=pod

=head1 NAME

provider-rand - The random number generation library E<lt>-E<gt> provider
functions

=head1 SYNOPSIS

=for openssl multiple includes

 #include <openssl/core_dispatch.h>
 #include <openssl/core_names.h>

 /*
  * None of these are actual functions, but are displayed like this for
  * the function signatures for functions that are offered as function
  * pointers in OSSL_DISPATCH arrays.
  */

 /* Context management */
 void *OSSL_FUNC_rand_newctx(void *provctx, void *parent,
                             const OSSL_DISPATCH *parent_calls);
 void OSSL_FUNC_rand_freectx(void *ctx);

 /* Random number generator functions: NIST */
 int OSSL_FUNC_rand_instantiate(void *ctx, unsigned int strength,
                                int prediction_resistance,
                                const unsigned char *pstr, size_t pstr_len);
 int OSSL_FUNC_rand_uninstantiate(void *ctx);
 int OSSL_FUNC_rand_generate(void *ctx, unsigned char *out, size_t outlen,
                             unsigned int strength, int prediction_resistance,
                             const unsigned char *addin, size_t addin_len);
 int OSSL_FUNC_rand_reseed(void *ctx, int prediction_resistance,
                           const unsigned char *ent, size_t ent_len,
                           const unsigned char *addin, size_t addin_len);

 /* Random number generator functions: additional */
 size_t OSSL_FUNC_rand_nonce(void *ctx, unsigned char *out, size_t outlen,
                             int strength, size_t min_noncelen, size_t max_noncelen);
 int OSSL_FUNC_rand_verify_zeroization(void *ctx);

 /* Context Locking */
 int OSSL_FUNC_rand_enable_locking(void *ctx);
 int OSSL_FUNC_rand_lock(void *ctx);
 void OSSL_FUNC_rand_unlock(void *ctx);

 /* RAND parameter descriptors */
 const OSSL_PARAM *OSSL_FUNC_rand_gettable_params(void *provctx);
 const OSSL_PARAM *OSSL_FUNC_rand_gettable_ctx_params(void *provctx);
 const OSSL_PARAM *OSSL_FUNC_rand_settable_ctx_params(void *provctx);

 /* RAND parameters */
 int OSSL_FUNC_rand_get_params(OSSL_PARAM params[]);
 int OSSL_FUNC_rand_get_ctx_params(void *ctx, OSSL_PARAM params[]);
 int OSSL_FUNC_rand_set_ctx_params(void *ctx, const OSSL_PARAM params[]);

=head1 DESCRIPTION

This documentation is primarily aimed at provider authors. See L<provider(7)>
for further information.

The RAND operation enables providers to implement random number generation
algorithms and random number sources and make
them available to applications via the API function L<EVP_RAND(3)>.

=head2 Context Management Functions

OSSL_FUNC_rand_newctx() should create and return a pointer to a provider side
structure for holding context information during a rand operation.
A pointer to this context will be passed back in a number of the other rand
operation function calls.
The parameter I<provctx> is the provider context generated during provider
initialisation (see L<provider(7)>).
The parameter I<parent> specifies another rand instance to be used for
seeding purposes.  If NULL and the specific instance supports it, the
operating system will be used for seeding.
The parameter I<parent_calls> points to the dispatch table for I<parent>.
Thus, the parent need not be from the same provider as the new instance.

OSSL_FUNC_rand_freectx() is passed a pointer to the provider side rand context in
the I<mctx> parameter.
If it receives NULL as I<ctx> value, it should not do anything other than
return.
This function should free any resources associated with that context.

=head2 Random Number Generator Functions: NIST

These functions correspond to those defined in NIST SP 800-90A and SP 800-90C.

OSSL_FUNC_rand_instantiate() is used to instantiate the DRBG I<ctx> at a requested
security I<strength>.  In addition, I<prediction_resistance> can be requested.
Additional input I<addin> of length I<addin_len> bytes can optionally
be provided.

