL *pool, unsigned char *buffer)

{

    pool->buffer = buffer;

    OPENSSL_cleanse(pool->buffer, pool->len);

    pool->len = 0;

}

/*

 * If |entropy_factor| bits contain 1 bit of entropy, how many bytes does one

 * need to obtain at least |bits| bits of entropy?

 */

#define ENTROPY_TO_BYTES(bits, entropy_factor) \

    (((bits) * (entropy_factor) + 7) / 8)

/*

 * Checks whether the |pool|'s entropy is available to the caller.

 * This is the case when entropy count and buffer length are high enough.

 * Returns

 *

 *  |entropy|  if the entropy count and buffer size is large enough

 *      0      otherwise

 */

size_t ossl_rand_pool_entropy_available(RAND_POOL *pool)

{

    if (pool->entropy < pool->entropy_requested)

        return 0;

    if (pool->len < pool->min_len)

        return 0;

    return pool->entropy;

}

/*

 * Returns the (remaining) amount of entropy needed to fill

 * the random pool.

 */

size_t ossl_rand_pool_entropy_needed(RAND_POOL *pool)

{

    if (pool->entropy < pool->entropy_requested)

        return pool->entropy_requested - pool->entropy;

    return 0;

}

/* Increase the allocation size -- not usable for an attached pool */

static int rand_pool_grow(RAND_POOL *pool, size_t len)

{

    if (len > pool->alloc_len - pool->len) {

        unsigned char *p;

        const size_t limit = pool->max_len / 2;

        size_t newlen = pool->alloc_len;

        if (pool->attached || len > pool->max_len - pool->len) {

            ERR_raise(ERR_LIB_RAND, ERR_R_INTERNAL_ERROR);

            return 0;

        }

        do

            newlen = newlen < limit ? newlen * 2 : pool->max_len;

        while (len > newlen - pool->len);

        if (pool->secure)

            p = OPENSSL_secure_zalloc(newlen);

        else

            p = OPENSSL_zalloc(newlen);

        if (p == NULL)

            return 0;

        memcpy(p, pool->buffer, pool->len);

        if (pool->secure)

            OPENSSL_secure_clear_free(pool->buffer, pool->alloc_len);

        else

            OPENSSL_clear_free(pool->buffer, pool->alloc_len);

        pool->buffer = p;

        pool->alloc_len = newlen;

    }

    return 1;

}

/*

 * Returns the number of bytes needed to fill the pool, assuming

 * the input has 1 / |entropy_factor| entropy bits per data bit.

 * In case of an error, 0 is returned.

 */

size_t ossl_rand_pool_bytes_needed(RAND_POOL *pool, unsigned int entropy_factor)

{

    size_t bytes_needed;

    size_t entropy_needed = ossl_rand_pool_entropy_needed(pool);

    if (entropy_factor < 1) {

        ERR_raise(ERR_LIB_RAND, RAND_R_ARGUMENT_OUT_OF_RANGE);

        return 0;

    }

    bytes_needed = ENTROPY_TO_BYTES(entropy_needed, entropy_factor);

    if (bytes_needed > pool->max_len - pool->len) {

        /* not enough space left */

        ERR_raise_data(ERR_LIB_RAND, RAND_R_RANDOM_POOL_OVERFLOW,

                       "entropy_factor=%u, entropy_needed=%zu, bytes_needed=%zu,"

                       "pool->max_len=%zu, pool->len=%zu",

                       entropy_factor, entropy_needed, bytes_needed,

                       pool->max_len, pool->len);

        return 0;

    }

    if (pool->len < pool->min_len &&

        bytes_needed < pool->min_len - pool->len)

        /* to meet the min_len requirement */

        bytes_needed = pool->min_len - pool->len;

    /*

     * Make sure the buffer is large enough for the requested amount

     * of data. This guarantees that existing code patterns where

     * ossl_rand_pool_add_begin, ossl_rand_pool_add_end or ossl_rand_pool_add

     * are used to collect entropy data without any error handling

     * whatsoever, continue to be valid.

     * Furthermore if the allocation here fails once, make sure that

     * we don't fall back to a less secure or even blocking random source,

     * as that could happen by the existing code patterns.

     * This is not a concern for additional data, therefore that

     * is not needed if rand_pool_grow fails in other places.

     */

    if (!rand_pool_grow(pool, bytes_needed)) {

        /* persistent error for this pool */

        pool->max_len = pool->len = 0;

        return 0;

    }

    return bytes_needed;

}

/* Returns the remaining number of bytes available */

size_t ossl_rand_pool_bytes_remaining(RAND_POOL *pool)

{

    return pool->max_len - pool->len;

}

/*

 * Add random bytes to the random pool.

 *

 * It is expected that the |buffer| contains |len| bytes of

 * random input which contains at least |entropy| bits of

 * randomness.

