Encrypting and Signing Isolated Storage Files
The System.Security.Cryptography and System.Security.Cryptography.X509Certificates namespaces contain classes that enable you to encrypt or sign files. In Silverlight, the primary cryptography scenario is encrypting isolated storage files that are used by Silverlight-based applications.
For a complete example of encrypting and decrypting an isolated storage file, see the System.Security.Cryptography.AesManaged class.
For a complete example of signing and checking the signature of an isolated storage file, see the System.Security.Cryptography.HMACSHA256 class.
For an overview of cryptography in the .NET Framework, see Cryptographic Services in the .NET Framework documentation.