Re: [TLS] HTTPS client-certificate-authentication in browsers

Peter Gutmann <> Thu, 28 July 2011 06:11 UTC

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From: Peter Gutmann <>
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Date: Thu, 28 Jul 2011 18:11:03 +1200
Subject: Re: [TLS] HTTPS client-certificate-authentication in browsers
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Martin Rex <> writes:
>Anders Rundgren wrote:
>> Lots of banks wants to use CCA for their users.
>That is a non sequitur.
>Banks (here in Germany) have abandoned tradtional TANs based on the 
>unconditional presumption that client PCs are infested with malware, and 
>most banks in Germany are currently replacing indexed TANs (iTAN) presumably 
>based on the perception that malware on clients (trojans/phishing) has caught 
>up with iTAN procedure complexity.
>At this point, with the presumption that all client PCs are thoroughly 
>infested with malware, going for a Single Sign-On mechanism would be 
>completely braindead and irresponsible.

That was my feeling as well.  Moving from TANs (or plain passwords if you're a 
US bank) to client certs is at best pointless and at worst a step backwards in 
security.  Even if you could overcome the monumental usability problems (and 
there's no evidence that we can do this), you end up with a mechanism that's 
even less secure than basic TANs because use of a TAN requires human 
intervention while a MITB (man-in-the-browser) can use your private key to 
sign whatever they want as often as they want without your knowledge.  Client- 
side PKI was designed for an attack model invented by cryptographers to 
justify the use of fun crypto stuff, but it has little (if anything) to do 
with the threats that we're actually facing today.