lfsr.h revision 40f53fa8d9c6a4fc38c0014495e7a42b08f52481
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews/*
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews * Copyright (C) 1999, 2000 Internet Software Consortium.
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews *
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews * Permission to use, copy, modify, and distribute this software for any
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews * purpose with or without fee is hereby granted, provided that the above
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews * copyright notice and this permission notice appear in all copies.
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews *
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews * DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews * INTERNET SOFTWARE CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT,
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews * FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews * NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews * WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews */
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews/* $Id: lfsr.h,v 1.8 2000/08/01 01:30:20 tale Exp $ */
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews#ifndef ISC_LFSR_H
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews#define ISC_LFSR_H 1
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews#include <isc/lang.h>
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews#include <isc/types.h>
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrewstypedef struct isc_lfsr isc_lfsr_t;
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews/*
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews * This function is called when reseeding is needed. It is allowed to
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews * modify any state in the LFSR in any way it sees fit OTHER THAN "bits".
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews *
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews * It MUST set "count" to a new value or the lfsr will never reseed again.
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews *
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews * Also, a reseed will never occur in the middle of an extraction. This
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews * is purely an optimization, and is probably what one would want.
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews */
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrewstypedef void (*isc_lfsrreseed_t)(isc_lfsr_t *, void *);
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews/*
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews * The members of this structure can be used by the application, but care
343aeac7176d28c4a1b9d246b1f7311b4cd5da7dFrancis Dupont * needs to be taken to not change state once the lfsr is in operation.
343aeac7176d28c4a1b9d246b1f7311b4cd5da7dFrancis Dupont */
343aeac7176d28c4a1b9d246b1f7311b4cd5da7dFrancis Dupontstruct isc_lfsr {
7867d18ce0ffa93055fbda3b9d2be8b168d898fcMark Andrews isc_uint32_t state; /* previous state */
c3c8823fed039b3a2b8e5ca8bc2f3301d1dd840eMark Andrews unsigned int bits; /* length */
isc_uint32_t tap; /* bit taps */
unsigned int count; /* reseed count (in BITS!) */
isc_lfsrreseed_t reseed; /* reseed function */
void *arg; /* reseed function argument */
};
ISC_LANG_BEGINDECLS
/*
* In all these functions it is important that the caller only use as many
* bits as the LFSR has state. Also, it isn't guaranteed that an LFSR of
* bit length 32 will have 2^32 unique states before repeating.
*/
void isc_lfsr_init(isc_lfsr_t *lfsr, isc_uint32_t state, unsigned int bits,
isc_uint32_t tap, unsigned int count,
isc_lfsrreseed_t reseed, void *arg);
/*
* Initialize an LFSR.
*
* Note:
*
* Putting untrusted values into this function will cause the LFSR to
* generate (perhaps) non-maximal length sequences.
*
* Requires:
*
* lfsr != NULL
*
* 8 <= bits <= 32
*
* tap != 0
*/
void isc_lfsr_generate(isc_lfsr_t *lfsr, void *data, unsigned int count);
/*
* Returns "count" bytes of data from the LFSR.
*
* Requires:
*
* lfsr be valid.
*
* data != NULL.
*
* count > 0.
*/
void isc_lfsr_skip(isc_lfsr_t *lfsr, unsigned int skip);
/*
* Skip "skip" states.
*
* Requires:
*
* lfsr be valid.
*/
isc_uint32_t isc_lfsr_generate32(isc_lfsr_t *lfsr1, isc_lfsr_t *lfsr2);
/*
* Given two LFSRs, use the current state from each to skip entries in the
* other. The next states are then xor'd together and returned.
*
* WARNING:
*
* This function is used only for very, very low security data, such
* as DNS message IDs where it is desired to have an unpredictable
* stream of bytes that are harder to predict than a simple flooding
* attack.
*
* Notes:
*
* Since the current state from each of the LFSRs is used to skip
* state in the other, it is important that no state be leaked
* from either LFSR.
*
* Requires:
*
* lfsr1 and lfsr2 be valid.
*
* 1 <= skipbits <= 31
*/
ISC_LANG_ENDDECLS
#endif /* ISC_LFSR_H */