Imported secret subkey unusable "ssb#"

[Ingo Klöcker]

On Sonntag, 18. April 2021 21:55:59 CEST Ingo Klöcker wrote:
> On Sonntag, 18. April 2021 02:06:40 CEST anon85786376 via Gnupg-users wrote:
> > When a batch mode key is created with "Subkey-Type: ECC" and
> > "Subkey-Curve:
> > Ed25519", the key is generated without errors and appears to function
> > normally. However, importing the secret keys will yield an unusable secret
> 
> > subkey:
> [...]
> 
> > $ gpg -K
> > /home/me/.gnupg/pubring.kbx
> > -----------------------------
> > sec   rsa3072 2021-04-17 [SC]
> > 
> >       1CB8F79F656BCD71BF9A89694C95665DD06F8126
> > 
> > uid           [ unknown] testkey
> > ssb#  ed25519 2021-04-17 [E]
> 
> I could reproduce the problem.

It turns out that --gen-key allows creating invalid keys. The problem is that 
ed25519 keys cannot be used for encryption. You need to create a key with an 
cv25519 encryption subkey, i.e.

$ gpg --batch --gen-key <<EOF
Key-Type: default
Subkey-Type: ECC
Subkey-Curve: cv25519
Name-Real: testkey
EOF

Then export and import of the secret key works without problems.

Regards,
Ingo
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