drbg_hmac.c

/*
 * Copyright 2011-2025 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 <stdlib.h>
#include <string.h>
#include <openssl/crypto.h>
#include <openssl/err.h>
#include <openssl/rand.h>
#include <openssl/proverr.h>
#include "internal/thread_once.h"
#include "prov/providercommon.h"
#include "prov/implementations.h"
#include "prov/provider_ctx.h"
#include "prov/hmac_drbg.h"
#include "drbg_local.h"
#include "crypto/evp.h"
#include "crypto/evp/evp_local.h"
#include "internal/provider.h"

static OSSL_FUNC_rand_newctx_fn drbg_hmac_new_wrapper;
static OSSL_FUNC_rand_freectx_fn drbg_hmac_free;
static OSSL_FUNC_rand_instantiate_fn drbg_hmac_instantiate_wrapper;
static OSSL_FUNC_rand_uninstantiate_fn drbg_hmac_uninstantiate_wrapper;
static OSSL_FUNC_rand_generate_fn drbg_hmac_generate_wrapper;
static OSSL_FUNC_rand_reseed_fn drbg_hmac_reseed_wrapper;
static OSSL_FUNC_rand_settable_ctx_params_fn drbg_hmac_settable_ctx_params;
static OSSL_FUNC_rand_set_ctx_params_fn drbg_hmac_set_ctx_params;
static OSSL_FUNC_rand_gettable_ctx_params_fn drbg_hmac_gettable_ctx_params;
static OSSL_FUNC_rand_get_ctx_params_fn drbg_hmac_get_ctx_params;
static OSSL_FUNC_rand_verify_zeroization_fn drbg_hmac_verify_zeroization;

static int drbg_hmac_set_ctx_params_locked(void *vctx, const OSSL_PARAM params[]);

/*
 * Called twice by SP800-90Ar1 10.1.2.2 HMAC_DRBG_Update_Process.
 *
 * hmac is an object that holds the input/output Key and Value (K and V).
 * inbyte is 0x00 on the first call and 0x01 on the second call.
 * in1, in2, in3 are optional inputs that can be NULL.
 * in1len, in2len, in3len are the lengths of the input buffers.
 *
 * The returned K,V is:
 *   hmac->K = HMAC(hmac->K, hmac->V || inbyte || [in1] || [in2] || [in3])
 *   hmac->V = HMAC(hmac->K, hmac->V)
 *
 * Returns zero if an error occurs otherwise it returns 1.
 */
static int do_hmac(PROV_DRBG_HMAC *hmac, unsigned char inbyte,
                   const unsigned char *in1, size_t in1len,
                   const unsigned char *in2, size_t in2len,
                   const unsigned char *in3, size_t in3len)
{
    EVP_MAC_CTX *ctx = hmac->ctx;

    if (!EVP_MAC_init(ctx, hmac->K, hmac->blocklen, NULL)
            /* K = HMAC(K, V || inbyte || [in1] || [in2] || [in3]) */
            || !EVP_MAC_update(ctx, hmac->V, hmac->blocklen)
            || !EVP_MAC_update(ctx, &inbyte, 1)
            || !(in1 == NULL || in1len == 0 || EVP_MAC_update(ctx, in1, in1len))
            || !(in2 == NULL || in2len == 0 || EVP_MAC_update(ctx, in2, in2len))
            || !(in3 == NULL || in3len == 0 || EVP_MAC_update(ctx, in3, in3len))
            || !EVP_MAC_final(ctx, hmac->K, NULL, sizeof(hmac->K)))
        return 0;

   /* V = HMAC(K, V) */
    return EVP_MAC_init(ctx, hmac->K, hmac->blocklen, NULL)
           && EVP_MAC_update(ctx, hmac->V, hmac->blocklen)
           && EVP_MAC_final(ctx, hmac->V, NULL, sizeof(hmac->V));
}

