How to back up my key

[Einar Ryeng]

On Mon, Jul 15, 2013 at 03:25:15PM +0800, Martin wrote:
> 
> I'm new to GPG and unfortunately, the longer I browse the internet and read
> about the topic, the lesser I know :(
> 
> I would like to hear your opinions on this setup:
> 
> 1. I have turned my Raspberry Pi into my super secure offline computer.
> 
> 2. I will create my GPG keys on this system and store them on a USB drive
> inside a TrueCrypt container. 
> 
> 3. I would like to have further backups of that drive, who knows, it might
> get damaged some day and I don't want to lose my key that way.

So far so good, with a couple of minor modifications. And i sort of agree with
you on the TrueCrypt stuff, it's always better if people just erase USB drives
they incidentally find. However, you probably shouldn't carry your keys around
like that anyway.

> My questions are the following:
> 
> a) Do you see any flaws in that setup?

Not exactly flaws, but I would have done some minor changes/additions:

When you create a key pair, you create one master key and one or more subkeys.
The master key is the one that should be used only in a safe environment. This
key is used for operations on your private keys (revoking, making new subkeys,
etc) and for signing other people's keys. All of these are relatively
infrequent operations, except signing other keys which you propably will do
quite frequently until your key is well connected to those you communicate
with. 

Therefore: 
 1) 1 USB drive that will ONLY be used in the secure environment, containing
    your master key and all subkeys.
 2) A backup of 1), also ONLY for secure environment.
 3) A USB drive or some other means to transfer your subkeys for encryption and
    signing to your laptop.

If you suspect your laptop has been compromised, someone may have gained access
to your encryption and signing subkeys, which means that they can act as you.
Luckily, because your master key is safe, you can just revoke your subkeys and
create new ones. Your web of trust connections to anyone else will not be
affected, except that they need to fetch the new version of your keys from the
keyservers. On the other hand, if someone compromises your master key, you would
need to go another round signing people's keys.

To be a bit more paranoid, or to allow for using GPG on computers you don't
trust as much as your own laptop, you can use a hardware RSA implementation
like the CryptoStick from the German Privacy Foundation. These can contain keys
which cannot be extracted without physical access to the key and a quite
laborous process at a fairly decent electronics lab.

(Btw, you also want to create revocation certificates for your key when you make
it, just to be certain that you're able to revoke it if you should come to
lose either your key or your passphrase.)

Cheers,

-- 
Einar Ryeng