Feeds

PGP, GPG defeated

Not broken, just beaten

  • alert
  • submit to reddit

Build a business case: developing custom apps

OpenPGP and GnuPG are susceptible to a chosen-cyphertext attack which would allow an adversary capable of intercepting an encrypted message to use the intended recipient as an unwitting 'decryption oracle', researchers Kahil Jallad, Jonathan Katz and Bruce Schneier report in a recent paper.

In a nutshell, Jane sends an encrypted e-mail message to Dick. Unfortunately, Bill intercepts Jane's message and forwards her message to Dick following a bit of tinkering. When Dick receives it, he's puzzled by an incomprehensible message. If he replies to Bill for clarification with the cyphertext in his reply, and if he has his crypto program set on cruise control, Bill may well be able to read Jane's message.

Of course there are numerous complications which we'll get to presently, but conceptually that's all there is to it. It's similar to a man-in-the-middle attack, only Dick and Jane are not kept under the illusion that they're communicating with each other.

The authors have confirmed that the attack can be exploited practically.

However, it's not exactly easy. One obstacle for the attacker, Bill, is to tempt Dick into replying. If they're already acquainted, this should be easy. If they're strangers, then a bit of social engineering will be in order. The most obvious point of failure, then, is the problem of causing Dick to take action.

On the technical front, there are a number of conditions which have to be met for the attack to succeed. First, Dick has to set his PGP or GPG application to encrypt automatically, or somehow choose to encrypt a reply to what appears to be a nonsense message. Second, if he uses the crypto application's compression feature (which is normal) the attack will fail. With GPG it fails because of an integrity check which is not actually required by the standard, but which is widely employed. With PGP it fails because, while the standard requires that 'uncompressed' be a valid condition, no one follows the requirement.

If Dick's reply is not compressed by the crypto app, but is compressed with an outside application, the attack will succeed.

What this example shows is that the standard is wrong and that the attack is unlikely in the real world merely because the rules are not being followed. The team recommends, obviously, that the standard be modified to protect against this sort of attack. It also illustrates the importance of a holistic approach to crypto applications.

It's not enough that an algorithm is strong. As we reported recently, a buffer overflow vulnerability in Network Associates' PGP plugin for MS Outlook on Windows was capable of compromising the user's privacy, and even of giving up his machine. In this case, too, there was no 'breaking' of the algorithm. It was simply an attack against a component of a crypto application, which in practical terms is just as bad.

The research team's paper describes the chosen-cyphertext attack in gruesome detail, parts of which, I readily confess, went in one eye and out the other as I read it. ®

5 things you didn’t know about cloud backup

More from The Register

next story
PEAK LANDFILL: Why tablet gloom is good news for Windows users
Sinofsky's hybrid strategy looks dafter than ever
Leaked Windows Phone 8.1 Update specs tease details of Nokia's next mobes
New screen sizes, dual SIMs, voice over LTE, and more
Fiendishly complex password app extension ships for iOS 8
Just slip it in, won't hurt a bit, 1Password makers urge devs
Mozilla keeps its Beard, hopes anti-gay marriage troubles are now over
Plenty on new CEO's todo list – starting with Firefox's slipping grasp
Apple: We'll unleash OS X Yosemite beta on the MASSES on 24 July
Starting today, regular fanbois will be guinea pigs, it tells Reg
Another day, another Firefox: Version 31 is upon us ALREADY
Web devs, Mozilla really wants you to like this one
Secure microkernel that uses maths to be 'bug free' goes open source
Hacker-repelling, drone-protecting code will soon be yours to tweak as you see fit
Cloudy CoreOS Linux distro declares itself production-ready
Lightweight, container-happy Linux gets first Stable release
prev story

Whitepapers

7 Elements of Radically Simple OS Migration
Avoid the typical headaches of OS migration during your next project by learning about 7 elements of radically simple OS migration.
Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
Consolidation: The Foundation for IT Business Transformation
In this whitepaper learn how effective consolidation of IT and business resources can enable multiple, meaningful business benefits.
Solving today's distributed Big Data backup challenges
Enable IT efficiency and allow a firm to access and reuse corporate information for competitive advantage, ultimately changing business outcomes.
A new approach to endpoint data protection
What is the best way to ensure comprehensive visibility, management, and control of information on both company-owned and employee-owned devices?