Astoria - new Tor client designed to be more resistant to timing attacks

AntiTree antitree at
Tue May 26 07:31:57 PDT 2015

The research shows that being AS-aware will reduce timing attacks (that
NSA, GCHQ and other well funded groups can support) from 58% chance of
exploitation, to 5.8% by strategically creating circuits with more
divergent AS owners. I wouldn't get hung up on Astoria itself as it's
mostly just a PoC for additional value to their grant writers and
university. The functions can be (relatively) easily integrated into Tor in
the future. I suspect there may be some expansion on the Tor circuit
building algorithm it uses. [1]

It's also a great summary of the new threat model based on some of the
recent disclosures. No longer academic threats, we now see examples of
timing attacks in the wild.



On Sat, May 23, 2015 at 2:28 AM Jesse Taylor <jessetaylor84 at>

>  Curious to hear your thoughts on this
> <>:
> ---
> *With the threat of powerful intelligence agencies, like the* *NSA
> <>**, looming large, researchers have built a
> new* *Tor <>* *client called* *Astoria
> <>* *designed specifically to make
> eavesdropping harder for the world's richest, most aggressive, and most
> capable spies.*
> *Tor, the world's most popular anonymity network, works like this: A user
> fires up the client and connects to the network through what's called an
> entry node. To reach a website anonymously, the user's Internet traffic is
> then passed encrypted through a so-called middle relay and then an exit
> relay (and back again). That user-relay connection is called a circuit. The
> website on the receiving end doesn't know who is visiting, only that a
> faceless Tor user has connected.* *An eavesdropper shouldn't be able to
> know who the Tor user is either, thanks to the encrypted traffic being
> routed through 6,000 nodes in the network.* *But something called "timing
> attacks" change the situation. When an adversary takes control of both the
> entry and exit relays, research shows they can potentially deanonymize Tor
> users **within minutes <>**.*
> *A full 58 percent of Tor circuits are vulnerable to network-level
> attackers, such as the NSA or Britain's Government Communications
> Headquarters (GCHQ), when they access popular websites, according to new* *research
> <>* *from American and Israeli
> academics. Chinese users are the most vulnerable of all to these kinds of
> attacks, with researchers finding 85.7 percent of all Tor circuits from the
> country to be vulnerable.*
> *Even though Tor is designed to provide complete anonymity to its users,
> the NSA's position means they can potentially see and measure both traffic
> entering the Tor network and the traffic that comes out. When an
> intelligence agency can see both,**simple statistics
> <>* *help an autonomous
> system at their control match the data up in a timing attack and discover
> the identity of the sender.* *Anonymity over.* *This kind of threat has
> been known to Tor developers for over a decade. They've been trying to make
> eavesdropping difficult for spy agencies for just as long.*
> *To counter the threat, American-Israeli researchers built Astoria, a new
> Tor client focused on defeating autonomous systems that can break Tor's
> anonymity.* *Astoria reduces the number of vulnerable circuits from 58
> percent to 5.8 percent, the researchers say. The new solution is the first
> designed to beat even the most** recently
> <>* *proposed
> <>* *asymmetric correlation
> attacks on Tor.*
> *Designed to beat such attacks, Astoria differs most significantly from
> Tor's default client in how it selects the circuits that connect a user to
> the network and then to the outside Internet. The tool, at its foundation,
> is an algorithm designed to more accurately predict attacks and then
> securely select relays that mitigate timing attack opportunities for
> top-tier adversaries.*
> *Astoria adroitly considers how circuits should, according to the
> researchers, be made "when there are no safe possibilities," how to safely
> balance the growing bandwidth load across the Tor network, and how to keep
> Tor's performance "reasonable" and relatively fast even when Astoria is in
> its most secure configuration.* *All this while under the unblinking gaze
> of the world's best intel services.* *Defeating timing attacks against
> Tor completely isn't possible because of how Tor is built, but making the
> attacks more costly and less likely to succeed is a pastime that Tor
> developers have dedicated a decade to. Astoria follows in those footsteps.* *By
> choosing relays based on lowering the threat of eavesdropping by autonomous
> systems and then choosing randomly if no safe passage is possible, Astoria
> aims to minimize the information gained by an adversary watching an entire
> circuit.*
> *"In addition to providing high-levels of security against such attacks,
> Astoria also has performance that is within a reasonable distance from the
> current Tor client," the researchers wrote. "Unlike other AS-aware Tor
> clients, Astoria also considers how circuits should be built in the worst
> case--i.e., when there are no safe relays that are available. Further,
> Astoria is a good network citizen and works to ensure that the all circuits
> created by it are load-balanced across the volunteer driven Tor network."*
> *In an upgrade aimed at making Tor even more usable for the average
> person, the newest Tor Browser allows a sliding scale of security that
> balances speed and usability with strong security preferences.* *Similarly,
> Astoria provides multiple security options. However, it's both most
> effective and most usable when at its highest security level, the
> researchers say, so "Astoria is a usable substitute for the vanilla Tor
> client only in scenarios where security is a high priority."*
> ---
> Source:
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