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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_HASH_H
#define ISC_HASH_H 1
#include <stdbool.h>
#include <isc/deprecated.h>
#include <isc/types.h>
/*****
***** 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
LIBISC_EXTERNAL_DATA extern isc_hash_t *isc_hashctx;
isc_result_t
isc_hash_ctxcreate(isc_mem_t *mctx, isc_entropy_t *entropy, size_t 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)
ISC_DEPRECATED;
/*!<
* \brief Attach to a hash object.
*
* This function is only necessary for the multiple-context mode.
*/
void
isc_hash_ctxdetach(isc_hash_t **hctxp)
ISC_DEPRECATED;
/*!<
* \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, bool case_sensitive)
ISC_DEPRECATED;
unsigned int
isc_hash_calc(const unsigned char *key, unsigned int keylen,
bool case_sensitive)
ISC_DEPRECATED;
/*!<
* \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 false if the hash key
* is a DNS name.
*/
/*@}*/
void
isc__hash_setvec(const uint16_t *vec)
ISC_DEPRECATED;
/*!<
* \brief Set the contents of the random vector used in hashing.
*
* WARNING: This function is meant to be used only in testing code. It
* must not be used anywhere in normally running code.
*
* The hash context must have been created beforehand, otherwise this
* function is a nop.
*
* 'vec' is not documented here on purpose. You should know what you are
* doing before using this function.
*/
const void *
isc_hash_get_initializer(void);
void
isc_hash_set_initializer(const void *initializer);
uint32_t
isc_hash_function(const void *data, size_t length,
bool case_sensitive,
const uint32_t *previous_hashp);
uint32_t
isc_hash_function_reverse(const void *data, size_t length,
bool case_sensitive,
const uint32_t *previous_hashp);
/*!<
* \brief Calculate a hash over data.
*
* This hash function is useful for hashtables. The hash function is
* opaque and not important to the caller. The returned hash values are
* non-deterministic and will have different mapping every time a
* process using this library is run, but will have uniform
* distribution.
*
* isc_hash_function() calculates the hash from start to end over the
* input data. isc_hash_function_reverse() calculates the hash from the
* end to the start over the input data. The difference in order is
* useful in incremental hashing; for example, a previously hashed
* value for 'com' can be used as input when hashing 'example.com'.
*
* This is a new variant of isc_hash_calc() and will supersede
* isc_hash_calc() eventually.
*
* 'data' is the data to be hashed.
*
* 'length' is the size of the data to be hashed.
*
* 'case_sensitive' specifies whether the hash key should be treated as
* case_sensitive values. It should typically be false if the hash key
* is a DNS name.
*
* 'previous_hashp' is a pointer to a previous hash value returned by
* this function. It can be used to perform incremental hashing. NULL
* must be passed during first calls.
*/
ISC_LANG_ENDDECLS
#endif /* ISC_HASH_H */
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