OSSL_FUNC_rand_uninstantiate() is used to uninstantiate the DRBG I<ctx>.  After being
uninstantiated, a DRBG is unable to produce output until it is instantiated
anew.

OSSL_FUNC_rand_generate() is used to generate random bytes from the DRBG I<ctx>.
It will generate I<outlen> bytes placing them into the buffer pointed to by
I<out>.  The generated bytes will meet the specified security I<strength> and,
if I<prediction_resistance> is true, the bytes will be produced after reseeding
from a live entropy source.  Additional input I<addin> of length I<addin_len>
bytes can optionally be provided.

=head2 Random Number Generator Functions: Additional

OSSL_FUNC_rand_nonce() is used to generate a nonce of the given I<strength> with a
length from I<min_noncelen> to I<max_noncelen>. If the output buffer I<out> is
NULL, the length of the nonce should be returned.

OSSL_FUNC_rand_verify_zeroization() is used to determine if the internal state of the
DRBG is zero.  This capability is mandated by NIST as part of the self
tests, it is unlikely to be useful in other circumstances.

=head2 Context Locking

When DRBGs are used by multiple threads, there must be locking employed to
ensure their proper operation.  Because locking introduces an overhead, it
is disabled by default.

OSSL_FUNC_rand_enable_locking() allows locking to be turned on for a DRBG and all of
its parent DRBGs.  From this call onwards, the DRBG can be used in a thread
safe manner.

OSSL_FUNC_rand_lock() is used to lock a DRBG.  Once locked, exclusive access
is guaranteed.

OSSL_FUNC_rand_unlock() is used to unlock a DRBG.

=head2 Rand Parameters

See L<OSSL_PARAM(3)> for further details on the parameters structure used by
these functions.

OSSL_FUNC_rand_get_params() gets details of parameter values associated with the
provider algorithm and stores them in I<params>.

OSSL_FUNC_rand_set_ctx_params() sets rand parameters associated with the given
provider side rand context I<ctx> to I<params>.
Any parameter settings are additional to any that were previously set.

OSSL_FUNC_rand_get_ctx_params() gets details of currently set parameter values
associated with the given provider side rand context I<ctx> and stores them
in I<params>.

OSSL_FUNC_rand_gettable_params(), OSSL_FUNC_rand_gettable_ctx_params(), and
OSSL_FUNC_rand_settable_ctx_params() all return constant B<OSSL_PARAM> arrays
as descriptors of the parameters that OSSL_FUNC_rand_get_params(),
OSSL_FUNC_rand_get_ctx_params(), and OSSL_FUNC_rand_set_ctx_params() can handle,
respectively.

Parameters currently recognised by built-in rands are as follows. Not all
parameters are relevant to, or are understood by all rands:

=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 OSSL_FUNC_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
instantiate 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_COUNTER>) <unsigned integer>

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

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

=item "cipher" (B<OSSL_DRBG_PARAM_CIPHER>) <UTF8 string>

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

Sets the name of the underlying cipher, digest or MAC to be used.
It must name a suitable algorithm for the DRBG that's being used.

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

Sets the properties to be queried when trying to fetch an underlying algorithm.
This must be given together with the algorithm naming parameter to be
considered valid.

=back

=head1 RETURN VALUES

OSSL_FUNC_rand_newctx() should return the newly created
provider side rand context, or NULL on failure.

OSSL_FUNC_rand_gettable_params(), OSSL_FUNC_rand_gettable_ctx_params() and
OSSL_FUNC_rand_settable_ctx_params() should return a constant B<OSSL_PARAM>
array, or NULL if none is offered.

OSSL_FUNC_rand_nonce() returns the size of the generated nonce, or 0 on error.

All of the remaining functions should return 1 for success or 0 on error.

=head1 SEE ALSO

L<provider(7)>,
L<RAND(7)>,
L<EVP_RAND(7)>

=head1 HISTORY

The provider RAND interface was introduced in 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