rand_lib.c

/*
 * Copyright 1995-2018 The OpenSSL Project Authors. All Rights Reserved.
 *
 * Licensed under the OpenSSL license (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 "internal/rand_int.h"
#include <openssl/engine.h>
#include "internal/thread_once.h"
#include "rand_lcl.h"
#ifdef OPENSSL_SYS_UNIX
# include <sys/types.h>
# include <unistd.h>
# include <sys/time.h>
#endif
#include "e_os.h"

/* Macro to convert two thirty two bit values into a sixty four bit one */
#define TWO32TO64(a, b) ((((uint64_t)(a)) << 32) + (b))

/*
 * Check for the existence and support of POSIX timers.  The standard
 * says that the _POSIX_TIMERS macro will have a positive value if they
 * are available.
 *
 * However, we want an additional constraint: that the timer support does
 * not require an extra library dependency.  Early versions of glibc
 * require -lrt to be specified on the link line to access the timers,
 * so this needs to be checked for.
 *
 * It is worse because some libraries define __GLIBC__ but don't
 * support the version testing macro (e.g. uClibc).  This means
 * an extra check is needed.
 *
 * The final condition is:
 *      "have posix timers and either not glibc or glibc without -lrt"
 *
 * The nested #if sequences are required to avoid using a parameterised
 * macro that might be undefined.
 */
#undef OSSL_POSIX_TIMER_OKAY
#if defined(_POSIX_TIMERS) && _POSIX_TIMERS > 0
# if defined(__GLIBC__)
#  if defined(__GLIBC_PREREQ)
#   if __GLIBC_PREREQ(2, 17)
#    define OSSL_POSIX_TIMER_OKAY
#   endif
#  endif
# else
#  define OSSL_POSIX_TIMER_OKAY
# endif
#endif

#ifndef OPENSSL_NO_ENGINE
/* non-NULL if default_RAND_meth is ENGINE-provided */
static ENGINE *funct_ref;
static CRYPTO_RWLOCK *rand_engine_lock;
#endif
static CRYPTO_RWLOCK *rand_meth_lock;
static const RAND_METHOD *default_RAND_meth;
static CRYPTO_ONCE rand_init = CRYPTO_ONCE_STATIC_INIT;

int rand_fork_count;

#ifdef OPENSSL_RAND_SEED_RDTSC
/*
 * IMPORTANT NOTE:  It is not currently possible to use this code
 * because we are not sure about the amount of randomness it provides.
 * Some SP900 tests have been run, but there is internal skepticism.
 * So for now this code is not used.
 */
# error "RDTSC enabled?  Should not be possible!"

/*
 * Acquire entropy from high-speed clock
 *
 * Since we get some randomness from the low-order bits of the
 * high-speed clock, it can help.
 *
 * Returns the total entropy count, if it exceeds the requested
 * entropy count. Otherwise, returns an entropy count of 0.
 */
size_t rand_acquire_entropy_from_tsc(RAND_POOL *pool)
{
    unsigned char c;
    int i;

    if ((OPENSSL_ia32cap_P[0] & (1 << 4)) != 0) {
        for (i = 0; i < TSC_READ_COUNT; i++) {
            c = (unsigned char)(OPENSSL_rdtsc() & 0xFF);
            rand_pool_add(pool, &c, 1, 4);
        }
    }
    return rand_pool_entropy_available(pool);
}
#endif

#ifdef OPENSSL_RAND_SEED_RDCPU
size_t OPENSSL_ia32_rdseed_bytes(unsigned char *buf, size_t len);
size_t OPENSSL_ia32_rdrand_bytes(unsigned char *buf, size_t len);

extern unsigned int OPENSSL_ia32cap_P[];

