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Re: [kitten] [EXTERNAL] Re: Question about AES mode in Kerberos

Luke Howard Bentata <lukeh@padl.com> Fri, 06 January 2023 21:36 UTC

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From: Luke Howard Bentata <lukeh@padl.com>
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Date: Sat, 07 Jan 2023 08:36:37 +1100
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To: Ken Hornstein <kenh@pobox.com>
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Subject: Re: [kitten] [EXTERNAL] Re: Question about AES mode in Kerberos
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> On 6 Jan 2023, at 11:20 pm, Ken Hornstein <kenh@pobox.com> wrote:
> 
>> Nico points out we should use this opportunity to encrypt the AP-REP
>> enc-part in the initiator sub-session rather than the ticket session
>> key. Otherwise you can replay an AP-REP against an AP-REQ made with the
>> same ticket, which would be bad for GCM (as we are using a deterministic
>> IV). I haven’t updated the draft yet to reflect this.
> 
> My understanding is the AP-REP enc-part contains the authenticator
> timestamp from the AP-REQ, so replaying an AP-REP shouldn't be possible
> regardless of the details of the encryption mode.  Unless I am
> misunderstanding something which is always possible.

Right you are – comment withdrawn :)

Cheers,
Luke

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