Re: Erasing an OTP file on a SD card.

From: Giorgio (giorgio_at_bignami.zzn.com)
Date: 07/30/04

  • Next message: Milan VXdgsvt: "Re: Please suggest a simple 8-bit cipher" 
    Date: 30 Jul 2004 02:17:21 -0700

    cesarbremer@raseac.com.br (Cesar Bremer Pinheiro) wrote in message news:<4c3656f.0407290903.2ab5096d@posting.google.com>...
    > I agree with you. I implemented One Time Pad under AES 256 bits CBC
    > random IV, this is an option to the user, only works under the
    > symmetric encryption. In our system you can't use OTP alone.
    That's good, in the sense that if it's properly implemented you can
    reasonably assume that the AES security level is the minimum effort to
    crack the system. This is a costless and clever way to provide a
    reasonably quantificable security to the worst case, however the point
    is that whole system will never be unconditionally sure like the OTP
    algorithm element.
    This is the reason of diffidence toward OTP in cryptography, maybe in
    an ideal case even an average implementation of the system is far more
    secure than other systems, but in the worst case it has no advantage
    but however you have always to manage the "cost" of pad excange and
    protection.
    Usually in cryptography works are toward making the system behave
    secure in the worst case, not in the best or even in the most
    probable.

    > About erasing SDCard: In our case, if our client is worried against
    > attackers recovering erased data in a SDCard, i think he have a very
    > important information inside the SDCard to be protected, and enough
    > money to destroy the SDCard after using it.
    If you provide this system you should also provide to the user this
    information and means for secure deletion (as for the state of art of
    data recovery) or secure destruction, in an emergency situation the
    user may have not have the time to melt or pulverize the device with
    bare hands or such means... implementing secure means to make the
    "worst case" less probable is not easy and may be not cheap.

    > And about OTP Random data generators. We have a lot of good random
    > data generators today in the market, i don't see problems using one of
    > them.
    There is usually no problem in using those devices i.e. for provide
    random data to scientific simulation, but for being used for an OTP
    implementation you should make it tamper proof, an attacker should not
    be able to open it to replace it with a dummy rng, or to analize the
    radiation of the device.

    As said, making the worst case less probable is not easy and may be
    not cheap, and may require constant update about state of art of
    tecnologies that may be used to tamper the whole system (if even those
    informations are made public), however, it seem you are aware of the
    problem you will encounter in OTP implementation so, good work!
     Giorgio

  • Next message: Milan VXdgsvt: "Re: Please suggest a simple 8-bit cipher"

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