I want to make 2 applications. The first will crypt the file and sign it. The second will be encrypt and verify the data. I use the following code as example.
using System;
using System.Security.Cryptography;
using System.Text;
class RSACSPSample
{
static void Main()
{
try
{
// Create a UnicodeEncoder to convert between byte array and string.
ASCIIEncoding ByteConverter = new ASCIIEncoding();
string dataString = "Data to Sign";
// Create byte arrays to hold original, encrypted, and decrypted data.
byte[] originalData = ByteConverter.GetBytes(dataString);
byte[] signedData;
// Create a new instance of the RSACryptoServiceProvider class
// and automatically create a new key-pair.
RSACryptoServiceProvider RSAalg = new RSACryptoServiceProvider();
// Export the key information to an RSAParameters object.
// You must pass true to export the private key for signing.
// However, you do not need to export the private key
// for verification.
RSAParameters Key = RSAalg.ExportParameters(true);
// Hash and sign the data.
signedData = HashAndSignBytes(originalData, Key);
// Verify the data and display the result to the
// console.
if(VerifySignedHash(originalData, signedData, Key))
{
Console.WriteLine("The data was verified.");
}
else
{
Console.WriteLine("The data does not match the signature.");
}
}
catch(ArgumentNullException)
{
Console.WriteLine("The data was not signed or verified");
}
}
public static byte[] HashAndSignBytes(byte[] DataToSign, RSAParameters Key)
{
try
{
// Create a new instance of RSACryptoServiceProvider using the
// key from RSAParameters.
RSACryptoServiceProvider RSAalg = new RSACryptoServiceProvider();
RSAalg.ImportParameters(Key);
// Hash and sign the data. Pass a new instance of SHA1CryptoServiceProvider
// to specify the use of SHA1 for hashing.
return RSAalg.SignData(DataToSign, new SHA1CryptoServiceProvider());
}
catch(CryptographicException e)
{
Console.WriteLine(e.Message);
return null;
}
}
public static bool VerifySignedHash(byte[] DataToVerify, byte[] SignedData, RSAParameters Key)
{
try
{
// Create a new instance of RSACryptoServiceProvider using the
// key from RSAParameters.
RSACryptoServiceProvider RSAalg = new RSACryptoServiceProvider();
RSAalg.ImportParameters(Key);
// Verify the data using the signature. Pass a new instance of SHA1CryptoServiceProvider
// to specify the use of SHA1 for hashing.
return RSAalg.VerifyData(DataToVerify, new SHA1CryptoServiceProvider(), SignedData);
}
catch(CryptographicException e)
{
Console.WriteLine(e.Message);
return false;
}
}
}
The problem is I can not understand how can I get OriginalData (1-st parameter) for the function VerifySignedHash? I mean the application (signature checker) will read the signed data. How can I convert the signed data to original data for the data verifying?