/*
 * SP800-90Ar1 10.1.2.2 HMAC_DRBG_Update_Process
 *
 *
 * Updates the drbg objects Key(K) and Value(V) using the following algorithm:
 *   K,V = do_hmac(hmac, 0, in1, in2, in3)
 *   if (any input is not NULL)
 *     K,V = do_hmac(hmac, 1, in1, in2, in3)
 *
 * where in1, in2, in3 are optional input buffers that can be NULL.
 *       in1len, in2len, in3len are the lengths of the input buffers.
 *
 * Returns zero if an error occurs otherwise it returns 1.
 */
static int drbg_hmac_update(PROV_DRBG_HMAC *hmac,
                            const unsigned char *in1, size_t in1len,
                            const unsigned char *in2, size_t in2len,
                            const unsigned char *in3, size_t in3len)
{
    /* (Steps 1-2) K = HMAC(K, V||0x00||provided_data). V = HMAC(K,V) */
    if (!do_hmac(hmac, 0x00, in1, in1len, in2, in2len, in3, in3len))
        return 0;
    /* (Step 3) If provided_data == NULL then return (K,V) */
    if (in1len == 0 && in2len == 0 && in3len == 0)
        return 1;
    /* (Steps 4-5) K = HMAC(K, V||0x01||provided_data). V = HMAC(K,V) */
    return do_hmac(hmac, 0x01, in1, in1len, in2, in2len, in3, in3len);
}

/*
 * SP800-90Ar1 10.1.2.3 HMAC_DRBG_Instantiate_Process:
 *
 * This sets the drbg Key (K) to all zeros, and Value (V) to all 1's.
 * and then calls (K,V) = drbg_hmac_update() with input parameters:
 *   ent = entropy data (Can be NULL) of length ent_len.
 *   nonce = nonce data (Can be NULL) of length nonce_len.
 *   pstr = personalization data (Can be NULL) of length pstr_len.
 *
 * Returns zero if an error occurs otherwise it returns 1.
 */
int ossl_drbg_hmac_init(PROV_DRBG_HMAC *hmac,
                        const unsigned char *ent, size_t ent_len,
                        const unsigned char *nonce, size_t nonce_len,
                        const unsigned char *pstr, size_t pstr_len)
{
    if (hmac->ctx == NULL) {
        ERR_raise(ERR_LIB_PROV, PROV_R_MISSING_MAC);
        return 0;
    }

    /* (Step 2) Key = 0x00 00...00 */
    memset(hmac->K, 0x00, hmac->blocklen);
    /* (Step 3) V = 0x01 01...01 */
    memset(hmac->V, 0x01, hmac->blocklen);
    /* (Step 4) (K,V) = HMAC_DRBG_Update(entropy||nonce||pers string, K, V) */
    return drbg_hmac_update(hmac, ent, ent_len, nonce, nonce_len, pstr,
                            pstr_len);
}
static int drbg_hmac_instantiate(PROV_DRBG *drbg,
                                 const unsigned char *ent, size_t ent_len,
                                 const unsigned char *nonce, size_t nonce_len,
                                 const unsigned char *pstr, size_t pstr_len)
{
    return ossl_drbg_hmac_init((PROV_DRBG_HMAC *)drbg->data, ent, ent_len,
                               nonce, nonce_len, pstr, pstr_len);
}

static int drbg_hmac_instantiate_wrapper(void *vdrbg, unsigned int strength,
                                         int prediction_resistance,
                                         const unsigned char *pstr,
                                         size_t pstr_len,
                                         const OSSL_PARAM params[])
{
    PROV_DRBG *drbg = (PROV_DRBG *)vdrbg;
    int ret = 0;

    if (drbg->lock != NULL && !CRYPTO_THREAD_write_lock(drbg->lock))
        return 0;

    if (!ossl_prov_is_running()
            || !drbg_hmac_set_ctx_params_locked(drbg, params))
        goto err;
    ret = ossl_prov_drbg_instantiate(drbg, strength, prediction_resistance,
                                     pstr, pstr_len);
 err:
    if (drbg->lock != NULL)
        CRYPTO_THREAD_unlock(drbg->lock);
    return ret;
}


/*
 * SP800-90Ar1 10.1.2.4 HMAC_DRBG_Reseed_Process:
 *
 * Reseeds the drbg's Key (K) and Value (V) by calling
 * (K,V) = drbg_hmac_update() with the following input parameters:
 *   ent = entropy input data (Can be NULL) of length ent_len.
 *   adin = additional input data (Can be NULL) of length adin_len.
 *
 * Returns zero if an error occurs otherwise it returns 1.
 */
static int drbg_hmac_reseed(PROV_DRBG *drbg,
                            const unsigned char *ent, size_t ent_len,
                            const unsigned char *adin, size_t adin_len)
{
    PROV_DRBG_HMAC *hmac = (PROV_DRBG_HMAC *)drbg->data;

