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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_ENTROPY_H
#define ISC_ENTROPY_H 1
/*****
***** Module Info
*****/
/*! \file isc/entropy.h
* \brief The entropy API
*
* \li MP:
* The entropy object is locked internally. All callbacks into
* application-provided functions (for setup, gathering, and
* shutdown of sources) are guaranteed to be called with the
* entropy API lock held. This means these functions are
* not permitted to call back into the entropy API.
*
* \li Reliability:
* No anticipated impact.
*
* \li Resources:
* A buffer, used as an entropy pool.
*
* \li Security:
* While this code is believed to implement good entropy gathering
* and distribution, it has not been reviewed by a cryptographic
* expert.
* Since the added entropy is only as good as the sources used,
* this module could hand out bad data and never know it.
*
* \li Standards:
* None.
*/
/***
*** Imports
***/
#include <stdbool.h>
#include <stdio.h>
#include <isc/lang.h>
#include <isc/types.h>
/*@{*/
/*% Entropy callback function. */
typedef isc_result_t (*isc_entropystart_t)(isc_entropysource_t *source,
void *arg, bool blocking);
typedef isc_result_t (*isc_entropyget_t)(isc_entropysource_t *source,
void *arg, bool blocking);
typedef void (*isc_entropystop_t)(isc_entropysource_t *source, void *arg);
/*@}*/
/***
*** Flags.
***/
/*!
* \brief
* Extract only "good" data; return failure if there is not enough
* data available and there are no sources which we can poll to get
* data, or those sources are empty.
*
*
*/
#define ISC_ENTROPY_GOODONLY 0x00000001U
/*!
* \brief
* Extract as much good data as possible, but if there isn't enough
* at hand, return what is available. This flag only makes sense
* when used with _GOODONLY.
*/
#define ISC_ENTROPY_PARTIAL 0x00000002U
/*!
* \brief
* Block the task until data is available. This is contrary to the
* ISC task system, where tasks should never block. However, if
* this is a special purpose application where blocking a task is
* acceptable (say, an offline zone signer) this flag may be set.
* This flag only makes sense when used with _GOODONLY, and will
* block regardless of the setting for _PARTIAL.
*/
#define ISC_ENTROPY_BLOCKING 0x00000004U
/*!
* \brief
* Estimate the amount of entropy contained in the sample pool.
* If this is not set, the source will be gathered and periodically
* mixed into the entropy pool, but no increment in contained entropy
* will be assumed. This flag only makes sense on sample sources.
*/
#define ISC_ENTROPYSOURCE_ESTIMATE 0x00000001U
/*
* For use with isc_entropy_usebestsource().
*/
/*!
* \brief
* Use the keyboard as the only entropy source.
*/
#define ISC_ENTROPY_KEYBOARDYES 1
/*!
* \brief
* Never use the keyboard as an entropy source.
*/
#define ISC_ENTROPY_KEYBOARDNO 2
/*!
* \brief
* Use the keyboard as an entropy source only if opening the
* random device fails.
*/
#define ISC_ENTROPY_KEYBOARDMAYBE 3
ISC_LANG_BEGINDECLS
/***
*** Functions
***/
isc_result_t
isc_entropy_create(isc_mem_t *mctx, isc_entropy_t **entp);
/*!<
* \brief Create a new entropy object.
*/
void
isc_entropy_attach(isc_entropy_t *ent, isc_entropy_t **entp);
/*!<
* Attaches to an entropy object.
*/
void
isc_entropy_detach(isc_entropy_t **entp);
/*!<
* \brief Detaches from an entropy object.
*/
isc_result_t
isc_entropy_createfilesource(isc_entropy_t *ent, const char *fname);
/*!<
* \brief Create a new entropy source from a file.
*
* The file is assumed to contain good randomness, and will be mixed directly
* into the pool with every byte adding 8 bits of entropy.
*
* The file will be put into non-blocking mode, so it may be a device file,
* such as /dev/random. /dev/urandom should not be used here if it can
* be avoided, since it will always provide data even if it isn't good.
* We will make as much pseudorandom data as we need internally if our
* caller asks for it.
*
* If we hit end-of-file, we will stop reading from this source. Callers
* who require strong random data will get failure when our pool drains.
* The file will never be opened/read again once EOF is reached.
*/
void
isc_entropy_destroysource(isc_entropysource_t **sourcep);
/*!<
* \brief Removes an entropy source from the entropy system.
*/
isc_result_t
isc_entropy_createsamplesource(isc_entropy_t *ent,
isc_entropysource_t **sourcep);
/*!<
* \brief Create an entropy source that consists of samples. Each sample is
* added to the source via isc_entropy_addsamples(), below.
*/
isc_result_t
isc_entropy_createcallbacksource(isc_entropy_t *ent,
isc_entropystart_t start,
isc_entropyget_t get,
isc_entropystop_t stop,
void *arg,
isc_entropysource_t **sourcep);
/*!<
* \brief Create an entropy source that is polled via a callback.
*
* This would be used when keyboard input is used, or a GUI input method.
* It can also be used to hook in any external entropy source.
