Does ready two-way hash function for strings with fixed hash length exist in Java?

Question

I need use hash and en-hashed (two-way) function for strings. Hash should be fixed length (5-6 symbols).

Example:

String hashed = MagicHashLib.hash("long string"); //hash is hd45dk as an example
String enhashedLongString = MagicHashLib.enhash(hash);

Does exist already implemented algorithm in Java? Or I should write my own?

Hashes are supposed to be one-way. That makes a hash :) So, you may not be talking about hashing here, indeed. — vahdet, Jun 01 '18 at 09:08
An operation opposite to hashing. I haven't found correct antonym for "hashing", sorry — Aureum, Jun 01 '18 at 09:08
@Jun: Once hashed, there is no way to get the original String. It's a one-way function. — Nikolas Charalambidis, Jun 01 '18 at 09:09

Shanu Gupta · Answer 1 · 2018-06-01T09:11:44.070

2

What you are looking for is called encryption and decryption.

Hashing is always one-way. You cannot feasibly recover original string from its hashed value.

For brief explanation about differences between hashing and encryption see this answer

edited Jun 01 '18 at 09:11

answered Jun 01 '18 at 09:10

Shanu Gupta

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*You cannot recover original string from its hashed value*: not entirely correct. It just takes a very very very very very very very ... very very long time – Lino Jun 01 '18 at 09:10
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Added the term "feasibly". – Shanu Gupta Jun 01 '18 at 09:12
I see. Thank you! – Aureum Jun 01 '18 at 09:13

score 1 · Accepted Answer · answered Jun 01 '18 at 09:13

I don't think such hash exists, regardless of the programming language.

Here is a quote from the hash function wikipedia page:

A hash function is any function that can be used to map data of arbitrary size to data of fixed size.

It means that you have a fixed set of values, e.g. a 6 character long hash can store 16^6 different values. However, you can create the hash value of any string. So a hash function maps potentially infinite different values to a fixed sets of values. Hence there will be collisions. So you cannot tell just by the hash value which was the right original value.

A simplistic example from an imaginary hash function: John maps to abc. Jane maps to ghi. Doe also maps to abc. So when you see abc as a hashed value, where did that come from? Was it John? Was it Doe?

Thanks for pointing it out! Changed to `16^6` because that's the usual radix in hashes. But it's a matter of radix anyway. You can include other chars as &, #. But that would be weird :) — Tamas Rev, Jun 01 '18 at 09:19

Does ready two-way hash function for strings with fixed hash length exist in Java?

2 Answers2