pgpfan:forward_secrecy
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pgpfan:forward_secrecy [2020/06/09 11:57] – state that with was only implied b.walzer | pgpfan:forward_secrecy [2020/07/14 17:51] – The major rewrite b.walzer | ||
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======Forward Secrecy====== | ======Forward Secrecy====== | ||
- | The PGP protocol is sometimes criticized because it lacks a feature called [[wp> | + | The PGP protocol is sometimes criticized because it lacks a feature called [[wp> |
- | Forward secrecy requires an end to end, bidirectional communications channel to establish | + | Some process is used to come up with a temporary key known only to you and your correspondent (e.g. [[wp> |
- | =====Message Archives===== | + | The first important point is that forward secrecy depends on the integrity of the encryption. If someone manages to break the encryption on your old messages they will still get access to them. |
- | If someone gains access to one of your private PGP encryption keys then they can decrypt all the archived email that was originally sent to the associated identity. A system with forward secrecy | + | The second important point comes from the first. Since forward secrecy |
- | There is no practical security difference between PGP and a system providing forward secrecy for the case of message archives. | + | If someone compromises your end device then they have access to whatever you have access to. They can acquire any passwords or passphrases with a key logger. They can see what you see on the screen either at the character stream level or with screenshots. There are two important implications here: |
- | =====Post-Compromise===== | + | * They get access to any saved messages. For forward secrecy to work you must give up message archiving. |
+ | * They get access to any transferred messages. Forward secrecy is of no value after a compromise. | ||
- | If someone gains access | + | Forward secrecy requires an end to end, bidirectional communications channel |
- | Gaining access to a pass-phrase protected PGP private key requires at least enough access to install a key-logger (or equivalent). That much access would normally allow an attacker to get access to the messages | + | In the case of something like encrypted email where archived |
- | A system providing forward secrecy has a theoretical advantage in this case, but in practice the advantage would likely be minimal. | + | [[pgpfan: |
- | + | ||
- | =====Pre-Compromise===== | + | |
- | + | ||
- | This assumes that there is someone with enough foresight to record your encrypted messages off the network. That message archive can be decrypted if they have access to your PGP private key, as before. That archive is useless in the case of a forward secrecy supporting system as the decryption key(s) have been destroyed. | + | |
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- | This is the advantage of forward secrecy. | + | |
- | + | ||
- | =====Conclusions===== | + | |
- | + | ||
- | Forward secrecy removes the value of encrypted messages collected off the network before a compromise. Forward secrecy increases protocol complexity. The cost of that complexity has to be weighed against the possibility of that particular attack. | + | |
- | + | ||
- | The value provided by a forward secrecy system is mostly negated for those messages that are archived. If you truly want the messages to be gone for others you have to have to make them gone for you as well. This is a fairly heavy price to pay. | + | |
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- | I should point out here that the deletion of a PGP private key removes access to all archived messages, everywhere, instantly as there is no separate archiving system. That is a benefit of the PGP encrypt once scheme. Key deletion is thus a PGP answer to forward secrecy. Modern PGP systems use separate signing and encryption keys by default so it would be reasonably easy to recover from such a deletion. That is even if you did not have the foresight to use a dedicated key for the discussion that was to be forgotten. You would still retain all your identities. | + | |
pgpfan/forward_secrecy.txt · Last modified: 2022/03/19 21:50 by b.walzer