Chink in encryption armor discovered

Chink in encryption armor discovered

Summary: An underlying design flaw in the widely used encryption protocol OpenSSH has been made public by researchers.

TOPICS: Security
An underlying flaw in the widely used encryption protocol Open Secure Shell (OpenSSH) has been made public by researchers from the Royal Holloway, University of London.

The flaw, which lies in version 4.7 of OpenSSH on Debian/GNU Linux, allows 32 bits of encrypted text to be rendered in plaintext, according to a research team from the Royal Holloway Information Security Group (ISG).

An attacker has a 2^{-18} (that is, one in 262,144) chance of success. ISG lead professor Kenny Patterson told ZDNet UK last Monday that the flaw was more significant than previous vulnerabilities in OpenSSH.

"This is a design flaw in OpenSSH," said Patterson. "The other vulnerabilities have been more about coding errors."

According to Patterson, a man-in-the-middle attacker could sit on a network and grab blocks of encrypted text as they are sent from client to server. By re-transmitting the blocks to the server, an attacker can work out the first four bytes of corresponding plaintext. The attacker can do this by counting how many bytes the attacker sends until the server generates an error message and tears down the connection, then working backwards to deduce what was in the OpenSSH encryption field before encryption.

The attack relies on flaws in the RFC (Request for Comments) internet standards that define SSH, said Patterson.

Patterson gave a talk on Monday at the IEEE Symposium on Security and Privacy in California to explain his group's research findings. The three ISG academics involved in the research were Patterson, Martin Albrecht and Gaven Watson.

This vulnerability was first made public in November 2008 by the UK Centre for the Protection of National Infrastructure (CPNI), although full details of the flaw were not then given. According to the CPNI advisory, the OpenSSH flaw could be mitigated by IT professionals using AES in counter mode (CTR) to encrypt, instead of cipher-block chaining mode (CBC).

Patterson said his group had worked with OpenSSH developers to mitigate the flaw, and that OpenSSH version 5.2 contained countermeasures.

"They've fixed [OpenSSH]; they've put countermeasures in place to stop our attack," said Patterson. "But the standard has not changed."

Patterson said that he did not believe this flaw had been exploited in the wild, and that to deduce a message of appreciable length could take days. In addition, proprietary SSH vendors had been informed of the issue in advance, and had put countermeasures in their code. However, Patterson added that it always takes time for sysadmins to apply patches to servers and clients, no matter whether the software is open source or proprietary.

This article was originally posted on ZDNet UK.

Topic: Security

Tom Espiner

About Tom Espiner

Tom is a technology reporter for He covers the security beat, writing about everything from hacking and cybercrime to threats and mitigation. He also focuses on open source and emerging technologies, all the while trying to cut through greenwash.

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  • It's KINK! not Chink!

    What's with everyone using the word chink to
    describe a kink in armor?

    Unless of course this is a racial slur aimed at
    Chinese hackers. Maybe I should read the
    article before I comment.
    • No, it's "c h i n k".

      Maybe you should look up the phrase before you comment. There is no such phrase as "kink in the armor". But I digress...
    • check your dictionary?


      (meaning 1 - "a crack, cleft, or fissure: a c[b][/b]hink in a wall.")
      Kink is practically synonymous in the context, but there's absolutely nothing wrong with the world used in this article (just something wrong with the over-the-top racism filter on comments).

      C[b][/b]hink is more appropriate to the armour metaphor.
  • See that! Even ZDNet thinks so

    It actually bleeped out C H I N K
  • RE: ***** in encryption armor discovered

    Oh come on now! Do you also see little green men running around your home at night, how about monsters under your bed? You and the rest of the "politically correct police" see things where they don't exist. Get a life already and realize that chink and kin may be interchangeable!
  • Chink is a proper word for gap or small hole.

    The word in question is chink. it is not a racial slur, it is a description of a gap or small hole.

    the whole problem with politically correct speach is that if politics is the art of compromise and one is already correct, there is no room for compromise. therefore it is all politically wrong.
  • RE: ***** in encryption armor discovered

    lol... its part of the title and ZDNet sensors it.
    gosh that hallarious... I've seen it happen before on
    a ZDNet blog, but I don't remember what word.
  • RE: ***** in encryption armor discovered


    Sounds dangerous.........

    For the OpenSSH users ;)
  • not debian specific, worse...

    Article reads like this is a debian flaw. It is an openssh flaw, and per the original advisory, "We expect any RFC-compliant SSH implementation to be vulnerable to some form of the attack." So, probably an anyssh flaw.

  • Uh, say what?

    "An underlying flaw in the widely used encryption protocol Open Secure Shell (OpenSSH) ..."

    There's no protocol called "Open Secure Shell". SSH is the protocol name, OpenSSH is an implementation. It's 2009 and we still don't have any tech journos who can write cogently about this kind of crap? Unreal.
  • Thanks OpenBSD for fixing OpenSSH, for every OS!

    Thanks OpenBSD for putting together some counter measures for those of us still using Debian with an old version of OpenSSH!

    Nice to see OpenBSD do this, even though the [IETF?] hasn't changed the 'standards' flaw(s) in those RFC's.

    My $0.02.