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Re: [Cfrg] Encrypt in place guidance

Henry B Hotz <hbhotz@oxy.edu> Tue, 31 March 2020 18:55 UTC

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From: Henry B Hotz <hbhotz@oxy.edu>
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Date: Tue, 31 Mar 2020 11:55:37 -0700
Cc: cfrg@ietf.org
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References: <83571efb-a32f-6a59-a496-de56716f07da@htt-consult.com>
To: Robert Moskowitz <rgm-sec@htt-consult.com>
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Subject: Re: [Cfrg] Encrypt in place guidance
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What about format preserving encryption?

Personal email. hbhotz@oxy.edu

> On Mar 31, 2020, at 11:30 AM, Robert Moskowitz <rgm-sec@htt-consult.com> wrote:
> 
> The problem is in the Unmanned Aircraft broadcast messages (see DRIP work).
> 
> In the System Message defined in ASTM F3411-19 there are 8 bytes of sensitive Operator Information that I want to encrypt.  I can get a shared secret via the PK mechanism in ECIES.
> 
> The challenge is in encrypting, then decrypting these 8 bytes.
> 
> There is no room for expansion in the message.  All we have are these 8 bytes.
> 
> There is nothing unique in each System Message to use an an IV. There are 7 bytes of mission information and 1 byte of flags that are constant for a given mission (but may be the same in a later mission).
> 
> There are 8 reserved bytes, but I feel they left out 4 bytes of important Operator Information (thus making 12 bytes to encrypt). So no grabbing those reserved bytes.
> 
> Since this information is of limited value for some period after the completion of the mission, I was considering just using AES-ECB.
> 
> Opps.   I need 16 bytes for the output of AES-ECB.  Or at least that is my reading of the ECB mode.
> 
> So I am seeking guidance here on what cipher to use in this particular situation.
> 
> Thank you.
> 
> 
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