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Re: [Ntp] The trick to timestamp with authentication

Hal Murray <hmurray@megapathdsl.net> Thu, 03 December 2020 08:08 UTC

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To: Watson Ladd <watsonbladd@gmail.com>
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From: Hal Murray <hmurray@megapathdsl.net>
In-Reply-To: Message from Watson Ladd <watsonbladd@gmail.com> of "Wed, 02 Dec 2020 21:44:04 PST." <CACsn0c=K=T4_ZTGyfGcmNR_e9+7DYOaNBipKjxiNYJYcdYma2g@mail.gmail.com>
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Date: Thu, 03 Dec 2020 00:08:42 -0800
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Subject: Re: [Ntp] The trick to timestamp with authentication
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watsonbladd@gmail.com said:
> AES-GCM and Poly1305 are linear. In order to adjust the timestamp in one
> step, it suffices to line everything up so that the hardware can compute the
> correction in the same cycle as the stamp by isolating the stamp in one block
> of the CWC hash.

I think I'm missing a critical step.  Who/where is doing this "adjusting"?

The whole point of authentication is to prevent MITM "adjustments".

The only place I can see where something like that would make sense would be 
at the transmit network chip.  Why can't it do the whole authentication?  (The 
transmit side has the key.  The receive side can do the adjustment in 
postprocessing software.)


-- 
These are my opinions.  I hate spam.

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