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resource hash_init ( string $algo [, int $options= 0 [, string $key= NULL ]] )

algo: Name of selected hashing algorithm (i.e. "md5", "sha256", "haval160,4", etc..)
options: Optional settings for hash generation, currently supports only one option: HASH_HMAC. When specified, the key must be specified.
key: When HASH_HMAC is specified for options , a shared secret key to be used with the HMAC hashing method must be supplied in this parameter.

Пример #1 Incremental hashing example


<?php
$ctx = hash_init('md5');
hash_update($ctx, 'The quick brown fox ');
hash_update($ctx, 'jumped over the lazy dog.');
echo hash_final($ctx);
?>

Результат выполнения данного примера:

5c6ffbdd40d9556b73a21e63c3e0e904

hash() - Generate a hash value (message digest)
hash_file() - Generate a hash value using the contents of a given file
hash_hmac() - Generate a keyed hash value using the HMAC method
hash_hmac_file() - Generate a keyed hash value using the HMAC method and the contents of a given file