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  • Practicality of codebook in current-day secret communications

    From Mok-Kong Shen@21:1/5 to All on Wed Feb 24 21:50:28 2016
    Codebook appears, if I don't err, to be an antiquitated topic rarely
    touched upon in discussions of modern cryptography. Couldn't codebook nonetheless be of high practical utility and even be extremely
    advantageous in certain critical fields of modern secret
    communications? Consider e.g. the hypothetical situation where
    a manager has to securely correspond with his representative who is
    negotiating with the customer in a bid under rival competitions. It
    seems that the essential instructions and responses could be
    realistically formulated as sentences and phrases of an appropriately
    designed codebook having entries of, say, 256 in number. That is, one
    needs only to suitably employ a highly limited number of code words in
    entirely neutral appearing text messages or to otherwise transmit
    somehow a small number of bits denoting the indices of the involved
    sentences or phrases in the codebook in certain appropriate way (e.g.
    the scheme http://s13.zetaboards.com/Crypto/topic/6939954/1/). Note
    that the codebook need not be static but can preferrably be dynamic,
    i.e. dependent on a session key.

    Thus seen, top secret communication isn't necessarily a hard problem,
    or is it? Since no encrypted stuffs are involved, the scheme avoids
    from the outset issues like enforcing delivery of encryption keys or
    implanting of "official" backdoors.

    M. K. Shen

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  • From Mok-Kong Shen@21:1/5 to All on Sat Feb 27 23:23:24 2016
    Am 24.02.2016 um 21:50 schrieb Mok-Kong Shen:
    [snip]
    ........ Note
    that the codebook need not be static but can preferrably be dynamic,
    i.e. dependent on a session key.
    [snip]

    Edited:

    It may be remarked that the codebook need not be static but can
    preferrably be dynamic, i.e. the mapping between the codewords and
    their meanings is dependent on a session key, being a random
    permutation (Fisher and Yates algorithm or alternatives) determined by
    it. The codewords are preferrably to be chosen to be certain commonly
    employed words, e.g. surnames etc. in order to ease the composition of
    a fairly natural covertext. In case it is desired to have integrity
    check, one could employ two disjoint sets of codewords that are
    independently permuted w.r.p.t. the set of meanings so that each
    meaning (or only those meanings that are classified as important) will
    be trasmitted via the coexistence of at least one keyword from each set.

    M. K. Shen

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