/*
 * Acquire entropy using Intel-specific cpu instructions
 *
 * Uses the RDSEED instruction if available, otherwise uses
 * RDRAND if available.
 *
 * For the differences between RDSEED and RDRAND, and why RDSEED
 * is the preferred choice, see https://goo.gl/oK3KcN
 *
 * Returns the total entropy count, if it exceeds the requested
 * entropy count. Otherwise, returns an entropy count of 0.
 */
size_t rand_acquire_entropy_from_cpu(RAND_POOL *pool)
{
    size_t bytes_needed;
    unsigned char *buffer;

    bytes_needed = rand_pool_bytes_needed(pool, 8 /*entropy_per_byte*/);
    if (bytes_needed > 0) {
        buffer = rand_pool_add_begin(pool, bytes_needed);

        if (buffer != NULL) {

            /* If RDSEED is available, use that. */
            if ((OPENSSL_ia32cap_P[2] & (1 << 18)) != 0) {
                if (OPENSSL_ia32_rdseed_bytes(buffer, bytes_needed)
                    == bytes_needed)
                    return rand_pool_add_end(pool,
                                             bytes_needed,
                                             8 * bytes_needed);
            }

            /* Second choice is RDRAND. */
            if ((OPENSSL_ia32cap_P[1] & (1 << (62 - 32))) != 0) {
                if (OPENSSL_ia32_rdrand_bytes(buffer, bytes_needed)
                    == bytes_needed)
                    return rand_pool_add_end(pool,
                                             bytes_needed,
                                             8 * bytes_needed);
            }

            return rand_pool_add_end(pool, 0, 0);
        }
    }

    return rand_pool_entropy_available(pool);
}
#endif


/*
 * Implements the get_entropy() callback (see RAND_DRBG_set_callbacks())
 *
 * If the DRBG has a parent, then the required amount of entropy input
 * is fetched using the parent's RAND_DRBG_generate().
 *
 * Otherwise, the entropy is polled from the system entropy sources
 * using rand_pool_acquire_entropy().
 *
 * If a random pool has been added to the DRBG using RAND_add(), then
 * its entropy will be used up first.
 */
size_t rand_drbg_get_entropy(RAND_DRBG *drbg,
                             unsigned char **pout,
                             int entropy, size_t min_len, size_t max_len,
                             int prediction_resistance)
{
    size_t ret = 0;
    size_t entropy_available = 0;
    RAND_POOL *pool;

    if (drbg->parent && drbg->strength > drbg->parent->strength) {
        /*
         * We currently don't support the algorithm from NIST SP 800-90C
         * 10.1.2 to use a weaker DRBG as source
         */
        RANDerr(RAND_F_RAND_DRBG_GET_ENTROPY, RAND_R_PARENT_STRENGTH_TOO_WEAK);
        return 0;
    }

    pool = rand_pool_new(entropy, min_len, max_len);
    if (pool == NULL)
        return 0;

    if (drbg->pool) {
        rand_pool_add(pool,
                      rand_pool_buffer(drbg->pool),
                      rand_pool_length(drbg->pool),
                      rand_pool_entropy(drbg->pool));
        rand_pool_free(drbg->pool);
        drbg->pool = NULL;
    }

    if (drbg->parent) {
        size_t bytes_needed = rand_pool_bytes_needed(pool, 8);
        unsigned char *buffer = rand_pool_add_begin(pool, bytes_needed);

        if (buffer != NULL) {
            size_t bytes = 0;

            /*
             * Get random from parent, include our state as additional input.
             * Our lock is already held, but we need to lock our parent before
             * generating bits from it. (Note: taking the lock will be a no-op
             * if locking if drbg->parent->lock == NULL.)
             */
            rand_drbg_lock(drbg->parent);
            if (RAND_DRBG_generate(drbg->parent,
                                   buffer, bytes_needed,
                                   prediction_resistance,
                                   (unsigned char *)drbg, sizeof(*drbg)) != 0)
                bytes = bytes_needed;
            rand_drbg_unlock(drbg->parent);

            entropy_available = rand_pool_add_end(pool, bytes, 8 * bytes);
        }

    } else {
        if (prediction_resistance) {
            /*
             * We don't have any entropy sources that comply with the NIST
             * standard to provide prediction resistance (see NIST SP 800-90C,
             * Section 5.4).
             */
            RANDerr(RAND_F_RAND_DRBG_GET_ENTROPY,
                    RAND_R_PREDICTION_RESISTANCE_NOT_SUPPORTED);
            return 0;
        }

