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Re: [Ntp] WGLC: draft-ietf-ntp-using-nts-for-ntp

"Dieter Sibold" <dsibold.ietf@gmail.com> Tue, 11 December 2018 18:34 UTC

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From: Dieter Sibold <dsibold.ietf@gmail.com>
To: Marcus Dansarie <marcus@dansarie.se>
Cc: ntp@ietf.org
Date: Tue, 11 Dec 2018 19:34:41 +0100
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Subject: Re: [Ntp] WGLC: draft-ietf-ntp-using-nts-for-ntp
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Hi Marcus,
thanks for your reply. See comments below.
- Dieter



Dieter Sibold
dsibold.ietf@gmail.com

On 11 Dec 2018, at 17:18, Marcus Dansarie wrote:

> Thank you! My replies follow inline.
>
> Kind regards,
> Marcus
>
>
> On 2018-12-10 23:08, Dieter Sibold wrote:
>> Hi Marcus,
>> here are my comments for pull request #15
>>
>>
>>
>> 077f0da6
>> The current documents translates correctly without any errors.
>> Therefore, I would imply that the additional section closing tag is 
>> one
>> too much.
>
> This appears to have been due to an error on my end. My apologies.
>
>> ---------------------
>> a7c4f563
>> I don't get why you want to relax this requirement. Please explain.
>
> There may be some (weird) cases where a user wishes to manually 
> instruct
> their NTP client to use the received cookies with a different NTP
> server. I also believe SHALL should be reserved for cases where
> non-compliance could cause security issues or cause the protocol to
> break. This is not an important issue for me, however, and I'll be
> perfectly happy even if this isn't included.

Ok, understand. I have no strong opinion on this matter. Perhaps there 
are other comments?



>
>> ---------------------
>> 2b436df8
>> I agree in principal. I suggest following changes
>>
>> ### original
>>         <t>
>>           Implementers must be aware of the possibility of 
>> "NTS stripping"
>>           attacks, where an attacker tricks clients into 
>> reverting to plain
>>           NTP. Naive client implementations might, for 
>> example, revert
>>           automatically if the NTS-KE handshake fails. A 
>> man-in-the-middle
>>           attacker can easily cause this to happen. Even 
>> clients that
>> already
>>           hold valid cookies can be vulnerable, since an 
>> attacker can
>> force a
>>           client to reperform the NTS-KE handshake by 
>> sending faked NTP
>> mode 4
>>           replies with the NTS NAK kiss code. Forcing a 
>> client to
>> reperform the
>>           NTS-KE handshake can also be the first step in 
>> more advanced
>> attacks.
>>         </t>
>>
>> ### new
>>         <t>
>>           Implementers must be aware of the possibility of 
>> "NTS stripping"
>>           attacks, where an attacker tricks clients into 
>> reverting to plain
>>           NTP. Naive client implementations might, for 
>> example, revert
>>           automatically to plain NTP if the NTS-KE handshake 
>> fails. A
>> man-in-the-middle
>>           attacker can easily cause this to happen. Even 
>> clients that
>> already
>>           hold valid cookies can be vulnerable, since an 
>> attacker can
>> force a
>>           client to repeat the NTS-KE handshake by sending 
>> faked NTP mode 4
>>           replies with the NTS NAK kiss code. Forcing a 
>> client to repeat
>> the
>>           NTS-KE handshake can also be the first step in 
>> more advanced
>> attacks.
>>         </t>
>>
>
> Ok.
>
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