Updated: 2022/Sep/29
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EVP_RAND(3) OpenSSL EVP_RAND(3)
NAME
EVP_RAND, EVP_RAND_fetch, EVP_RAND_free, EVP_RAND_up_ref, EVP_RAND_CTX,
EVP_RAND_CTX_new, EVP_RAND_CTX_free, EVP_RAND_instantiate,
EVP_RAND_uninstantiate, EVP_RAND_generate, EVP_RAND_reseed,
EVP_RAND_nonce, EVP_RAND_enable_locking, EVP_RAND_verify_zeroization,
EVP_RAND_get_strength, EVP_RAND_get_state, EVP_RAND_get0_provider,
EVP_RAND_CTX_get0_rand, EVP_RAND_is_a, EVP_RAND_get0_name,
EVP_RAND_names_do_all, EVP_RAND_get0_description,
EVP_RAND_CTX_get_params, EVP_RAND_CTX_set_params,
EVP_RAND_do_all_provided, EVP_RAND_get_params,
EVP_RAND_gettable_ctx_params, EVP_RAND_settable_ctx_params,
EVP_RAND_CTX_gettable_params, EVP_RAND_CTX_settable_params,
EVP_RAND_gettable_params, EVP_RAND_STATE_UNINITIALISED,
EVP_RAND_STATE_READY, EVP_RAND_STATE_ERROR - EVP RAND routines
LIBRARY
libcrypto, -lcrypto
SYNOPSIS
#include <openssl/evp.h>
typedef struct evp_rand_st EVP_RAND;
typedef struct evp_rand_ctx_st EVP_RAND_CTX;
EVP_RAND *EVP_RAND_fetch(OSSL_LIB_CTX *libctx, const char *algorithm,
const char *properties);
int EVP_RAND_up_ref(EVP_RAND *rand);
void EVP_RAND_free(EVP_RAND *rand);
EVP_RAND_CTX *EVP_RAND_CTX_new(EVP_RAND *rand, EVP_RAND_CTX *parent);
void EVP_RAND_CTX_free(EVP_RAND_CTX *ctx);
EVP_RAND *EVP_RAND_CTX_get0_rand(EVP_RAND_CTX *ctx);
int EVP_RAND_get_params(EVP_RAND *rand, OSSL_PARAM params[]);
int EVP_RAND_CTX_get_params(EVP_RAND_CTX *ctx, OSSL_PARAM params[]);
int EVP_RAND_CTX_set_params(EVP_RAND_CTX *ctx, const OSSL_PARAM params[]);
const OSSL_PARAM *EVP_RAND_gettable_params(const EVP_RAND *rand);
const OSSL_PARAM *EVP_RAND_gettable_ctx_params(const EVP_RAND *rand);
const OSSL_PARAM *EVP_RAND_settable_ctx_params(const EVP_RAND *rand);
const OSSL_PARAM *EVP_RAND_CTX_gettable_params(EVP_RAND_CTX *ctx);
const OSSL_PARAM *EVP_RAND_CTX_settable_params(EVP_RAND_CTX *ctx);
const char *EVP_RAND_get0_name(const EVP_RAND *rand);
const char *EVP_RAND_get0_description(const EVP_RAND *rand);
int EVP_RAND_is_a(const EVP_RAND *rand, const char *name);
const OSSL_PROVIDER *EVP_RAND_get0_provider(const EVP_RAND *rand);
void EVP_RAND_do_all_provided(OSSL_LIB_CTX *libctx,
void (*fn)(EVP_RAND *rand, void *arg),
void *arg);
int EVP_RAND_names_do_all(const EVP_RAND *rand,
void (*fn)(const char *name, void *data),
void *data);
int EVP_RAND_instantiate(EVP_RAND_CTX *ctx, unsigned int strength,
int prediction_resistance,
const unsigned char *pstr, size_t pstr_len,
const OSSL_PARAM params[]);
int EVP_RAND_uninstantiate(EVP_RAND_CTX *ctx);
int EVP_RAND_generate(EVP_RAND_CTX *ctx, unsigned char *out, size_t outlen,
unsigned int strength, int prediction_resistance,
const unsigned char *addin, size_t addin_len);
int EVP_RAND_reseed(EVP_RAND_CTX *ctx, int prediction_resistance,
const unsigned char *ent, size_t ent_len,
const unsigned char *addin, size_t addin_len);
int EVP_RAND_nonce(EVP_RAND_CTX *ctx, unsigned char *out, size_t outlen);
int EVP_RAND_enable_locking(EVP_RAND_CTX *ctx);
int EVP_RAND_verify_zeroization(EVP_RAND_CTX *ctx);
unsigned int EVP_RAND_get_strength(EVP_RAND_CTX *ctx);
int EVP_RAND_get_state(EVP_RAND_CTX *ctx);
#define EVP_RAND_STATE_UNINITIALISED 0
#define EVP_RAND_STATE_READY 1
#define EVP_RAND_STATE_ERROR 2
DESCRIPTION
The EVP RAND routines are a high-level interface to random number
generators both deterministic and not. If you just want to generate
random bytes then you don't need to use these functions: just call
RAND_bytes() or RAND_priv_bytes(). If you want to do more, these calls
should be used instead of the older RAND and RAND_DRBG functions.
