Re: PGP Signed Messages

From: Jack Lloyd (lloydat_private)
Date: Tue Oct 16 2001 - 08:41:33 PDT

  • Next message: Shaun Dewberry: "RE: Civil Disobedience"

    > BTW PGP key ID's can easily be faked, you can make arbitrary keys with any
    > PGP key ID you want. Don't forget to include the fingerprint (at least then
    > it's only mostly useless as opposed to completely useless).
    
    In the case of the old (PGP 2.6.2) key format, yes, PGP key ids are easily
    spoofable (the key id was the low 32 bits of the modulus). However, the
    newer format (used for all(?) DSA/Elgamal and some RSA keys) uses the low
    32 bits of the fingerprint, which is a cryptographic hash of the entire
    key.  Thus one must generate about 2^31 keys to find a single one which
    matches the key id (by the usual birthday paradox attack on a hash
    function). Lets say you can generate and test 100 keys per second (my 1 Ghz
    Athlon can generate 1 key in about 10 seconds with gnupg 1.0.6). In that
    case, assuming my math isn't wrong, it would take you about 250 days to
    forge a key id. Certainly possible, but quite a bit of work.
    
    I'm fairly certain that having the entire fingerprint on hand gives you
    pretty much full certainty that the key is legit.
    
    BTW, the GPG for pine plugins automatically verify signatures, and displays
    the GPG output, ie either "Good signature from ... " or "BAD signature from
    ..." every time you open the mail. The problems you mention are real, but a
    problem of 1) bad mail client support, and 2) overly trusting people, not
    the PGP format itself.
    
    Regards,
    
    Jack
    



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