Form1.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Configuration;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;



namespace MyEncryptionForKey
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void btnEncrypt_Click(object sender, EventArgs e)
        {
            if(!string.IsNullOrEmpty(txtEncryptionPlainWord.Text))
                txtEncryptedWord.Text = Encrypt(txtEncryptionPlainWord.Text);
        }

        private void btnDecrypt_Click(object sender, EventArgs e)
        {
            if (!string.IsNullOrEmpty(txtEncryptedWordToDecrypt.Text))
                txtDecryptWord.Text = Decrypt(txtEncryptedWordToDecrypt.Text);
        }

        public string Encrypt(string plainText)
        {
            string passPhrase = ConfigurationManager.AppSettings["EncryptionPassword"]; ;
            string saltValue = ConfigurationManager.AppSettings["EncryptionSalt"];
            string hashAlgorithm = "SHA1";
            int passwordIterations = 2;
            string initVector = "@1B2c3D4e5F6g7H8";
            int keySize = 256;
            var initVectorBytes = Encoding.ASCII.GetBytes(initVector);
            var saltValueBytes = Encoding.ASCII.GetBytes(saltValue);
            var plainTextBytes = Encoding.UTF8.GetBytes(plainText);
            var password = new PasswordDeriveBytes(passPhrase, saltValueBytes, hashAlgorithm, passwordIterations);
            byte[] keyBytes = password.GetBytes(keySize / 8);
            var symmetricKey = new RijndaelManaged();
            symmetricKey.Mode = CipherMode.CBC;
            ICryptoTransform encryptor = symmetricKey.CreateEncryptor(keyBytes, initVectorBytes);
            var memoryStream = new MemoryStream();
            var cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write);
            cryptoStream.Write(plainTextBytes, 0, plainTextBytes.Length);
            cryptoStream.FlushFinalBlock();
            var cipherTextBytes = memoryStream.ToArray();
            memoryStream.Close();
            cryptoStream.Close();
            string cipherText = Convert.ToBase64String(cipherTextBytes);
            return cipherText;
        }
         public string Decrypt(string cipherText)
        {
            string passPhrase = ConfigurationManager.AppSettings["EncryptionPassword"];
            string saltValue = ConfigurationManager.AppSettings["EncryptionSalt"];
            string hashAlgorithm = "SHA1";
            int passwordIterations = 2;
            string initVector = "@1B2c3D4e5F6g7H8";
            int keySize = 256;
            // Convert strings defining encryption key characteristics into byte
            // arrays. Let us assume that strings only contain ASCII codes.
            // If strings include Unicode characters, use Unicode, UTF7, or UTF8
            // encoding.
            var initVectorBytes = Encoding.ASCII.GetBytes(initVector);
            var saltValueBytes = Encoding.ASCII.GetBytes(saltValue);

            // Convert our ciphertext into a byte array.
            var cipherTextBytes = Convert.FromBase64String(cipherText);

            // First, we must create a password, from which the key will be 
            // derived. This password will be generated from the specified 
            // passphrase and salt value. The password will be created using
            // the specified hash algorithm. Password creation can be done in
            // several iterations.
            var password = new PasswordDeriveBytes(passPhrase, saltValueBytes, hashAlgorithm, passwordIterations);

            // Use the password to generate pseudo-random bytes for the encryption
            // key. Specify the size of the key in bytes (instead of bits).
            byte[] keyBytes = password.GetBytes(keySize / 8);

            // Create uninitialized Rijndael encryption object.
            var symmetricKey = new RijndaelManaged();

            // It is reasonable to set encryption mode to Cipher Block Chaining
            // (CBC). Use default options for other symmetric key parameters.
            symmetricKey.Mode = CipherMode.CBC;

            // Generate decryptor from the existing key bytes and initialization 
            // vector. Key size will be defined based on the number of the key 
            // bytes.
            ICryptoTransform decryptor = symmetricKey.CreateDecryptor(keyBytes, initVectorBytes);

            // Define memory stream which will be used to hold encrypted data.
            var memoryStream = new MemoryStream(cipherTextBytes);

            // Define cryptographic stream (always use Read mode for encryption).
            var cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read);

            // Since at this point we don't know what the size of decrypted data
            // will be, allocate the buffer long enough to hold ciphertext;
            // plaintext is never longer than ciphertext.
            var plainTextBytes = new byte[cipherTextBytes.Length];

            // Start decrypting.
            int decryptedByteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length);

            // Close both streams.
            memoryStream.Close();
            cryptoStream.Close();

            // Convert decrypted data into a string. 
            // Let us assume that the original plaintext string was UTF8-encoded.
            string plainText = Encoding.UTF8.GetString(plainTextBytes, 0, decryptedByteCount);

            // Return decrypted string.   
            return plainText;
        }
    }
}