After creating a EVP_RAND_CTX for the required algorithm using
EVP_RAND_CTX_new(), inputs to the algorithm are supplied either by
passing them as part of the EVP_RAND_instantiate() call or using calls
to EVP_RAND_CTX_set_params() before calling EVP_RAND_instantiate().
Finally, call EVP_RAND_generate() to produce cryptographically secure
random bytes.
Types
EVP_RAND is a type that holds the implementation of a RAND.
EVP_RAND_CTX is a context type that holds the algorithm inputs.
EVP_RAND_CTX structures are reference counted.
Algorithm implementation fetching
EVP_RAND_fetch() fetches an implementation of a RAND algorithm, given a
library context libctx and a set of properties. See "ALGORITHM
FETCHING" in crypto(7) for further information.
The returned value must eventually be freed with EVP_RAND_free(3).
EVP_RAND_up_ref() increments the reference count of an already fetched
RAND.
EVP_RAND_free() frees a fetched algorithm. NULL is a valid parameter,
for which this function is a no-op.
Context manipulation functions
EVP_RAND_CTX_new() creates a new context for the RAND implementation
rand. If not NULL, parent specifies the seed source for this
implementation. Not all random number generators need to have a seed
source specified. If a parent is required, a NULL parent will utilise
the operating system entropy sources. It is recommended to minimise
the number of random number generators that rely on the operating
system for their randomness because this is often scarce.
EVP_RAND_CTX_free() frees up the context ctx. If ctx is NULL, nothing
is done.
EVP_RAND_CTX_get0_rand() returns the EVP_RAND associated with the
context ctx.
Random Number Generator Functions
EVP_RAND_instantiate() processes any parameters in params and then
instantiates the RAND ctx with a minimum security strength of
<strength> and personalisation string pstr of length <pstr_len>. If
prediction_resistance is specified, fresh entropy from a live source
will be sought. This call operates as per NIST SP 800-90A and SP
800-90C.
EVP_RAND_uninstantiate() uninstantiates the RAND ctx as per NIST SP
800-90A and SP 800-90C. Subsequent to this call, the RAND cannot be
used to generate bytes. It can only be freed or instantiated again.
EVP_RAND_generate() produces random bytes from the RAND ctx with the
additional input addin of length addin_len. The bytes produced will
meet the security strength. If prediction_resistance is specified,
fresh entropy from a live source will be sought. This call operates as
per NIST SP 800-90A and SP 800-90C.
EVP_RAND_reseed() reseeds the RAND with new entropy. Entropy ent of
length ent_len bytes can be supplied as can additional input addin of
length addin_len bytes. In the FIPS provider, both are treated as
additional input as per NIST SP-800-90Ar1, Sections 9.1 and 9.2.
Additional seed material is also drawn from the RAND's parent or the
operating system. If prediction_resistance is specified, fresh entropy
from a live source will be sought. This call operates as per NIST SP
800-90A and SP 800-90C.
EVP_RAND_nonce() creates a nonce in out of maximum length outlen bytes
from the RAND ctx. The function returns the length of the generated
nonce. If out is NULL, the length is still returned but no generation
takes place. This allows a caller to dynamically allocate a buffer of
the appropriate size.
EVP_RAND_enable_locking() enables locking for the RAND ctx and all of
its parents. After this ctx will operate in a thread safe manner,
albeit more slowly. This function is not itself thread safe if called
with the same ctx from multiple threads. Typically locking should be
enabled before a ctx is shared across multiple threads.