    /* (Step 2) (K,V) = HMAC_DRBG_Update(entropy||additional_input, K, V) */
    return drbg_hmac_update(hmac, ent, ent_len, adin, adin_len, NULL, 0);
}

static int drbg_hmac_reseed_wrapper(void *vdrbg, int prediction_resistance,
                                    const unsigned char *ent, size_t ent_len,
                                    const unsigned char *adin, size_t adin_len)
{
    PROV_DRBG *drbg = (PROV_DRBG *)vdrbg;

    return ossl_prov_drbg_reseed(drbg, prediction_resistance, ent, ent_len,
                                 adin, adin_len);
}

/*
 * SP800-90Ar1 10.1.2.5 HMAC_DRBG_Generate_Process:
 *
 * Generates pseudo random bytes and updates the internal K,V for the drbg.
 * out is a buffer to fill with outlen bytes of pseudo random data.
 * adin is an additional_input string of size adin_len that may be NULL.
 *
 * Returns zero if an error occurs otherwise it returns 1.
 */
int ossl_drbg_hmac_generate(PROV_DRBG_HMAC *hmac,
                            unsigned char *out, size_t outlen,
                            const unsigned char *adin, size_t adin_len)
{
    EVP_MAC_CTX *ctx = hmac->ctx;
    const unsigned char *temp = hmac->V;

    /* (Step 2) if adin != NULL then (K,V) = HMAC_DRBG_Update(adin, K, V) */
    if (adin != NULL
            && adin_len > 0
            && !drbg_hmac_update(hmac, adin, adin_len, NULL, 0, NULL, 0))
        return 0;

    /*
     * (Steps 3-5) temp = NULL
     *             while (len(temp) < outlen) {
     *                 V = HMAC(K, V)
     *                 temp = temp || V
     *             }
     */
    for (;;) {
        if (!EVP_MAC_init(ctx, hmac->K, hmac->blocklen, NULL)
            || !EVP_MAC_update(ctx, temp, hmac->blocklen))
            return 0;

        if (outlen > hmac->blocklen) {
            if (!EVP_MAC_final(ctx, out, NULL, outlen))
                return 0;
            temp = out;
        } else {
            if (!EVP_MAC_final(ctx, hmac->V, NULL, sizeof(hmac->V)))
                return 0;
            memcpy(out, hmac->V, outlen);
            break;
        }
        out += hmac->blocklen;
        outlen -= hmac->blocklen;
    }
    /* (Step 6) (K,V) = HMAC_DRBG_Update(adin, K, V) */
    if (!drbg_hmac_update(hmac, adin, adin_len, NULL, 0, NULL, 0))
        return 0;

    return 1;
}

static int drbg_hmac_generate(PROV_DRBG *drbg,
                              unsigned char *out, size_t outlen,
                              const unsigned char *adin, size_t adin_len)
{
    return ossl_drbg_hmac_generate((PROV_DRBG_HMAC *)drbg->data, out, outlen,
                                    adin, adin_len);
}

static int drbg_hmac_generate_wrapper(void *vdrbg,
     unsigned char *out, size_t outlen, unsigned int strength,
     int prediction_resistance, const unsigned char *adin, size_t adin_len)
{
    PROV_DRBG *drbg = (PROV_DRBG *)vdrbg;

    return ossl_prov_drbg_generate(drbg, out, outlen, strength,
                                   prediction_resistance, adin, adin_len);
}

static int drbg_hmac_uninstantiate(PROV_DRBG *drbg)
{
    PROV_DRBG_HMAC *hmac = (PROV_DRBG_HMAC *)drbg->data;

