Re: [Ntp] Antw: Re: Antw: [EXT] Re: Quick review of WGLC for status change for draft‑ietf‑ntp‑update‑registries

[Ulrich Windl <[e-mail]>]

Hi Harlan,

if you have ntpd with a key configuration file all is fine:
Known keys are processed, and unknown keys are dropped.
BUT: If you want to analyze packets on the wire (tcpdump, wireshark) without
having the key definitions, it's hard to impossible.

That was my point of criticism: I think the packet structure should be
parsable without knowing the keys behind the key ID.

Regards,
Ulrich

>>> Harlan Stenn <[e-mail]> schrieb am 11.08.2022 um 11:50 in
Nachricht
<[e-mail]>:
> On 8/9/2022 3:34 AM, Ulrich Windl wrote:
>>>>> Harlan Stenn <[e-mail]> schrieb am 09.08.2022 um 11:11 in
>> Nachricht
>> <[e-mail]>:
>>> On 8/9/2022 1:02 AM, Miroslav Lichvar wrote:
>>>> On Mon, Aug 08, 2022 at 06:48:28PM ‑0700, Harlan Stenn wrote:
>>>>> On 8/8/2022 5:58 AM, Miroslav Lichvar wrote:
>>>>>> If you allow short extension fields, you will not be able to detect
>>>>>> whether a request contains an unknown extension field or an Autokey
>>>>>> MAC using an old cookie. The protocol may be able recover, but that's
>>>>>> not how things should be done.
>>>>>>
>>>>>> Here is an example:
>>>>>>
>>>>>> 04 1b 00 14 cc e2 c8 47 71 95 79 64 c4 71 e8 72 7e bf fb cd
>>>>>>
>>>>>> Which of the two is it?
>>>>>>
>>>>>
>>>>> More context, please.
>>>>>
>>>>> What is that set of bytes?
>>>>
>>>> It's the UDP data following the NTP header.
>>>
>>> I don't do this stuff in my head as well as I used to.
>>>
>>> Is there a symmetric key for keyID 1051?  If so, what hash algorithm was
>>> used?
>> 
>> Should the parsing of the packet really depend on knowing what hash 
> algorithm
>> a specific key ID uses?
> 
> In general, no.
> 
> More below.
> 
>> It's quite likely that a server receives packets with a key it does not 
> know.
> 
> If a packet is authenticated with a keyID the receiving system does not 
> understand, then the receiving system CANNOT authenticate the packet. 
> In this case, it's expected that the receiving system will drop the packet.
> 
> Do you disagree?
> 
> I asked about the algorithm that was used because it is possible for 
> MACs to have different payload lengths.
> 
> The receiving system can see if the keyID is known, and if it is, the 
> expected algorithm will dictate the length of the MAC payload.
> 
> If that payload length does not match, then the field in question cannot 
> be a legacy MAC.
> -- 
> Harlan Stenn <[e-mail]>
> http://networktimefoundation.org - be a member!