sodium_crypto_pwhash

Derive a key from a password, using Argon2

Description

string sodium_crypto_pwhash(
    int $length,
    #[\SensitiveParameter]string $password,
    string $salt,
    int $opslimit,
    int $memlimit,
    int $algo = SODIUM_CRYPTO_PWHASH_ALG_DEFAULT
)

This function provides low-level access to libsodium's crypto_pwhash key derivation function. Unless you have specific reason to use this function, you should use sodium_crypto_pwhash_str or password_hash functions instead.

A common reason to use this particular function is to derive the seeds for cryptographic keys from a password and salt, and then use these seeds to generate the actual keys needed for some purpose (e.g. sodium_crypto_sign_detached).

Parameters

length: int; The length of the password hash to generate, in bytes.
password: string; The password to generate a hash for.
salt: A salt to add to the password before hashing. The salt should be unpredictable, ideally generated from a good random number source such as random_bytes, and have a length of exactly SODIUM_CRYPTO_PWHASH_SALTBYTES bytes.
opslimit: Represents a maximum amount of computations to perform. Raising this number will make the function require more CPU cycles to compute a key. There are some constants available to set the operations limit to appropriate values depending on intended use, in order of strength: SODIUM_CRYPTO_PWHASH_OPSLIMIT_INTERACTIVE, SODIUM_CRYPTO_PWHASH_OPSLIMIT_MODERATE and SODIUM_CRYPTO_PWHASH_OPSLIMIT_SENSITIVE.
memlimit: The maximum amount of RAM that the function will use, in bytes. There are constants to help you choose an appropriate value, in order of size: SODIUM_CRYPTO_PWHASH_MEMLIMIT_INTERACTIVE, SODIUM_CRYPTO_PWHASH_MEMLIMIT_MODERATE, and SODIUM_CRYPTO_PWHASH_MEMLIMIT_SENSITIVE. Typically these should be paired with the matching opslimit values.
algo: int A number indicating the hash algorithm to use. By default SODIUM_CRYPTO_PWHASH_ALG_DEFAULT (the currently recommended algorithm, which can change from one version of libsodium to another), or explicitly using SODIUM_CRYPTO_PWHASH_ALG_ARGON2ID13, representing the Argon2id algorithm version 1.3.

Return Values

Returns the derived key. The return value is a binary string of the hash, not an ASCII-encoded representation, and does not contain additional information about the parameters used to create the hash, so you will need to keep that information if you are ever going to verify the password in future. Use sodium_crypto_pwhash_str to avoid needing to do all that.

Examples

Example #1 sodium_crypto_pwhash example

<?php
//Need to keep the salt if we're ever going to be able to check this password
$salt = random_bytes(SODIUM_CRYPTO_PWHASH_SALTBYTES);
//Using bin2hex to keep output readable
echo bin2hex(
    sodium_crypto_pwhash(
        16, // == 128 bits
        'password',
        $salt,
        SODIUM_CRYPTO_PWHASH_OPSLIMIT_INTERACTIVE,
        SODIUM_CRYPTO_PWHASH_MEMLIMIT_INTERACTIVE,
        SODIUM_CRYPTO_PWHASH_ALG_ARGON2ID13
    )
);
?>

The above example will output something similar to:

a18f346ba57992eb7e4ae6abf3fd30ee