[openpgp] SLH-DSA code points

[Falko Strenzke <[e-mail]>]

During yesterday's session the discussion came up between Daniel and me 
whether we need all three currently proposed SLH-DSA code points in the 
PQC draft, namely 128f, 128s, and 256s (all with SHAKE).

I attached a visualization of the time and space performance also with 
comparison to ML-DSA-87 (256bit sec, L5). Please note there are two 
sheets which only differ in that one displays the charts linearly, the 
other logarithmically.

My argument for the current triple is that

- 128s is the only SLH-DSA variant coming near ML-DSA regarding 
signature size,
- 128f is a factor of 100 worse in signature generation than ML-DSA, but 
still 10x faster than 128s. Thus where signing time is a cost factor, 
128f has a clear advantage.

So both 128s and 128f seem highly relevant to achieve performance time 
or space wise somewhat close to ML-DSA.

Then of course 256s seems clearly required to have at least one variant 
for 256 bit security.

- Falko

-- 

*MTG AG*
Dr. Falko Strenzke
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