Derives a key from a password, using scrypt

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- PHP Manual
- Sodium Functions
- Derives a key from a password, using scrypt

# sodium_crypto_pwhash_scryptsalsa208sha256

(PHP 7 >= 7.2.0, PHP 8)

sodium_crypto_pwhash_scryptsalsa208sha256 — Derives a key from a password, using scrypt

### Description

sodium_crypto_pwhash_scryptsalsa208sha256(
int `$length`,
string `$password`,
string `$salt`,
int `$opslimit`,
int `$memlimit`
): string

This is the scrypt counterpart to sodium_crypto_pwhash().

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`

  The length of the password hash to generate, in bytes.

`password`

  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 at least `SODIUM_CRYPTO_PWHASH_SCRYPTSALSA208SHA256_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_SCRYPTSALSA208SHA256_OPSLIMIT_INTERACTIVE` and `SODIUM_CRYPTO_PWHASH_SCRYPTSALSA208SHA256_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_SCRYPTSALSA208SHA256_MEMLIMIT_INTERACTIVE` and `SODIUM_CRYPTO_PWHASH_SCRYPTSALSA208SHA256_MEMLIMIT_SENSITIVE`. Typically these should be paired with the matching `opslimit` values.

### Return Values

A string of bytes of the desired length.