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    SubjectRe: partially encrypted filesystem
    In article <Pine.LNX.4.53.0312031627440.3725@chaos>,
    Richard B. Johnson <> wrote:
    | On Wed, 3 Dec 2003, Kallol Biswas wrote:
    | >
    | > Hello,
    | > We have a requirement that a filesystem has to support
    | > encryption based on some policy. The filesystem also should be able
    | > to store data in non-encrypted form. A search on web shows a few
    | > encrypted filesystems like "Crypto" from Suse Linux, but we need a
    | > system where encryption will be a choice per file. We have a hardware
    | > controller to apply encryption algorithm. If a filesystem provides hooks
    | > to use a hardware controller to do the encryption work then the cpu can
    | > be freed from doing the extra work.
    | >
    | > Any comment on this?
    | >
    | > Kallol
    | > NucleoDyne Systems.
    | >
    | > 408-718-8164
    | I think you just need your application to encrypt data where needed.
    | Or to read/write to an encrypted file-system which always encrypts.
    | You really don't want policy inside the kernel.
    | Let's say you decided to ignore me and do it anyway. The file-systems
    | are a bunch of inodes. Every time you want to read or write one, something
    | has to decide if it's encrypted and, if it is, how to encrypt or
    | decrypt it. Even the length of the required read or write becomes
    | dependent upon the type of encryption being used. Surely you don't
    | want to use an algorithm where a N-byte string gets encoded into a
    | N-byte string because to do so gives away the length, from which
    | one can derive other aspects, resulting in discovering the true content.
    | So, you need variable-length inodes --- what a mess. The result
    | would be one of the slowest file-systems you could devise.
    | Encrypted file-systems, where you encrypt everything that goes
    | on the media work. Making something that could be either/or,
    | while possible, is not likely going to be very satisfying.

    Well said. This isn't the way to do it as you say, although you could
    add an O_CRYPTO flag to creat() if you really wanted to.

    Crypto in the program is definitely the better solution.
    bill davidsen <>
    CTO, TMR Associates, Inc
    Doing interesting things with little computers since 1979.
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