GPG smartcard shrinks in size

NIIBE Yutaka gniibe at
Tue Aug 9 02:05:11 CEST 2016

On 08/09/2016 07:09 AM, Cannon wrote:
> Using the OpenPGP Smartcard V2.1 used to store 4096 key. Then was used
> to store 3072 length key for short time. Problem is that I am unable to
> use it for 4096 keys anymore. How to reset card so I can use it again
> for 4096 key?

No worries.  I think that you can just generate keys of 4096 or put
keys of 4096 by keytocard.

OpenPGP Smartcard supports multiple key length.  Since the card
protocol only supports a single information of key length per key, a
card looks like as if it only supports a specific key size.  (There is
no way in the protocol to represent multiple key length information.)

When a user invokes "generate" or "keytocard" command, GnuPG will
adjust the key attribute of a card to a specific size of key length.
Once it is generated or written by keytocard, you will see it's 4096.

Or, do you have a specific problem when you say "unable to use it for
4096 keys anymore"?  Please describe the problem.

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