    OPENSSL_cleanse(hmac->K, sizeof(hmac->K));
    OPENSSL_cleanse(hmac->V, sizeof(hmac->V));
    return ossl_prov_drbg_uninstantiate(drbg);
}

static int drbg_hmac_uninstantiate_wrapper(void *vdrbg)
{
    PROV_DRBG *drbg = (PROV_DRBG *)vdrbg;
    int ret;

    if (drbg->lock != NULL && !CRYPTO_THREAD_write_lock(drbg->lock))
        return 0;

    ret = drbg_hmac_uninstantiate(drbg);

    if (drbg->lock != NULL)
        CRYPTO_THREAD_unlock(drbg->lock);

    return ret;
}

static int drbg_hmac_verify_zeroization(void *vdrbg)
{
    PROV_DRBG *drbg = (PROV_DRBG *)vdrbg;
    PROV_DRBG_HMAC *hmac = (PROV_DRBG_HMAC *)drbg->data;
    int ret = 0;

    if (drbg->lock != NULL && !CRYPTO_THREAD_read_lock(drbg->lock))
        return 0;

    PROV_DRBG_VERIFY_ZEROIZATION(hmac->K);
    PROV_DRBG_VERIFY_ZEROIZATION(hmac->V);

    ret = 1;
 err:
    if (drbg->lock != NULL)
        CRYPTO_THREAD_unlock(drbg->lock);
    return ret;
}

static int drbg_hmac_new(PROV_DRBG *drbg)
{
    PROV_DRBG_HMAC *hmac;

    hmac = OPENSSL_secure_zalloc(sizeof(*hmac));
    if (hmac == NULL)
        return 0;

    OSSL_FIPS_IND_INIT(drbg)

    drbg->data = hmac;
    /* See SP800-57 Part1 Rev4 5.6.1 Table 3 */
    drbg->max_entropylen = DRBG_MAX_LENGTH;
    drbg->max_noncelen = DRBG_MAX_LENGTH;
    drbg->max_perslen = DRBG_MAX_LENGTH;
    drbg->max_adinlen = DRBG_MAX_LENGTH;

    /* Maximum number of bits per request = 2^19  = 2^16 bytes */
    drbg->max_request = 1 << 16;
    return 1;
}

static void *drbg_hmac_new_wrapper(void *provctx, void *parent,
                                   const OSSL_DISPATCH *parent_dispatch)
{
    return ossl_rand_drbg_new(provctx, parent, parent_dispatch,
                              &drbg_hmac_new, &drbg_hmac_free,
                              &drbg_hmac_instantiate, &drbg_hmac_uninstantiate,
                              &drbg_hmac_reseed, &drbg_hmac_generate);
}

static void drbg_hmac_free(void *vdrbg)
{
    PROV_DRBG *drbg = (PROV_DRBG *)vdrbg;
    PROV_DRBG_HMAC *hmac;

    if (drbg != NULL && (hmac = (PROV_DRBG_HMAC *)drbg->data) != NULL) {
        EVP_MAC_CTX_free(hmac->ctx);
        ossl_prov_digest_reset(&hmac->digest);
        OPENSSL_secure_clear_free(hmac, sizeof(*hmac));
    }
    ossl_rand_drbg_free(drbg);
}

static int drbg_hmac_get_ctx_params(void *vdrbg, OSSL_PARAM params[])
{
    PROV_DRBG *drbg = (PROV_DRBG *)vdrbg;
    PROV_DRBG_HMAC *hmac = (PROV_DRBG_HMAC *)drbg->data;
    const char *name;
    const EVP_MD *md;
    OSSL_PARAM *p;
    int ret = 0, complete = 0;

    if (!ossl_drbg_get_ctx_params_no_lock(drbg, params, &complete))
        return 0;

    if (complete)
        return 1;

    if (drbg->lock != NULL && !CRYPTO_THREAD_read_lock(drbg->lock))
        return 0;

    p = OSSL_PARAM_locate(params, OSSL_DRBG_PARAM_MAC);
    if (p != NULL) {
        if (hmac->ctx == NULL)
            goto err;
        name = EVP_MAC_get0_name(EVP_MAC_CTX_get0_mac(hmac->ctx));
        if (!OSSL_PARAM_set_utf8_string(p, name))
            goto err;
    }

    p = OSSL_PARAM_locate(params, OSSL_DRBG_PARAM_DIGEST);
    if (p != NULL) {
        md = ossl_prov_digest_md(&hmac->digest);
        if (md == NULL || !OSSL_PARAM_set_utf8_string(p, EVP_MD_get0_name(md)))
            goto err;
    }

    ret = ossl_drbg_get_ctx_params(drbg, params);
 err:
    if (drbg->lock != NULL)
        CRYPTO_THREAD_unlock(drbg->lock);

