Re: What is md5sum?

From: Bill Unruh (unruh_at_string.physics.ubc.ca)
Date: 06/30/04 

Date: Wed, 30 Jun 2004 15:41:43 +0000 (UTC)

Carlos Moreno <moreno_at_mochima_dot_com@xx.xxx> writes:

]P.T. Breuer wrote:
]>>
]>>When did I say that the rest of the universe is wrong?? The
]>
]> When you say that md5sum does not identify a files contents uniquely.

]Actually, you are the one that says that that means the rest of
]the universe is wrong.

]I *know* for a fact that md5sum does not guarantee that a file
]is unique. You still have not proven the opposite. You say

There are two separate questions. Is it mathematically possible that there
exist-- in the mathematical sense-- two files with the same MD5sum. Yes.
Is it possible that there exist in the world as we know it and experience
it two files with the same md5sum? He and I answer no.
IF md5 were shown to be cryptographically weak, I would change my answer,
because in that case human ingenuity could create them. But transfer by ftp
will not.

]that MD5 *is* unique to a file (because of the very nature of
]the energy of the solar system or something like that). Why
]don't *you* prove that?? Using your very logic, if you say
]that MD5 is unique to every file, then show me, show me *ALL*
]the files that have ever existed and *will ever* exist, and
]their MD5s -- if they're all different, then you have proved
]your case and I will believe you and I will admit that I am
]mistaken. But you *have to prove it*, and not ask me to show
]you a counter-example.

Actually you were the one who started this with a claim that I was WRONG to
state to a user asking about md5 that the same md5sum meant that his file
was the same as the original.

]Your statement seems much more definitive than mine -- I'm
]simply saying that it is possible for something to happen

No, for you are using the word possible in a sense that noone else ever
uses it in real life (rather than in mathematics). To tell a user that this
is possible is simply to lie and decieve for to state that it is possible
in common useage means it is something he should be concerned about at some
level.

]even if I haven't seen it (or will see it) happen. You are
]saying that there are not and there can not be two different
]files with the same MD5 -- *prove it*. And you know, I
]will not accept any B.S. with philosophical blahblahs about
]the nature of the universe. I only believe in what I see;

No you do not. That is just the issue. You are asking that user to be
concerned about something they will never see.

]HEY!! What do you mean convinced that the mechanism was capable??
]We're not talking abstract philosophical B.S. here!! You should

Yes, you were the one who started this by talking abstract philosophical BS.

Relevant Pages

  • Re: What is md5sum?
    ... Mathematics is not an approximation of anything. ... > of the sitauation in the real universe? ... you need *at least* the number of digits of the sequence to do that. ... > the same md5sum, you find yourself curiously unable to CHOOSE a pair to ...
    (comp.os.linux.setup)
  • Re: What is md5sum?
    ... > When did I say that the rest of the universe is wrong?? ... When you say that md5sum does not identify a files contents uniquely. ... draw mechanism was capable of producing them, ... Unfortunately this mathematical construction is not physically FEASIBLE ...
    (comp.os.linux.setup)
  • Re: What is md5sum?
    ... There could be a trojan planted in his md5sum which always reports the md5 ... ]statement, which IS INCORRECT. ... If the file you download from the net has the same md5sum as the original, ...
    (comp.os.linux.setup)
  • Re: What is md5sum?
    ... been accompanied by a "in practical terms", ... > the same md5sum, it has been changed. ... statement, which IS INCORRECT. ... then the MD5 must be the same (which is equivalent to saying ...
    (comp.os.linux.setup)
  • Re: What is md5sum?
    ... ]>]> When you say that md5sum does not identify a files contents uniquely. ... ]> IF md5 were shown to be cryptographically weak, I would change my answer, ... IF such a thing were to occur (Ie a weakness in MD5) I would advise people ... ]is wrong -- adding that in practical terms, ...
    (comp.os.linux.setup)