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Date: Thu, 6 Dec 2012 17:23:49 +0530
From: Dhiru Kholia <>
Subject: Re: support for weak kerberos etypes

On Thu, Dec 6, 2012 at 5:00 PM, magnum <> wrote:
> 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?

rc4-hmac is etype 23. No idea about how this one is different from XP
ones. I am guessing that the XP ones aren't used any more (and don't
matter much).

> 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.

Yes, Input format needs to be extended.

Do you plan to use a new file for implementing etype 17 using OpenCL?

I will extend krb5-ng (CPU format) to support etype 17 soon.

> 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

Looks good.

I can make output hashes in this format and add support
for rc4-hmac.

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

mskrb5 to krb5pa-md5 and krb5ng to krb5pa-sha1 sounds good.


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