scd: binary data returned when sending direct APDU

Ingo Klöcker kloecker at
Wed Dec 21 18:58:32 CET 2022

On Mittwoch, 21. Dezember 2022 17:51:39 CET Alexandre Vaissière via Gnupg-
users wrote:
> I am trying to send arbitrary APDU commands via scd. When doing that I
> noticed that scd answers me with binary data. For example:
> gpg-connect-agent
> > scd apdu 00 A4 04 00 07 A0 00 00 05 27 21 01
> D yZ��... <other binary data>
> OK
> As assuan protocol is supposed to transmit utf-8 encoded string data, I
> would have expected an hexified string as returned data (as the input
> data is). Is that a bug or the expected behaviour?

I suppose this is intended behavior (because data is often text and you don't 
want to get that in hex). You may want to use `gpg-connect-agent --hex`.

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