For an embedded device, TLS certificate validation presents some unique challenges. The obvious problem is the limited processing power, but the real issue is that a typical root CA bundle is well over 100KB and there may not be enough storage available for it. One possible workaround is simply authenticating the server’s public key based on a hash, similar to how SSH works. While there are some drawbacks, this is secure if implemented correctly. If not… well, that’s where I come in.

Sometimes hacking requires doing things that, while possible to do with some algorithm, simply aren’t supported by any existing implementation. Usually for good reason. A good example of this that I’ve run into in the past is needing to initialize a hash algorithm with a specific state. There’s really not any reason to do this unless you’re trying to execute a length extension attack, and with the exception of HashPump (which was written specifically for that use case) I’m not aware of any library that supports it. I recently ran into this with problem with RSA.

In the spring of 2014, I found a bug in several browsers, including Epiphany, Xombrero, Opera Mini and Midori. They were loading subresources, such as scripts, from HTTPS servers without doing proper certificate validation. I tracked this down to some bad defaults in webkit which have since been fixed.

Sometimes I do things for no real reasons other than “because I can” and/or “it amuses me”. For example, embedding a snarky message into my HTTPS certificate.