On Sep 19, 2012, at 4:48 PM, "[email protected]" <[email protected]> wrote: > Every three months I, the Grantor, encrypt my secret in a new > secret-encrypting-key and place that secret in my box. (I keep my box > away from others - maybe put it in a safe). > > I also encrypt that secret-encrypting key in a public key but not too > strong a public key, one that can be broken in three months time. > > I then throw away the private key to that public key (I don't need it, > I know my secret). > > I give the public-key encrypted secret-encrypting key to the trustee, > heck I can publish it on the web if I want. > > If I should die, I will stop re-encrypting the secret and the trustee > (that I never really trusted) can break the public key and get to the > secret.
This doesn't work or doesn't help. If the "trustee" doesn't have access to the "safe" until after you're dead, then the encryption is unimportant: just keep your secrets in the safe unencrypted. If they can access the encrypted message before your dead, they can decrypt it in a few months, even if you stay on the right side of the grass. Separately, I think it's impracticable to know the available computation time for key breaking, so it's difficult to estimate how long it will take the trustee to recover the message after gaining access to the encrypted message. I don't know of any way to solve the original problem other than changing the framing to allow somewhat trusted third parties (distribute secret shares to a dozen people, requiring 10 of them to agree to recover the decryption key, hope that they don't conspire to recover it until after you're dead), having access to a secure agent (software running somewhere that releases the secret if you don't check in for 30 days), or the ability to invalidate an old secret store (e.g., physically hide the secret somewhere, move it every 30 days, and encrypt the location with a 60-day weak key, but see the above challenge of predicting how long it will take to crack--a key long enough to be safe for 60 days against all attackers may take your trustee a couple of years to crack once you're dead). - Tim _______________________________________________ cryptography mailing list [email protected] http://lists.randombit.net/mailman/listinfo/cryptography
