PHP Manual: Initialize an incremental hashing context

Description

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

Parameters

algo

Name of selected hashing algorithm (e.g. "sha256"). For a list of supported algorithms see hash_algos.

Note:
Non-cryptographic hash functions are not allowed if the HASH_HMAC flag is specified.

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