RSA and xml-formatted public key in cocoa

How can I fill RSA structure with xml-formatted public key for using with RSA functions on Mac OS X. In other words: There are following windows c# statements:

 RSACryptoServiceProvider rSA = new RSAC开发者_C百科ryptoServiceProvider();
 rSA.FromXmlString(xmlKey);
 return rSA.VerifyData(Encoding.UTF8.GetBytes(message), "MD5", signature);

how can I convert it to use with cocoa frameworks.

Thanks, Vlad

I have found the solution to the problem. First I convert XML-formatted RSA key to pem-format. Second I use SSCrypto framework to verify data.