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    SubjectRe: A patch to loop.c for better cryption support
    Date
    Marc Mutz  wrote:
    >> There are some who believe that "not unique" IVs (across multiple
    >> filesystems) facilitates some methods of cryptanalysis.
    >
    >Do you have a paper reference?

    There's no paper, because it's too trivial to appear in a paper.
    But you can find this weakness described in any good crypto textbook.
    See, e.g., Bruce Schneier's _Applied Cryptography_; the section on
    CBC mode says that IV's must not repeat. (However, it does get one
    thing wrong: it claims that it's ok to use a serial number for your
    IV. This is not correct, and I can give a reference for this latter,
    subtler point, if you like.)

    >As CTR mode _requires_ unique IVs (CBC does not),

    Sorry, that turns out not to be the case. Both CBC and CTR mode
    require unique IV's (for security).

    >the upper half of the
    >IV could be initialized from the key

    It's a bad idea to include key material in your IV. (Kerberos did
    it, and there were some attacks as a result.) I recommend against it.
    -
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