one ecc key-pair for both encryption and signature?

[Bernhard Reiter]

Am Freitag 07 Januar 2022 20:23:33 schrieb Robert J. Hansen via Gnupg-users:
> > There is anequivalence given (two functions) in the Ed25519 wikipedia
> > page, but I don't know if this allows the same curve used in both
> > algorithms.

> Likewise, Edwards DSA can be tortured into becoming a Curve25519 key.
> But once you do that, *you're no longer using Edwards DSA*.

Can you be more specific why this is a problem?
Is it because the two transformation functions
 a) create numerical problems
 b) or runtime problems letting out information about the private key (thus 
being a side channel) 
 c) or just the additional time needed for them
?

(Andrew and Robert, thanks for your answers, you have already helped me to 
understand that detail better.)

Regards,
Bernhard


-- 
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