WS-Security and SSL

Over the holiday season I’ve been catching up on a (few) of the unread posts in my feedreader, which is how I stumbled rather belatedly onto a set of back and forth blog rants between Peter Lacey and Gunner Peterson. The subject of thier discourse is the relative merits of the WS-* and REST Web Services stacks.

The REST/WS-* debate is shaping up to be another of those dogmatic, eternal flame wars (like vi vs. emacs). I usually avoid these kind of black hole discussions like the plague, but I feel compelled to comment on this particular one.

Specifically I’m quite disturbed by Peterson’s repeated attempts (this being the most blatent) to claim that SSL is insecure or is somehow less secure than WS-Security. This is of course totally bullshit.

Message oriented security technologies (like WS-Security) provide *additional* security functionality beyond that provide by transport security (like SSL or IPSEC), but they also introduce significant additional risks. Message oriented security technologies in general expose a much greater attack surface than transport oriented security.

The WS-Security specifically is also a very new, very immature spec that is *very* complicated. It would be incredible naive to assume that current generation WS-Security libraries are sufficiently hardened. The complexity and flexibility of the spec itself is also cause for concern, just take a peek at how many non-obvious pitfalls have to be avoided to securely use the username/password token in WS-Security! Any implementation of WS-Security is also dependant upon the security of the XML parsing library used, and securing against XML based attacks is still a discipline in it’s infancy.

The obvious truth is that WS-Security and SSL are complementary, not competing technologies. I’ve never seen a WS-Security protected web service exposed to the Internet without SSL, nor do I ever expect to see one. (or at least, to see one survive 🙂 )

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