Somewhat OT, encryption question

Robert Moskowitz rgm at
Thu Nov 27 01:33:51 UTC 2014

On 11/26/2014 07:10 PM, Bruno Wolff III wrote:
> On Wed, Nov 26, 2014 at 20:47:25 +0000,
>  Bill Oliver <vendor at> wrote:
>> On Wed, 26 Nov 2014, Bill Oliver wrote:
>> Actually, let me be more specific.  Let's say I have data on a flash
>> drive that is encrypted using gpg.  We can even say the flash drive
>> itself is encrypted.
>> Now let's say that flash drive is stolen, lost, etc. *and* the
>> passphrase is compromised.  I want the data on the flash drive to be
>> available *only on one computer* even if the passphrase is known.
> If you don't need to decrypt data in the field, you can use public key 
> encryption. You won't be able to decrypt the data without the private 
> key. (Which you wouldn't have with you or the flash drive.)

NOBODY encrypts lots of data with asymmetric cryptography.  Rather, 
using RSA say, you create a random AES key, encrypt the data with that, 
THEN encrypt the little key data with the public key.

If your private key is on a USB dongle with your software supporting it, 
it all works together.

> TPMs provide a way to keep a secret on a computer that can't easily be 
> extracted (otherwise you could supply the data in an emulated 
> environment). I don't know if there is anything in Fedora for using 
> say, luks with a TPM in a way that prevents the TPM info from being 
> sniffed in a similar manner to how your passphrase is compromised. 
> There has been some work with using TPMs with luks, but I don't know 
> how the process works.

But you really need a trusted OS to use the TPM properly.  With signed 
code and so forth.  Yes, if you have software that stores your keys in 
the TPM, other, untrustworthy software could interceed.  Thus you really 
want a trust chain if you are going for a TPM approach.
> Note, that if this scenario comes about because someone grabs you and 
> the flash drive, but not your computer, there could be dire 
> consequences to not being able to decrypt the drive. Particularly if 
> the people holding don't believe you, when you say you can't decrypt it.

Oh, it can get worst than that.  If you get stopped in US customs, they 
can legally require you show them what you are bringing in. People have 
spent some time in jail working out that they have protection from 
exposing what they are carrying.  Just be prepared to be stopped or use 
only microSD cards that you hide very well...

Are you paranoid enough?

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