one ecc key-pair for both encryption and signature?

[Bernhard Reiter]

Am Freitag 07 Januar 2022 15:21:45 schrieb Andrew Gallagher via Gnupg-users:
> On 07/01/2022 14:06, Bernhard Reiter wrote:
> > With 2.2.33 is is not possible to create a single ecc key-pair
> > that can do "sign" and "encrypt".
>
> it is best practice to keep the encryption-capable subkey distinct.

Is this the only reason?
Then RSA should be limited in the same way.
(Because there it is possible, so I guess that there is another reason.)

Am Freitag 07 Januar 2022 15:26:50 schrieb Robert J. Hansen via Gnupg-users:
> Ed25519 is (effectively) a Schnorr signature done over an Edwards curve.
>   Schnorr signatures have really no capability of being used for
> encryption, unless you want to do it just a few bytes at a time.

Reading https://en.wikipedia.org/wiki/Curve25519
| Curve25519 is an elliptic curve [..] designed for use with the elliptic 
| curve Diffie–Hellman (ECDH) key agreement scheme 
-> encrypt

| The curve is birationally equivalent to a twisted Edwards curve
| used in the Ed25519 signature scheme. 

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.

Regards
Bernhard
-- 
www.intevation.de/~bernhard   +49 541 33 508 3-3
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