English Decrypting Strings

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08.01.12 12:16:21 pm
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PyKemis
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I've really never done anything like this before-so I wouldn't even know where to start. A link to a tutorial or even a brief explanation would be awesome.

I know what the starting starting string as well as the finished string, I'm trying to figure out how to get there...

ex. Start: 0, End: 1 ---> End=Start+1

Though it's not that simple.

Code:
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Start:
     4fac03205c8d45b39935bced884830b42b84492b

End:
     81b252639f9bcef0a2b1c5130a55d810


The starting string is always 40 characters, the end string is always 32 characters.

The starting string is always a to f and numbers, I'm not sure about the end string though, it looks like it as well.

The end string is derived from the start, so the answer must be end = function(start).

Here are more values returned from the same question:

Code:
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4fac03205c8d45b39935bced884830b42b84492b //start
81b252639f9bcef0a2b1c5130a55d810 //end

5b6e35d137184dc78ac1a1e9761f11d9c6d19f11
bac60a464c975d822da781dcdd169de2

9628031f3cce44e59e757497dc205e361b6c6464
76ed1d8ed36eb56fcb574bb3aee7219a

0b22eff17eb04cf8b6464676f474ee20cef2937e
425aefb9e4598e0c0af814377358b04a

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
4168161b130aff2fc266c8235420df61


Extremely difficult...or it could just be sha1(md5(start)), (jk it's not, and I don't even know the answer).
edited 1×, last 08.01.12 01:50:23 pm
08.01.12 02:46:05 pm
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DannyDeth
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Lol! SHA1 and MD5 are hashing algorithms, not encryption algorithms.

Anyway, because there are numerous encryption algorithms around, you need to specify exactly what it is, and also, are you sure the smaller string is the output of the encryption algorithm? Usually when you encrypt something it gets larger, not smaller.

Now, the entire point of encryption is being unable to crack it, so you really will find it nearly impossible unless you are experienced in the field.
08.01.12 06:28:07 pm
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Flacko
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You can't decrypt a hash specially if the resulting hash is smaller than the input (data loss)

You can try to crack it using a brute force method that hashes every possible string to get which inputs produce the same hash (thing that will take a while, since there are about 16^40 possible inputs)
09.01.12 12:54:46 am
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PyKemis
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ya wrong terminology used, it's not really possible to get the "function" used to make start into end - even if you know the starting and ending string...but are there any methods I could try?
09.01.12 02:57:14 pm
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CrAshBoY
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2 things i want to say about it:

The start is a 20 byte hex input. You can see that by the fact that the input characters are limited by [0-9],[a-f].

The end result is a 16 byte hex output..
md5( ) produces these kind of output.

It's really hard to guess what's going on here..
You could try to first test something like aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa, then change one character : aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaab

if it's possible to do it with custom inputs.

Also , where did you get this question from? Might help...
09.01.12 03:08:38 pm
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Alistaire
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If you want to decript it, you should find out what the encripting word is.

Ex:

AAAAAAAA

Encripting word: A512BC2A

BA23CD3B

(If every letter is +1, and the 5 is the maximal number..)

Hard to find such shit tho.

----

You should start with looking how long the encripting word is..
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09.01.12 04:06:11 pm
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Flacko
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user PyKemis has written:
are there any methods I could try?


user Flacko has written:
You can try to crack it using a brute force method that hashes every possible string to get which inputs produce the same hash you're looking for (thing that will take a while, since there are about 16^40 possible inputs)
09.01.12 04:28:17 pm
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ThunderByte
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A Dictionary Attack would be better, because if the string is long it needs years with a brood force attack.
09.01.12 05:16:06 pm
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DC
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from where did you get these strings/hashs and why do you need to know how it works?
note that this forum doesn't allow illegal stuff. including the decryption of stuff which is not meant to be decrypted by you.

I would start by trying the common hash algorithms with the same input and see if you get the same output but those algorithms could also be combined or use a salt - or be random self-created algorithms. so this is a pretty complicated task if you have no chance to see the code that generates this stuff. you need much time, patience and experience to figure out stuff like that.
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09.01.12 05:34:28 pm
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Alistaire
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user DC has written:
you need much time, patience and experience to figure out stuff like that.


You could start with making encriptions yourself instead of trying to decript shit. There are gazillions of encripting programs; try one out and see for yourself how it works. If you don't even know if the generated encriptions are stable, it's a hell of a job.

Another thing; you can start with

AAAAAAAAAAAAAAA

then

BAAAAAAAAAAAAAA

and see what the hex actually represents..
Maybe it's not in alfabetical order and it's like

1 = A
2 = 3
3 = C
4 = 5
5 = B
etc.
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09.01.12 08:51:44 pm
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palomino
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user DC has written:
note that this forum doesn't allow illegal stuff.

Why though? There are a lot of forums with stuff like this and their owners are just fine.
Besides. Decrypting stuff for educational purposes is legal AFAIK. At least, it's nothing bad.
zugcxdxtczgvhioj
09.01.12 10:17:00 pm
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Banaan
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@user Alistaire: That's all too simple. The output is shorter than the input and.

It's none of the standard (and less standard) 128-bits hashes (MD5, Tiger, RIPEMD, HAVAL). Maybe MD2 or MD4? Otherwise you might have to try pretty much every combination of hashes, with lastly a 128 bits...

Could it be that it's just MD5 with a salt?
09.01.12 10:21:59 pm
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oxytamine
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user palomino has written:
Why though? There are a lot of forums with stuff like this and their owners are just fine.
Besides. Decrypting stuff for educational purposes is legal AFAIK. At least, it's nothing bad.

Same question over there. I won't even mention my boards...
11.01.12 05:52:20 am
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Bloodshot
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There are many common algorithms, a myriad of uncommon algorithms, and creating an 'algorithms' takes only a very little amount of imagination and code (for something simple).
If you want to know how it technically works, a string is an array of characters. Characters are just bytes, numbers. Any operations from there depend on the implementation, but you can do whatever you can do with a set of numbers. Which is a lot. And, yeah, although less data does not necessarily indicate data loss (See: compression), it does usually for these scenarios. The difficulty of finding out how the String was transformed grows exponentially

Hashing is different, it is really not meant to go back to the original content, just provide a marker for equating.
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