        /* Get entropy by polling system entropy sources. */
        entropy_available = rand_pool_acquire_entropy(pool);
    }

    if (entropy_available > 0) {
        ret   = rand_pool_length(pool);
        *pout = rand_pool_detach(pool);
    }

    rand_pool_free(pool);
    return ret;
}

/*
 * Find a suitable source of time.  Start with the highest resolution source
 * and work down to the slower ones.  This is added as additional data and
 * isn't counted as randomness, so any result is acceptable.
 *
 * Returns 0 when we weren't able to find any time source
 */
static uint64_t get_timer_bits(void)
{
    uint64_t res = OPENSSL_rdtsc();

    if (res != 0)
        return res;
#if defined(_WIN32)
    {
        LARGE_INTEGER t;
        FILETIME ft;

        if (QueryPerformanceCounter(&t) != 0)
            return t.QuadPart;
        GetSystemTimeAsFileTime(&ft);
        return TWO32TO64(ft.dwHighDateTime, ft.dwLowDateTime);
    }
#elif defined(__sun) || defined(__hpux)
    return gethrtime();
#elif defined(_AIX)
    {
        timebasestruct_t t;

        read_wall_time(&t, TIMEBASE_SZ);
        return TWO32TO64(t.tb_high, t.tb_low);
    }
#else

# if defined(OSSL_POSIX_TIMER_OKAY)
    {
        struct timespec ts;
        clockid_t cid;

#  ifdef CLOCK_BOOTTIME
        cid = CLOCK_BOOTTIME;
#  elif defined(_POSIX_MONOTONIC_CLOCK)
        cid = CLOCK_MONOTONIC;
#  else
        cid = CLOCK_REALTIME;
#  endif

        if (clock_gettime(cid, &ts) == 0)
            return TWO32TO64(ts.tv_sec, ts.tv_nsec);
    }
# endif
# if defined(__unix__) \
     || (defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE >= 200112L)
    {
        struct timeval tv;

        if (gettimeofday(&tv, NULL) == 0)
            return TWO32TO64(tv.tv_sec, tv.tv_usec);
    }
# endif
    {
        time_t t = time(NULL);
        if (t == (time_t)-1)
            return 0;
        return t;
    }
#endif
}

/*
 * Generate additional data that can be used for the drbg. The data does
 * not need to contain entropy, but it's useful if it contains at least
 * some bits that are unpredictable.
 *
 * Returns 0 on failure.
 *
 * On success it allocates a buffer at |*pout| and returns the length of
 * the data. The buffer should get freed using OPENSSL_secure_clear_free().
 */
size_t rand_drbg_get_additional_data(unsigned char **pout, size_t max_len)
{
    RAND_POOL *pool;
    CRYPTO_THREAD_ID thread_id;
    size_t len;
#ifdef OPENSSL_SYS_UNIX
    pid_t pid;
#elif defined(OPENSSL_SYS_WIN32)
    DWORD pid;
#endif
    uint64_t tbits;

    pool = rand_pool_new(0, 0, max_len);
    if (pool == NULL)
        return 0;

#ifdef OPENSSL_SYS_UNIX
    pid = getpid();
    rand_pool_add(pool, (unsigned char *)&pid, sizeof(pid), 0);
#elif defined(OPENSSL_SYS_WIN32)
    pid = GetCurrentProcessId();
    rand_pool_add(pool, (unsigned char *)&pid, sizeof(pid), 0);
#endif

    thread_id = CRYPTO_THREAD_get_current_id();
    if (thread_id != 0)
        rand_pool_add(pool, (unsigned char *)&thread_id, sizeof(thread_id), 0);

    tbits = get_timer_bits();
    if (tbits != 0)
        rand_pool_add(pool, (unsigned char *)&tbits, sizeof(tbits), 0);

    /* TODO: Use RDSEED? */

    len = rand_pool_length(pool);
    if (len != 0)
        *pout = rand_pool_detach(pool);
    rand_pool_free(pool);

    return len;
}

/*
 * Implements the cleanup_entropy() callback (see RAND_DRBG_set_callbacks())
 *
 */
void rand_drbg_cleanup_entropy(RAND_DRBG *drbg,
                               unsigned char *out, size_t outlen)
{
    OPENSSL_secure_clear_free(out, outlen);
}

void rand_fork()
{
    rand_fork_count++;
}

DEFINE_RUN_ONCE_STATIC(do_rand_init)
{
    int ret = 1;

