- NAME
- DESCRIPTION
  - Identity
  - Supported parameters
- NOTES
- EXAMPLES
- CONFORMING TO
- SEE ALSO
- COPYRIGHT

# NAME

EVP_RAND-HMAC-DRBG - The HMAC DRBG EVP_RAND implementation

# DESCRIPTION

Support for the HMAC deterministic random bit generator through the EVP_RAND API.

## Identity

"HMAC-DRBG" is the name for this implementation; it can be used with the EVP_RAND_fetch() function.

## Supported parameters

The supported parameters are:

"state" (OSSL_RAND_PARAM_STATE) <integer>
"strength" (OSSL_RAND_PARAM_STRENGTH) <unsigned integer>
"max_request" (OSSL_RAND_PARAM_MAX_REQUEST) <unsigned integer>
"reseed_requests" (OSSL_DRBG_PARAM_RESEED_REQUESTS) <unsigned integer>
"reseed_time_interval" (OSSL_DRBG_PARAM_RESEED_TIME_INTERVAL) <integer>
"min_entropylen" (OSSL_DRBG_PARAM_MIN_ENTROPYLEN) <unsigned integer>
"max_entropylen" (OSSL_DRBG_PARAM_MAX_ENTROPYLEN) <unsigned integer>
"min_noncelen" (OSSL_DRBG_PARAM_MIN_NONCELEN) <unsigned integer>
"max_noncelen" (OSSL_DRBG_PARAM_MAX_NONCELEN) <unsigned integer>
"max_perslen" (OSSL_DRBG_PARAM_MAX_PERSLEN) <unsigned integer>
"max_adinlen" (OSSL_DRBG_PARAM_MAX_ADINLEN) <unsigned integer>
"reseed_counter" (OSSL_DRBG_PARAM_RESEED_COUNTER) <unsigned integer>
"properties" (OSSL_DRBG_PARAM_PROPERTIES) <UTF8 string>
"mac" (OSSL_DRBG_PARAM_MAC) <UTF8 string>
"digest" (OSSL_DRBG_PARAM_DIGEST) <UTF8 string>

  These parameters work as described in "PARAMETERS" in EVP_RAND(3).

# NOTES

A context for HMAC DRBG can be obtained by calling:

     EVP_RAND *rand = EVP_RAND_fetch(NULL, "HMAC-DRBG", NULL);
     EVP_RAND_CTX *rctx = EVP_RAND_CTX_new(rand);

# EXAMPLES

     EVP_RAND *rand;
     EVP_RAND_CTX *rctx;
     unsigned char bytes[100];
     OSSL_PARAM params[3], *p = params;
     unsigned int strength = 128;

     rand = EVP_RAND_fetch(NULL, "HMAC-DRBG", NULL);
     rctx = EVP_RAND_CTX_new(rand, NULL);
     EVP_RAND_free(rand);

     *p++ = OSSL_PARAM_construct_utf8_string(OSSL_DRBG_PARAM_MAC, SN_hmac, 0);
     *p++ = OSSL_PARAM_construct_utf8_string(OSSL_DRBG_PARAM_DIGEST, SN_sha256, 0);
     *p = OSSL_PARAM_construct_end();
     EVP_RAND_instantiate(rctx, strength, 0, NULL, 0, params);

     EVP_RAND_generate(rctx, bytes, sizeof(bytes), strength, 0, NULL, 0);

     EVP_RAND_CTX_free(rctx);

# CONFORMING TO

NIST SP 800-90A and SP 800-90B

# SEE ALSO

EVP_RAND(3), "PARAMETERS" in EVP_RAND(3)

# COPYRIGHT

Copyright 2020-2021 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.