This program was written to simulate a TLS1 handshake connection, with the long term goal being to implement TLS with email. TLS1 (Transport Layer Security) is only slightly different from SSL3 (Secure Sockets Layer) developed by Netscape. TLS was what the IETF adopted based upon SSL3. This evident in the version number used within the actual protocols. SSL3 is version 3.0 and TLS1 is version 3.1. If you examine the Wikipedia Page on the subject (http://en.wikipedia.org/wiki/Transport_Layer_Security), you will see that virtually all major servers and browsers support TLS 1.0. The same cannot be said for SSL, and the IETF has been strongly recommending that support for fallback to SSL2 be dropped as insecure.
To understand how it all works, you should understand a little bit about Cryptography in general. Cryptography is not really that difficult, but it is very convoluted. There are many competing implementations, and not all of them work together. And the standards don't help that much, as they deal with the issues at the lowest level. Working at that level with VB would be a difficult undertaking and probably not work that well. We could purchase a library/control with all the built-in functions for all or most of the standards, and that would have made life simpler. But then we would have been tied to that control for any fixes or updates. The newer Microsoft Operating Systems come complete with several Crypto Libraries built in, called Cryptographic Service Providers (or CSP's). The one we are interested in is the RSA/Schannel Cryptographic Provider, which provides support for TLS. Microsoft discourages applications from using this CSP directly, choosing instead to limit their support to CSP developers and vendors. But that does not mean it cannot be done. It simply means that information on most of the calls is limited.
J.A. Coutts
To understand how it all works, you should understand a little bit about Cryptography in general. Cryptography is not really that difficult, but it is very convoluted. There are many competing implementations, and not all of them work together. And the standards don't help that much, as they deal with the issues at the lowest level. Working at that level with VB would be a difficult undertaking and probably not work that well. We could purchase a library/control with all the built-in functions for all or most of the standards, and that would have made life simpler. But then we would have been tied to that control for any fixes or updates. The newer Microsoft Operating Systems come complete with several Crypto Libraries built in, called Cryptographic Service Providers (or CSP's). The one we are interested in is the RSA/Schannel Cryptographic Provider, which provides support for TLS. Microsoft discourages applications from using this CSP directly, choosing instead to limit their support to CSP developers and vendors. But that does not mean it cannot be done. It simply means that information on most of the calls is limited.
J.A. Coutts