Re: [Full-Disclosure] Time Expiry Alogorithm??

From: Pavel Kankovsky (peak_at_argo.troja.mff.cuni.cz)
Date: 11/19/04

  • Next message: Xavier Beaudouin: "Re: [in] Re: [Full-Disclosure] IE is just as safe as FireFox" 
    To: full-disclosure@lists.netsys.com
Date: Fri, 19 Nov 2004 18:06:59 +0100 (CET)

    On Fri, 19 Nov 2004, Gautam R. Singh wrote:

    > I was just wondering is there any encrytpion alogortim which expires
    > with time. For example an email message maybe decrypted withing 48
    > hours of its delivery otherwise it become usless or cant be decrypted
    > with the orignal key

    No.

    If a certain deterministic computation (e.g. decryption) can be made in
    time T, then it can be made in any time T' > T. Even if the computation
    needs cooperation by your computer that refuses to cooperate when the
    time limit expires (e.g. the recipient of the message needs to ask you
    for an extra key), you can always do the computation once and save the
    result (e.g. the plaintext). Well, I admit, this holds unless your
    computer has been possesed by Palladium (and is not *your* computer
    anymore).

    On the other hand, the power of hardware as well as the knowledge of
    cryptanalysis oincreases as the time passes, ergo any cipher is going to
    expire...in the sense someone will become able to break it and recover
    the plaintext without the (a priori) knowledge of the encryption key.

    --Pavel Kankovsky aka Peak [ Boycott Microsoft--http://www.vcnet.com/bms ]
    "Resistance is futile. Open your source code and prepare for assimilation."

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  • Next message: Xavier Beaudouin: "Re: [in] Re: [Full-Disclosure] IE is just as safe as FireFox"

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