Somewhat OT, encryption question

Bill Oliver vendor at
Thu Nov 27 17:01:15 UTC 2014

On Thu, 27 Nov 2014, Robert Moskowitz wrote:

> On 11/27/2014 11:34 AM, Bill Oliver wrote:
>>  On Wed, 26 Nov 2014, 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.)
>> > 
>> >  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.
>> > 
>> >  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.
>> > 
>>  That's part of the point.  Were I to be carrying a flash drive, for
>>  instance, and be required to provide a passphrase, I need to be able to
>>  provide it *and* a cogent, truthful, and believable explanation of why it
>>  doesn't work and there's *nothing I can do" to make it work short of
>>  returning home and retrieving my computer.  There are many situations
>>  nowadays where people can be coerced into giving up their passphrases.  In
>>  the US, this can happen at the border.  In other countries, every move you
>>  make is under some sort of surveillance, often covert, and getting
>>  information in and out can be problematic.
>>  What I would like to be able to do is go to a remote site, acquire/select
>>  data for my personal access and use at my office, encrypt it using a
>>  public key, and then not be able to decrypt it until I got back to my
>>  office and put it in *my* computer.
> RSA crypto can do this with only your public key traveling.
> You encrypt the data with a random AES key.  You encrypt your key with your 
> RSA public key.  Only when you get back home where your private key lives, 
> can you decrypt it.
> In fact, most email programs that support S/MIME can do this.
> Set up an account foo at with an email client that supports S/MIME. 
> Import your public key from your home email into it. Encrypt your document to 
> your home email account with your home email public key.  You have no way of 
> decrypting it until you get home to the computer where your private key 
> lives.
> All standard stuff.  Just need the right email accounts and software.
> You will probably need a cert for the foo at account, but that will only 
> be used to sign the source of the email, not encrypt it.

Thanks.  I'll read up on that.


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