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  •  Alright - hopefully Hesk will chime back in (1+ / 0-)
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    because i'm not sure I understand all the implications of what he/she's saying, but this is my best interpretation.  I apologize for the length.

    Basically, you can do two things with a key, you can either digitally sign something, so that everyone knows it was generated by you and no one else, or you can decrypt a message sent to you.  To do these two things, you need two different types of key, a private key and a public key.  

    To digitally sign something, all you need is a private key.  As long as no one else has access to it, it would be very hard to reproduce, and therefore gives a guarantee that something signed by it is from you.  Signed does not mean encrypted, though.

    Encryption requires two keys, a private and a public.  Messages are encrypted with the public, and decrypted with the private.  Therefore, to send someone else an encrypted message, you need their public key.  If someone sends you a message encrypted with your public key, you decrypt it with your private key.  

    Alright, so what this means is that in order to decrypt something on your phone, for instance, you need to have a private key on it.  This puts it at risk.  So what you do is you make a master private key that you keep on a disconnected computer.  You then generate a set of subkeys that you sign with the master private.  That way anyone sending you encrypted info knows that public key is actually from you.  Those keys are the ones you then put on your connected devices.  If they get compromised in some way, you can then use your master private key to revoke the old subkeys (mark them as invalid), and generate a new set for use instead.  Again, because both the revokation and the new issuance are signed by your master private, everyone knows that neither are faked.

    OK, so back to your questions:
    1) If the master private stays on the disconnected computer, then no one will have access to it unless they have physical access to the computer.  However, the private subkey gets copied to a connected device, so it could, in theory, be compromised.  It's regarded as somewhat sacrificial in that regard.

    2) Yes.  However, you wouldn't do that whenever you use your email.  You would keep using it until you thought it might be compromised.  In that case, you would issue a new subkey from the master, and use that instead.  Also, keep in mind that you are using the private key to decrypt messages sent to you.  If you wanted to send an encrypted message, you would need the public key of someone else.  They would have their own private key that they would use to decrypt it.

    As you can see, this gets quite complicated.  PGP (or the open-source version, GPG) handles a lot of the details for you.

    One last thing: the private key is itself often encrypted.  What this means is that even if someone were to acquire your private key, they would not necessarily be able to use it.  In that sense, I think what Hesk is proposing is more along the lines of ensuring that the keys are generated correctly, and allowing you to revoke keys reliably, so that in the worst case where someone acquired your old private subkey and broke the encryption, you could be confident that future communications are protected by a new subkey.

    To believe that markets determine value is to believe that milk comes from plastic bottles. Bromley (1985)

    by sneakers563 on Thu Sep 12, 2013 at 05:31:49 PM PDT

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