#ifndef OPENSSL_NO_ENGINE
    rand_engine_lock = CRYPTO_THREAD_lock_new();
    ret &= rand_engine_lock != NULL;
#endif
    rand_meth_lock = CRYPTO_THREAD_lock_new();
    ret &= rand_meth_lock != NULL;

    return ret;
}

void rand_cleanup_int(void)
{
    const RAND_METHOD *meth = default_RAND_meth;

    if (meth != NULL && meth->cleanup != NULL)
        meth->cleanup();
    RAND_set_rand_method(NULL);
#ifndef OPENSSL_NO_ENGINE
    CRYPTO_THREAD_lock_free(rand_engine_lock);
#endif
    CRYPTO_THREAD_lock_free(rand_meth_lock);
}

/*
 * RAND_poll() reseeds the default RNG using random input
 *
 * The random input is obtained from polling various entropy
 * sources which depend on the operating system and are
 * configurable via the --with-rand-seed configure option.
 */
int RAND_poll(void)
{
    int ret = 0;

    RAND_POOL *pool = NULL;

    const RAND_METHOD *meth = RAND_get_rand_method();

    if (meth == RAND_OpenSSL()) {
        /* fill random pool and seed the master DRBG */
        RAND_DRBG *drbg = RAND_DRBG_get0_master();

        if (drbg == NULL)
            return 0;

        rand_drbg_lock(drbg);
        ret = rand_drbg_restart(drbg, NULL, 0, 0);
        rand_drbg_unlock(drbg);

        return ret;

    } else {
        /* fill random pool and seed the current legacy RNG */
        pool = rand_pool_new(RAND_DRBG_STRENGTH,
                             RAND_DRBG_STRENGTH / 8,
                             DRBG_MINMAX_FACTOR * (RAND_DRBG_STRENGTH / 8));
        if (pool == NULL)
            return 0;

        if (rand_pool_acquire_entropy(pool) == 0)
            goto err;

        if (meth->add == NULL
            || meth->add(rand_pool_buffer(pool),
                         rand_pool_length(pool),
                         (rand_pool_entropy(pool) / 8.0)) == 0)
            goto err;

        ret = 1;
    }

err:
    rand_pool_free(pool);
    return ret;
}

/*
 * The 'random pool' acts as a dumb container for collecting random
 * input from various entropy sources. The pool has no knowledge about
 * whether its randomness is fed into a legacy RAND_METHOD via RAND_add()
 * or into a new style RAND_DRBG. It is the callers duty to 1) initialize the
 * random pool, 2) pass it to the polling callbacks, 3) seed the RNG, and
 * 4) cleanup the random pool again.
 *
 * The random pool contains no locking mechanism because its scope and
 * lifetime is intended to be restricted to a single stack frame.
 */
struct rand_pool_st {
    unsigned char *buffer;  /* points to the beginning of the random pool */
    size_t len; /* current number of random bytes contained in the pool */

    size_t min_len; /* minimum number of random bytes requested */
    size_t max_len; /* maximum number of random bytes (allocated buffer size) */
    size_t entropy; /* current entropy count in bits */
    size_t requested_entropy; /* requested entropy count in bits */
};

/*
 * Allocate memory and initialize a new random pool
 */

RAND_POOL *rand_pool_new(int entropy, size_t min_len, size_t max_len)
{
    RAND_POOL *pool = OPENSSL_zalloc(sizeof(*pool));

    if (pool == NULL) {
        RANDerr(RAND_F_RAND_POOL_NEW, ERR_R_MALLOC_FAILURE);
        goto err;
    }

    pool->min_len = min_len;
    pool->max_len = max_len;

    pool->buffer = OPENSSL_secure_zalloc(pool->max_len);
    if (pool->buffer == NULL) {
        RANDerr(RAND_F_RAND_POOL_NEW, ERR_R_MALLOC_FAILURE);
        goto err;
    }

    pool->requested_entropy = entropy;

    return pool;

err:
    OPENSSL_free(pool);
    return NULL;
}

/*
 * Free |pool|, securely erasing its buffer.
 */
void rand_pool_free(RAND_POOL *pool)
{
    if (pool == NULL)
        return;

