Why is MD5 a one-way cypher?

[HairyHun]

I always wondered.

How can there be a one way cypher?


I mean the algoryth has steps to get from A to B.
If A, coded, is always be, then there must be set steps in the algorythm
So you should be able to do the steps in reverse.

Now if B is not reversable to A. Then there should be some randomness generator along the way. Then how can A always be encrypted into B?


The things that keep me up at night...

HH

 

[RuDeDoGg]

Here's how I understand it (from reading Wikipedia):
MD5 is not a cipher, it's a fixed length hash. A hash is like a random function that is predictable only by using the same input. MD5 hashs can not be reversed. The only way is with rainbow/hash tables, just a lot of words(probably dictionary words and common passwords), etc put into a hash (which makes reversing passwords hard, if the person isn't a tard, and it's probably pretty CPU intensive to search all those hashs).

A Cipher is meant to be encoded, and decoded. Hash's, MD5, SHA-1 etc are not, they are only good if you know the original value, to verify it, while letting the admin/database not hold any valuable information. That is why using hash's are used to verify a users password.

PS: after looking up some rainbow tables, they are massive, multiple GB databases.

 

[CygnusX]

MD5 is not decodable because it uses the modulo function.

23 mod 5 = 3
18 mod 5 = 3
From left to right, it always gives the same result. From you cannot go from right to left.

Perhaps there are other factors besides module that make MD5 not decodable too, but randomness is not one of them.

 

[fcreature]

Its all in the mod function.