Smartcards and tokens

Lou Wynn lewisurn at
Thu Dec 15 08:34:20 CET 2016

I've come cross a simple and secure approach at this post:

In the MAKING BACKUPS section, this method simply places your gnupg
directory in an encrypted usb drive and make a symlink to it like this:

ln -s /Volumes/EncDrive/gnupg ~/.gnupg

That's all. As long as you use a good passphrase, this is very secure
method to me. When you unplug the USB, your keys are gone. If your USB
drive is lost, its content is encrypted by your passphrase, so no worry
about it.

On 12/14/2016 05:35 PM, NIIBE Yutaka wrote:
> sivmu <sivmu at> wrote:
>> One question remaining is what is the difference between the openpgp
>> smartcard and the USB based tokens.
> I think that the OpenPGP card (the physical smartcard) is included in
> Nitrokey Pro USB Token.  So, it's exactly same from the view point of
> smartcard.
> When you want to use a smartcard, you need a card reader to access the
> card.  And the card reader you use would bring another attack vectors.
> In this point, Nitrokey Pro USB Token is the best approach, I suppose.
> IIUC, Yubikey products are JavaCard implementations and somehow emulate
> OpenPGP card protocol by "app", and they work as CCID card reader +
> OpenPGP card.
> In Nitrokey Start USB Token, there is no OpenPGP card physically, but it
> is implemented by Gnuk, the software.
>> Also how much would you trust those vendors and can the use of such
>> tokens actually decrease security?
> This is the point.
> The hardware OpenPGP card in Nitrokey Pro USB Token could be replaced by
> man in the middle (or its vendor).  The hardware MCU chip in Nitrokey
> Start USB Token could be replaced, too.  The software (Gnuk) in Nitrokey
> Start USB Token could be replaced (with JTAG/SWD debugger), too.  Or, we
> should consider possibility of backdoor of OpenPGP card.  Well, I don't
> know about Yubikey.
> When it is replaced to be malicious one to enable an access by others
> (to your private keys), or it already has a backdoor in the first place,
> it kills the purpose of USB security token.
> Here, the question is: how can we build up such a "trust"?
> It seems for me that there are two different approaches; (1) physical
> difficulty (for example, plastic molding for "protection"), (2)
> reproducibility and transparency/openness.  Note that some method of
> former makes latter difficult.
> For myself, I take (2), and I did my best to make my product as
> reproducible.  (Since I don't manufacture semiconductor things,
> reproducibility is not 100%, and this part of manufacturing and
> technology is not open at all.)  And I intentionally deliver my product
> in a style of "transparent" or "open".
> Distribution channel is also difficult.  I do in person, and I ask FSF
> for my TRNG.  Are there any good method?
> Obvious drawback of the apporoach (2) is that people with enough
> concern/attention have tendency to do it under their control.
> Reasonable.  Since it's reproducible (somehow), it's possible, by
> definition.  And then, I can't sell many.

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