I am trying to understand how the physical limits of computation apply to crytography, and came up with the scenario below as a sort of gedanken. I would be grateful to see how others answer it.
Assume that Alice
used the default GnuPG (aka "GPG") settings, except for the following:
and then used GPG to create a 4096-bit RSA PGP encryption key pair whose private key is protected by a 10-word Diceware passphrase;
and then used the public key of that key pair to encrypt a plain text 1kB long;
and then stored the resulting ciphertext, along with the key pair, on a CD-ROM which she then gave to Bob, and nowhere else;
and then perished, vaporised by a meteorite along with the laptop she used to perform the above tasks, leaving Bob's CD the only record of her key pair and ciphertext.
Assume also the existence of a computer, bound by the physical limits of computation as presently understood (e.g. these), but otherwise optimised to efficiently perform the tasks in question (e.g. a hypothetical quantum computer).
Finally, assume that this computer is adequately powered, and immune to catastrophes (such as the death of the Sun), during its tasks.
What is the minimum energy, in SI units (i.e. J, or kJ, or MJ, etc), such a computer would require, in order to determine the plaintext, if the CD-ROM's data are available to it?
Please explain your answer, thanks!
P.S. Please migrate this question to security.stackexchange.com if you believe it would be more appropriate there.