Feature Request: functions to use as KDF

[My1]

One thing that would totally be awesome would be having a side-function that just takes the parameters including a salt and outputs a key which then can be used for example to encrypt stuff.

especially as the description notes it as a sucessor to PBKDF, which obviously is a KDF.

[charlesportwoodii]

argon2_hash(string $string [, const $algorithm = HASH_ARGON2ID] [, array $options ] [, bool $raw = false ]);

The raw option outputs the KDF you're looking for per the Argon2 spec sans the salt option.

If you need a salt, use sodium, as it supersedes this library.

https://paragonie.com/book/pecl-libsodium/read/07-password-hashing.md#crypto-pwhash

$salt = random_bytes(SODIUM_CRYPTO_PWHASH_SALTBYTES);
$out_len = SODIUM_CRYPTO_SIGN_SEEDBYTES;
$seed = sodium_crypto_pwhash(
    $out_len,
    $password,
    $salt,
    SODIUM_CRYPTO_PWHASH_OPSLIMIT_INTERACTIVE,
    SODIUM_CRYPTO_PWHASH_MEMLIMIT_INTERACTIVE
);

[My1]

well for a KDF you obviously need the salt option because you need to be able to generate that key later to access what's been crypted with it.

That they only do Argon2i for that is sad though.

[charlesportwoodii]

With this library, the salt is generated automatically for you. It simply doesn't provide an option to pass your own.

The default in libsodium was changed to Argon2id, so if your sodium extension is compiled against the latest, it'll use Argon2id by default. The last option however lets you specify the algorithm: https://github.com/jedisct1/libsodium-php/blob/master/libsodium.c#L1811. The constant you'd pass is SODIUM_CRYPTO_PWHASH_ALG_ARGON2ID13.

Reference the sodium extension source code for more details on how to accomplish what you're trying to do.