What is Web Services Enhancements ( WSE) and its various versions?

Web Services Enhancements (WSE) is an add-on to the Microsoft .NET Framework which includes a set of classes that implement additional WS-* Web service specifications chiefly in areas such as security, reliable messaging, and sending attachments. [1] Web services communicate via SOAP messages.

WSE provides extensions to the SOAP protocol and allows the definition of custom security, reliable messaging, policy, etc. Developers can add these capabilities at design time using code or at deployment time through the use of a policy file.

WSE 1.0 for .NET Framework 1.0 was released in December 2002. It was based on the draft version of WS-Security. It is not supported anymore and is not compatibile with .NET 2.0.

WSE 2.0 was released for Visual Studio .NET 2003 and the .NET Framework 1.1 in May 2004. It introduced major secure communication improvements (signing and encryption of user-defined SOAP headers, Kerberos Security Context Tokens, delegated trust etc), a new lightweight messaging infrastructure, a new programming model, support for SOAP based messaging over TCP as an alternative to HTTP, a policy framework based on WS-Policy and WSDL, WS-Addressing, WS-Trust, WS-SecureConversation support.

WSE 3.0 was released in October 2005 and has design time support with Visual Studio 2005. It includes policy framework enhancements including security based on policy assertions (associating CLR client proxies with policy files), turnkey security scenarios for securing end to end messages, extensibility mechanisms for user-defined policies in code and a simplified policy model applied to a message exchange instead of on a per-message level.