Authenticated shared-key encryption

# sodium_crypto_secretbox

(PHP 7 >= 7.2.0, PHP 8)

sodium_crypto_secretbox — Authenticated shared-key encryption

### Description

sodium_crypto_secretbox(#[\SensitiveParameter] string `$message`, string `$nonce`, #[\SensitiveParameter] string `$key`): string

Encrypt a message with a symmetric (shared) key.

### Parameters

`message`
  The plaintext message to encrypt.
`nonce`
  A number that must be only used once, per message. 24 bytes long. This is a large enough bound to generate randomly (i.e. random_bytes()).
`key`
  Encryption key (256-bit).

### Return Values

Returns the encrypted string.

### Errors/Exceptions

- If `nonce` has a length of bytes different than `SODIUM_CRYPTO_SECRETBOX_NONCEBYTES` (24 bytes), a SodiumException will be thrown.
- If `key` has a length of bytes different than `SODIUM_CRYPTO_SECRETBOX_KEYBYTES` (32 bytes), a SodiumException will be thrown.
- Throws a SodiumException on failure.

### Examples

Example #1 sodium_crypto_secretbox() example

`<?php
// The $key must be kept confidential
$key = sodium_crypto_secretbox_keygen();
// Do not reuse $nonce with the same key
$nonce = random_bytes(SODIUM_CRYPTO_SECRETBOX_NONCEBYTES);
$plaintext = "message to be encrypted";
$ciphertext = sodium_crypto_secretbox($plaintext, $nonce, $key);
var_dump(bin2hex($ciphertext));
// The same nonce and key are required to decrypt the $ciphertext
var_dump(sodium_crypto_secretbox_open($ciphertext, $nonce, $key));
?>`

The above example will output something similar to:

    string(78) "3a1fa3e9f7b72ef8be51d40abf8e296c6899c185d07b18b4c93e7f26aa776d24c50852cd6b1076"
    string(23) "message to be encrypted"

### See Also

- sodium_crypto_secretbox_open() - Authenticated shared-key decryption
- sodium_crypto_secretbox_keygen() - Generate random key for sodium_crypto_secretbox
- random_bytes() - Get cryptographically secure random bytes

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