# what's the possibility of key conflict with MD4?

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Hi, all

Sorry for this naive quesiton. What's the possiblity that two different
message will give out the same signature with MD4?

Thanks a lot!

Andy

## Re: what's the possibility of key conflict with MD4?

:Sorry for this naive quesiton. What's the possiblity that two different
:message will give out the same signature with MD4?

There is a 100% probability that for any given message, that
there is an infinite number of other messages that have the
same MD4 signature. The hard part is finding them.

I tend to see more about MD5 than about MD4; I do not recall
what the state of the art says about MD4. If I recall correctly,
people have found some theoretical weaknesses in MD5 (and, if memory
servers, even a way to compute a message with the same MD5 signature
in some cases). DES, on the other hand, did not suffer from the
same weakness.
--
History is a pile of debris               -- Laurie Anderson

## Re: what's the possibility of key conflict with MD4?

roberson@ibd.nrc-cnrc.gc.ca (Walter Roberson) writes:

Yes.

MD4 and MD5 are both weak. Both have been broken, and it is easy in both
cases to find files with the same MD5 sums.

Find another file wtih same sum as a given file is still difficult.

DES is NOT a hash. So mentioning it is irrelevant. "My toyota and my ford
both burn a lot of gas, but my swimming pool does not suffer the same
weakness."

## Re: what's the possibility of key conflict with MD4?

Two given messages. roughly 1/2^N where N is the number of bits in the md4
signature.
If you have many messages, then the probablility that two of them will
share a signature is given by the birthday calculation-- and by the time
you get to roughly 2^(N/2) messages the probability is roughly  1/2 that
two of them share a signature.

Hi, all

Thank a lot!

Andy

Andy wrote:

I always do :-)