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/*
* Copyright (C) 2004-2007, 2009 Internet Systems Consortium, Inc. ("ISC")
* Copyright (C) 2003 Internet Software Consortium.
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
* REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
* AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
* INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
* LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
* OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
* PERFORMANCE OF THIS SOFTWARE.
*/
/* $Id: hash.h,v 1.12 2009-01-17 23:47:43 tbox Exp $ */
#ifndef ISC_HASH_H
#define ISC_HASH_H 1
/*****
***** Module Info
*****/
/*! \file isc/hash.h
*
* \brief The hash API
* provides an unpredictable hash value for variable length data.
* A hash object contains a random vector (which is hidden from clients
* of this API) to make the actual hash value unpredictable.
*
* The algorithm used in the API guarantees the probability of hash
* collision; in the current implementation, as long as the values stored
* in the random vector are unpredictable, the probability of hash
* collision between arbitrary two different values is at most 1/2^16.
*
* Although the API is generic about the hash keys, it mainly expects
* DNS names (and sometimes IPv4/v6 addresses) as inputs. It has an
* upper limit of the input length, and may run slow to calculate the
* hash values for large inputs.
*
* This API is designed to be general so that it can provide multiple
* different hash contexts that have different random vectors. However,
* it should be typical to have a single context for an entire system.
* To support such cases, the API also provides a single-context mode.
*
* \li MP:
* The hash object is almost read-only. Once the internal random vector
* is initialized, no write operation will occur, and there will be no
* need to lock the object to calculate actual hash values.
*
* \li Reliability:
* In some cases this module uses low-level data copy to initialize the
* random vector. Errors in this part are likely to crash the server or
* corrupt memory.
*
* \li Resources:
* A buffer, used as a random vector for calculating hash values.
*
* \li Security:
* This module intends to provide unpredictable hash values in
* adversarial environments in order to avoid denial of service attacks
* to hash buckets.
* Its unpredictability relies on the quality of entropy to build the
* random vector.
*
* \li Standards:
* None.
*/
/***
*** Imports
***/
#include <isc/types.h>
/***
*** Functions
***/
ISC_LANG_BEGINDECLS
isc_result_t
isc_hash_ctxcreate(isc_mem_t *mctx, isc_entropy_t *entropy, unsigned int limit,
isc_hash_t **hctx);
isc_result_t
isc_hash_create(isc_mem_t *mctx, isc_entropy_t *entropy, size_t limit);
/*!<
* \brief Create a new hash object.
*
* isc_hash_ctxcreate() creates a different object.
*
* isc_hash_create() creates a module-internal object to support the
* single-context mode. It should be called only once.
*
* 'entropy' must be NULL or a valid entropy object. If 'entropy' is NULL,
* pseudo random values will be used to build the random vector, which may
* weaken security.
*
* 'limit' specifies the maximum number of hash keys. If it is too large,
* these functions may fail.
*/
void
isc_hash_ctxattach(isc_hash_t *hctx, isc_hash_t **hctxp);
/*!<
* \brief Attach to a hash object.
*
* This function is only necessary for the multiple-context mode.
*/
void
isc_hash_ctxdetach(isc_hash_t **hctxp);
/*!<
* \brief Detach from a hash object.
*
* This function is for the multiple-context mode, and takes a valid
* hash object as an argument.
*/
void
isc_hash_destroy(void);
/*!<
* \brief This function is for the single-context mode, and is expected to be used
* as a counterpart of isc_hash_create().
*
* A valid module-internal hash object must have been created, and this
* function should be called only once.
*/
/*@{*/
void
isc_hash_ctxinit(isc_hash_t *hctx);
void
isc_hash_init(void);
/*!<
* \brief Initialize a hash object.
*
* It fills in the random vector with a proper
* source of entropy, which is typically from the entropy object specified
* at the creation. Thus, it is desirable to call these functions after
* initializing the entropy object with some good entropy sources.
*
* These functions should be called before the first hash calculation.
*
* isc_hash_ctxinit() is for the multiple-context mode, and takes a valid hash
* object as an argument.
*
* isc_hash_init() is for the single-context mode. A valid module-internal
* hash object must have been created, and this function should be called only
* once.
*/
/*@}*/
/*@{*/
unsigned int
isc_hash_ctxcalc(isc_hash_t *hctx, const unsigned char *key,
unsigned int keylen, isc_boolean_t case_sensitive);
unsigned int
isc_hash_calc(const unsigned char *key, unsigned int keylen,
isc_boolean_t case_sensitive);
/*!<
* \brief Calculate a hash value.
*
* isc_hash_ctxinit() is for the multiple-context mode, and takes a valid hash
* object as an argument.
*
* isc_hash_init() is for the single-context mode. A valid module-internal
* hash object must have been created.
*
* 'key' is the hash key, which is a variable length buffer.
*
* 'keylen' specifies the key length, which must not be larger than the limit
* specified for the corresponding hash object.
*
* 'case_sensitive' specifies whether the hash key should be treated as
* case_sensitive values. It should typically be ISC_FALSE if the hash key
* is a DNS name.
*/
/*@}*/
ISC_LANG_ENDDECLS
#endif /* ISC_HASH_H */
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