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Generating Signatures

Digital signatures are usually applied to hash values that represent larger data. The following example applies a digital signature to a hash value. First, a new instance of the RSACryptoServiceProvider class is created to generate a public/private key pair. Next, the RSACryptoServiceProvider is passed to a new instance of the RSAPKCS1SignatureFormatter class. This transfers the private key to the RSAPKCS1SignatureFormatter, which actually performs the digital signing. Before you can sign the hash code, you must specify a hash algorithm to use. This example uses the SHA1 algorithm. Finally, the RSAPKCS1SignatureFormatter.CreateSignature method is called to perform the signing.

class Class1
{
   static void Main()
   {
      //The hash value to sign.
      byte[] HashValue = {59,4,248,102,77,97,142,201,210,12,224,93,25,41,100,197,213,134,130,135};

      //The value to hold the signed value.
      byte[] SignedHashValue;

      //Generate a public/private key pair.
      RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();

      //Create an RSAPKCS1SignatureFormatter object and pass it the 
      //RSACryptoServiceProvider to transfer the private key.
      RSAPKCS1SignatureFormatter RSAFormatter = new RSAPKCS1SignatureFormatter(RSA);

      //Set the hash algorithm to SHA1.
      RSAFormatter.SetHashAlgorithm("SHA1");

      //Create a signature for HashValue and assign it to 
      //SignedHashValue.
      SignedHashValue = RSAFormatter.CreateSignature(HashValue);
   }
}

The .NET Framework provides the System.Security.Cryptography.XML namespace, which allows you sign XML. Signing XML is important when you want to verify that the XML originates from a certain source. For example, if you are using a stock quote service that uses XML, you can verify the source of the XML if it is signed.

The classes in this namespace follow the World Wide Web Consortium recommendation "XML-Signature Syntax and Processing," described at www.w3.org.

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