    return ret;
}

static const OSSL_PARAM *drbg_hmac_gettable_ctx_params(ossl_unused void *vctx,
                                                       ossl_unused void *p_ctx)
{
    static const OSSL_PARAM known_gettable_ctx_params[] = {
        OSSL_PARAM_utf8_string(OSSL_DRBG_PARAM_MAC, NULL, 0),
        OSSL_PARAM_utf8_string(OSSL_DRBG_PARAM_DIGEST, NULL, 0),
        OSSL_PARAM_DRBG_GETTABLE_CTX_COMMON,
        OSSL_FIPS_IND_GETTABLE_CTX_PARAM()
        OSSL_PARAM_END
    };
    return known_gettable_ctx_params;
}

static int drbg_fetch_algs_from_prov(const OSSL_PARAM params[],
                                     OSSL_LIB_CTX *libctx,
                                     EVP_MAC_CTX **macctx,
                                     EVP_MD **digest)
{
    OSSL_PROVIDER *prov = NULL;
    const OSSL_PARAM *p;
    EVP_MD *md = NULL;
    EVP_MAC *mac = NULL;
    int ret = 0;

    if (macctx == NULL || digest == NULL)
        return 0;

    if ((p = OSSL_PARAM_locate_const(params,
                                     OSSL_PROV_PARAM_CORE_PROV_NAME)) == NULL)
        return 0;
    if (p->data_type != OSSL_PARAM_UTF8_STRING)
        return 0;
    if ((prov = ossl_provider_find(libctx, (const char *)p->data, 1)) == NULL)
        return 0;

    p = OSSL_PARAM_locate_const(params, OSSL_ALG_PARAM_DIGEST);
    if (p) {
        if (p->data_type != OSSL_PARAM_UTF8_STRING)
            goto done;

        md = evp_digest_fetch_from_prov(prov, (const char *)p->data, NULL);
        if (md) {
            EVP_MD_free(*digest);
            *digest = md;
        } else {
            goto done;
        }
    }

    p = OSSL_PARAM_locate_const(params, OSSL_ALG_PARAM_MAC);
    if (p == NULL) {
        ret = 1;
        goto done;
    }

    if (p->data_type != OSSL_PARAM_UTF8_STRING)
        goto done;

    EVP_MAC_CTX_free(*macctx);
    *macctx = NULL;

    mac = evp_mac_fetch_from_prov(prov, (const char *)p->data, NULL);
    if (mac) {
        *macctx = EVP_MAC_CTX_new(mac);
        /* The context holds on to the MAC */
        EVP_MAC_free(mac);
        ret = 1;
    }

done:
    ossl_provider_free(prov);
    return ret;
}

static int drbg_hmac_set_ctx_params_locked(void *vctx, const OSSL_PARAM params[])
{
    PROV_DRBG *ctx = (PROV_DRBG *)vctx;
    PROV_DRBG_HMAC *hmac = (PROV_DRBG_HMAC *)ctx->data;
    OSSL_LIB_CTX *libctx = PROV_LIBCTX_OF(ctx->provctx);
    EVP_MD *prov_md = NULL;
    const EVP_MD *md;
    int md_size;

    if (!OSSL_FIPS_IND_SET_CTX_PARAM(ctx, OSSL_FIPS_IND_SETTABLE0, params,
                                     OSSL_DRBG_PARAM_FIPS_DIGEST_CHECK))
        return 0;

    /* try to fetch mac and digest from provider */
    (void)ERR_set_mark();
    if (!drbg_fetch_algs_from_prov(params, libctx, &hmac->ctx, &prov_md)) {
        (void)ERR_pop_to_mark();
        /* fall back to full implementation search */
        if (!ossl_prov_digest_load_from_params(&hmac->digest, params, libctx))
            return 0;

        if (!ossl_prov_macctx_load_from_params(&hmac->ctx, params,
                                               NULL, NULL, NULL, libctx))
            return 0;
    } else {
        (void)ERR_clear_last_mark();
        if (prov_md)
            ossl_prov_digest_set_md(&hmac->digest, prov_md);
    }

    md = ossl_prov_digest_md(&hmac->digest);
    if (md != NULL && !ossl_drbg_verify_digest(ctx, libctx, md))
        return 0;   /* Error already raised for us */

