Smartcard working completely with GPG2 and incompletely with GPG1.4

[NIIBE Yutaka]

Hello,

chris.p.16 at gmx.de wrote:
> With GnuPG 2, signing, encrypting and decrypting a file works without
> any problems. With 1.4, I can encrypt and sign a file, but I can't
> decrypt it. It's failing with the message:
[...]
>
> gpg: public key decryption failed: general error
> gpg: decryption failed: secret key not available
[...]
> sec#  rsa4096/E728903D  created: 2014-04-12  expires: never     
> ssb>  rsa4096/3A07266F  created: 2014-04-12  expires: never     
>                         card-no: 0005 00005031
> ssb>  rsa4096/43F27C98  created: 2017-01-24  expires: never     
>                         card-no: 0005 00005031

I located the cause of this issue.  It is not the issue of scdaemon
incompatibility of GnuPG 2.1, which I addressed yesterday.

With GnuPG 1.4 for smartcard can't work well for RSA 4096-bit keys.  (I
think that it can also occur with the combination of GnuPG 1.4 and GnuPG
2.0.)

In the code of g10/cardglue.c, the buffer length is 1002-byte by the
definition of ASSUAN_LINELENGTH [0], but this length is not enough for
the checking at [1].  (To represent encrypted value of 4096-bit itself,
it requires 1024-byte by hex string.)

[0] https://git.gnupg.org/cgi-bin/gitweb.cgi?p=gnupg.git;a=blob;f=include/assuan.h;h=1170f959df353f33373565c729981891dcd0100c;hb=refs/heads/STABLE-BRANCH-1-4#l91
[1] https://git.gnupg.org/cgi-bin/gitweb.cgi?p=gnupg.git;a=blob;f=g10/cardglue.c;h=809b315e564831aac8727d3c905e53016749f76e;hb=refs/heads/STABLE-BRANCH-1-4#l1395
--