hash_init()

hash_init() — Initialize an incremental hashing context.

Built-in function of PHP 8.5. The manual lists it as available in PHP 5 >= 5.1.2, PHP 7, PHP 8, PECL hash >= 1.1. This page is the reference card: signature, parameters and return value, plus the changelog and the example the manual provides.

Signature

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

Parameters

Parameter	Type	What it takes
$algo	string	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	int	Optional settings for hash generation, currently supports only one option: HASH_HMAC. When specified, the key must be specified.
$key	string	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	array	An array of options for the various hashing algorithms. Currently, only the "seed" parameter is supported by the MurmurHash variants.

Return value

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

Example

A runnable snippet:

$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);

Output:

68b1282b91de2c054c36629cb8dd447f12f096d3e3c587978dc2248444633483 bool(true)

Changelog

Version	Change
8.4.0	Passing options of a wrong type is now deprecated.
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.