Question

I have two AsymmetricAlgorithm objects that contain an RSA Private and RSA Public key. The private key was retrieved out of the Windows-MY keystore and the Public key from a user’s certificate. How can I use these keys along with RSACryptoServiceProvider to encrypt data using the RSA algorithm in C#? In other words, how can I specify that I want to use keys that I already have?

Answer 1

#region "RSA Encrypt/Decrypt"  
public string RSAEncrypt(string str, string publicKey)  
{  
  //---Creates a new instance of RSACryptoServiceProvider---  
  try {  
     RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();  
     //---Loads the public key---  
     RSA.FromXmlString(publicKey);  
     byte[] EncryptedStr = null;  

     //---Encrypts the string---  
     EncryptedStr = RSA.Encrypt(ASCII.GetBytes(str), false);  
     //---Converts the encrypted byte array to string---  
     int i = 0;  
     System.Text.StringBuilder s = new System.Text.StringBuilder();  
     for (i = 0; i <= EncryptedStr.Length - 1; i++) {  
         //Console.WriteLine(EncryptedStr(i))  
         if (i != EncryptedStr.Length - 1) {  
             s.Append(EncryptedStr[i] + " ");  
         } else {  
             s.Append(EncryptedStr[i]);  
         }  
     }  

     return s.ToString();  
   } catch (Exception err) {  
     Interaction.MsgBox(err.ToString());  
   }  
}  

public string RSADecrypt(string str, string privateKey)  
{  
  try {  
     //---Creates a new instance of RSACryptoServiceProvider---  
     RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();  
     //---Loads the private key---  
     RSA.FromXmlString(privateKey);  

     //---Decrypts the string---  
     byte[] DecryptedStr = RSA.Decrypt(HexToByteArr(str), false);  
     //---Converts the decrypted byte array to string---  
     System.Text.StringBuilder s = new System.Text.StringBuilder();  
     int i = 0;  
     for (i = 0; i <= DecryptedStr.Length - 1; i++) {  
         //Console.WriteLine(DecryptedStr(i))  
         s.Append(System.Convert.ToChar(DecryptedStr[i]));  
     }  
     //Console.WriteLine(s)  
     return s.ToString();  
  } catch (Exception err) {  
     Interaction.MsgBox(err.ToString());  
  }  
}  
#endregion 

The Public Key (arg) should look like this:
<RSAKeyValue>
<Modulus>yNi8BvATA77f+/6cU6z[…]9VULgU=</Modulus>
<Exponent>AQAB</Exponent>
</RSAKeyValue>

The Private Key (arg) should look like this:
<RSAKeyValue>
<Modulus>yNi8BvATA77f+/6cU6z[…]9VULgU=</Modulus>
<Exponent>AQAB</Exponent>
<P>8ZlZPmko3sam9pvD/l[…]ba0MWLjj9dyUMvmTQ6L8m9IQ==</P>
<Q>1NGHjXyEa9SjUwY[…]v+op2YyyglMeK/Gt5SL0v6xqQZQ==</Q>
<DP>LpjE/aSKnWzzBt1E[…]i5f63Ak9wVG3ZPnwVDwefNkMAQ==</DP>
<DQ>qAgb8AGNiJom[…]8x3qaD3wx+UbnM5v3aE5Q==</DQ>
<InverseQ>fQ4+7r3Nmgvz113L[…]uJqEgCNzw==</InverseQ>
<D>B4n7JNeGHzHe/nqEK[…]GaOBtuz0QTgE=</D>
</RSAKeyValue>