public static string DecryptString(string data, string password)
    {

        byte[] allBytes = ToByteArray(data);
        byte[] one = ToByteArray("1");
        string plaintext = null;
        // this is all of the bytes

        byte[] passwordByteArray = ToByteArray(password);

        using (var aes = Aes.Create())
        {
            aes.KeySize = KeySize;
            aes.BlockSize = BlockSize;
            aes.Mode = CipherMode.CBC;

            // get the key salt
            byte[] keySalt = new byte[KeySize / 8];
            Array.Copy(allBytes, keySalt, keySalt.Length);

            // Yii2 says
            //$key = $this->hkdf($this->kdfHash, $secret, $keySalt, $info, $keySize);
            //
            //Yii2 hkdf says
            //$prKey = hash_hmac($algo, $inputKey, $salt, true);
            //$hmac = '';
            //$outputKey = '';
            //for ($i = 1; $i <= $blocks; $i++) {
            //  $hmac = hash_hmac($algo, $hmac . $info . chr($i), $prKey, true);
            //  $outputKey .= $hmac;
            //}
            // chr($i) is the char byte of 1;
            // the blocksize is 1
            // info here is nothing

            // hash first key with keysalt and password
            HMACSHA256 hmac = new HMACSHA256(keySalt);
            byte[] computedHash = hmac.ComputeHash(passwordByteArray);

            // hash primary key with one byte and computed hash
            HMACSHA256 hmac2 = new HMACSHA256(one);
            byte[] prKey = hmac2.ComputeHash(computedHash);

            // if we want to verify the mac hash this is where we would do it.
            // Yii2 encryption data.
            // $encrypted = openssl_encrypt($data, $this->cipher, $key, OPENSSL_RAW_DATA, $iv);
            //
            //$authKey = $this->hkdf($this->kdfHash, $key, null, $this->authKeyInfo, $keySize);
            //hashed = $this->hashData($iv. $encrypted, $authKey);
            //hashed = [macHash][data]

            // get the MAC code
            byte[] MAC = new byte[MacHashSize / 8];
            Array.Copy(allBytes, keySalt.Length, MAC, 0, MAC.Length);

            // get our IV
            byte[] iv = new byte[BlockSize / 8];
            Array.Copy(allBytes, (keySalt.Length + MAC.Length), iv, 0, iv.Length);

            // get the data we need to decrypt
            byte[] cipherBytes = new byte[allBytes.Length - iv.Length - MAC.Length - keySalt.Length];
            Array.Copy(allBytes, (keySalt.Length + MAC.Length + iv.Length), cipherBytes, 0, cipherBytes.Length);

            // Create a decrytor to perform the stream transform.
            var decryptor = aes.CreateDecryptor(prKey, iv);

            // Create the streams used for decryption.
            using (MemoryStream msDecrypt = new MemoryStream(cipherBytes))
            {
                using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
                {
                    using (StreamReader srDecrypt = new StreamReader(csDecrypt))
                    {
                         //Read the decrypted bytes from the decrypting stream
                         //and place them in a string.
                        plaintext = srDecrypt.ReadToEnd();
                    }
                }
            }
        }

        return plaintext;
    }

    public static byte[] ToByteArray(string value)
    {
        byte[] allBytes = new byte[value.Length];
        int i = 0;
        foreach (byte bite in value)
        {
            allBytes[i] = Convert.ToByte(bite);
            i++;
        }

        return allBytes;
    }