EVP_RAND-CTR-DRBG(7ossl) OpenSSL EVP_RAND-CTR-DRBG(7ossl)
NAME
EVP_RAND-CTR-DRBG - The CTR DRBG EVP_RAND implementation
DESCRIPTION
Support for the counter deterministic random bit generator through the
EVP_RAND API.
Identity
"CTR-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>
"cipher" (OSSL_DRBG_PARAM_CIPHER) <UTF8 string>
These parameters work as described in "PARAMETERS" in EVP_RAND(3).
"use_derivation_function" (OSSL_DRBG_PARAM_USE_DF) <integer>
This Boolean indicates if a derivation function should be used or
not. A nonzero value (the default) uses the derivation function. A
zero value does not.
"fips-indicator" (OSSL_DRBG_PARAM_FIPS_APPROVED_INDICATOR) <integer>
The OpenSSL FIPS provider returns 1 if the operation is FIPS
approved, or 0 otherwise. See "FIPS indicators" in fips_module(7)
for more information.
NOTES
A context for CTR DRBG can be obtained by calling:
EVP_RAND *rand = EVP_RAND_fetch(NULL, "CTR-DRBG", NULL);
EVP_RAND_CTX *rctx = EVP_RAND_CTX_new(rand, NULL);
The default CTR-DRBG implementation attempts to fetch the required
internal algorithms from the provider they are built into (eg the default
provider) regardless of the properties provided. Should the provider not
implement the required algorithms then properties will be used to find a
different implementation.
EXAMPLES
EVP_RAND *rand;
EVP_RAND_CTX *rctx;
unsigned char bytes[100];
OSSL_PARAM params[2], *p = params;
unsigned int strength = 128;
rand = EVP_RAND_fetch(NULL, "CTR-DRBG", NULL);
rctx = EVP_RAND_CTX_new(rand, NULL);
EVP_RAND_free(rand);
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_DRBG_PARAM_CIPHER,
SN_aes_256_ctr, 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 2020-2026 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>.
3.6.5 2026-09-29 EVP_RAND-CTR-DRBG(7ossl)
openssl 3.6.5 - Generated Sat Oct 3 09:49:13 CDT 2026