using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;

namespace Aes_Example
{
    class AesExample
    {
        // Mensagem que sera criptografada.
        const string mensagem = "Mensagem que sera criptografada.";
        // Senha definida da operadora.
        const String chave = "uexDPnPr";

        public static void Main()
        {
            try
            {
                byte[] pwdBytes = BuildKey(chave);

                byte[] encrypted = EncryptStringToBytes_Aes(mensagem, pwdBytes);
                string roundtrip = DecryptStringFromBytes_Aes(encrypted, pwdBytes);

                Console.WriteLine("Original:   {0}", mensagem);
                Console.WriteLine("Criptografado: {0}", Convert.ToBase64String(encrypted));
                Console.WriteLine("Descriptografado: {0}", roundtrip);
                Console.ReadKey();

            }
            catch (Exception e)
            {
                Console.WriteLine("Error: {0}", e.Message);
            }
        }
        
        static byte[] BuildKey(string chave)
        {
        	SHA256Managed sha256algorithm = new SHA256Managed();
        	byte[] originalKeyBytes = Encoding.UTF8.GetBytes(chave);
        	byte[] keyBytes = sha256algorithm.ComputeHash(originalKeyBytes);
        	// primeiros 16 bytes do SHA-256        	
        	Array.Resize(ref keyBytes, 16);

        	return keyBytes;
        }
        
        static SymmetricAlgorithm GetCipher(byte[] key)
        {
        	Aes aesAlg = Aes.Create("AES");
        	aesAlg.BlockSize = 128;
            aesAlg.KeySize = 128;
            aesAlg.Mode = CipherMode.ECB;
            aesAlg.Padding =  PaddingMode.PKCS7;  
            aesAlg.Key = key;
            aesAlg.IV = new byte[16];

            
            return aesAlg;
        }
        
        static byte[] EncryptStringToBytes_Aes(string plainText, byte[] Key)
        {
            // Check arguments.
            if (plainText == null || plainText.Length <= 0)
                throw new ArgumentNullException("plainText");
            if (Key == null || Key.Length <= 0)
                throw new ArgumentNullException("Key");
            byte[] encrypted;
            // Create an Aes object
            // with the specified key and IV.
            using (SymmetricAlgorithm aesAlg = GetCipher(Key))
            {
                // Create a decrytor to perform the stream transform.
                ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);

                // Create the streams used for encryption.
                using (MemoryStream msEncrypt = new MemoryStream())
                {
                    using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
                    {
                        using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
                        {

                            //Write all data to the stream.
                            swEncrypt.Write(plainText);
                        }
                        encrypted = msEncrypt.ToArray();
                    }
                }
            }

            // Return the encrypted bytes from the memory stream.
            return encrypted;
        }

        static string DecryptStringFromBytes_Aes(byte[] cipherText, byte[] Key)
        {
            // Check arguments.
            if (cipherText == null || cipherText.Length <= 0)
                throw new ArgumentNullException("cipherText");
            if (Key == null || Key.Length <= 0)
                throw new ArgumentNullException("Key");

            // Declare the string used to hold
            // the decrypted text.
            string plaintext = null;

            // Create an Aes object
            // with the specified key and IV.
            using (SymmetricAlgorithm aesAlg = GetCipher(Key))
            {

                // Create a decrytor to perform the stream transform.
                ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);

                // Create the streams used for decryption.
                using (MemoryStream msDecrypt = new MemoryStream(cipherText))
                {
                    using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
                    {
                        using (StreamReader srDecrypt = new StreamReader(csDecrypt))
                        {

                            // Read the decrypted bytes from the decrypting  stream
                            // and place them in a string.
                            plaintext = srDecrypt.ReadToEnd();
                        }
                    }
                }
            }
            return plaintext;
        }
    }
}