Csharp/CSharp Tutorial/Security/RSA

Asymmetric cryptography

using System;
using System.IO;
using System.Security.Cryptography;
class MainClass
{
  public static void Main() 
  {
    RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
    Byte[] testData = {1, 2, 3, 4, 5, 6, 7, 8};
    Byte[] encryptedData = rsa.Encrypt(testData, false);
    Console.WriteLine("Encrypted data:");
    for(int i=0; i<encryptedData.GetLength(0); i++)
    {
      Console.Write("{0} ", encryptedData[i]);
    }
    Byte[] decryptedData = rsa.Decrypt(encryptedData, false);
    Console.WriteLine("Decrypted Data:");
    for(int i=0; i<decryptedData.GetLength(0); i++)
    {
      Console.Write("{0} ", decryptedData[i]);
    }
  }
}

Encrypted data:
105 216 155 138 34 149 122 27 220 172 6 69 23 21 224 142 30 166 81 141 15 234 144 235 122 187 99 245
 222 252 154 234 211 79 251 80 253 221 94 91 222 86 225 17 0 96 161 179 155 251 123 140 38 6 161 78
111 193 19 222 251 74 172 104 100 61 39 106 113 67 69 45 237 47 194 189 62 168 98 230 196 149 249 11
3 29 19 66 10 84 73 110 142 142 255 120 138 200 207 79 190 151 164 53 4 198 254 78 203 86 102 233 10
7 216 13 41 166 125 155 58 48 214 27 116 93 211 176 191 183 Decrypted Data:
1 2 3 4 5 6 7 8

Encrypt with RSACryptoServiceProvider

using System;
using System.IO;
using System.Security;
using System.Security.Cryptography;
using System.Collections.Generic;
using System.Text;
    class Program
    {
        static void Main(string[] args)
        {
            RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
            StreamReader sr = File.OpenText("myKey.xml");
            string rsaXml = sr.ReadToEnd();
            sr.Close();
            rsa.FromXmlString(rsaXml);
            string messageToJane = "this is a test";
            byte[] encrypted = rsa.Encrypt(System.Text.ASCIIEncoding.ASCII.GetBytes(messageToJane), false);
            FileStream fs = new FileStream("Message.dat", FileMode.Create);
            fs.Write(encrypted, 0, encrypted.Length);
            fs.Close();
        }
    }

RSACryptoServiceProvider reads from xml key

using System;
using System.IO;
using System.Security;
using System.Security.Cryptography;
using System.Collections.Generic;
using System.Text;
    class Program
    {
        static void Main(string[] args)
        {
            StreamReader sr = File.OpenText("myKey.xml");
            string myKey = sr.ReadToEnd();
            sr.Close();
            RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
            rsa.FromXmlString(myKey);
            FileStream fs = new FileStream("Message.dat", FileMode.Open);
            byte[] encrypted = new byte[fs.Length];
            fs.Read(encrypted, 0, (int)fs.Length);
            byte[] decrypted = rsa.Decrypt(encrypted, false);
            fs.Close();
            Console.WriteLine(System.Text.ASCIIEncoding.ASCII.GetString(decrypted));
            
        }
    }

Using RSACryptoServiceProvider

using System;
using System.IO;
using System.Security.Cryptography;
using System.Collections.Generic;
using System.Text;
    class Program
    {
        static void Main(string[] args)
        {
            string verifiableMesage = "this is a test";
            SHA1Managed sha = new SHA1Managed();
            byte[] hashValue = sha.ruputeHash(System.Text.ASCIIEncoding.ASCII.GetBytes(verifiableMesage));
            StreamReader sr = File.OpenText("Key.xml");
            string myKey = sr.ReadToEnd();
            RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
            rsa.FromXmlString(myKey);
            RSAPKCS1SignatureFormatter sigFormatter = new RSAPKCS1SignatureFormatter(rsa);
            sigFormatter.SetHashAlgorithm("SHA1");
            byte[] signedHash = sigFormatter.CreateSignature(hashValue);
            FileStream fs = new FileStream("signedHash.dat", FileMode.Create);
            fs.Write(signedHash, 0, signedHash.Length);
            fs.Close();
        }
    }

Using RSAPKCS1SignatureDeformatter

using System;
using System.IO;
using System.Security;
using System.Security.Cryptography;
using System.Collections.Generic;
using System.Text;
    class Program
    {
        static void Main(string[] args)
        {
            string verifiableMesage = "this is a test";
            string     wrongMessage = "this is another test";
            SHA1Managed sha = new SHA1Managed();
            byte[] verifiableMessageHash = sha.ruputeHash(System.Text.ASCIIEncoding.ASCII.GetBytes(verifiableMesage));
            byte[] wrongMessageHash = sha.ruputeHash(System.Text.ASCIIEncoding.ASCII.GetBytes(wrongMessage));
            FileStream fs = new FileStream("signedHash.dat", FileMode.Open);
            byte[] fileHash = new byte[fs.Length];
            fs.Read(fileHash, 0, (int)fs.Length);
            fs.Close();
            StreamReader sr = File.OpenText("myKey.xml");
            string myKey = sr.ReadToEnd();
            sr.Close();
            RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
            rsa.FromXmlString(myKey);
            RSAPKCS1SignatureDeformatter sigDeformatter = new RSAPKCS1SignatureDeformatter(rsa);
            sigDeformatter.SetHashAlgorithm("SHA1");
            Console.WriteLine(sigDeformatter.VerifySignature(verifiableMessageHash, fileHash));
            Console.WriteLine(sigDeformatter.VerifySignature(wrongMessageHash, fileHash) == false);
        }
    }