    OPENSSL_secure_clear_free(pool->buffer, pool->max_len);
    OPENSSL_free(pool);
}

/*
 * Return the |pool|'s buffer to the caller (readonly).
 */
const unsigned char *rand_pool_buffer(RAND_POOL *pool)
{
    return pool->buffer;
}

/*
 * Return the |pool|'s entropy to the caller.
 */
size_t rand_pool_entropy(RAND_POOL *pool)
{
    return pool->entropy;
}

/*
 * Return the |pool|'s buffer length to the caller.
 */
size_t 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().
 */
unsigned char *rand_pool_detach(RAND_POOL *pool)
{
    unsigned char *ret = pool->buffer;
    pool->buffer = NULL;
    return ret;
}


/*
 * If every byte of the input contains |entropy_per_bytes| bits of entropy,
 * how many bytes does one need to obtain at least |bits| bits of entropy?
 */
#define ENTROPY_TO_BYTES(bits, entropy_per_bytes) \
    (((bits) + ((entropy_per_bytes) - 1))/(entropy_per_bytes))


/*
 * 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 rand_pool_entropy_available(RAND_POOL *pool)
{
    if (pool->entropy < pool->requested_entropy)
        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 rand_pool_entropy_needed(RAND_POOL *pool)
{
    if (pool->entropy < pool->requested_entropy)
        return pool->requested_entropy - pool->entropy;

    return 0;
}

/*
 * Returns the number of bytes needed to fill the pool, assuming
 * the input has 'entropy_per_byte' entropy bits per byte.
 * In case of an error, 0 is returned.
 */

size_t rand_pool_bytes_needed(RAND_POOL *pool, unsigned int entropy_per_byte)
{
    size_t bytes_needed;
    size_t entropy_needed = rand_pool_entropy_needed(pool);

    if (entropy_per_byte < 1 || entropy_per_byte > 8) {
        RANDerr(RAND_F_RAND_POOL_BYTES_NEEDED, RAND_R_ARGUMENT_OUT_OF_RANGE);
        return 0;
    }

    bytes_needed = ENTROPY_TO_BYTES(entropy_needed, entropy_per_byte);

    if (bytes_needed > pool->max_len - pool->len) {
        /* not enough space left */
        RANDerr(RAND_F_RAND_POOL_BYTES_NEEDED, RAND_R_RANDOM_POOL_OVERFLOW);
        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;

    return bytes_needed;
}

/* Returns the remaining number of bytes available */
size_t 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.
 *
 * Return available amount of entropy after this operation.
 * (see rand_pool_entropy_available(pool))
 */
size_t rand_pool_add(RAND_POOL *pool,
                     const unsigned char *buffer, size_t len, size_t entropy)
{
    if (len > pool->max_len - pool->len) {
        RANDerr(RAND_F_RAND_POOL_ADD, RAND_R_ENTROPY_INPUT_TOO_LONG);
        return 0;
    }

    if (len > 0) {
        memcpy(pool->buffer + pool->len, buffer, len);
        pool->len += len;
        pool->entropy += entropy;
    }

    return rand_pool_entropy_available(pool);
}

/*
 * 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, rand_pool_add_end() needs to be called
 * to finish the udpate operation (see next comment).
 */
unsigned char *rand_pool_add_begin(RAND_POOL *pool, size_t len)
{
    if (len == 0)
        return NULL;

    if (len > pool->max_len - pool->len) {
        RANDerr(RAND_F_RAND_POOL_ADD_BEGIN, RAND_R_RANDOM_POOL_OVERFLOW);
        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
 * 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.
 */
size_t rand_pool_add_end(RAND_POOL *pool, size_t len, size_t entropy)
{
    if (len > pool->max_len - pool->len) {
        RANDerr(RAND_F_RAND_POOL_ADD_END, RAND_R_RANDOM_POOL_OVERFLOW);
        return 0;
    }

    if (len > 0) {
        pool->len += len;
        pool->entropy += entropy;
    }

    return rand_pool_entropy_available(pool);
}

int RAND_set_rand_method(const RAND_METHOD *meth)
{
    if (!RUN_ONCE(&rand_init, do_rand_init))
        return 0;

