=pod

=head1 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_set_callbacks,
EVP_RAND_verify_zeroization, EVP_RAND_strength, EVP_RAND_state,
EVP_RAND_provider, EVP_RAND_CTX_rand, EVP_RAND_is_a, EVP_RAND_number,
EVP_RAND_name, EVP_RAND_names_do_all, EVP_RAND_get_ctx_params,
EVP_RAND_set_ctx_params, EVP_RAND_do_all_provided, EVP_RAND_get_params,
EVP_RAND_gettable_ctx_params, EVP_RAND_settable_ctx_params,
EVP_RAND_gettable_params, EVP_RAND_STATE_UNINITIALISED, EVP_RAND_STATE_READY,
EVP_RAND_STATE_ERROR - EVP RAND routines

=head1 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(OPENSSL_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_rand(EVP_RAND_CTX *ctx);
 int EVP_RAND_get_params(EVP_RAND *rand, OSSL_PARAM params[]);
 int EVP_RAND_get_ctx_params(EVP_RAND_CTX *ctx, OSSL_PARAM params[]);
 int EVP_RAND_set_ctx_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);
 int EVP_RAND_number(const EVP_RAND *rand);
 const char *EVP_RAND_name(const EVP_RAND *rand);
 int EVP_RAND_is_a(const EVP_RAND *rand, const char *name);
 const OSSL_PROVIDER *EVP_RAND_provider(const EVP_RAND *rand);
 void EVP_RAND_do_all_provided(OPENSSL_CTX *libctx,
                               void (*fn)(EVP_RAND *rand, void *arg),
                               void *arg);
 void 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);
 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_set_callbacks(EVP_RAND_CTX *ctx, OSSL_CALLBACK *get_entropy,
                            OSSL_CALLBACK *cleanup_entropy,
                            OSSL_CALLBACK *get_nonce,
                            OSSL_CALLBACK *cleanup_nonce, void *arg);
 int EVP_RAND_verify_zeroization(EVP_RAND_CTX *ctx);
 unsigned int EVP_RAND_strength(EVP_RAND_CTX *ctx);
 int EVP_RAND_state(EVP_RAND_CTX *ctx);

 #define EVP_RAND_STATE_UNINITIALISED    0
 #define EVP_RAND_STATE_READY            1
 #define EVP_RAND_STATE_ERROR            2

=head1 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 B<EVP_RAND_CTX> for the required algorithm using
EVP_RAND_CTX_new(), inputs to the algorithm are supplied
using calls to EVP_RAND_set_ctx_params() before
calling EVP_RAND_instantiate() and then EVP_RAND_generate() to produce
cryptographically secure random bytes.

=head2 Types

B<EVP_RAND> is a type that holds the implementation of a RAND.

B<EVP_RAND_CTX> is a context type that holds the algorithm inputs.

=head2 Algorithm implementation fetching

EVP_RAND_fetch() fetches an implementation of a RAND I<algorithm>, given
a library context I<libctx> and a set of I<properties>.
See L<provider(7)/Fetching algorithms> for further information.

The returned value must eventually be freed with
L<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.

=head2 Context manipulation functions

EVP_RAND_CTX_new() creates a new context for the RAND implementation I<rand>.
If not NULL, I<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 I<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 I<ctx>.  If I<ctx> is NULL, nothing
is done.

EVP_RAND_CTX_rand() returns the B<EVP_RAND> associated with the context
I<ctx>.

=head2 Random Number Generator Functions

EVP_RAND_instantiate() instantiates the RAND I<ctx> with a minimum security
strength of <strength> and personalisation string I<pstr> of length <pstr_len>.
If I<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 I<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 I<ctx> with the
additional input I<addin> of length I<addin_len>.  The bytes
produced will meet the security I<strength>.
If I<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 I<ent> of length I<ent_len> bytes can be supplied as can additional
input I<addin> of length I<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 I<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 I<out> of maximum length I<outlen>
bytes from the RAND I<ctx>. The function returns the length of the generated
nonce. If I<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 I<ctx> and all of
its parents.  After this I<ctx> will operate in a thread safe manner, albeit
more slowly.

EVP_RAND_set_callbacks() sets callbacks on the RAND I<ctx> to accept
external entropy and nonce input.  The callback I<get_entropy> fills a buffer
with new randomness and the callback I<cleanup_entropy> clears and frees the
buffer.  Likewise for I<get_nonce> and I<cleanup_nonce>.  In all cases the
callbacks are passed I<arg> in addition to an OSSL_PARAM array.

EVP_RAND_get_params() retrieves details about the implementation
I<rand>.
The set of parameters given with I<params> determine exactly what
parameters should be retrieved.
Note that a parameter that is unknown in the underlying context is
simply ignored.

EVP_RAND_get_ctx_params() retrieves chosen parameters, given the
context I<ctx> and its underlying context.
The set of parameters given with I<params> determine exactly what
parameters should be retrieved.
Note that a parameter that is unknown in the underlying context is
simply ignored.

