Reverse md5sum?

[QuantumMonkey]

Every program has an md5sum, it's like a digital fingerprint. These are used to show if a program has been tampered with.

I was wondering, is there a way to "reverse" the md5sum of a program? Like, putting in the md5sum into a program and it creates the program that owns that md5sum.

This would be very interesting and it could be used a lot instead of downloading.

 

[SYL\X/3K]

There might be a third party software that ""might" be able to update the md5checksum, as i seen this possibility.
E.g. Swat 4 uses an application called "UCC.exe" with a batch script containing:

cd .\System\

..\..\Content\System\UCC.exe mastermd5 -c

pause

 

[office politics]

http://en.m.wikipedia.org/wiki/Md5sum

States that there is an unlimited amount of files that can generate any given hash.

 

[office politics]

Im confused why it says that. Wiki may need an update. The real answer is that a md5 hash only works one way.

 

[InfiniteLoop]

the reason is because an md5 hash, any hash really is lossy. i.e. data is lost in the hashing of a file/password/etc. that is why the hash on a 650mb iso is still only 4kb or whatever.

the reason that there is a theoretical number of files that can have the same hash is because of this lossy-ness. hash collisions in the real world, however, are not an issue.

 

[kmote]

the reason is because an md5 hash, any hash really is lossy. i.e. data is lost in the hashing of a file/password/etc. that is why the hash on a 650mb iso is still only 4kb or whatever.

the reason that there is a theoretical number of files that can have the same hash is because of this lossy-ness. hash collisions in the real world, however, are not an issue.

This is the correct answer.