Aes дешифрация байтов c#

Вот вам полный пример шифровнии и дешифровании

 static void Main(string[] args)
    {
        try
        {
            string original = "This is my encription string";
            var myAes = Aes.Create();
            var encriptKey = myAes.Key;
            var encriptIV = myAes.IV;
            byte[] encrypted = EncriptDecryptClass.EncryptString(myAes, original, encriptKey, encriptIV);
            string decrypted = EncriptDecryptClass.DecryptString(myAes, encrypted, encriptKey, encriptIV);
            Console.WriteLine("Original:   {0}", original);
            Console.WriteLine("Enxription Text");
            foreach (var item in encrypted)
            {
                Console.Write(item);
            }
            Console.WriteLine("\n");
            Console.WriteLine("Decript Text: {0}", decrypted);
        }
        catch (Exception e)
        {
            Console.WriteLine("Error: {0}", e.Message);
        }
    }
    public static class EncriptDecryptClass
    {
        public static byte[] EncryptString(Aes aesAlgoritm, 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("IV");
            byte[] encrypted;
            ICryptoTransform encryptor = aesAlgoritm.CreateEncryptor(Key, 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;
        }
        public static string DecryptString(Aes aesAlgoritm, 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("IV");
            string plaintext = null;
            ICryptoTransform decryptor = aesAlgoritm.CreateDecryptor(Key, 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;
        }
    }  

И добавьте

using System.IO;
using System.Security.Cryptography;
Вот вам еще один способ для реализации этого

  static void Main(string[] args)
    {
        string original = "This is my encription string";
        string password = "myPassword";
        Console.WriteLine(original);
        var encript = CryptoClass.EncryptStringAES(original, password);
        using (StreamWriter write=new StreamWriter(@"C:\doc.txt"))
        {
            write.Write(encript);
        }
        Console.WriteLine(encript);
        string str;
        using (FileStream fs = new FileStream(@"C:\doc.txt", FileMode.Open))
        {
            using (StreamReader read = new StreamReader(fs))
            {
                str = read.ReadToEnd();
            }
        }
        var decript = CryptoClass.DecryptStringAES(str, password);
        Console.WriteLine(decript);
    }
    public class CryptoClass
    {
        public static byte[] GenerateRandomSalt()
        {
            byte[] data = new byte[32];
            using (RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider())
            {.
                for (int i = 0; i < 10; i++)
                {.
                    rng.GetBytes(data);
                }
            }
            return data;
        }
        private static byte[] _salt = GenerateRandomSalt();
        public static string EncryptStringAES(string plainText, string sharedSecret)
        {
            if (string.IsNullOrEmpty(plainText))
                throw new ArgumentNullException("plainText");
            if (string.IsNullOrEmpty(sharedSecret))
                throw new ArgumentNullException("sharedSecret");
            string outStr = null;                      
            RijndaelManaged aesAlg = null;         
            try
            {
                Rfc2898DeriveBytes key = new Rfc2898DeriveBytes(sharedSecret, _salt);
                aesAlg = new RijndaelManaged();
                aesAlg.Key = key.GetBytes(aesAlg.KeySize / 8);
                ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);
                using (MemoryStream msEncrypt = new MemoryStream())
                {
                    msEncrypt.Write(BitConverter.GetBytes(aesAlg.IV.Length), 0, sizeof(int));
                    msEncrypt.Write(aesAlg.IV, 0, aesAlg.IV.Length);
                    using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
                    {
                        using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
                        {
                            swEncrypt.Write(plainText);
                        }
                    }
                    outStr = Convert.ToBase64String(msEncrypt.ToArray());
                }
            }
            finally
            {
                if (aesAlg != null)
                    aesAlg.Clear();
            }
            return outStr;
        }
        public static string DecryptStringAES(string cipherText, string sharedSecret)
        {
            if (string.IsNullOrEmpty(cipherText))
                throw new ArgumentNullException("cipherText");
            if (string.IsNullOrEmpty(sharedSecret))
                throw new ArgumentNullException("sharedSecret");
            RijndaelManaged aesAlg = null;
            string plaintext = null;
            try
            {
                Rfc2898DeriveBytes key = new Rfc2898DeriveBytes(sharedSecret, _salt);               
                byte[] bytes = Convert.FromBase64String(cipherText);
                using (MemoryStream msDecrypt = new MemoryStream(bytes))
                { 
                    aesAlg = new RijndaelManaged();
                    aesAlg.Key = key.GetBytes(aesAlg.KeySize / 8);
                    aesAlg.IV = ReadByteArray(msDecrypt);
                    ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);
                    using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
                    {
                        using (StreamReader srDecrypt = new StreamReader(csDecrypt))
                            plaintext = srDecrypt.ReadToEnd();
                    }
                }
            }
            finally
            {
                if (aesAlg != null)
                    aesAlg.Clear();
            }
            return plaintext;
        }
        private static byte[] ReadByteArray(Stream s)
        {
            byte[] rawLength = new byte[sizeof(int)];
            if (s.Read(rawLength, 0, rawLength.Length) != rawLength.Length)
            {
                throw new SystemException("Stream did not contain properly formatted byte array");
            }
            byte[] buffer = new byte[BitConverter.ToInt32(rawLength, 0)];
            if (s.Read(buffer, 0, buffer.Length) != buffer.Length)
            {
                throw new SystemException("Did not read byte array properly");
            }
            return buffer;
        }

Чтобы дешифратор заработал, необходимо было удалить соль на этапе шифрования (я добавлял ее в конец).