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Diffstat (limited to 'lib/isc/include/isc/hash.h')
| -rw-r--r-- | lib/isc/include/isc/hash.h | 185 |
1 files changed, 185 insertions, 0 deletions
diff --git a/lib/isc/include/isc/hash.h b/lib/isc/include/isc/hash.h new file mode 100644 index 0000000..b80966c --- /dev/null +++ b/lib/isc/include/isc/hash.h @@ -0,0 +1,185 @@ +/* + * Copyright (C) 2004-2007 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 1.10 2007/06/19 23:47:18 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. + * + * Altough 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 */ |