Re: Public Key Encryption with RSACryptoServiceProvider
From: AlBruAn (albruan_at_hotmail.com.(donotspam))
Date: 06/25/04
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Date: Fri, 25 Jun 2004 11:55:01 -0700
"Pieter Philippaerts" wrote:
> "AlBruAn" <AlBruAn@discussions.microsoft.com> wrote in message
> > I'm attempting to use the RSACryptoServiceProvider class to encrypt some
> licensing information I'm storing in SQL Server, but I'm encountering a "Bad
> Data" CryptographicException when I try decrypting the data and wonder how I
> can get around this issue. I'm not storing any information in SQL Server
> until I can get the mechanics of encryption working properly. Anyway...
> > I've generated a pair of public and private keys using
> RSACryptoServiceProvider's ToXml function, passing false and true arguments,
> respectively, to it. I then persist these keys to the root directory of my
> C: drive using an XmlTextWriter.
> > When it's time to encrypt a license number, I create a new instance of the
> RSACryptoServiceProvider object and read in the public key using its FromXml
> function. I then call the Encrypt function, passing it the license number
> and specifying no OAEP padding. My final step is to persist the encrypted
> values to a separate file in the root directory of my C: drive.
>
> From your description, there doesn't seem to be an abvious error. Could you
> post the source code you're using so we can take a closer look?
>
> > Even tho' I'm using the string "123" as my "license number" and using the
> same
> > public key, I'm getting different values for the encrypted "license
> number".
>
> This is normal; whenever you encrypt something, the RSACryptoServiceProvider
> will add a special padding to your data to make sure the length is equal to
> the modulus size of your public key. This padding consists mostly of random
> bytes, hence the difference.
>
> Regards,
> Pieter Philippaerts
>
>
It's rather long, but here is the class I wrote to try using the RSACryptoServiceProvider:
using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;
using System.Xml;
namespace TryRSA
{
class EncryptDecrypt
{
public void DoThis(string Msg, bool Encode)
{
try
{
UnicodeEncoding ByteConverter = new UnicodeEncoding();
byte[] dataToEncrypt = ByteConverter.GetBytes("Data to Encrypt");
byte[] encryptedData;
byte[] decryptedData;
//Create a new instance of RSACryptoServiceProvider to generate
//public and private key data.
RSACryptoServiceProvider RSA = new RSACryptoServiceProvider(1024);
// Generate and persist the private and/or public keys
GenKeys(RSA, Encode);
if (Encode == true)
{
encryptedData = RSAEncrypt(dataToEncrypt, false);
string encoded;
StreamWriter sw = new StreamWriter("C:\\Encrypted.dat");
UTF8Encoding utf8 = new UTF8Encoding();
encoded = utf8.GetString(encryptedData);
sw.WriteLine(encoded);
sw.Close();
}
else
{
StreamReader sr = new StreamReader("C:\\Encrypted.dat");
string encoded = sr.ReadLine();
sr.Close();
UTF8Encoding utf8 = new UTF8Encoding();
encryptedData = utf8.GetBytes(encoded);
decryptedData = RSADecrypt(encryptedData, false);
Console.WriteLine("Decrypted plaintext: {0}", ByteConverter.GetString(decryptedData));
}
}
catch(ArgumentNullException)
{
Console.WriteLine("Encryption failed.");
}
}
static public byte[] RSAEncrypt(byte[] DataToEncrypt, bool DoOAEPPadding)
{
try
{
RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();
RSA.FromXmlString(publicKey);
return RSA.Encrypt(DataToEncrypt, DoOAEPPadding);
}
catch(CryptographicException e)
{
Console.WriteLine(e.Message);
return null;
}
}
static public byte[] RSADecrypt(byte[] DataToDecrypt, bool DoOAEPPadding)
{
try
{
RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();
RSA.FromXmlString(privateKey);
return RSA.Decrypt(DataToDecrypt, DoOAEPPadding);
}
catch(CryptographicException e)
{
Console.WriteLine(e.ToString());
return null;
}
}
static private string _publicKey;
static private string publicKey
{
get { return _publicKey; }
set { _publicKey = value; }
}
static private string _privateKey;
static private string privateKey
{
get { return _privateKey; }
set { _privateKey = value; }
}
public void GenKeys(RSACryptoServiceProvider RSA, bool Encode)
{
string publicKeyFileName = "C:\\public.key";
string privateKeyFileName = "C:\\private.key";
if (Encode == true)
{
// Public key
if (!File.Exists(publicKeyFileName))
{
publicKey = RSA.ToXmlString(false);
FileStream FileWriter = new FileStream(publicKeyFileName, FileMode.Create);
XmlTextWriter XmlWriter = new XmlTextWriter(FileWriter, System.Text.Encoding.UTF8);
XmlWriter.WriteRaw(publicKey);
XmlWriter.Close();
FileWriter.Close();
}
else
{
FileStream FileReader = new FileStream(publicKeyFileName, FileMode.Open);
XmlTextReader XmlReader = new XmlTextReader(FileReader);
XmlDocument XmlDoc = new XmlDocument();
XmlDoc.Load(XmlReader);
publicKey = XmlDoc.InnerXml;
XmlReader.Close();
FileReader.Close();
}
}
else
{
// Private key
if (!File.Exists(privateKeyFileName))
{
privateKey = RSA.ToXmlString(true);
FileStream FileWriter = new FileStream(privateKeyFileName, FileMode.Create);
XmlTextWriter XmlWriter = new XmlTextWriter(FileWriter, System.Text.Encoding.UTF8);
XmlWriter.WriteRaw(privateKey);
XmlWriter.Close();
FileWriter.Close();
}
else
{
FileStream FileReader = new FileStream(privateKeyFileName, FileMode.Open);
XmlTextReader XmlReader = new XmlTextReader(FileReader);
XmlDocument XmlDoc = new XmlDocument();
XmlDoc.Load(XmlReader);
privateKey = XmlDoc.InnerXml;
XmlReader.Close();
FileReader.Close();
}
}
}
}
}
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