Re: This Week's Finds in Mathematical Physics (Week 226)

On Sat, 11 Feb 2006, John Baez mentioned that md5sum was "broken" about a year ago. I just wanted to add:

1. If I am not mistaken, sha-1 and md5sum are different algorithms (IIRC, both are known to be insecure). Anyone interested can probably figure this out from the official specs:

SHA-1 hash algorithm:
http://www.ietf.org/rfc/rfc3174.txt

md5sum message-digest algorithm:

http://www.faqs.org/rfcs/rfc1321.html

2. The latest versions of the open source utility gpg supports a more secure algorithm, SHA-512, which AFAIK has not been broken; see

Tony Stieber, "GnuPG Hacks", Linux Journal, March 2006.

3. Even insecure checksum utilities are probably better than none at all. Indeed, checking the given example

gpg --print-md md5 letter_of_rec.ps order.ps
A2 5F 7F 0B 29 EE 0B 39 68 C8 60 73 85 33 A4 B9
A2 5F 7F 0B 29 EE 0B 39 68 C8 60 73 85 33 A4 B9

Oh NOOOOOO!!! But wait, there's more:

gpg --print-md sha1 letter_of_rec.ps order.ps
0783 5FDD 04C9 AFD2 8304 6BD3 0A36 2A65 16B7 E216
3548 DB4D 0AF8 FD2F 1DBE 0228 8575 E8F9 F539 BFA6

gpg --print-md RIPEMD160 letter_of_rec.ps order.ps
9069 8ACC 6D67 6608 657B 9C26 F047 59A1 DC0E 6CA1
C1BB DE12 B312 EAAD DD3D D3B8 4CA1 CB1B BA47 DD13

Ah HAAAAAA!!! Gotcha, Alice!

For more on cryptographic hash functions and their woes, try these:

9) Cryptographic hash function, Wikipedia,
http://en.wikipedia.org/wiki/Cryptographic_hash

Of course, bear in mind that anyone can edit, blah, blah (including unregistered users, contrary to widely publicized news reports based upon a fundamental misunderstanding).

So, people are getting wary of SHA-1.

Something to think about when you are reading articles at that website which anyone can <s>poison</s> edit.

These are huge and wonderful philosophico-physico-mathematical questions with serious practical implications.

You mean the Weyl curvature hypothesis? :-/

But while we should never neglect incompleteness entirely, I was fascinated to discover from my readings a few years back that even first order logic has its fascinations!

Joel Spencer, The Strange Logic of Random Graphs, Springer 2001

Here's a thought: "Everyone knows" that if on day D, mathematician M is studying an example of size S in class C, he is more likely to be studying a "secretly special" representative R than a generic representative G of size S. Why? Because the secretly special reps show up in disguise in other areas, and M was probably hacking through the jungle from one of those places when he got lost and ate a poisoned cache.

Kinda like the "random appearing" md5sum of the empty file.

Is scientific creativity nothing but a hash sum hack?

Bite me, Brian!

"T. Essel"

.

Relevant Pages

  • Re: SHA-1 vs. triple-DES for password encryption?
    ... be better to use a standard algorithm rather than a home-grown one. ... SHA-1 and 3DES have been reviewed for some time. ... This is where a hash comes in nicely. ... Longer passwords and hashes aid in making the hash much harder to work with. ...
    (SecProg)
  • Re: sort unique
    ... given that a hash table is not ... IMO if the vendor's algorithm does something "obvious", ... function to eliminate keys that hash to the same bucket per some ... strings of random lengths, and two strings are ...
    (comp.lang.lisp)
  • Re: out of memory
    ... read only the smaller file into a hash. ... the smaller file will fit into RAM. ... Depending upon the sorting algorithm this would be Ologor ... put your relevant data into a database and use ...
    (comp.lang.perl.misc)
  • Re: freebsd-updates install_verify routine excessive stating
    ... The algorithm with awk is still the fastest in theory. ... ASSUMING you have a good hash function that yields such result. ... to have enough free inodes on your file system. ...
    (freebsd-hackers)
  • Re: Probabalistic algorithms.
    ... >Hashing is typically just an optimisation. ... all the hash does is guarantee that given some ... >hard to factor the composite into its two prime factors. ... >algorithm that's dfaster than brute force factorisation, ...
    (comp.lang.pascal.delphi.misc)