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/*
* Copyright (C) Internet Systems Consortium, Inc. ("ISC")
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, you can obtain one at https://mozilla.org/MPL/2.0/.
*
* See the COPYRIGHT file distributed with this work for additional
* information regarding copyright ownership.
*/
#ifndef ISC_RANDOM_H
#define ISC_RANDOM_H 1
#include <isc/lang.h>
#include <isc/types.h>
#include <isc/entropy.h>
#include <isc/mem.h>
#include <isc/mutex.h>
/*! \file isc/random.h
* \brief Implements pseudo random number generators.
*
* Two pseudo-random number generators are implemented, in isc_random_*
* and isc_rng_*. Neither one is very strong; they should not be used
* in cryptography functions.
*
* isc_random_* is based on arc4random if it is available on the system.
* Otherwise it is based on the posix srand() and rand() functions.
* It is useful for jittering values a bit here and there, such as
* timeouts, etc, but should not be relied upon to generate
* unpredictable sequences (for example, when choosing transaction IDs).
*
* isc_rng_* is based on ChaCha20, and is seeded and stirred from the
* system entropy source. It is stronger than isc_random_* and can
* be used for generating unpredictable sequences. It is still not as
* good as using system entropy directly (see entropy.h) and should not
* be used for cryptographic functions such as key generation.
*/
ISC_LANG_BEGINDECLS
typedef struct isc_rng isc_rng_t;
/*%<
* Opaque type
*/
void
isc_random_seed(uint32_t seed);
/*%<
* Set the initial seed of the random state.
*/
void
isc_random_get(uint32_t *val);
/*%<
* Get a random value.
*
* Requires:
* val != NULL.
*/
uint32_t
isc_random_jitter(uint32_t max, uint32_t jitter);
/*%<
* Get a random value between (max - jitter) and (max).
* This is useful for jittering timer values.
*/
isc_result_t
isc_rng_create(isc_mem_t *mctx, isc_entropy_t *entropy, isc_rng_t **rngp);
/*%<
* Creates and initializes a pseudo random number generator. The
* returned RNG can be used to generate pseudo random numbers.
*
* The reference count of the returned RNG is set to 1.
*
* Requires:
* \li mctx is a pointer to a valid memory context.
* \li entropy is an optional entopy source (can be NULL)
* \li rngp != NULL && *rngp == NULL is where a pointer to the RNG is
* returned.
*
* Ensures:
*\li If result is ISC_R_SUCCESS:
* *rngp points to a valid RNG.
*
*\li If result is failure:
* *rngp does not point to a valid RNG.
*
* Returns:
*\li #ISC_R_SUCCESS Success
*\li #ISC_R_NOMEMORY Resource limit: Out of Memory
*/
void
isc_rng_attach(isc_rng_t *source, isc_rng_t **targetp);
/*%<
* Increments a reference count on the passed RNG.
*
* Requires:
* \li source the RNG struct to attach to (is refcount is incremented)
* \li targetp != NULL && *targetp == NULL where a pointer to the
* reference incremented RNG is returned.
*/
void
isc_rng_detach(isc_rng_t **rngp);
/*%<
* Decrements a reference count on the passed RNG. If the reference
* count reaches 0, the RNG is destroyed.
*
* Requires:
* \li rngp != NULL the RNG struct to decrement reference for
*/
uint16_t
isc_rng_random(isc_rng_t *rngctx);
/*%<
* Returns a pseudo random 16-bit unsigned integer.
*/
uint16_t
isc_rng_uniformrandom(isc_rng_t *rngctx, uint16_t upper_bound);
/*%<
* Returns a uniformly distributed pseudo-random 16-bit unsigned integer
* less than 'upper_bound'.
*/
ISC_LANG_ENDDECLS
#endif /* ISC_RANDOM_H */
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