Blind RSA signature using .NET cryptography API?

Question

I'd like to implement a blind RSA signature in .NET. Is there any way to use the standard System.Security.Cryptography APIs to achieve this?

The "obvious" idea doesn't work:

using (var rsa = new RSACryptoServiceProvider())
  signed = rsa.Decrypt(messageBytes, false);
                // CryptographicException: bad data

I appreciate the dangers of blind signature but let's ignore those for a moment. Also, I'm not interested in other types of digital signatures.

Answer 1

You are going to have to roll you own. You can use the BigInteger class of .NET 4 or just use the Bouncycastle C# library.