Initialize an incremental hashing context

Description

hash_init(
    string $algo,
    int $flags = 0,
    string $key = "",
    array $options = []
): HashContext

Parameters

algo: Name of selected hashing algorithm (i.e. "md5", "sha256", "haval160,4", etc..). For a list of supported algorithms see hash_algos().
flags: 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 flags, a shared secret key to be used with the HMAC hashing method must be supplied in this parameter.
options: An array of options for the various hashing algorithms. Currently, only the "seed" parameter is supported by the MurmurHash variants.

Return Values

Returns a Hashing Context for use with hash_update(), hash_update_stream(), hash_update_file(), and hash_final().

Errors/Exceptions

Throws a ValueError exception if algo is unknown or is a non-cryptographic hash function, or if key is empty.

Changelog

Version	Description
8.1.0	The `options` parameter has been added.
8.0.0	Now throws an ValueError exception if the `algo` is unknown or is a non-cryptographic hash function, or if `key` is empty. Previously, `false` was returned and an `E_WARNING` message was emitted.
7.2.0	Usage of non-cryptographic hash functions (adler32, crc32, crc32b, fnv132, fnv1a32, fnv164, fnv1a64, joaat) with `HASH_HMAC` was disabled.
7.2.0	Return HashContext instead of resource.

Examples

Example #1 Incremental hashing example

<?php
$hash = hash('sha256', 'The quick brown fox jumped over the lazy dog.');

$ctx = hash_init('sha256');
hash_update($ctx, 'The quick brown fox ');
hash_update($ctx, 'jumped over the lazy dog.');
$incremental_hash = hash_final($ctx);

echo $incremental_hash, PHP_EOL;
var_dump($hash === $incremental_hash);
?>

The above example will output:

68b1282b91de2c054c36629cb8dd447f12f096d3e3c587978dc2248444633483
bool(true)

hash_init