Re:Illegal Hashes
by nine_k on Monday November 28, 2022 @07:57PM
(#33782245)
This argument is pretty old. The way it's shown here is needlessly limiting. Consider the library that contains every permutation of letters:
«All—the detailed history of the future, the autobiographies of the
archangels, the faithful catalog of the Library, thousands and thousands of
false catalogs, the proof of the falsity of those false catalogs, a proof of the
falsity of the true catalog, the gnostic gospel of Basilides, the commentary
upon that gospel, the commentary on the commentary on that gospel, the
true story of your death, the translation of every book into every language,
the interpolations of every book into all books...» (J.L. Borges, The Library of Babel.)
More interesting is to analyze the probability of finding a file with a hash form a particular set. MD5 gives 160 bit; if it's a good hash that does not have large gaps in its values, this is roughly 1.46e+48 values.
Let the set of the forbidden values have 1.46 billion elements, that is, 1.46e+9. This should be enough for all the hashes of copyrighted works, and all the forbidden blasphemous utterances. Then the chance of hitting one of them is going to be 1e-39.
This chance is so low that it's hard to imagine. Take a mega-lottery with 10M = 1e+7 tickets; it's the chance of winning it six times in a row, by buying a single random ticket every time.
This is, of course, assuming that MD5 has no preimage attack; AFAIK such an attack is not known by now.
«All—the detailed history of the future, the autobiographies of the archangels, the faithful catalog of the Library, thousands and thousands of false catalogs, the proof of the falsity of those false catalogs, a proof of the falsity of the true catalog, the gnostic gospel of Basilides, the commentary upon that gospel, the commentary on the commentary on that gospel, the true story of your death, the translation of every book into every language, the interpolations of every book into all books...» (J.L. Borges, The Library of Babel.)
More interesting is to analyze the probability of finding a file with a hash form a particular set. MD5 gives 160 bit; if it's a good hash that does not have large gaps in its values, this is roughly 1.46e+48 values.
Let the set of the forbidden values have 1.46 billion elements, that is, 1.46e+9. This should be enough for all the hashes of copyrighted works, and all the forbidden blasphemous utterances. Then the chance of hitting one of them is going to be 1e-39.
This chance is so low that it's hard to imagine. Take a mega-lottery with 10M = 1e+7 tickets; it's the chance of winning it six times in a row, by buying a single random ticket every time.
This is, of course, assuming that MD5 has no preimage attack; AFAIK such an attack is not known by now.