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hash.h
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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 */