EVP_RAND_set_ctx_params() passes chosen parameters to the underlying
context, given a context I<ctx>.
The set of parameters given with I<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(), EVP_RAND_gettable_ctx_params() and
EVP_RAND_settable_ctx_params() get a constant B<OSSL_PARAM> array that
describes the retrievable and settable parameters, i.e. parameters that
can be used with EVP_RAND_get_params(), EVP_RAND_get_ctx_params()
and EVP_RAND_set_ctx_params(), respectively.
See L<OSSL_PARAM(3)> for the use of B<OSSL_PARAM> as parameter descriptor.

=head2 Information functions

EVP_RAND_strength() returns the security strength of the RAND I<ctx>.

EVP_RAND_state() returns the current state of the RAND I<ctx>.
States defined by the OpenSSL DRBGs are:

=over 4

=item *

EVP_RAND_STATE_UNINITIALISED: this DRBG is currently uninitalised.
The instantiate call will change this to the ready state.

=item *

EVP_RAND_STATE_READY: this DRBG is currently ready to generate output.

=item *

EVP_RAND_STATE_ERROR: this DRBG is in an error state.

=back

EVP_RAND_is_a() returns 1 if I<rand> is an implementation of an
algorithm that's identifiable with I<name>, otherwise 0.

EVP_RAND_provider() returns the provider that holds the implementation
of the given I<rand>.

EVP_RAND_do_all_provided() traverses all RAND implemented by all activated
providers in the given library context I<libctx>, and for each of the
implementations, calls the given function I<fn> with the implementation method
and the given I<arg> as argument.

EVP_RAND_number() returns the internal dynamic number assigned to
I<rand>.

EVP_RAND_name() returns the canonical name of I<rand>.

EVP_RAND_names_do_all() traverses all names for I<rand>, and calls
I<fn> with each name and I<data>.

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.

=head1 PARAMETERS

The standard parameter names are:

=over 4

=item "state" (B<OSSL_RAND_PARAM_STATE>) <integer>

Returns the state of the random number generator.

=item "strength" (B<OSSL_RAND_PARAM_STRENGTH>) <unsigned integer>

Returns the bit strength of the random number generator.

=back

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:

=over 4

=item "reseed_requests" (B<OSSL_DRBG_PARAM_RESEED_REQUESTS>) <unsigned integer>

Reads or set the number of generate requests before reseeding the
associated RAND ctx.

=item "reseed_time_interval" (B<OSSL_DRBG_PARAM_RESEED_TIME_INTERVAL>) <integer>

Reads or set the number of elapsed seconds before reseeding the
associated RAND ctx.

=item "max_request" (B<OSSL_DRBG_PARAM_RESEED_REQUESTS>) <unsigned integer>

Specifies the maximum number of bytes that can be generated in a single
call to OP_rand_generate.

=item "min_entropylen" (B<OSSL_DRBG_PARAM_MIN_ENTROPYLEN>) <unsigned integer>

=item "max_entropylen" (B<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.

=item "min_noncelen" (B<OSSL_DRBG_PARAM_MIN_NONCELEN>) <unsigned integer>

=item "max_noncelen" (B<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.

=item "max_perslen" (B<OSSL_DRBG_PARAM_MAX_PERSLEN>) <unsigned integer>

=item "max_adinlen" (B<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.

=item "reseed_counter" (B<OSSL_DRBG_PARAM_RESEED_CTR>) <unsigned integer>

Specifies the number of times the DRBG has been seeded or reseeded.

=item "properties" (B<OSSL_RAND_PARAM_PROPERTIES>) <UTF8 string>

=item "mac" (B<OSSL_RAND_PARAM_MAC>) <UTF8 string>

=item "digest" (B<OSSL_RAND_PARAM_DIGEST>) <UTF8 string>

=item "cipher" (B<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 B<OSSL_RAND_PARAM_PROPERTIES>.

=back

=head1 RETURN VALUES

EVP_RAND_fetch() returns a pointer to a newly fetched B<EVP_RAND>, or
NULL if allocation failed.

EVP_RAND_provider() returns a pointer to the provider for the RAND, or
NULL on error.

EVP_RAND_CTX_rand() returns a pointer to the B<EVP_RAND> associated with the
context.

EVP_RAND_name() returns the name of the random number generation algorithm.

EVP_RAND_number() returns the provider specific identification number
for the specified algorithm.

EVP_RAND_up_ref() returns 1 on success, 0 on error.

EVP_RAND_CTX_new() returns either the newly allocated
B<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_strength() returns the strenght 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.

=head1 SEE ALSO

L<RAND_bytes(3)>,
L<EVP_RAND-CTR-DRBG(7)>,
L<EVP_RAND-HASH-DRBG(7)>,
L<EVP_RAND-HMAC-DRBG(7)>,
L<EVP_RAND-TEST-RAND(7)>,
L<provider-rand(7)>

=head1 HISTORY

This functionality was added to OpenSSL 3.0.

=head1 COPYRIGHT

Copyright 2020 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
L<https://www.openssl.org/source/license.html>.

=cut