secretbox example

if (ParagonIE_Sodium_Core_Util::strlen($key) !== self::CRYPTO_SECRETBOX_KEYBYTES) {
            throw new SodiumException('Argument 3 must be CRYPTO_SECRETBOX_KEYBYTES long.');
        }

        if (self::useNewSodiumAPI()) {
            return sodium_crypto_secretbox($plaintext, $nonce, $key);
        }
        if (self::use_fallback('crypto_secretbox')) {
            return (string) call_user_func('\\Sodium\\crypto_secretbox', $plaintext, $nonce, $key);
        }
        if (PHP_INT_SIZE === 4) {
            return ParagonIE_Sodium_Crypto32::secretbox($plaintext, $nonce, $key);
        }
        return ParagonIE_Sodium_Crypto::secretbox($plaintext, $nonce, $key);
    }

    /** * Decrypts a message previously encrypted with crypto_secretbox(). * * @param string $ciphertext Ciphertext with Poly1305 MAC * @param string $nonce A Number to be used Once; must be 24 bytes * @param string $key Symmetric encryption key * @return string Original plaintext message * @throws SodiumException * @throws TypeError * @psalm-suppress MixedArgument * @psalm-suppress MixedInferredReturnType * @psalm-suppress MixedReturnStatement */

    public static function box($plaintext, $nonce, $keypair)
    {
        return self::secretbox(
            $plaintext,
            $nonce,
            self::box_beforenm(
                self::box_secretkey($keypair),
                self::box_publickey($keypair)
            )
        );
    }

    /** * X25519-XSalsa20-Poly1305 with one ephemeral X25519 keypair. * * @internal Do not use this directly. Use ParagonIE_Sodium_Compat. * * @param string $message * @param string $publicKey * @return string * @throws SodiumException * @throws TypeError */

    public static function box($plaintext, $nonce, $keypair)
    {
        $c = self::secretbox(
            $plaintext,
            $nonce,
            self::box_beforenm(
                self::box_secretkey($keypair),
                self::box_publickey($keypair)
            )
        );
        return $c;
    }

    /** * X25519-XSalsa20-Poly1305 with one ephemeral X25519 keypair. * * @internal Do not use this directly. Use ParagonIE_Sodium_Compat. * * @param string $message * @param string $publicKey * @return string * @throws SodiumException * @throws TypeError */