Re: [Cfrg] Encrypt in place guidance

[Robert Moskowitz <[e-mail]>]

On 3/31/20 2:55 PM, Henry B Hotz wrote:
> What about format preserving encryption?

Can you point me to info on this?

I am only marginally familiar with it.  Not something I have had 
occation to study.

Thanks.

>
> Personal email. [e-mail]
>
>> On Mar 31, 2020, at 11:30 AM, Robert Moskowitz <[e-mail]> 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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