EVP_RAND_get_params() retrieves details about the implementation rand.
The set of parameters given with params determine exactly what
parameters should be retrieved. Note that a parameter that is unknown
in the underlying context is simply ignored.
EVP_RAND_CTX_get_params() retrieves chosen parameters, given the
context ctx and its underlying context. The set of parameters given
with params determine exactly what parameters should be retrieved.
Note that a parameter that is unknown in the underlying context is
simply ignored.
EVP_RAND_CTX_set_params() passes chosen parameters to the underlying
context, given a context ctx. The set of parameters given with params
determine exactly what parameters are passed down. Note that a
parameter that is unknown in the underlying context is simply ignored.
Also, what happens when a needed parameter isn't passed down is defined
by the implementation.
EVP_RAND_gettable_params() returns an OSSL_PARAM(3) array that
describes the retrievable and settable parameters.
EVP_RAND_gettable_params() returns parameters that can be used with
EVP_RAND_get_params().
EVP_RAND_gettable_ctx_params() and EVP_RAND_CTX_gettable_params()
return constant OSSL_PARAM(3) arrays that describe the retrievable
parameters that can be used with EVP_RAND_CTX_get_params().
EVP_RAND_gettable_ctx_params() returns the parameters that can be
retrieved from the algorithm, whereas EVP_RAND_CTX_gettable_params()
returns the parameters that can be retrieved in the context's current
state.
EVP_RAND_settable_ctx_params() and EVP_RAND_CTX_settable_params()
return constant OSSL_PARAM(3) arrays that describe the settable
parameters that can be used with EVP_RAND_CTX_set_params().
EVP_RAND_settable_ctx_params() returns the parameters that can be
retrieved from the algorithm, whereas EVP_RAND_CTX_settable_params()
returns the parameters that can be retrieved in the context's current
state.
Information functions
EVP_RAND_get_strength() returns the security strength of the RAND ctx.
EVP_RAND_get_state() returns the current state of the RAND ctx. States
defined by the OpenSSL RNGs are:
⊕ EVP_RAND_STATE_UNINITIALISED: this RNG is currently uninitialised.
The instantiate call will change this to the ready state.
⊕ EVP_RAND_STATE_READY: this RNG is currently ready to generate
output.
⊕ EVP_RAND_STATE_ERROR: this RNG is in an error state.
EVP_RAND_is_a() returns 1 if rand is an implementation of an algorithm
that's identifiable with name, otherwise 0.
EVP_RAND_get0_provider() returns the provider that holds the
implementation of the given rand.
EVP_RAND_do_all_provided() traverses all RAND implemented by all
activated providers in the given library context libctx, and for each
of the implementations, calls the given function fn with the
implementation method and the given arg as argument.
EVP_RAND_get0_name() returns the canonical name of rand.
EVP_RAND_names_do_all() traverses all names for rand, and calls fn with
each name and data.
EVP_RAND_get0_description() returns a description of the rand, meant
for display and human consumption. The description is at the
discretion of the rand implementation.
EVP_RAND_verify_zeroization() confirms if the internal DRBG state is
currently zeroed. This is used by the FIPS provider to support the
mandatory self tests.
PARAMETERS
The standard parameter names are:
"state" (OSSL_RAND_PARAM_STATE) <integer>
Returns the state of the random number generator.
"strength" (OSSL_RAND_PARAM_STRENGTH) <unsigned integer>
Returns the bit strength of the random number generator.
For rands that are also deterministic random bit generators (DRBGs),
these additional parameters are recognised. Not all parameters are
relevant to, or are understood by all DRBG rands:
"reseed_requests" (OSSL_DRBG_PARAM_RESEED_REQUESTS) <unsigned integer>
Reads or set the number of generate requests before reseeding the
associated RAND ctx.
"reseed_time_interval" (OSSL_DRBG_PARAM_RESEED_TIME_INTERVAL) <integer>
Reads or set the number of elapsed seconds before reseeding the
associated RAND ctx.
"max_request" (OSSL_DRBG_PARAM_RESEED_REQUESTS) <unsigned integer>
Specifies the maximum number of bytes that can be generated in a
single call to OSSL_FUNC_rand_generate.
