HMAC MD5 on Windows Phone 7 / Silverlight

I'm trying to generate a HMAC_MD5 algorithm on Windows Phone 7. As as I discovered , HMACMD5 class in not implemented in WP7. On the other hand, I found a MD5 Silverlight library ( http://archive.msdn.开发者_StackOverflow社区microsoft.com/SilverlightMD5 ), but I cannot generate a new MD5 signature based on predefined key. Any hints ? Thanks, Alex

If the Silverlight library won't work (though as Matt points out, without code it's hard to say what might be going wrong), Bouncy Castle supports just about every encryption type out there and it has Compact Framework support, so it's likely to work fine in Windows Phone.