using System.Security;
using System.Security.Cryptography;

public class RSAPKCS1SHA256SignatureDescription : SignatureDescription
{
  public RSAPKCS1SHA256SignatureDescription()
  {
   KeyAlgorithm = typeof(RSACryptoServiceProvider).FullName;
   DigestAlgorithm = typeof(SHA256CryptoServiceProvider).FullName;
   FormatterAlgorithm = typeof(RSAPKCS1SignatureFormatter).FullName;
   DeformatterAlgorithm = typeof(RSAPKCS1SignatureDeformatter).FullName;
  }

  public override AsymmetricSignatureDeformatter CreateDeformatter(AsymmetricAlgorithm key)
  {
   if (key == null)
   {
    throw new ArgumentNullException("key");
   }

   RSAPKCS1SignatureDeformatter deformatter = new RSAPKCS1SignatureDeformatter(key);
   deformatter.SetHashAlgorithm("SHA256");
   return deformatter;
  }

  public override AsymmetricSignatureFormatter CreateFormatter(AsymmetricAlgorithm key)
  {
   if (key == null)
   {
    throw new ArgumentNullException("key");
   }

   RSAPKCS1SignatureFormatter formatter = new RSAPKCS1SignatureFormatter(key);
   formatter.SetHashAlgorithm("SHA256");
   return formatter;
  }
}

if (CryptoConfig.CreateFromName("http://www.w3.org/2001/04/xmldsig-more#rsa-sha256") == null)
{
  CryptoConfig.AddAlgorithm(typeof(RSAPKCS1SHA256SignatureDescription),
      "http://www.w3.org/2001/04/xmldsig-more#rsa-sha256");
}

if (CryptoConfig.CreateFromName("http://www.w3.org/2001/04/xmlenc#sha256") == null)
{
  CryptoConfig.AddAlgorithm(typeof(SHA256CryptoServiceProvider), "http://www.w3.org/2001/04/xmlenc#sha256");
}