"min_entropylen" (OSSL_DRBG_PARAM_MIN_ENTROPYLEN) <unsigned integer>
"max_entropylen" (OSSL_DRBG_PARAM_MAX_ENTROPYLEN) <unsigned integer>
Specify the minimum and maximum number of bytes of random material
that can be used to seed the DRBG.
"min_noncelen" (OSSL_DRBG_PARAM_MIN_NONCELEN) <unsigned integer>
"max_noncelen" (OSSL_DRBG_PARAM_MAX_NONCELEN) <unsigned integer>
Specify the minimum and maximum number of bytes of nonce that can
be used to seed the DRBG.
"max_perslen" (OSSL_DRBG_PARAM_MAX_PERSLEN) <unsigned integer>
"max_adinlen" (OSSL_DRBG_PARAM_MAX_ADINLEN) <unsigned integer>
Specify the minimum and maximum number of bytes of personalisation
string that can be used with the DRBG.
"reseed_counter" (OSSL_DRBG_PARAM_RESEED_COUNTER) <unsigned integer>
Specifies the number of times the DRBG has been seeded or reseeded.
"properties" (OSSL_RAND_PARAM_PROPERTIES) <UTF8 string>
"mac" (OSSL_RAND_PARAM_MAC) <UTF8 string>
"digest" (OSSL_RAND_PARAM_DIGEST) <UTF8 string>
"cipher" (OSSL_RAND_PARAM_CIPHER) <UTF8 string>
For RAND implementations that use an underlying computation MAC,
digest or cipher, these parameters set what the algorithm should
be.
The value is always the name of the intended algorithm, or the
properties in the case of OSSL_RAND_PARAM_PROPERTIES.
NOTES
The use of a nonzero value for the prediction_resistance argument to
EVP_RAND_instantiate(), EVP_RAND_generate() or EVP_RAND_reseed() should
be used sparingly. In the default setup, this will cause all public
and private DRBGs to be reseeded on next use. Since, by default,
public and private DRBGs are allocated on a per thread basis, this can
result in significant overhead for highly multi-threaded applications.
For normal use-cases, the default "reseed_requests" and
"reseed_time_interval" thresholds ensure sufficient prediction
resistance over time and you can reduce those values if you think they
are too high. Explicitly requesting prediction resistance is intended
for more special use-cases like generating long-term secrets.
An EVP_RAND_CTX needs to have locking enabled if it acts as the parent
of more than one child and the children can be accessed concurrently.
This must be done by explicitly calling EVP_RAND_enable_locking().
The RAND life-cycle is described in life_cycle-rand(7). In the future,
the transitions described there will be enforced. When this is done,
it will not be considered a breaking change to the API.
RETURN VALUES
EVP_RAND_fetch() returns a pointer to a newly fetched EVP_RAND, or NULL
if allocation failed.
EVP_RAND_get0_provider() returns a pointer to the provider for the
RAND, or NULL on error.
EVP_RAND_CTX_get0_rand() returns a pointer to the EVP_RAND associated
with the context.
EVP_RAND_get0_name() returns the name of the random number generation
algorithm.
EVP_RAND_up_ref() returns 1 on success, 0 on error.
EVP_RAND_names_do_all() returns 1 if the callback was called for all
names. A return value of 0 means that the callback was not called for
any names.
EVP_RAND_CTX_new() returns either the newly allocated EVP_RAND_CTX
structure or NULL if an error occurred.
EVP_RAND_CTX_free() does not return a value.
EVP_RAND_nonce() returns the length of the nonce.
EVP_RAND_get_strength() returns the strength of the random number
generator in bits.
EVP_RAND_gettable_params(), EVP_RAND_gettable_ctx_params() and
EVP_RAND_settable_ctx_params() return an array of OSSL_PARAMs.
EVP_RAND_verify_zeroization() returns 1 if the internal DRBG state is
currently zeroed, and 0 if not.
The remaining functions return 1 for success and 0 or a negative value
for failure.
SEE ALSO
RAND_bytes(3), EVP_RAND-CTR-DRBG(7), EVP_RAND-HASH-DRBG(7),
EVP_RAND-HMAC-DRBG(7), EVP_RAND-TEST-RAND(7), provider-rand(7),
life_cycle-rand(7)
HISTORY
This functionality was added to OpenSSL 3.0.
COPYRIGHT
Copyright 2020-2023 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>.
3.0.12 2023-05-31 EVP_RAND(3)