agent_genkey failed: Invalid flag

[NIIBE Yutaka]

Hello,

Patrick Brunschwig wrote:
> gpg reports the following error:
>
> gpg: agent_genkey failed: Invalid flag
> gpg: key generation failed: Invalid flag
> [GNUPG:] ERROR key_generate 16777288
> [GNUPG:] KEY_NOT_CREATED
>
> Any idea what could be wrong here?

The error is from libgcrypt.  I think that libgcrypt is too old
to use Ed25519/Curve25519.

When generating Ed25519/Curve25519 key/subkey, gpg uses three flags:

        comp
	eddsa
	djb-tweak

It seems that some flag(s) is not supported by libgcrypt in the user's
system.

Meaning:

comp: compact format
      (only use x or y-coordinate to represent an EC point)
eddsa: use for EdDSA
djb-tweak: specify bits of secret is tweaked DJB's method;
           MSB is set, LSBs are cleared.
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