# sodium_crypto_pwhash

(PHP 7 >= 7.2.0)

sodium_crypto_pwhash — Derive a key from a password

### 说明

sodium_crypto_pwhash ( int `$length` , string `$password` , string `$salt` , int `$opslimit` , int `$memlimit` [, int `$alg` ] ) : string

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.

### 参数

`length`

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

`password`

  string; The password to generate a hash for.

`salt`

  string A salt to add to the password before hashing. The salt should be unpredictable, ideally generated from a good random mumber source such as random_bytes(), and have a length of at least `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.

`alg`

  integer 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.

### 返回值

Returns the derived key, 或者在失败时返回 `FALSE`. 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.

### 范例

Example #1 password_hash() 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
        )
    );
    ?>

以上例程的输出类似于：

    a18f346ba57992eb7e4ae6abf3fd30ee