[fpc-pascal] MD5 decryption?

Ewald ewald at yellowcouch.org
Wed Dec 11 19:55:55 CET 2013

Once upon a time, silvioprog said:
> 2013/12/11 Ewald <ewald at yellowcouch.org <mailto:ewald at yellowcouch.org>>
> Go to: http://md5decryption.com <http://md5decryption.com/>
> In "Please input the MD5 hash that you would like to be decrypted:"
> field, put: 7db4a8dae498d1b4686ebd1f79326602
> See the result in "Decrypted Text:" field.
Yes, I've seen the  site, what they probably do is a reverse lookup in a
table, but it cannot be called `decryption`. Encryption is two way: an
output can be converted back to the original input. This is not the case
with a hashing function. Take for example a very simple function that
xor's all input bytes together (with MD5 it boils down to the same,
albeit a bit more complex). If I give you the output $F0, how do you
know what was the original input? The answer is you don't. It could be
[$80 $70] as well as it could have been [$C0 $FF $30 $FF]...

While both algorithm types (encryption and hashing) are related (the
above xor example classified as a checksum, whereas xor encryption also
exists), they are definitly not the same.


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