open Truecrypt container with password xor keyfile

Question

i am using a truecrypt container on a flash drive, which I back up periodically. Last days the container crashed and I lost some important data. This made me think about my backup strategy and I think it might be smarter to sync the difference when mount the USB at home.

I would like to script the mount and rsync of the drive when it will be plugged. for this I don't want to put the password to open in the script. when i am not in my apartment, I'd prefer the usage of a password instead of the key file. Is it possible to open a truecrypt (or veracrypt,...) with a password when i am outside and with a key file at home?

Answer 1

Technically: maybe yes
The password and any keyfiles are mixed together to derive the container key.

PW X KF = CK ("X" being the mixing algorithm.)

The mixing algorithm is not that great. -- For example there is a way to construct keyfiles, that don't change the resulting container key at all. -- So I guess it might be feasible that you could start with a password of your choice and then run a little script that generates a keyfile from that password.

So that
No-Password X KF = CK
and
PW X No-Keyfile = CK

So this would work if you input either PW or KF. (But annoyingly not if you input both.)

Practically: Why bother?
But to what end? I don't think you would gain anything security-wise. If you have the keyfile lying around somewhere and that gets copied that's just as bad as having the password lying around and that being copied.

Answer 2

No, this can't be done. Once you specify encryption with a keyfile and/or password, you have to use them for any decryption. If security is important to you, you can only specify encryption done with a keyfile and a password, and use them both whether you're outside or at home.