Real Coders Coding

• Published:July 29th, 2008
• Comments:10 Comments
• Category:.NET 2.0, .NET 3.5, Security, Utilities
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So, I've been hoping to make a nice little generic encryption module that essentially just wraps the .Net System stuff.  Why?  'Cause I'd like to move some data around with reasonable security (it doesn't have to be completely hacker-proof, just reasonably obscured -- the data I'm covering isn't worth that much, but it's worth more than zero so it deserves some due process.) This is done with that atitude, if you want hard-core encryption, then your better off not using a wrapper (set your .IV cleverly, don't resize improper-length keys, etc.) Alternatively, use an existing, clean, third party app (or write your own -- R4 is not too terrible to code and is very powerful, especially if you tweak it during the implementation).

Here, I wanted quick, easy, and portable. I've read .Net makes things simple -- didn't really feel that way, so I tried to wrap one of the stronger algorithims, the AesCryptoServiceProvider, into something simple to call.  There are a couple of things to say before the code drops: Microsoft mediates all it's encryption with a "machinekey" -- this can be found in all sorts of places depending on which OS you are using -- I think a common place to find it might be in the IIS configs.  I haven't spent time dealing with this, but it will bite you if you use a web farm -- to use encrpytion across the farm, you're gonna need to sync your machinekeys or you'll only be able to decrypt data which has been encrypted on the same machine (fine for most apps, woe on a webfarm).  I had a couple of false steps with this code, here are the caveats: this builds in 3.5, so you'll have trouble building or running it on anything older than Windows XP (you can run it on Win2000, but that's another article).  There seems to be a common practice of scanning an encrypted byte array buffer and cutting it at the first zero byte -- this will often work, but also fail occasionally enough to drive you nuts -- errors will kick from the StreamReader's ReadToEnd method -- instead use .ToArray (as below) on the memorystream to avoid accidentally truncating your encrypted data.

OK, so, here is the code -- hopefully the formatting is tolerable, I'll have to trim it up a bit, so, sorry if you run into trouble with that (feel free to yell in the comments).

 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
 
using System.Security.Cryptography;
 
namespace AesWrapper
{
public class Encryptor
{
///
/// Encrypts the sourceString, returns this result as an Aes encrypted, BASE64 encoded string
///
/// a plain, Framework string (ASCII, null terminated)
/// returns an Aes encrypted, BASE64 encoded string
public static string EncryptString(string plainSourceStringToEncrypt, byte[] key)
{
//Set up the encryption objects
AesCryptoServiceProvider acsp = Encryptor.GetProvider(key);
byte[] sourceBytes = System.Text.ASCIIEncoding.ASCII.GetBytes(plainSourceStringToEncrypt);
ICryptoTransform ictE = acsp.CreateEncryptor();
 
//Set up stream to contain the encryption
System.IO.MemoryStream msS = new System.IO.MemoryStream();
 
//Perform the encrpytion, storing output into the stream
CryptoStream csS = new CryptoStream(msS, ictE, CryptoStreamMode.Write);
csS.Write(sourceBytes, 0, sourceBytes.Length);
csS.FlushFinalBlock();
 
//sourceBytes are now encrypted as an array of secure bytes
byte[] encryptedBytes = msS.ToArray(); //.ToArray() is important, don't mess with the buffer
 
//return the encrypted bytes as a BASE64 encoded string
return System.Convert.ToBase64String(encryptedBytes);
}
 
///
/// Decrypts a BASE64 encoded string of encrypted data, returns a plain string
///
/// an Aes encrypted AND base64 encoded string
/// any byte array (16 bytes long is optimal)
/// returns a plain string
public static string DecryptString(string base64StringToDecrypt, byte[] key)
{
//Set up the encryption objects
AesCryptoServiceProvider acsp = Encryptor.GetProvider(key);
byte[] RawBytes = System.Convert.FromBase64String(base64StringToDecrypt);
ICryptoTransform ictD = acsp.CreateDecryptor();
//RawBytes now contains original byte array, still in Encrypted state
 
//Decrypt into stream
System.IO.MemoryStream msD = new System.IO.MemoryStream(RawBytes, 0, RawBytes.Length);
CryptoStream csD = new CryptoStream(msD, ictD, CryptoStreamMode.Read);
//csD now contains original byte array, fully decrypted
 
//return the content of msD as a regular string
return (new System.IO.StreamReader(csD)).ReadToEnd();
}
 
private static AesCryptoServiceProvider GetProvider(byte[] key)
{
//Set up the encryption objects
AesCryptoServiceProvider result = new AesCryptoServiceProvider();
byte[] RealKey = Encryptor.GetKey(key, result);
result.Key = RealKey;
result.IV = RealKey;
return result;
}
 
private static byte[] GetKey(byte[] suggestedKey, AesCryptoServiceProvider p)
{
byte[] kRaw = suggestedKey;
List<byte> kList = new List</byte><byte>;
for (int i = 0; i < p.LegalKeySizes[0].MinSize/8; i++ )
{
kList.Add(kRaw[i % kRaw.Length]);
}
byte[] k = kList.ToArray();
return k;
}
 
}
 
}

Ok, that's that.  The methods are all static, so, after you add a reference to the class, you can call it like this (testSource is any typical source string, button3 is just a button on my test form):

private void button3_Click(object sender, EventArgs e)
{
byte[] kRaw = { 2, 3, 5, 7, 11, 17 }; //whatever key you want
MessageBox.Show(testSource); //raw source
string enc = AesWrapper.Encryptor.EncryptString(testSource, kRaw);
MessageBox.Show(enc); //ecrypted
MessageBox.Show(AesWrapper.Encryptor.DecryptString(enc,kRaw)); //decrypted
}