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Comment by ryandrake | Hacker News Reader

It's unexpected to anyone with intuition about how a computer traditionally is supposed to work. As a general principle, as a user, I expect a file on one computer to be usable on another computer. Or, at the very least, if I need to obtain some other thing from the original computer to "unlock" that file, I should be able to do it. The idea of a file that is only usable on a particular computer feels weird.

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> As a general principle, as a user, I expect a file on one computer to be usable on another computer.

As a general rule, I expect a file on an encrypted disk to be unreadable for anyone who lacks the encryption key(s).

> if I need to obtain some other thing from the original computer to "unlock" that file, I should be able to do it.

You can export your passwords to a plain text CSV from the original computer.

As a general rule, I expect a file on an encrypted disk to be encrypted with a key derived from a password I provide.

I think it's time to update your expectations. Hardware security modules have been around for quite a while. You shouldn't assume that your chosen password is the only input to the key derivation, or even that the raw key itself will always be obtainable.

I never assumed that my chosen password was the only input to the key derivation. Just that my chosen password is at least one of the inputs to the key derivation. LUKS has been around for quite a while.

You're asking for the encryption key to be derivable by an unrelated system that only has the encrypted file and your password.

Yes, that's kind of what you need to be able to successfully back up and restore an encrypted file. Why are you making it sound like that's such a strange thing to want?

Yes, in general that's how I expect (or at least want) things to work. And I'm a tech-savvy software developer.

Your average non-technical user will absolutely expect it to work this way, and if it doesn't, will be at best confused, and at worst incredibly angry that their photos are gone.

The sane way for encryption keys stored in hardware (secure enclave or tpm like) is to onboard user when the key is not derived from user password. Just like they do for FDE to export a recovery key and then you can adjust your expectations when you know (been told) whats going on.

No, I'm asking for what LUKS has done for two decades. Keyslots are alternatives, not requirements, so a TPM slot and a passphrase slot coexist and either one alone unwraps the master key.

BitLocker does the same with key protectors. Even on a local account with no internet, there's always a 48-digit recovery password that opens the volume on a completely different machine.

Two of the three major platforms ship a portable passphrase path alongside the hardware one, so this being unavailable here is a product decision, not a law of key derivation.

As a general rule, if I'm the user of both disks I expect to have the encryption key(s).

> You can export your passwords to a plain text CSV from the original computer.

Exporting a private key from a keychain is hard to automate (the password of the keychain is asked for all exports, and HAS to be typed manually IIRC).

The right way to do that is FDE, where you can't even mount the filesystem to see the files without having the decryption key.

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