framework/base/Security.php
protected function encrypt($data, $passwordBased, $secret, $info)
    {
        if (!extension_loaded('openssl')) {
            throw new InvalidConfigException('Encryption requires the OpenSSL PHP extension');
        }
        if (!isset($this->allowedCiphers[$this->cipher][0], $this->allowedCiphers[$this->cipher][1])) {
            throw new InvalidConfigException($this->cipher . ' is not an allowed cipher');
        }

        list($blockSize, $keySize) = $this->allowedCiphers[$this->cipher];

        $keySalt = $this->generateRandomKey($keySize);
        if ($passwordBased) {
            $key = $this->pbkdf2($this->kdfHash, $secret, $keySalt, $this->derivationIterations, $keySize);
        } else {
            $key = $this->hkdf($this->kdfHash, $secret, $keySalt, $info, $keySize);
        }

        $iv = $this->generateRandomKey($blockSize);

        $encrypted = openssl_encrypt($data, $this->cipher, $key, OPENSSL_RAW_DATA, $iv);
        if ($encrypted === false) {
            throw new \yii\base\Exception('OpenSSL failure on encryption: ' . openssl_error_string());
        }

        $authKey = $this->hkdf($this->kdfHash, $key, null, $this->authKeyInfo, $keySize);
        $hashed = $this->hashData($iv . $encrypted, $authKey);

        /*
         * Output: [keySalt][MAC][IV][ciphertext]
         * - keySalt is KEY_SIZE bytes long
         * - MAC: message authentication code, length same as the output of MAC_HASH
         * - IV: initialization vector, length $blockSize
         */
        return $keySalt . $hashed;
    }
protected function encrypt($data, $passwordBased, $secret, $info)
    {
        if (!extension_loaded('openssl')) {
            throw new InvalidConfigException('Encryption requires the OpenSSL PHP extension');
        }
        if (!isset($this->allowedCiphers[$this->cipher][0], $this->allowedCiphers[$this->cipher][1])) {
            throw new InvalidConfigException($this->cipher . ' is not an allowed cipher');
        }

        list($blockSize, $keySize) = $this->allowedCiphers[$this->cipher];

        $keySalt = $this->generateRandomKey($keySize);
        if ($passwordBased) {
            $key = $this->pbkdf2($this->kdfHash, $secret, $keySalt, $this->derivationIterations, $keySize);
        } else {
            $key = $this->hkdf($this->kdfHash, $secret, $keySalt, $info, $keySize);
        }

        $iv = $this->generateRandomKey($blockSize);

        $encrypted = openssl_encrypt($data, $this->cipher, $key, OPENSSL_RAW_DATA, $iv);
        if ($encrypted === false) {
            throw new \yii\base\Exception('OpenSSL failure on encryption: ' . openssl_error_string());
        }

        $authKey = $this->hkdf($this->kdfHash, $key, null, $this->authKeyInfo, $keySize);
        $hashed = $this->hashData($iv . $encrypted, $authKey);

        /*
         * Output: [keySalt][MAC][IV][ciphertext]
         * - keySalt is KEY_SIZE bytes long
         * - MAC: message authentication code, length same as the output of MAC_HASH
         * - IV: initialization vector, length $blockSize
         */
        return $keySalt . $hashed;
    }
Encrypts data.

@param string $data data to be encrypted
@param bool $passwordBased set true to use password-based key derivation
@param string $secret the encryption password or key
@param string|null $info context/application specific information, e.g. a user ID
See [RFC 5869 Section 3.2](https://tools.ietf.org/html/rfc5869#section-3.2) for more details.

@return string the encrypted data
@throws InvalidConfigException on OpenSSL not loaded
@throws Exception on OpenSSL error
@see decrypt()