Supporting fixed length keypad input

[NIIBE Yutaka]

I reconsider again.

Asking user by pinentry (if using keypad and length of PIN) is good in
theory.  But, such a pop-up dialog would be not only annoying but also
not-easy-to-use.

On 2013-01-10 at 10:03 +0900, NIIBE Yutaka wrote:
> I think that we need an option for gpg to enable/disable use of keypad
> for particular card usage.  SCDaemon would inquire this option to gpg
> through GPG-Agent.  Or, gpg would inform SCDaemon through GPG-Agent.

No, this is not a solution for all cases.  Only it works for gpg.

There is a important case of SSH authentication through GPG-Agent, which
cannot be solved by the solution above.  Scute is another case.

Thus, I think that getting user's preference from card (the login-data DO)
would be only a way to handle this.

The flag would be:

	None:	Don't use keypad
	0:	Use variable length input,
		if keypad is available by reader, and the feature is supported
	N,M:	Use fixed length input, if keypad is available by reader
		N for user PIN, M for admin PIN.
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