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hash_hkdf
(PHP 7 >= 7.1.2)
hash_hkdf — Generate a HKDF key derivation of a supplied key input
Description
$algo
, string $ikm
[, int $length = 0
[, string $info = ''
[, string $salt = ''
]]] ) : stringParameters
-
algo -
Name of selected hashing algorithm (i.e. "sha256", "sha512", "haval160,4", etc..) See hash_algos() for a list of supported algorithms.
Note:
Non-cryptographic hash functions are not allowed.
-
ikm -
Input keying material (raw binary). Cannot be empty.
-
length -
Desired output length in bytes. Cannot be greater than 255 times the chosen hash function size.
If
lengthis 0, the output length will default to the chosen hash function size. -
info -
Application/context-specific info string.
-
salt -
Salt to use during derivation.
While optional, adding random salt significantly improves the strength of HKDF.
Return Values
Returns a string containing a raw binary representation of the derived key
(also known as output keying material - OKM); or FALSE on failure.
Errors/Exceptions
An E_WARNING will be raised if ikm
is empty, algo is unknown/non-cryptographic,
length is less than 0 or too large
(greater than 255 times the size of the hash function).
Examples
Example #1 hash_hkdf() example
<?php
// Generate a random key, and salt to strengthen it during derivation.
$inputKey = random_bytes(32);
$salt = random_bytes(16);
// Derive a pair of separate keys, using the same input created above.
$encryptionKey = hash_hkdf('sha256', $inputKey, 32, 'aes-256-encryption', $salt);
$authenticationKey = hash_hkdf('sha256', $inputKey, 32, 'sha-256-authentication', $salt);
var_dump($encryptionKey !== $authenticationKey); // bool(true)
?>
The above example produces a pair of separate keys, suitable for creation of an encrypt-then-HMAC construct, using AES-256 and SHA-256 for encryption and authentication respectively.
See Also
- hash_pbkdf2() - Generate a PBKDF2 key derivation of a supplied password
- » RFC 5869
- » userland implementation
English translation
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Document created the 30/01/2003, last modified the 26/10/2018
Source of the printed document:https://www.gaudry.be/en/php-rf-function.hash-hkdf.html
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References
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