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Date: Thu, 6 Dec 2012 12:30:33 +0100
From: magnum <>
Subject: Re: support for weak kerberos etypes

On 18 Nov, 2012, at 18:15 , buawig <> wrote:
> for kerberos setups that are vulnerable to etype downgrade attacks[1]
> it would be great to have john support for a few weaker etypes that
> require less cracking effort than etype 18 (aes256-cts-hmac-sha1-96).
> The following etypes are supported by a default Windows 7 client:
> etype 	| name
> - ------------------------
> 23	| rc4-hmac 	(support available)
> 17	| aes128-cts-hmac-sha1-96
> 18	| aes256-cts-hmac-sha1-96 (support available)
> WinXP (pcap file from [2]):
> - -133?	| rc4-hmac-old*
> - -128?	| rc4-md4*

Which of these does our current mskrb5 format support? Etype 23? What's the difference in the XP ones?

Also, etype 17 would be super-easy to add (provided the only difference is the AES) to our current krb5ng and krb5ng-opencl formats if someone provides a sample pcap. It wont be any faster than etype 18 though. As far as I can read, it would need to be modified to support this etype... would we also need to change the input format? Maybe add the etype as a separate field.

BTW if we can add rc4-hmac support to too it would be very nice. I'm willing to change mskrb5's input format (it could still support the old one too) making it the "same" as the new one. Something like this should be usable for both:

$ krb5pa $ user $ realm $ etype $ salttype $ timetamp $ checksum

New tag $krb5pa$, where pa stands for pre-auth. Spaces added for readability only. The "salttype" is the current 0/1 field from krb5ng. Timestamp size is 36 bytes for mskrb5 and 44 for krb5ng. Checksum size is 16 bytes for mskrb5 and 12 for krb5ng.

We could want to rename mskrb5 to krb5pa-md5 and krb5ng to krb5pa-sha1. Or would krb5pa-sha1-96 be better?


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