Generate a 128-bit string in C#

Question

I am developing a class project in C# that encrypts the users and admins passwords. To encrypt I'm using the TripleDESCryptoServiceProvider.

In the configuration app the user enters the key to be used for encryption and decryption of the passwords. I want to have a button to generate a key to help the user but I'm at a loss as to how I generate the 128 bits randomly. How a generate a key with 128-bits?

Answer 1

Take a look at the RNGCryptoServiceProvider class, specifically the GetNonZeroBytes method. You could run that string of bytes though a base64 encoding to make it human readable, perhaps.

Answer 2

To generate a random value for crypto use, you should use RNGCryptoServiceProvider:

byte[] bytes = new byte[16];
var rng = new RNGCryptoServiceProvider();
rng.GetBytes(bytes);

To turn this sequence of bytes into a string you could use hex (BitConverter.ToString) or Base64 (Convert.ToBase64String).

---

But there are some strange points here:

• 3DES uses a 168 bit key
• If you want to use symmetric encryption, you should probably use AES. 3DES isn't totally broken, but it's pretty much for legacy use only.
• Be careful about the Block cipher mode of operation you're choosing. You typically need a proper IV, a MAC and a secure chaining mode
• Often you actually should hash passwords instead of encrypting them. See How to securely hash passwords? on security.SE for details.

Answer 3

I understand perfectly what you want Instead of passing urls with htttp: //mydomain.com? Id = 123, you want to pass with an encrypted value. And when someone clicks on this url with encrypted id, you want to decrypt the value of the url.

There are 2 procedures for this:

In encryption: 1 - Convert the "ID" (usually an integer) to a string. Example var NewId = Convert.ToString ((ID); 2 - Use a phrase to shuffle the encryption. Example: "I love chocolate" (this phrase can be fished from your parameter database if you have one ...)

In decryption: 1 - Use the same blocking phrase to unscramble. 2 - Convert what was decrypted to an integer again, using Convert.ToInt32 (Shuffled Variable Above)

You will have to implement 2 functions:

Function for encrypt:

private string Encrypt(string clearText)
    {
        string EncryptionKey = "I love chocolate";
        byte[] clearBytes = System.Text.Encoding.Unicode.GetBytes(clearText);
        using (Aes encryptor = Aes.Create())
        {
            Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(EncryptionKey, new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 });
            encryptor.Key = pdb.GetBytes(32);
            encryptor.IV = pdb.GetBytes(16);
            using (MemoryStream ms = new MemoryStream())
            {
                using (CryptoStream cs = new CryptoStream(ms, encryptor.CreateEncryptor(), CryptoStreamMode.Write))
                {
                    cs.Write(clearBytes, 0, clearBytes.Length);
                    cs.Close();
                }
                clearText = Convert.ToBase64String(ms.ToArray());
            }
        }
        return clearText;
    }

Function for Decryption:

private string Decrypt(string cipherText)
    {
        string EncryptionKey = "I love chocolate";
        byte[] cipherBytes = Convert.FromBase64String(cipherText);
        using (Aes encryptor = Aes.Create())
        {
            Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(EncryptionKey, new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 });
            encryptor.Key = pdb.GetBytes(32);
            encryptor.IV = pdb.GetBytes(16);
            using (MemoryStream ms = new MemoryStream())
            {
                using (CryptoStream cs = new CryptoStream(ms, encryptor.CreateDecryptor(), CryptoStreamMode.Write))
                {
                    cs.Write(cipherBytes, 0, cipherBytes.Length);
                    cs.Close();
                }
                cipherText = System.Text.Encoding.Unicode.GetString(ms.ToArray());
            }
        }
        return cipherText;
    }

When encrypting an ID as ID = "123", you will have a value for the ID as ID = "B8 + iXv5 / 8BUQEbHt8 // fGA ==".

When you decrypt the ID value "B8 + iXv5 / 8BUQEbHt8 // fGA ==" you will get "123" again.

A sample in C#:

  var OriginalId = 123;
          var EncrypetedId = Encrypt(Convert.ToString(OriginalId));
          //for recovering original value
          var OriginalID = Convert.ToInt32(Decrypt(EncrypetedId));

I hope this can help you.