Somewhat OT, encryption question

[Bruno Wolff III]

On Wed, Nov 26, 2014 at 20:33:51 -0500,
  Robert Moskowitz <rgm at htt-consult.com> wrote:
>
>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 billoblog.com> 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.

Yes of course. The idea was that you could do the encryption with 
say pgp, erase the originally (carefully) and then you wouldn't be 
able to decrypt the data without having the private key (which would 
be on some other device than the computer the file was on). Using 
asymmetric cryptography is what allows you to do that. Just using 
a symmetric key wouldn't. That the bulk of the encryption is really 
done symmetricly with just the symmetric key encrypted with the public 
key is just an immplementation detail.

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

But that doesn't seem to be what he wants. He wants to make sure that 
that having the encrypted data, and his passphrase is not good enough 
to recover the plaintext. If the private key is on the same machine he 
is using his passphrase on, then they may both may be compromised together 
(the scenario didn't say how the passphrase was compromised so it isn't 
clear of this is a likely or unlikely case).

>>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, 

Worse than what? I was implying torture and/or death. While some people 
have been intercepted in US customs and sent off to be tortured, I haven't 
heard of this happening because of not being able to decrypt data.

Actually, England is a worse place for this as there it is against the 
law not to decrypt data at the police's request. But even there, I think 
you get a chance to prove you can't decrypt it.