    CRYPTO_THREAD_write_lock(rand_meth_lock);
#ifndef OPENSSL_NO_ENGINE
    ENGINE_finish(funct_ref);
    funct_ref = NULL;
#endif
    default_RAND_meth = meth;
    CRYPTO_THREAD_unlock(rand_meth_lock);
    return 1;
}

const RAND_METHOD *RAND_get_rand_method(void)
{
    const RAND_METHOD *tmp_meth = NULL;

    if (!RUN_ONCE(&rand_init, do_rand_init))
        return NULL;

    CRYPTO_THREAD_write_lock(rand_meth_lock);
    if (default_RAND_meth == NULL) {
#ifndef OPENSSL_NO_ENGINE
        ENGINE *e;

        /* If we have an engine that can do RAND, use it. */
        if ((e = ENGINE_get_default_RAND()) != NULL
                && (tmp_meth = ENGINE_get_RAND(e)) != NULL) {
            funct_ref = e;
            default_RAND_meth = tmp_meth;
        } else {
            ENGINE_finish(e);
            default_RAND_meth = &rand_meth;
        }
#else
        default_RAND_meth = &rand_meth;
#endif
    }
    tmp_meth = default_RAND_meth;
    CRYPTO_THREAD_unlock(rand_meth_lock);
    return tmp_meth;
}

#ifndef OPENSSL_NO_ENGINE
int RAND_set_rand_engine(ENGINE *engine)
{
    const RAND_METHOD *tmp_meth = NULL;

    if (!RUN_ONCE(&rand_init, do_rand_init))
        return 0;

    if (engine != NULL) {
        if (!ENGINE_init(engine))
            return 0;
        tmp_meth = ENGINE_get_RAND(engine);
        if (tmp_meth == NULL) {
            ENGINE_finish(engine);
            return 0;
        }
    }
    CRYPTO_THREAD_write_lock(rand_engine_lock);
    /* This function releases any prior ENGINE so call it first */
    RAND_set_rand_method(tmp_meth);
    funct_ref = engine;
    CRYPTO_THREAD_unlock(rand_engine_lock);
    return 1;
}
#endif

void RAND_seed(const void *buf, int num)
{
    const RAND_METHOD *meth = RAND_get_rand_method();

    if (meth->seed != NULL)
        meth->seed(buf, num);
}

void RAND_add(const void *buf, int num, double randomness)
{
    const RAND_METHOD *meth = RAND_get_rand_method();

    if (meth->add != NULL)
        meth->add(buf, num, randomness);
}

/*
 * This function is not part of RAND_METHOD, so if we're not using
 * the default method, then just call RAND_bytes().  Otherwise make
 * sure we're instantiated and use the private DRBG.
 */
int RAND_priv_bytes(unsigned char *buf, int num)
{
    const RAND_METHOD *meth = RAND_get_rand_method();
    RAND_DRBG *drbg;
    int ret;

    if (meth != RAND_OpenSSL())
        return RAND_bytes(buf, num);

    drbg = RAND_DRBG_get0_private();
    if (drbg == NULL)
        return 0;

    /* We have to lock the DRBG before generating bits from it. */
    rand_drbg_lock(drbg);
    ret = RAND_DRBG_bytes(drbg, buf, num);
    rand_drbg_unlock(drbg);
    return ret;
}

int RAND_bytes(unsigned char *buf, int num)
{
    const RAND_METHOD *meth = RAND_get_rand_method();

    if (meth->bytes != NULL)
        return meth->bytes(buf, num);
    RANDerr(RAND_F_RAND_BYTES, RAND_R_FUNC_NOT_IMPLEMENTED);
    return -1;
}

#if OPENSSL_API_COMPAT < 0x10100000L
int RAND_pseudo_bytes(unsigned char *buf, int num)
{
    const RAND_METHOD *meth = RAND_get_rand_method();

    if (meth->pseudorand != NULL)
        return meth->pseudorand(buf, num);
    return -1;
}
#endif

int RAND_status(void)
{
    const RAND_METHOD *meth = RAND_get_rand_method();

    if (meth->status != NULL)
        return meth->status();
    return 0;
}