michaelrash

The design decisions that govern fwknop provide guidance on how fwknop is different from knockknock: http://www.cipherdyne.org/fwknop/docs/fwknop-tutorial.html#d...

Not exactly. OpenSSH gated by SPA can only be interacted with by an attacker that can either hijack an SPA-authenticated connection, or is on the same network as the SPA client if the client must go through a NAT. This is a fairly limited set of possible attackers. For those not in this set, how can they interact with OpenSSH without first breaking SPA?

There are some similarities between this and SPA:

-> | SPA / fwknop | ssh

There are important differences too though (beyond the fact that SPA is not encrypting/decrypting traffic for SSH itself). SPA is a UDP authenticator so it cannot be scanned.

Design goals: http://www.cipherdyne.org/fwknop/docs/fwknop-tutorial.html#d...

An adversary who can watch port knocking sequences is one reason why SPA was developed:

http://www.cipherdyne.org/fwknop/docs/fwknop-tutorial.html#w...

SPA is applicable to arbitrary services - not just SSH. Essentially it is a lightweight UDP authenticator, and it can be applied to commercial VPN's, webservers, or anything else. Achieving asymmetric costs on attackers is easily achievable for many such services.

Some information on this is located in the fwknop tutorial:

http://www.cipherdyne.org/fwknop/docs/fwknop-tutorial.html

Here is a rebuttal to the "why not" argument:

http://www.cipherdyne.org/blog/2013/10/port-knocking-why-you...

Ok, that sounds like a reasonable alternative, and Brendan Greeg is certainly a powerful force in this area. I'll run dtrace and see what happens, but I'm going to let a current long-running fuzzing run finish first.

On the VM, AFL is rewriting the same small file millions of times, and the fuzzed program is reading this file from disk (as opposed to stdin). I think the main question is why does the OS X activity monitor show a massive spike in disk writes when AFL is started and a corresponding decrease when it is stopped? This is 100% reproducible, and the magnitude of the change is unmistakable. It is absolutely clear that the spike in disk writes is due to AFL activity. Further, this same spike does not happen when running under a RAM disk on the VM. I'm confident you would see the same result. So, either the OS X activity monitor has some special way to measure caching in the VM and that is what it is showing (surely this is unlikely), or the writes really are hitting the SSD when not running under the RAM disk. If not the later, what other (realistic) possibility is there?

Remember from the article that AFL is being run from a VM. So, my guess is that OS X (host) doesn't know anything about whether what is being written on the VM is a small file or not. There are two possibilities: 1) either the OS X activity monitor is actually measuring disk+cache when it says "disk writes" or 2) disk writes really are happening as fast as shown in the graphs. My bet is the later. What saves things here is the usage of the RAM disk on the guest, since at least that is a clean mechanism for really only using RAM instead of disk - and that carries through from the guest to the host.

First, let me state that I have a lot of respect for Moxie. That out of the way, knockknock is not above criticism too:

1) It is possible to mount a MITM attack against knockknock just by intercepting a knockknock packet, changing the source IP, and retransmitting. This is a consequence of knockknock not encrypting the source IP within any payload (which involve only packet headers in the knockknock implementation). fwknop does not suffer from this problem because it encrypts the IP to be allowed within the SPA payload. 2) You mention time synchronization issues above. Well, knockknock uses AES in CTR mode, and this also requires synchronization between the client and server of a different kind. If synchronization were a problem for fwknop, then you must apply this critique to knockknock too. You _can_ disable time sync in fwknop if you really want to, but it was added to prevent MITM attacks.

Here are the design goals that fwknop is developed around:

http://www.cipherdyne.org/fwknop/docs/fwknop-tutorial.html#d...