Common Darknet Weaknesses: An Overview of Attack Strategies

Adrian Crenshaw, a well-known InfoSec expert and author of Irongeek.com, provides a comprehensive overview of known darknets at AIDE Conference.

About Adrian

About Adrian

Hello everyone! My name is Adrian Crenshaw, and my presentation today is Darknets: An Overview of Attack Strategies. First of all, a little bit about me, if anybody hasn’t been at my presentations before. I’ll make this brief. I run Irongeek.com. I have an interest in InfoSec education. I don’t know everything – I’m just a geek with time on my hands; it’s possible that I get a few things wrong – if so, let me know, I’d be interested in knowing the technical details of what exactly is going on. And I am an (ir)regular on the ISDPodcast, usually every Thursday. I’m also a researcher for Tenacity Institute.

Darknets/Cipherspaces - background

Darknets/Cipherspaces – background

A little background: first of all, what technologies is this talk going to be about? There’s pretty much a million definitions of darknets, but my particular one is, essentially, “anonymizing networks” – generally speaking, the use of encryption and proxies, or systems of several nodes, where you cascade through them to hide who is actually who, who is communicating with who on a network (see right-hand image). Darknets are sometimes also referred to as Cipherspaces; I kind of like this term better because sometimes people use the term “darknet” when they mean only friend to friend, obviously, darknet in the broader sense of Tor in general, I2P in general, and so forth. I’ll be using the terms “Tor” and “I2P” a lot here – those are the two darknets I’m going to be talking the most about; they’ve got major deployment, so these are the ones that I’ll use whenever I use an example. Those seem to be the biggest contenders out of this particular space. When I say “contenders” I don’t necessarily imply competition; they both have slightly different focuses.

A few notes. A lot of this stuff gets subtle, a lot of the attacks get subtle, and getting it to actually function might be a crapshoot. Terms vary from researcher to researcher, so you go out there and read terms in academia, and you’re like: “Ok, what do you mean by this?” I’ve come across the terms “sybil” and “sockpuppet”. I used to be more familiar with the term “sockpuppet” – until I started looking into research and academia, I never heard the term “sybil”.

A few subtleties

A few subtleties

Many of these weaknesses are interrelated (see right-hand image): sometimes one weakness can be used with another weakness to greatly amplify the attack and be able to get past someone’s anonymity. There’s a bunch of anonymizing networks out there; just to name a few: Morphmix, Tarzan, Mixminion, and so forth. But, like I said, I2P and Tor are the two I’ve played the most with. Also, I’m going to try to go more real world with some of these attacks, where this can be actually used vs. some academic stuff. I will be talking about traffic analysis attacks, but I really think application level attacks is probably where the biggest risk is when using these networks.

The threat model

The threat model

Threat model – you can’t protect against everything. I mean, a darknet is not going to protect you from someone sitting in your house looking over your shoulder at your monitor. That’s just the way it is. It’s not going to protect you necessarily, depending on the darknet, from a state agency that can actually, in theory, get ISP records from all ISPs in the United States. Depending on who your adversary is, there’re different threat models (see right-hand image).

Some protocols are actually going to be a lost cause, I will talk about that here in a bit. Most of the people who are using these darknets are using HTTP-based protocols, but some of these protocols, like BitTorrent, unless you’re using a heavy modification – it’s kind of a lost cause.

Some users may end up doing things to reveal themselves. For instance, Tor’s model – if you go out and use protocols that give away your identity, or you use the same name on Tor-hidden services as you do on the public Internet, nothing is going to protect you. Or if you allow six billion different plugins in your browser and use Tor, there’s no guarantee that it’s going to protect you.

Also, different attacks give different levels of information. Some just give details about the Client/Host, who it is behind an IP address. If you have 2 IP addresses, it sometimes just reduces the anonymity set, and it reduces the total amount of people you could possibly be. Instead of being an I2P user, you might say it’s an I2P user in Indiana. That would be an example of reducing someone’s anonymity set. Or possibly because of the posts they make and the things they say or the time they make it, you can get an idea of where in the world they are.

If you allow six billion different plugins in your browser and use Tor, there’s no guarantee that it’s going to protect you.

There’s also active vs. passive attackers. It’s attackers that actually sit there and mess with the network to be able to find out more information. Passive attackers are people who just sit there and sniff traffic but don’t necessarily modify it. Location, location, location – this is kind of similar to the active vs. passive. It denotes if someone’s inside the network already, or they’re outside it, like an ISP.

Adversaries, of course, vary by power. The nation states: like I said, depending on how draconian the laws are in a particular country – that makes a huge difference; also the size of the infrastructure. Government agencies have limited resources depending on what they have; they may have the power, in theory, to maybe say: “Hey, give me all records from this, this and this ISP”, to figure out where the traffic is bouncing through. I’m not sure they’d be able to necessarily track it all down.

It could be someone who runs an ISP, or could be someone who runs a whole lot of nodes. I’ll be talking about sybils and sockpuppets later on. To give you a quick overview of what that is, though, it’s, essentially, someone who controls more than one node in a network, and they can have nodes collude to find out more information.

There’re also some private interests groups that might be interested, for instance RIAA and the MPAA – these people are going to be able to get a tap on your Internet connection directly. And there’re people like me, shmucks with extra time on their hands.

Read next: Common Darknet Weaknesses 2: Tor and I2P

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