One Way Encryption and Decryption Acting Unexpectedly

Question

I have two functions that should encrypt and decrypt a given file:

        public static void Encrypt(string name, string skey)
        {
            using (var sourceStream = File.OpenRead(name))
            using (var destinationStream = File.Create(name + ".sav"))
            using (var provider = new AesCryptoServiceProvider())
            using (var cryptoTransform = provider.CreateEncryptor())
            using (var cryptoStream = new CryptoStream(destinationStream, cryptoTransform, CryptoStreamMode.Write))
            {
                provider.Padding = PaddingMode.None;
                List key = new List();
                key.AddRange(ASCIIEncoding.ASCII.GetBytes(skey));
                while (key.Count < 32)
                {
                    key.Add(0);
                }
                provider.Key = key.ToArray();
                destinationStream.Write(provider.IV, 0, provider.IV.Length);
                sourceStream.CopyTo(cryptoStream);
            }
        }

        public static void Decrypt(string name, string skey)
        {
            // Decrypt the source file and write it to the destination file.
            using (var sourceStream = File.OpenRead(name + ".sav"))
            using (var destinationStream = File.Create(name))
            using (var provider = new AesCryptoServiceProvider())
            {
                provider.Padding = PaddingMode.None;
                List key = new List();
                key.AddRange(ASCIIEncoding.ASCII.GetBytes(skey));
                while(key.Count < 32)
                {
                    key.Add(0);
                }
                var IV = new byte[provider.IV.Length];
                sourceStream.Read(IV, 0, IV.Length);
                using (var cryptoTransform = provider.CreateDecryptor(key.ToArray(), IV))
                using (var cryptoStream = new CryptoStream(sourceStream, cryptoTransform, CryptoStreamMode.Read))
                {
                    cryptoStream.CopyTo(destinationStream);
                }
            }
        }

Using the text document (d):



  d
  foo

The following program:

        static void Main(string[] args)
        {
            string pass = "foo";
            Encrypt("d", pass);
            Decrypt("d", pass);
        }

Results in the text document (d):

豄襚釞뮲冋ⵂૠɥ摸▪穨嶾⏘ﳿ僣ꙍ帏પ軆ꝍ遨䄩䰀玢⊟尩㯇Ўꉚ파 駧㪡襻긗몸뵊➯턊鏶㠌늸㗐蕛貣ㆪⲫ咻ꨱ壉뷢䅱眡�׀罹吗඘㶝�晊垚猰Ġ�淧脽ᣉ赮榑㄁舎㈁쾹͂쵎숵戥힠┻蔦쬦눲ꔲ빬䁔㸻�ⵄ➞ޅ㥿࠾ऱ룮﫪２侚神ヵ튙腶㖮衦ྗ

It seems that decrypting the message is causing the unexpected result however I don't what I should expect in the "*.sav" files besides random noise. Checking the watchlist provider.key is an array that reads out 102, 111, 111, 0 ... 0 in both Encrypt and Decrypt methods.

user_2057955 · Answer

Okay so your problem is that you are creating Encryptor but never set it's IV.

Change the Encrypt method like so:

public static void Encrypt(string name, string skey)
    {
        // First, process key
        List key = new List();
        key.AddRange(ASCIIEncoding.ASCII.GetBytes(skey));
        while (key.Count < 32)
        {
            key.Add(0);
        }

        using (var sourceStream = File.OpenRead(name))
        using (var destinationStream = File.Create(name + ".sav"))
        using (var provider = new AesCryptoServiceProvider())
        using (var cryptoTransform = provider.CreateEncryptor(key.ToArray(), provider.IV)) // when creating Encryptor pass the key and the IV of the provider.
        using (var cryptoStream = new CryptoStream(destinationStream, cryptoTransform, CryptoStreamMode.Write))
        {
            provider.Padding = PaddingMode.None;

            provider.Key = key.ToArray();
            destinationStream.Write(provider.IV, 0, provider.IV.Length);
            sourceStream.CopyTo(cryptoStream);
        }
    }

One Way Encryption and Decryption Acting Unexpectedly

1 Answers