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- MD5 for ninnies
- Water Cooler v2
January 17, 2006, 6:02 pm
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If I apply an MD5 hash on a character string, say, "Hello", and the
result is (just for the sake of brevity) DF94EX, then, given the hash
value, can I get back the original string "Hello" from it?
* I do know that two different strings will never yield the same MD5
* I also know that it is claimed that given a predetermined MD5 hash
value, no one can just point their finger at the original string that
was its seed, i.e it is not computationally possible to arrive at the
* I also know that there are some collision attacks on MD5, SHA and
* I also know that MD5 is a bit slower than MD4.
Re: MD5 for ninnies
I would say that's designed to be impossible, but absent a math degree
and a lot of experience in cryptography, allow me to hedge my bets and
say "designed to be EXTREMELY difficult and resource intensive."
I believe you (though not practically) can brute force your way to
find a string that yields the same MD5 hash as what seeked a given
md5 hash, but given the existence of collisions, I do not believe
there is any way to verify that you relaly got back to the original
string. However, if you have something that gets you to the same
md5hash, and the thing in question is really using md5sums, the string
you arrive at will work just as well as the orginal anyway.
Re: MD5 for ninnies
No. You can try all possible strings and see which gives the hash.
False. Different string WILL give the same hash value. Many many many
different strings will give the same hash value. A hash is not an
If the string is shorter than 8 bytes the chances are good that no other
less than 8 byte string will give the same hash value. If it is longer,
then the chances go up. If the string length is 16 bytes or longer then the
chances are certain that another string of the same or shorter length will
have the same hash value.
It is probably difficult. No one knows of a way right now to do better than
"try all strings" HOwever, it is possible to find two strings with the same
hash value in much less work ( something like 2^32 attempts).
MD4 is very weak. MD5 is stonger but see the above. SHA1 is stronger than
MD5 but still two strings with the same hash can be found with much less
than the expected amount of work.
It depends. If the original was a piece of text and the result is a piece
of gibberish, then the result is probably not useful.
- Lassi =?ISO-8859-15?Q?Hippel=E
January 17, 2006, 6:51 pm
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