Encryption with Generated K eys.

1. Encryption with Generated Keys. • Encryption: • Symmetric - • The same that is used to encrypt the data is also used to decrypt the data. • They are all "BLOCK CIPHERS" • Take unencrypted data and break it into blocks of all the same size. • Each block is encrypted. • "CIPHER BLOCK CHAINING" • Each Block is combined with the previous blocks encryption. • "INITIALIZATION VECTOR" (IV) • Data starting point • Must be stored like the key. • Use symmetric when the same application encrypts and decrypts the data. • .NET algorithms (System.Security.Cryptography, SymmetricAlgorithm class) • Data Encryption Standard (DES) • Triple Data Encryption Algorithm (3DES/TDEA) • RC2 • Rijndael/Advanced Encryption Standard (AES) • aesManaged classes

2. Encryption with Generated Keys. • Encryption: • Symmetric cont'd- • Generating Keys • RNGCryptoServiceProvider class (hashing) • Minimum and maximum key sizes (LegalKeySizes property) • DES: 64 - 64 bits • 3DES: 128 - 192 bits • RC2: 40 - 128 bits • AES: 128 - 256 bits • 128 (standard for SSL) is usually sufficient • Initialization Vectors • Size = to block size (BlockSize property) protected void FillOutDetailFields(SymmetricAlgorithmsymmetricAlgorithm) { this.keySize.Text = symmetricAlgorithm.KeySize.ToString(); this.blockSize.Text = symmetricAlgorithm.BlockSize.ToString(); this.key.Text = Convert.ToBase64String(symmetricAlgorithm.Key); this.initializationVector.Text = Convert.ToBase64String(symmetricAlgorithm.IV); }

3. Encryption with Generated Keys. • Encryption: • Symmetric cont'd- • Generating Keys protected void Page_Load(object sender, EventArgs e) { if (!Page.IsPostBack) { SymmetricAlgorithmsymmetricAlgorithm = this.CreateSymmetricAlgorithm(this.algorithm.Text); this.FillOutDetailFields(symmetricAlgorithm); } } static byte[] GenerateRandomBytes(int length) { byte[] key = new byte[length]; RNGCryptoServiceProvider provider = new RNGCryptoServiceProvider(); provider.GetBytes(key); return key; }

4. Encryption with Generated Keys. • Encryption: • 1. Choose an Algorithm • SymmetricAlgorithmsymmetricAlgorithm = this.CreateSymmetricAlgorithm(this.algorithm.Text); • 2. Create or retrieve key. • symmetricAlgorithm.Key = Convert.FromBase64String(this.key.Text); • 3. Generate the IV. • symmetricAlgorithm.IV = Convert.FromBase64String(this.initializationVector.Text); • 4. Convert the clear text data to an array of bytes. • 5. Encrypt the clear text byte array. • ICryptoTransformencryptor = symmetricAlgorithm.CreateEncryptor(symmetricAlgorithm.Key, symmetricAlgorithm.IV); • // Create the streams used for encryption. • MemoryStreammemoryStream = new MemoryStream(); • using (CryptoStreamcryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write)) • { • byte[] plainTextAsBytes = new UTF8Encoding(false).GetBytes(this.plainText.Text); • cryptoStream.Write(plainTextAsBytes, 0, plainTextAsBytes.Length); • } • symmetricAlgorithm.Clear(); • byte[] encryptedData = memoryStream.ToArray(); • 6. Store the encryption data and the IV. • this.encryptedValue.Text = Convert.ToBase64String(encryptedData); • 7. If the key is new store it.

5. Encryption with Generated Keys. Decryption: 1. Choose the same algorithm that was used to encrypt the data. SymmetricAlgorithmsymmetricAlgorithm = this.CreateSymmetricAlgorithm(this.algorithm.Text); 2. Retrieve the key that was used. symmetricAlgorithm.Key = Convert.FromBase64String(this.key.Text); 3. Retrieve the IV that was used. symmetricAlgorithm.IV = Convert.FromBase64String(this.initializationVector.Text); 4. Retrieve the encrypted data. 5. Decrypt the data. ICryptoTransformdecryptor = symmetricAlgorithm.CreateDecryptor(symmetricAlgorithm.Key, symmetricAlgorithm.IV); // Create the streams used for encryption. MemoryStreammemoryStream = new MemoryStream(); using (CryptoStreamcryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Write)) { byte[] encryptedBytes = Convert.FromBase64String(this.encryptedValue.Text); cryptoStream.Write(encryptedBytes, 0, encryptedBytes.Length); } symmetricAlgorithm.Clear(); 6. Convert the data back to its original form. this.plainText.Text = new UTF8Encoding(false).GetString(memoryStream.ToArray());