C#

using System.IO;
using System.Security.Cryptography;
private readonly string Key=@"MyKey";
private void EncryptFile(string inputFile, string outputFile)
        {
            try
            {
                // Your Key Here
                UnicodeEncoding UE = new UnicodeEncoding();
                byte[] key = UE.GetBytes(Key);
                string cryptFile = outputFile;
                FileStream fsCrypt = new FileStream(cryptFile, FileMode.Create);
                RijndaelManaged RMCrypto = new RijndaelManaged();
                CryptoStream cs = new CryptoStream(fsCrypt,
                    RMCrypto.CreateEncryptor(key, key),
                    CryptoStreamMode.Write);
                FileStream fsIn = new FileStream(inputFile, FileMode.Open);
                int data;
                while ((data = fsIn.ReadByte()) != -1)
                    cs.WriteByte((byte)data);

                fsIn.Close();
                cs.Close();
                fsCrypt.Close();
            }
            catch
            {
                XtraMessageBox.Show("Encryption failed!", "Error");
            }
        }
       
        ///<summary>
        /// Decrypts a file using Rijndael algorithm.
        ///</summary>
        ///<param name="inputFile"></param>
        ///<param name="outputFile"></param>
       
private void DecryptFile(string inputFile, string outputFile)
        {
            {
                 // Your Key Here
                UnicodeEncoding UE = new UnicodeEncoding();
                byte[] key = UE.GetBytes(Key);
                FileStream fsCrypt = new FileStream(inputFile, FileMode.Open);
                RijndaelManaged RMCrypto = new RijndaelManaged();
                CryptoStream cs = new CryptoStream(fsCrypt,
                    RMCrypto.CreateDecryptor(key, key),
                    CryptoStreamMode.Read);
                FileStream fsOut = new FileStream(outputFile, FileMode.Create);
                int data;
                while ((data = cs.ReadByte()) != -1)
                    fsOut.WriteByte((byte)data);
                fsOut.Close();
                cs.Close();
                fsCrypt.Close();
            }
        }