    if (md != NULL && hmac->ctx != NULL) {
        /* These are taken from SP 800-90 10.1 Table 2 */
        md_size = EVP_MD_get_size(md);
        if (md_size <= 0)
            return 0;
        hmac->blocklen = (size_t)md_size;
        /* See SP800-57 Part1 Rev4 5.6.1 Table 3 */
        ctx->strength = 64 * (int)(hmac->blocklen >> 3);
        if (ctx->strength > 256)
            ctx->strength = 256;
        ctx->seedlen = hmac->blocklen;
        ctx->min_entropylen = ctx->strength / 8;
        ctx->min_noncelen = ctx->min_entropylen / 2;
    }

    return ossl_drbg_set_ctx_params(ctx, params);
}

static int drbg_hmac_set_ctx_params(void *vctx, const OSSL_PARAM params[])
{
    PROV_DRBG *drbg = (PROV_DRBG *)vctx;
    int ret;

    if (drbg->lock != NULL && !CRYPTO_THREAD_write_lock(drbg->lock))
        return 0;

    ret = drbg_hmac_set_ctx_params_locked(vctx, params);

    if (drbg->lock != NULL)
        CRYPTO_THREAD_unlock(drbg->lock);

    return ret;
}

static const OSSL_PARAM *drbg_hmac_settable_ctx_params(ossl_unused void *vctx,
                                                       ossl_unused void *p_ctx)
{
    static const OSSL_PARAM known_settable_ctx_params[] = {
        OSSL_PARAM_utf8_string(OSSL_DRBG_PARAM_PROPERTIES, NULL, 0),
        OSSL_PARAM_utf8_string(OSSL_DRBG_PARAM_DIGEST, NULL, 0),
        OSSL_PARAM_utf8_string(OSSL_DRBG_PARAM_MAC, NULL, 0),
        OSSL_PARAM_DRBG_SETTABLE_CTX_COMMON,
        OSSL_FIPS_IND_SETTABLE_CTX_PARAM(OSSL_DRBG_PARAM_FIPS_DIGEST_CHECK)
        OSSL_PARAM_END
    };
    return known_settable_ctx_params;
}

const OSSL_DISPATCH ossl_drbg_ossl_hmac_functions[] = {
    { OSSL_FUNC_RAND_NEWCTX, (void(*)(void))drbg_hmac_new_wrapper },
    { OSSL_FUNC_RAND_FREECTX, (void(*)(void))drbg_hmac_free },
    { OSSL_FUNC_RAND_INSTANTIATE,
      (void(*)(void))drbg_hmac_instantiate_wrapper },
    { OSSL_FUNC_RAND_UNINSTANTIATE,
      (void(*)(void))drbg_hmac_uninstantiate_wrapper },
    { OSSL_FUNC_RAND_GENERATE, (void(*)(void))drbg_hmac_generate_wrapper },
    { OSSL_FUNC_RAND_RESEED, (void(*)(void))drbg_hmac_reseed_wrapper },
    { OSSL_FUNC_RAND_ENABLE_LOCKING, (void(*)(void))ossl_drbg_enable_locking },
    { OSSL_FUNC_RAND_LOCK, (void(*)(void))ossl_drbg_lock },
    { OSSL_FUNC_RAND_UNLOCK, (void(*)(void))ossl_drbg_unlock },
    { OSSL_FUNC_RAND_SETTABLE_CTX_PARAMS,
      (void(*)(void))drbg_hmac_settable_ctx_params },
    { OSSL_FUNC_RAND_SET_CTX_PARAMS, (void(*)(void))drbg_hmac_set_ctx_params },
    { OSSL_FUNC_RAND_GETTABLE_CTX_PARAMS,
      (void(*)(void))drbg_hmac_gettable_ctx_params },
    { OSSL_FUNC_RAND_GET_CTX_PARAMS, (void(*)(void))drbg_hmac_get_ctx_params },
    { OSSL_FUNC_RAND_VERIFY_ZEROIZATION,
      (void(*)(void))drbg_hmac_verify_zeroization },
    { OSSL_FUNC_RAND_GET_SEED, (void(*)(void))ossl_drbg_get_seed },
    { OSSL_FUNC_RAND_CLEAR_SEED, (void(*)(void))ossl_drbg_clear_seed },
    OSSL_DISPATCH_END
};