david wong

Hey ! I'm David, a security consultant at Cryptography Services, the crypto team of NCC Group . This is my blog about cryptography and security and other related topics that I find interesting.

Moxie and TLS February 2016

I have mix feelings about the UI of Signal, but watching these two videos from Moxie at different periods of TLS' life, I now have a brand new admiration for the person.

The two videos are here:

In both of them, he start talking about his sslsnif: a great tool that you can find here, written in C++ and that allows you to serve clients fallacious certs taking advantage of browsers vulnerabilities (such as not checking for basic constraints fields in the certificate chain, stop reading subject names after null bytes, etc...)

Another tools that he released, coded in python, is sslstrip. The thing takes advantage of the fact that almost no one types https:// in the address bar when navigating to a website directly. A man-in-the-middle attacker can stop the redirection to https and serve the entire website either through http or through another https website which url looks similar to the victim's website (thanks to some unicode to make it look like victimwebsite.com/something/?yourwebsite.com where yourwebsite.com is the real website being visited).

https' only purpose is to defend against man-in-the-middle attacker. Because of sslstrip, any active attacker on the network can render https completely useless. Security measures to prevent that, that I can think of, are HSTS headers, preloaded HSTS (see chrome's one) and HPKP (see Tim Taubert's blogpost.)

Both tools needs arpspoof to create the man-in-the-middle position. I've discovered another tool that seems to combine all of these tools in one (but I'm not really sure what's the difference here): bettercap. It looks good also.

Other tools I've discovered, that verify how the client's handle certificate verification: one is developed by some coworker and is called tlspretense, the other one is called x509test and seem to be pretty popular too. I have no idea how both these tools perform, I guess I will check that next time I to.

Well done! You've reached the end of my post. Now you can leave me a comment :)

Martin Rublik

Bettercap also implements sslstrip along with Leonardo Nve's workaround/bypass of HSTS. See more here https://www.bettercap.org/blog/sslstripping-and-hsts-bypass/