[saag] Re: Fwd: New Version Notification for draft-moskowi tz-ads-b-auth-02.txt

Thanks John!

On the strength of this, which backs what I have seen elsewhere, I am 
going to drop TESLA keys larger that 128 bits.  Still have a discussion 
about this in Security Considerations.

With each key only valid for a 5 second interval and channel limitations 
of 6.2 msg/sec (and short burst mode at 7 msg/sec, easy to overwhelm the 
channel if more is done), a symmetric key attack is too much of a moving 
target.  We MAY increase the interval to 10s, but probably not.

Bob

On 8/17/26 6:23 AM, John Mattsson wrote:
> Hi Bob,
>
> (Answering generic as I have not read your draft)
>
> There is no practical risk at all from quantum attacks on symmetric 
> cryptography. This is a misconception.
> https://datatracker.ietf.org/liaison/1942/
>
> >If I drop the MACing
>
> You should absolutely not drop MACs. A short authentication tag is 
> /much/​ better than no tag at all.
>
> >The TESLA MAC is 28 bits.
>
> 28 bits is short, but 5G uses 32-bit authentication tags, and I’m not 
> aware of any attacks against them in practice. How problematic or not 
> short tags are depends heavily on the use case. How many forgeries can 
> an attacker send per minute/hour/year/millenia? Does a single 
> successful forgery cause practical problems, or would an attacker need 
> to make several successful forgeries? Do the forgeries need to be 
> sequential? Do forgery result in chosen or random plaintext? Is the 
> risk of forgery larger than e.g., cosmic radiation corrupting data?
>
> KMAC is a strong MAC that behaves like an ideal MAC, including 
> reforgeability resistance.
>
> >But as the authentication key as from a hash-chain and ONLY used for 
> ~31 messages
>
> I don't think this is relevant. The integrity advantage per key is 
> completely irrelevant.
>
> Cheers,
> John Preuß Mattsson
>
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