Error message "gpg: Can't check signature: Broken public key"

[NIIBE Yutaka]

On 12/08/2015 08:51 AM, MFPA wrote:
> What does the error message "gpg: Can't check signature: Broken public
> key" mean?
> 
> One of the members of PGPNET reports getting that error
> message when verifying the signatures on my signed and encrypted
> messages to the group. He gets it for the signatures from my EDDSA subkey
> 0x1712BC461AF778E4, and says he uses GnuGP 2.1.8.

I don't think that GnuPG frontend or gpg-agent doesn't emit this
error.

It could be libgcrypt which generates this error.  EdDSA key is
represented by a point on the Ed25519 curve.  When the point is not on
the curve (the key is invalid), it complains by this error.

I validate your e-mail by the key of 0x1712BC461AF778E4 with no error.
So, I don't think there is a problem in your key.  The local copy
of your public key in his computer would be a problem.
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