How do I make the private key on a OpenPGP smartcard non exportable ?

[Henry Hertz Hobbit]

On 06/19/2013 03:21 PM, Heinz Diehl wrote:
> On 18.06.2013, NdK wrote: 
> 
>> If the key is generated on-card, you have no way to backup it. No need
>> for "unexportable" flag: simply there's no command to export it.
> 
> And if the key is generated off-card and properly moved to the
> smartcard afterwards, there's no way to export it either. It's only
> the stub which points to the smartcard left on disk.

Is the original poster still there?  I was going to write and decided
it was wiser to wait for these responses which I almost knew were
coming.  Try the backup from GPA's menu.  I doubt you will get anything
that can be exported. If you get a backupg.gpg (or similar), then try
importing your secret keys onto a second system with GPGWIN installed.
If all that flies (you were actually able to do a --export of your
private keys despite these two people's responses to the contrary
and then are able to do a --import on the second system) then try
these tests:

1. Make a detached signature of a file on system one (with
   OpenPGP card).  Copy the base file and the signature file to
   system two and see if it verifies.

2. Sign on second, copy to first, and see if it verifies on first.
   IOW, reverse of previous.

3. Enciper a file using public-key of said key you supposedly
   was able to import on either of the system.  By that I mean a
   public-key enciphering, not just a symmetric cipher, e.g.:
   http://www.securemecca.com/public/GnuPG/pcrypt.txt
   Copy the public-key enciphered file to the other system.
   Flash drive, et al.  Decipher it on the other system.

I don't think your tests will work.  In fact I don't believe you
will even get to these three tests.  What is the advantage of using
the OpenPGP key and having a public-key enciphered file over a
symmetric enciphered file?

Symmetric Enciphered:
=====================
Let's say your machine gets infected.  Let's also suppose that a
key logger has been installed.  I can assure you that most malware
today either has a mini key-logger as part of the initial install
or a key-logger can be downloaded and installed.  Actually, most
malware will almost do it automatically.  I have over 10,000
malware to back that statement up.  Either the key-logger got
the password to encipher the enciphered file or they saw it when
you temporarily deciphered the file.  So now all the hackers need
are either the plain-text file or the enciphered file and to know
what created the enciphered file.  But even if all the hackers
have are the enciphered file and the pass-phrase they are now
only one step away.

PeskySpammer has even installed SMTP agents on tens of thousands
of Microsoft Windows machines, one of which was at RIPE, one
more at ICANN, and one at Yahoo.  The hackers have your
file and its name alone or what is in the file header reveals
what was used to create the enciphered file.  Within a few minutes
they will have a deciphered file. The only thing that can protect
you is to NEVER encipher or decipher the file while the key-logger
is there and to never have the deciphered file available.  But
once they have the enciphered file and know the password to decipher
the file the game is over and you have lost.

OpenPGP Public-Key Enciphered:
==============================
All the same things hold.  Assume they know the key's pass-phrase.
They can also pull down the enciphered file.  But you cannot just
copy the keys since an OpenPGP card doesn't have a file system.
If you cannot --export the secret-keys then the hackers will never
get them.  FOILED!  The hackers have no choice but to move on
or set some sort of trigger that knows when you decipher the
public-key enciphered file.  The longer you let the unenciphered
file hang around the more likely it is to fly the coop.  So
even if the hackers know the pass-phrase (assume they do) and
have the public-key enciphered file, they can NOT decipher the
file.

Now do you see the difference between a symmetric enciphered
file and a public-key enciphered file where the OpenPGP keys
are on an OpenPGP card?  Just don't let the unenciphered file
hang around any longer than normal.  Do not just delete the
unenciphered file - securely erase it when you don't need
it.  If you need higher security use an OS which has moderately
more security (Linux) or even higher security (OpenBSD) with
an OpenPGP card to hold the keys.  Every layer of defense you
add encourabes the hackers to move on in search of an easier
target.