contrib/bind-9.5.2/lib/isc/include/isc/hash.h

   1 /*
   2  * Copyright (C) 2004-2007, 2009  Internet Systems Consortium, Inc. ("ISC")
   3  * Copyright (C) 2003  Internet Software Consortium.
   4  *
   5  * Permission to use, copy, modify, and/or distribute this software for any
   6  * purpose with or without fee is hereby granted, provided that the above
   7  * copyright notice and this permission notice appear in all copies.
   8  *
   9  * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
  10  * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
  11  * AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
  12  * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
  13  * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
  14  * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
  15  * PERFORMANCE OF THIS SOFTWARE.
  16  */
  17
  18 /* $Id: hash.h,v 1.10.128.2 2009/01/19 23:47:03 tbox Exp $ */
  19
  20 #ifndef ISC_HASH_H
  21 #define ISC_HASH_H 1
  22
  23 /*****
  24  ***** Module Info
  25  *****/
  26
  27 /*! \file isc/hash.h
  28  *
  29  * \brief The hash API
  30  *      provides an unpredictable hash value for variable length data.
  31  *      A hash object contains a random vector (which is hidden from clients
  32  *      of this API) to make the actual hash value unpredictable.
  33  *
  34  *      The algorithm used in the API guarantees the probability of hash
  35  *      collision; in the current implementation, as long as the values stored
  36  *      in the random vector are unpredictable, the probability of hash
  37  *      collision between arbitrary two different values is at most 1/2^16.
  38  *
  39  *      Although the API is generic about the hash keys, it mainly expects
  40  *      DNS names (and sometimes IPv4/v6 addresses) as inputs.  It has an
  41  *      upper limit of the input length, and may run slow to calculate the
  42  *      hash values for large inputs.
  43  *
  44  *      This API is designed to be general so that it can provide multiple
  45  *      different hash contexts that have different random vectors.  However,
  46  *      it should be typical to have a single context for an entire system.
  47  *      To support such cases, the API also provides a single-context mode.
  48  *
  49  * \li MP:
  50  *      The hash object is almost read-only.  Once the internal random vector
  51  *      is initialized, no write operation will occur, and there will be no
  52  *      need to lock the object to calculate actual hash values.
  53  *
  54  * \li Reliability:
  55  *      In some cases this module uses low-level data copy to initialize the
  56  *      random vector.  Errors in this part are likely to crash the server or
  57  *      corrupt memory.
  58  *
  59  * \li Resources:
  60  *      A buffer, used as a random vector for calculating hash values.
  61  *
  62  * \li Security:
  63  *      This module intends to provide unpredictable hash values in
  64  *      adversarial environments in order to avoid denial of service attacks
  65  *      to hash buckets.
  66  *      Its unpredictability relies on the quality of entropy to build the
  67  *      random vector.
  68  *
  69  * \li Standards:
  70  *      None.
  71  */
  72
  73 /***
  74  *** Imports
  75  ***/
  76
  77 #include <isc/types.h>
  78
  79 /***
  80  *** Functions
  81  ***/
  82 ISC_LANG_BEGINDECLS
  83
  84 isc_result_t
  85 isc_hash_ctxcreate(isc_mem_t *mctx, isc_entropy_t *entropy, unsigned int limit,
  86                    isc_hash_t **hctx);
  87 isc_result_t
  88 isc_hash_create(isc_mem_t *mctx, isc_entropy_t *entropy, size_t limit);
  89 /*!<
  90  * \brief Create a new hash object.
  91  *
  92  * isc_hash_ctxcreate() creates a different object.
  93  *
  94  * isc_hash_create() creates a module-internal object to support the
  95  * single-context mode.  It should be called only once.
  96  *
  97  * 'entropy' must be NULL or a valid entropy object.  If 'entropy' is NULL,
  98  * pseudo random values will be used to build the random vector, which may
  99  * weaken security.
 100  *
 101  * 'limit' specifies the maximum number of hash keys.  If it is too large,
 102  * these functions may fail.
 103  */
 104
 105 void
 106 isc_hash_ctxattach(isc_hash_t *hctx, isc_hash_t **hctxp);
 107 /*!<
 108  * \brief Attach to a hash object.
 109  *
 110  * This function is only necessary for the multiple-context mode.
 111  */
 112
 113 void
 114 isc_hash_ctxdetach(isc_hash_t **hctxp);
 115 /*!<
 116  * \brief Detach from a hash object.
 117  *
 118  * This function  is for the multiple-context mode, and takes a valid
 119  * hash object as an argument.
 120  */
 121
 122 void
 123 isc_hash_destroy(void);
 124 /*!<
 125  * \brief This function is for the single-context mode, and is expected to be used
 126  * as a counterpart of isc_hash_create().
 127  *
 128  * A valid module-internal hash object must have been created, and this
 129  * function should be called only once.
 130  */
 131
 132 /*@{*/
 133 void
 134 isc_hash_ctxinit(isc_hash_t *hctx);
 135 void
 136 isc_hash_init(void);
 137 /*!<
 138  * \brief Initialize a hash object.
 139  *
 140  * It fills in the random vector with a proper
 141  * source of entropy, which is typically from the entropy object specified
 142  * at the creation.  Thus, it is desirable to call these functions after
 143  * initializing the entropy object with some good entropy sources.
 144  *
 145  * These functions should be called before the first hash calculation.
 146  *
 147  * isc_hash_ctxinit() is for the multiple-context mode, and takes a valid hash
 148  * object as an argument.
 149  *
 150  * isc_hash_init() is for the single-context mode.  A valid module-internal
 151  * hash object must have been created, and this function should be called only
 152  * once.
 153  */
 154 /*@}*/
 155
 156 /*@{*/
 157 unsigned int
 158 isc_hash_ctxcalc(isc_hash_t *hctx, const unsigned char *key,
 159                  unsigned int keylen, isc_boolean_t case_sensitive);
 160 unsigned int
 161 isc_hash_calc(const unsigned char *key, unsigned int keylen,
 162               isc_boolean_t case_sensitive);
 163 /*!<
 164  * \brief Calculate a hash value.
 165  *
 166  * isc_hash_ctxinit() is for the multiple-context mode, and takes a valid hash
 167  * object as an argument.
 168  *
 169  * isc_hash_init() is for the single-context mode.  A valid module-internal
 170  * hash object must have been created.
 171  *
 172  * 'key' is the hash key, which is a variable length buffer.
 173  *
 174  * 'keylen' specifies the key length, which must not be larger than the limit
 175  * specified for the corresponding hash object.
 176  *
 177  * 'case_sensitive' specifies whether the hash key should be treated as
 178  * case_sensitive values.  It should typically be ISC_FALSE if the hash key
 179  * is a DNS name.
 180  */
 181 /*@}*/
 182
 183 ISC_LANG_ENDDECLS
 184
 185 #endif /* ISC_HASH_H */