Supporting fixed length keypad input

[Werner Koch]

On Tue,  8 Jan 2013 09:31, gniibe at fsij.org said:

> (1) Add a option to SCDaemon.  Say, "opt.keypad_fixed_length" or
>     something.  This is to enable handling of fixed length keypad
>     input for SCDaemon.

The problem here is that you may not know the length of the PIN.  The
card may have been used before with a different reader.  Depending on
the implementation of the reader the wrong PIN counter may soon go down
to zero.  An explicit agreement from the user will be better.

Or wait: We could extend the login data flags
(app-openpgp.c:parse_login_data) to declare that the length of the pin
is 6/8.  Only if that flag has been set the fixed length feature may be
used.

> (2) Add protocol between SCDaemon and GPG-Agent.  SCDaemon inquires
>     length of PIN to GPG-Agent, when needed.

gpg-agent should not know about such card or reader details.

> (3) Upon inquiry by SCDaemon for the length of PIN, GPG-Agent will
>     answer if it has the information at hand.  Or else, GPG-Agent will
>     invoke pinentry to ask the length to the user, and reply back to
>     SCDaemon.

It would be okay to use gpg-agent as a proxy to pop up a pinentry.
IIRC, we already do that in some cases.


Salam-Shalom,

   Werner

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