*
* Samples are added via isc_entropy_addcallbacksample(), below.
* _addcallbacksample() is the only function which may be called from
* within an entropy API callback function.
*/
void
isc_entropy_stopcallbacksources(isc_entropy_t *ent);
/*!<
* \brief Call the stop functions for callback sources that have had their
* start functions called.
*/
/*@{*/
isc_result_t
isc_entropy_addcallbacksample(isc_entropysource_t *source, uint32_t sample,
uint32_t extra);
isc_result_t
isc_entropy_addsample(isc_entropysource_t *source, uint32_t sample,
uint32_t extra);
/*!<
* \brief Add a sample to the sample source.
*
* The sample MUST be a timestamp
* that increases over time, with the exception of wrap-around for
* extremely high resolution timers which will quickly wrap-around
* a 32-bit integer.
*
* The "extra" parameter is used only to add a bit more unpredictable
* data. It is not used other than included in the hash of samples.
*
* When in an entropy API callback function, _addcallbacksource() must be
* used. At all other times, _addsample() must be used.
*/
/*@}*/
isc_result_t
isc_entropy_getdata(isc_entropy_t *ent, void *data, unsigned int length,
unsigned int *returned, unsigned int flags);
/*!<
* \brief Get random data from entropy pool 'ent'.
*
* If a hook has been set up using isc_entropy_sethook() and
* isc_entropy_usehook(), then the hook function will be called to get
* random data.
*
* Otherwise, randomness is extracted from the entropy pool set up in BIND.
* This may cause the pool to be loaded from various sources. Ths is done
* by stirring the pool and returning a part of hash as randomness.
* (Note that no secrets are given away here since parts of the hash are
* XORed together before returning.)
*
* 'flags' may contain ISC_ENTROPY_GOODONLY, ISC_ENTROPY_PARTIAL, or
* ISC_ENTROPY_BLOCKING. These will be honored if the hook function is
* not in use. If it is, the flags will be passed to the hook function
* but it may ignore them.
*
* Up to 'length' bytes of randomness are retrieved and copied into 'data'.
* (If 'returned' is not NULL, and the number of bytes copied is less than
* 'length' - which may happen if ISC_ENTROPY_PARTIAL was used - then the
* number of bytes copied will be stored in *returned.)
*
* Returns:
* \li ISC_R_SUCCESS on success
* \li ISC_R_NOENTROPY if entropy pool is empty
* \li other error codes are possible when a hook is in use
*/
void
isc_entropy_putdata(isc_entropy_t *ent, void *data, unsigned int length,
uint32_t entropy);
/*!<
* \brief Add "length" bytes in "data" to the entropy pool, incrementing the
* pool's entropy count by "entropy."
*
* These bytes will prime the pseudorandom portion even if no entropy is
* actually added.
*/
void
isc_entropy_stats(isc_entropy_t *ent, FILE *out);
/*!<
* \brief Dump some (trivial) stats to the stdio stream "out".
*/
unsigned int
isc_entropy_status(isc_entropy_t *end);
/*
* Returns the number of bits the pool currently contains. This is just
* an estimate.
*/
isc_result_t
isc_entropy_usebestsource(isc_entropy_t *ectx, isc_entropysource_t **source,
const char *randomfile, int use_keyboard);
/*!<
* \brief Use whatever source of entropy is best.
*
* Notes:
*\li If "randomfile" is not NULL, open it with
* isc_entropy_createfilesource().
*
*\li If "randomfile" is NULL and the system's random device was detected
* when the program was configured and built, open that device with
* isc_entropy_createfilesource().
*
*\li If "use_keyboard" is #ISC_ENTROPY_KEYBOARDYES, then always open
* the keyboard as an entropy source (possibly in addition to
* "randomfile" or the random device).
*
*\li If "use_keyboard" is #ISC_ENTROPY_KEYBOARDMAYBE, open the keyboard only
* if opening the random file/device fails. A message will be
* printed describing the need for keyboard input.
*
*\li If "use_keyboard" is #ISC_ENTROPY_KEYBOARDNO, the keyboard will
* never be opened.
*
* Returns:
*\li #ISC_R_SUCCESS if at least one source of entropy could be started.
*
*\li #ISC_R_NOENTROPY if use_keyboard is #ISC_ENTROPY_KEYBOARDNO and
* there is no random device pathname compiled into the program.
*
*\li A return code from isc_entropy_createfilesource() or
* isc_entropy_createcallbacksource().
*/
void
isc_entropy_usehook(isc_entropy_t *ectx, bool onoff);
/*!<
* \brief Configure entropy context 'ectx' to use the hook function
*
* Sets the entropy context to call the hook function for random number
* generation, if such a function has been configured via
* isc_entropy_sethook(), whenever isc_entropy_getdata() is called.
*/
void
isc_entropy_sethook(isc_entropy_getdata_t myhook);
/*!<
* \brief Set the hook function.
*
* The hook function is a global value: only one hook function
* can be set in the system. Individual entropy contexts may be
* configured to use it, or not, by calling isc_entropy_usehook().
*/
ISC_LANG_ENDDECLS
#endif /* ISC_ENTROPY_H */
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