The Scrypt RSA Library provides asymmetric encryption capabilities for Microsoft Silverlight 3+ and Windows Phone 7. In this initial release we've added RSA Encryption with support for key sizes from 256-bit to 4096-bit.
This library is fully compatible with .NET's built in RSACryptoServiceProvider. Successful testing has been done on a Windows Phone 7 device as well.
Read more: Windows Phone Geek