Online PHP editor | refs for XSCbd

<?php $password = 'My Plaintext Password'; $plaintext = 'This is my message'; $secretBox = new Secretbox(); $ciphertext = $secretBox->encrypt($plaintext, $password); var_dump($ciphertext); $decryptedPlaintext = $secretBox->decrypt($ciphertext, $password); var_dump($decryptedPlaintext); assertThat($decryptedPlaintext === $plaintext, 'Can decrypt'); assertThat( $secretBox->encrypt($plaintext, $password) !== $secretBox->encrypt($plaintext, $password), 'Should not result in same ciphertext' ); try { $failed = false; // modify ciphertext $ciphertext[65] = 'f'; $secretBox->decrypt($ciphertext, $password); } catch (\Exception $e) { $failed = true; } finally { assertThat($failed, 'Tempered chiphertext should result in exception'); } class Secretbox { public function encrypt(string $plaintext, string $password): string { // create a random salt for key derivation $salt = random_bytes(SODIUM_CRYPTO_PWHASH_SALTBYTES); $key = $this->deriveKeyFromUserPassword($password, $salt); $nonce = random_bytes(SODIUM_CRYPTO_SECRETBOX_NONCEBYTES); $ciphertext = sodium_crypto_secretbox($plaintext, $nonce, $key); sodium_memzero($password); sodium_memzero($key); return $salt.$nonce.$ciphertext; } public function decrypt(string $ciphertext, string $password): string { $salt = substr($ciphertext, 0, SODIUM_CRYPTO_PWHASH_SALTBYTES); $nonce = substr($ciphertext, SODIUM_CRYPTO_PWHASH_SALTBYTES, SODIUM_CRYPTO_SECRETBOX_NONCEBYTES); $ciphertext = substr($ciphertext, SODIUM_CRYPTO_PWHASH_SALTBYTES + SODIUM_CRYPTO_SECRETBOX_NONCEBYTES); $key = $this->deriveKeyFromUserPassword($password, $salt); $plaintext = sodium_crypto_secretbox_open($ciphertext, $nonce, $key); sodium_memzero($password); sodium_memzero($key); sodium_memzero($nonce); if ($plaintext === false) { throw new \InvalidArgumentException('Bad ciphertext'); } return $plaintext; } private function deriveKeyFromUserPassword(string $password, string $salt): string { $key = sodium_crypto_pwhash( SODIUM_CRYPTO_SECRETBOX_KEYBYTES, $password, $salt, SODIUM_CRYPTO_PWHASH_OPSLIMIT_INTERACTIVE, SODIUM_CRYPTO_PWHASH_MEMLIMIT_INTERACTIVE ); sodium_memzero($password); return $key; } } function assertThat(bool $expressionResult, string $message) { if (!$expressionResult) { throw new \RuntimeException($message); } }