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Here the namespace that is used is system.security.cryptography and the methods and properties of the rijndael method is used.

Here is source code of the C# Program to Encrypt/Decrypt using Rijndael Key. The C# program is successfully compiled and executed with Microsoft Visual Studio. The program output is also shown below.

/*
 * C# Program to Encrypt/Decrypt using Rijndael Key
 */
using System;
using System.IO;
using System.Security.Cryptography;
namespace RijndaelManage
{
    class Rijndael
    {
        public static void Main()
        {
            try
            {
 
                string original = "Data For Encryption!!!!!";
                using (RijndaelManaged myRijndael = new RijndaelManaged())
                {
 
                    myRijndael.GenerateKey();
                    myRijndael.GenerateIV();
                    byte[] encrypted = EncryptStringToBytes(original, 
                                       myRijndael.Key, myRijndael.IV); 
                    string aftdecryp = DecryptStringFromBytes(encrypted, 
                                       myRijndael.Key, myRijndael.IV);
                    Console.WriteLine("Original:   {0}", original);
                    Console.WriteLine("After Decryption: {0}", aftdecryp);
                }
 
            }
            catch (Exception e)
            {
                Console.WriteLine("Error: {0}", e.Message);
            }
        }
        static byte[] EncryptStringToBytes(string plainText, byte[] Key, byte[] IV)
        {
            if (plainText == null || plainText.Length <= 0)
                throw new ArgumentNullException("plainText");
            if (Key == null || Key.Length <= 0)
                throw new ArgumentNullException("Key");
            if (IV == null || IV.Length <= 0)
                throw new ArgumentNullException("Key");
            byte[] encrypted; 
            using (RijndaelManaged rijAlg = new RijndaelManaged())
            {
                rijAlg.Key = Key;
                rijAlg.IV = IV;
                ICryptoTransform encryptor = rijAlg.CreateEncryptor(rijAlg.Key, 
                                             rijAlg.IV); 
                using (MemoryStream msEncrypt = new MemoryStream())
                {
                    using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, 
                            encryptor, CryptoStreamMode.Write))
                    {
                        using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
                        {
                            swEncrypt.Write(plainText);
                        }
                        encrypted = msEncrypt.ToArray();
                    }
                }
            }
            return encrypted;
        }
        static string DecryptStringFromBytes(byte[] cipherText, byte[] Key, byte[] IV)
        { 
            if (cipherText == null || cipherText.Length <= 0)
                throw new ArgumentNullException("cipherText");
            if (Key == null || Key.Length <= 0)
                throw new ArgumentNullException("Key");
            if (IV == null || IV.Length <= 0)
                throw new ArgumentNullException("Key"); 
            string plaintext = null; 
            using (RijndaelManaged rijAlg = new RijndaelManaged())
            {
                rijAlg.Key = Key;
                rijAlg.IV = IV;
                ICryptoTransform decryptor = rijAlg.CreateDecryptor(rijAlg.Key, 
                                             rijAlg.IV); 
                using (MemoryStream msDecrypt = new MemoryStream(cipherText))
                {
                    using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, 
                           decryptor, CryptoStreamMode.Read))
                    {
                        using (StreamReader srDecrypt = new StreamReader(csDecrypt))
                        {
                            plaintext = srDecrypt.ReadToEnd();
                        }
                    }
                }
 
            }
 
            return plaintext;
         }
    }
}

This C# program is used to demonstrate how to generate a persistent (i.e. non-random) symmetric key using the Rijndael and use this key to encrypt and decrypt a text string. The key is derived from several characteristics passed to encryption and decryption routines.

This class uses a symmetric key algorithm (Rijndael/AES) to encrypt and decrypt data. As long as encryption and decryption routines use the same parameters to generate the keys, the keys are guaranteed to be the same. The class uses static functions with duplicate code to make it easier to demonstrate encryption and decryption logic.

Create a new instance of the Rijndael class. This generates a new key and initialization vector. The GenerateKey() method is used to override, when overridden in a derived class, generates a random key () to use for the algorithm. And Generate() method is used to override, when overridden in a derived class, generates a random initialization vector to use for the algorithm.

Encrypt the string to an array of bytes and decrypt the bytes to a string. Print the original data and the decrypted data. Using if condition statements check an argument. Create a Rijndael object with the specified key and IV.

Then decrypt to perform the stream transform and create the streams used for encryption. Using RijndaelManaged write all data to the stream and return the encrypted bytes from the memory stream. Using if condition statements check the arguments.

Declare the string used to hold, and create a Rijndael object with the specified key and IV. Create a decryptor to perform the stream transform and also create the streams used for decryption. Then we are reading the decrypted bytes from the decrypting stream and place them in a string.

C# Program to Encrypt/Decrypt a String using Rijndael Key