C# equivalent of DecryptByPassPhrase

Question

I have a requirement to decrypt a value that was encrypted on the database using EncryptByPassPhrase, but without accessing the database.

How do I get the encryption key from the passphrase?

I've looked at

Replicate T-SQL DecryptByPassPhrase in C#

and

C# Decrypt bytes from SQL Server EncryptByPassPhrase?

and my code is:

public static string AESDatabaseDecrypt(string encryptedString)
{
    passphrase =     "S0meFakePassPhrase01234!";
    encryptedString = "AQAAAOmuc52dnbVwTqEx1kp+4WhI89LYKHh3jg=="; // temporarily hard coded


    // setup encryption settings to match decryptbypassphrase
    TripleDESCryptoServiceProvider provider = new TripleDESCryptoServiceProvider();
    provider.Key = UTF8Encoding.UTF8.GetBytes(passphrase).Take(16).ToArray(); // stuck on getting key from passphrase
    provider.KeySize = 128;
    provider.Padding = PaddingMode.Zeros;
    // setup data to be decrypted
    byte[] encryptedStringAsByteArray = Convert.FromBase64String(encryptedString);

    // hack some extra bytes up to a multiple of 8
    encryptedStringAsByteArray = encryptedStringAsByteArray.Concat(new byte[] { byte.MinValue, byte.MinValue, byte.MinValue, byte.MinValue }).ToArray(); // add 4 empty bytes to make 32 bytes
    MemoryStream encryptedStringAsMemoryStream = new MemoryStream(encryptedStringAsByteArray);
    // decrypt
    CryptoStream cryptoStream = new CryptoStream(encryptedStringAsMemoryStream, provider.CreateDecryptor(), CryptoStreamMode.Read);
    // return the result
    StreamReader cryptoStreamReader = new StreamReader(cryptoStream);
    string decryptedString = cryptoStreamReader.ReadToEnd();
}

Answer 1

Well, I mean, the first thing that leaps out at me is that you're not actually returning a value from your method. Try adding return decryptedString; to the end and see what you get.