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    SubjectRe: mlock(1)
    On Sat, 25 Sep 2004 04:58:48 +0200, Andrea Arcangeli said:

    > I don't even think "save their key securely" (I mean saving anything
    > related to the swapsuspend encryption key on disk) is needed. A mixture
    > of a on-disk key + passphrase would not be more secure than a simple
    > "passphrase" alone, because the on-disk key would be in cleartext and
    > readable from the attacker. the only usable key is the one in the user memory,
    > it cannot be saved in the computer anywhere. Peraphs for additional
    > security (and to avoid having to type and remember it) one could use an
    > usb pen to store and fetch the key... but then I leave the fun to the
    > usb folks since to do that usb should kick off before resume overwrites
    > the kernel image ;)

    Well, obviously saving the actual key on the disk is a losing idea, but saving
    "key hashed by passphrase" would work (similar to how PGP or SSH don't save the
    actual key, but rather the key hashed by something).

    I suspect that having the *entire* key be the passphrase remembered by the user
    is also a non-starter security-wise (unless we do something like Jari Ruusu's
    loop-AES stuff does and forces a minimim 20-char passphrase) - there's going to
    be all too many blocks in the swsusp area that are "known plaintext" and easily
    brute-forceable for most passphrases that users are likely to actually use.

    So in order to make it at all secure, we really need to save on the disk
    a key with O(128 bits) of entropy, perturbed by enough bits that are *not*
    to be found anywhere on the machine so that it isn't a slam-dunk for an attacker.

    Do any of the crypto experts lurking have ideas/opinions on just how many
    bits we need to store externally (be it in a USB dongle, a thumbprint, a
    passphrase, whatever)?

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