Pasted

From memory, you pass the string to be encrypted/decrypted and the passphrase as a single string, separated by a comma. I think that was because this was also to be used in a DLL for use with Delphi etc, but anyway, the point is that this was the simple means of setting up and tearing down AES in C#. Apologies for lack of comments, easier to just strip than to have to sanitise too much for the web.
 
 
using System;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.Security.Cryptography;
using System.Text;
 
namespace BlahLib
{
    public interface IBlahLib
    {
        void TestMethod();
 
        string Encrypt(string original, string key);
        string Decrypt(string encrypted, string key);
        string GetKey(string passphrase);
    }
 
    [ClassInterface(ClassInterfaceType.None)]
    public class BlahLib : IBlahLib
    {
        public BlahLib()
        {
        }
        
        public void TestMethod()
        {
            MessageBox.Show("Hello from the BlahLib class");
        }
 
        public string GetKey(string passphrase)
        {
            RijndaelManaged aesEncryption = new RijndaelManaged();            
            aesEncryption.KeySize = 256;            
            aesEncryption.BlockSize = 128;            
            aesEncryption.Mode = CipherMode.ECB;            
            aesEncryption.Padding = PaddingMode.Zeros;
            aesEncryption.GenerateIV();            
 
            string ivStr = Convert.ToBase64String(aesEncryption.IV);
            byte[] keyText = ASCIIEncoding.UTF8.GetBytes(passphrase);
            string keyStr = Convert.ToBase64String(keyText);  
            string completeKey = ivStr + "," + keyStr;    
            return Convert.ToBase64String(ASCIIEncoding.UTF8.GetBytes(completeKey));        
        }
 
        public string Encrypt(string original, string key)
        {
            RijndaelManaged aesEncryption = new RijndaelManaged();
            aesEncryption.KeySize = 256;
            aesEncryption.BlockSize = 128;
            aesEncryption.Mode = CipherMode.ECB;
            aesEncryption.Padding = PaddingMode.Zeros;
            aesEncryption.IV =
                Convert.FromBase64String(ASCIIEncoding.UTF8.GetString(Convert.FromBase64String(key)).Split(',')[0]);
            aesEncryption.Key =
                Convert.FromBase64String(ASCIIEncoding.UTF8.GetString(Convert.FromBase64String(key)).Split(',')[1]);
 
            byte[] plainText = ASCIIEncoding.UTF8.GetBytes(original);
            ICryptoTransform crypto = aesEncryption.CreateEncryptor();
 
            byte[] cipherText = crypto.TransformFinalBlock(plainText, 0, plainText.Length);
            return Convert.ToBase64String(cipherText);
        }
 
        public string Decrypt(string encrypted, string key)
        {
            RijndaelManaged aesEncryption = new RijndaelManaged();
            aesEncryption.KeySize = 256;
            aesEncryption.BlockSize = 128;
            aesEncryption.Mode = CipherMode.ECB;
            aesEncryption.Padding = PaddingMode.Zeros;
            aesEncryption.IV =
                Convert.FromBase64String(ASCIIEncoding.UTF8.GetString(Convert.FromBase64String(key)).Split(',')[0]);
            aesEncryption.Key =
                Convert.FromBase64String(ASCIIEncoding.UTF8.GetString(Convert.FromBase64String(key)).Split(',')[1]);
 
            ICryptoTransform decrypto = aesEncryption.CreateDecryptor();
 
            byte[] encryptedText = Convert.FromBase64CharArray(encrypted.ToCharArray(), 0, encrypted.Length);
            return ASCIIEncoding.UTF8.GetString(decrypto.TransformFinalBlock(encryptedText, 0, encryptedText.Length));
        }
 
        
    }
}