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No, computer B just needs some way to access the encrypted key for the files from computer A. You can either have computer A create a master key that gets encr
by evgen 17y ago
No, computer B just needs some way to access the encrypted key for the files from computer A. You can either have computer A create a master key that gets encrypted with a user-supplied password and then handed out to any client that passes a "does user A approve of this transfer" check, or you can use fine-grained ACLs or capabilities similar to what is done in something like Tahoe-LAFS. The server does not need to see unencrypted data in either case.
- shrughes 17y agoThe hard part here is for computer A to be sure it's handing the information it thinks it's handing it to. No matter how you do it, computer A needs to be sure it's giving permission to computer B, and not somebody claiming to be computer B, and that involves either personally meeting beforehand to trade some kind of keys or trusting a third party.
- evgen 17y agoThus the additional re-encryption of the master key. If this re-encryption key is secure then you don't need to care who the master key is handed out to as only an authorized party can decrypt it. There are other, more complicated, crypto schemes that can make this process easier or more secure, but something like this has KISS appeal. An external channel is required here (to transmit the re-encryption key) but that can be as simple as a phone call or email; anything that does not need to pass through the third-party holding the data files.