 *

 * Returns 1 if the added amount is adequate, otherwise 0

 */

int ossl_rand_pool_add(RAND_POOL *pool,

                  const unsigned char *buffer, size_t len, size_t entropy)

{

    if (len > pool->max_len - pool->len) {

        ERR_raise(ERR_LIB_RAND, RAND_R_ENTROPY_INPUT_TOO_LONG);

        return 0;

    }

    if (pool->buffer == NULL) {

        ERR_raise(ERR_LIB_RAND, ERR_R_INTERNAL_ERROR);

        return 0;

    }

    if (len > 0) {

        /*

         * This is to protect us from accidentally passing the buffer

         * returned from ossl_rand_pool_add_begin.

         * The check for alloc_len makes sure we do not compare the

         * address of the end of the allocated memory to something

         * different, since that comparison would have an

         * indeterminate result.

         */

        if (pool->alloc_len > pool->len && pool->buffer + pool->len == buffer) {

            ERR_raise(ERR_LIB_RAND, ERR_R_INTERNAL_ERROR);

            return 0;

        }

        /*

         * We have that only for cases when a pool is used to collect

         * additional data.

         * For entropy data, as long as the allocation request stays within

         * the limits given by ossl_rand_pool_bytes_needed this rand_pool_grow

         * below is guaranteed to succeed, thus no allocation happens.

         */

        if (!rand_pool_grow(pool, len))

            return 0;

        memcpy(pool->buffer + pool->len, buffer, len);

        pool->len += len;

        pool->entropy += entropy;

    }

    return 1;

}

/*

 * Start to add random bytes to the random pool in-place.

 *

 * Reserves the next |len| bytes for adding random bytes in-place

 * and returns a pointer to the buffer.

 * The caller is allowed to copy up to |len| bytes into the buffer.

 * If |len| == 0 this is considered a no-op and a NULL pointer

 * is returned without producing an error message.

 *

 * After updating the buffer, ossl_rand_pool_add_end() needs to be called

 * to finish the update operation (see next comment).

 */

unsigned char *ossl_rand_pool_add_begin(RAND_POOL *pool, size_t len)

{

    if (len == 0)

        return NULL;

    if (len > pool->max_len - pool->len) {

        ERR_raise(ERR_LIB_RAND, RAND_R_RANDOM_POOL_OVERFLOW);

        return NULL;

    }

    if (pool->buffer == NULL) {

        ERR_raise(ERR_LIB_RAND, ERR_R_INTERNAL_ERROR);

        return NULL;

    }

    /*

     * As long as the allocation request stays within the limits given

     * by ossl_rand_pool_bytes_needed this rand_pool_grow below is guaranteed

     * to succeed, thus no allocation happens.

     * We have that only for cases when a pool is used to collect

     * additional data. Then the buffer might need to grow here,

     * and of course the caller is responsible to check the return

     * value of this function.

     */

    if (!rand_pool_grow(pool, len))

        return NULL;

    return pool->buffer + pool->len;

}

/*

 * Finish to add random bytes to the random pool in-place.

 *

 * Finishes an in-place update of the random pool started by

 * ossl_rand_pool_add_begin() (see previous comment).

 * It is expected that |len| bytes of random input have been added

 * to the buffer which contain at least |entropy| bits of randomness.

 * It is allowed to add less bytes than originally reserved.

 */

int ossl_rand_pool_add_end(RAND_POOL *pool, size_t len, size_t entropy)

{

    if (len > pool->alloc_len - pool->len) {

        ERR_raise(ERR_LIB_RAND, RAND_R_RANDOM_POOL_OVERFLOW);

        return 0;

    }

    if (len > 0) {

        pool->len += len;

        pool->entropy += entropy;

    }

    return 1;

}

/**

 * @brief Mix in the additional input into an existing entropy in the pool

 *

 * @param pool     A RAND_POOL to mix the additional input in

 * @param adin     A buffer with the additional input

 * @param adin_len A length of the additional input

 *

 * @return 1 if there is any existing entropy in the pool so the additional input

 *         can be mixed in, 0 otherwise.

 */

int ossl_rand_pool_adin_mix_in(RAND_POOL *pool, const unsigned char *adin,

                               size_t adin_len)

{

    if (adin == NULL || adin_len == 0)

        /* Nothing to mix in -> success */

        return 1;

    if (pool->buffer == NULL) {

        ERR_raise(ERR_LIB_RAND, ERR_R_INTERNAL_ERROR);

        return 0;

    }

    if (pool->len == 0) {

        ERR_raise(ERR_LIB_RAND, RAND_R_RANDOM_POOL_IS_EMPTY);

        return 0;

    }

    if (adin != NULL && adin_len > 0) {

        size_t i;

        /* xor the additional data into the pool */

        for (i = 0; i < adin_len; ++i)

            pool->buffer[i % pool->len] ^= adin[i];

    }

    return 1;

}