134 lines
3.5 KiB
C
134 lines
3.5 KiB
C
/*
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* Copyright (C) 1999-2001 Internet Software Consortium.
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM
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* DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL
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* INTERNET SOFTWARE CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT,
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* INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING
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* FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
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* NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
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* WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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/* $Id: lfsr.h,v 1.10 2001/03/05 18:18:16 mayer Exp $ */
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#ifndef ISC_LFSR_H
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#define ISC_LFSR_H 1
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#include <isc/lang.h>
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#include <isc/types.h>
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typedef struct isc_lfsr isc_lfsr_t;
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/*
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* This function is called when reseeding is needed. It is allowed to
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* modify any state in the LFSR in any way it sees fit OTHER THAN "bits".
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*
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* It MUST set "count" to a new value or the lfsr will never reseed again.
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*
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* Also, a reseed will never occur in the middle of an extraction. This
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* is purely an optimization, and is probably what one would want.
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*/
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typedef void (*isc_lfsrreseed_t)(isc_lfsr_t *, void *);
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/*
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* The members of this structure can be used by the application, but care
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* needs to be taken to not change state once the lfsr is in operation.
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*/
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struct isc_lfsr {
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isc_uint32_t state; /* previous state */
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unsigned int bits; /* length */
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isc_uint32_t tap; /* bit taps */
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unsigned int count; /* reseed count (in BITS!) */
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isc_lfsrreseed_t reseed; /* reseed function */
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void *arg; /* reseed function argument */
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};
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ISC_LANG_BEGINDECLS
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/*
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* In all these functions it is important that the caller only use as many
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* bits as the LFSR has state. Also, it isn't guaranteed that an LFSR of
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* bit length 32 will have 2^32 unique states before repeating.
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*/
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void
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isc_lfsr_init(isc_lfsr_t *lfsr, isc_uint32_t state, unsigned int bits,
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isc_uint32_t tap, unsigned int count,
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isc_lfsrreseed_t reseed, void *arg);
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/*
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* Initialize an LFSR.
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*
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* Note:
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*
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* Putting untrusted values into this function will cause the LFSR to
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* generate (perhaps) non-maximal length sequences.
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*
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* Requires:
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*
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* lfsr != NULL
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*
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* 8 <= bits <= 32
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*
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* tap != 0
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*/
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void
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isc_lfsr_generate(isc_lfsr_t *lfsr, void *data, unsigned int count);
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/*
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* Returns "count" bytes of data from the LFSR.
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*
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* Requires:
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*
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* lfsr be valid.
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*
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* data != NULL.
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*
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* count > 0.
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*/
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void
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isc_lfsr_skip(isc_lfsr_t *lfsr, unsigned int skip);
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/*
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* Skip "skip" states.
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*
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* Requires:
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*
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* lfsr be valid.
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*/
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isc_uint32_t
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isc_lfsr_generate32(isc_lfsr_t *lfsr1, isc_lfsr_t *lfsr2);
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/*
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* Given two LFSRs, use the current state from each to skip entries in the
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* other. The next states are then xor'd together and returned.
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*
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* WARNING:
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*
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* This function is used only for very, very low security data, such
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* as DNS message IDs where it is desired to have an unpredictable
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* stream of bytes that are harder to predict than a simple flooding
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* attack.
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*
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* Notes:
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*
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* Since the current state from each of the LFSRs is used to skip
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* state in the other, it is important that no state be leaked
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* from either LFSR.
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*
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* Requires:
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*
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* lfsr1 and lfsr2 be valid.
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*
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* 1 <= skipbits <= 31
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*/
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ISC_LANG_ENDDECLS
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#endif /* ISC_LFSR_H */
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