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Decrypting SHA-256 hashes

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Silvu is not online. Silvu
Joined: 05 Mar 2011
Total Posts: 19434
07 Jul 2012 03:49 PM
ok

I have a question for those of you who know about this kind of stuff.

The SHA-256 algorithm is supposedly one way, but there has to be some way to decrypt the hashes, right?

I'm not asking for a way to decrypt it, I'm just wondering if it's possible, because I don't think it's possible for it to the one way, but I don't know much about this kind of stuff.
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NecroBumpist is not online. NecroBumpist
Joined: 12 Sep 2010
Total Posts: 4198
07 Jul 2012 03:50 PM
No, you can't decrypt a SHA256 hash.

However, you (theoretically) can find an identical input that creates the same hash. This input might be the same as one used in the original hash.

Note: this has never been successfully done before and is technologically infeasible.

tl;dr AVI.nope
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eyeontheprizeREBOOT is not online. eyeontheprizeREBOOT
Joined: 30 Jan 2011
Total Posts: 1555
07 Jul 2012 03:52 PM
your best bet is rainbow tables
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lombardo2 is not online. lombardo2
Joined: 30 Nov 2008
Total Posts: 1604
07 Jul 2012 03:58 PM
There aren't successful (well at least practical) attacks on SHA-1 talking about SHA-256...
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TheCapacitor is not online. TheCapacitor
Joined: 19 Jan 2011
Total Posts: 7045
07 Jul 2012 06:36 PM
Even decrypting SHA1 would take thousands or millions of years, don't even get me started on SHA256.
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GigsD4X is online. GigsD4X
Joined: 06 Jun 2008
Total Posts: 3794
07 Jul 2012 08:10 PM
What people do in these cases is hash a bunch of random strings that are most likely to be what is hashed so that they could get what creates that hash and therefore have the "decrypted" content. And then there are those websites that have computers always generating random hashes so that they could have them all.
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Silvu is not online. Silvu
Joined: 05 Mar 2011
Total Posts: 19434
07 Jul 2012 08:39 PM
@Necro

Let's say you had credit card numbers encrypted in SHA-256 (no I don't have any mods), could you create a program that generates random hashes that would meet what you're looking for (the number of digits in a CC and only numbers) and then have it check the numbers against the Luhn algorithm?
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JulienDethurens is not online. JulienDethurens
Joined: 11 Jun 2009
Total Posts: 11046
07 Jul 2012 08:42 PM
It's impossible to decrypt hashes.

You can brute force them, but you just can't decrypt them.
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Silvu is not online. Silvu
Joined: 05 Mar 2011
Total Posts: 19434
07 Jul 2012 09:02 PM
@Julien

what makes it impossible?
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DrAgonmoray is not online. DrAgonmoray
Joined: 29 Jul 2008
Total Posts: 17428
07 Jul 2012 09:14 PM
"what makes it impossible?"

it's 1-way.
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Silvu is not online. Silvu
Joined: 05 Mar 2011
Total Posts: 19434
07 Jul 2012 09:16 PM
@Dr

there has to be some way to decrypt it

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DrAgonmoray is not online. DrAgonmoray
Joined: 29 Jul 2008
Total Posts: 17428
07 Jul 2012 09:17 PM
@Silvu
No, there doesn't. The data is gone. It's not encryption, it's hashing.
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Anaminus is not online. Anaminus
Top 100 Poster
Joined: 29 Nov 2006
Total Posts: 5945
07 Jul 2012 09:18 PM
@Silvu, Take any number and add its digits together. Then take the resulting number and do it again. Repeat until you have a one-digit number. This one-digit number is a hash of the number you started with.

Now ask whether it's possible to get the original number from this one-digit number.
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JulienDethurens is not online. JulienDethurens
Joined: 11 Jun 2009
Total Posts: 11046
07 Jul 2012 10:13 PM
The reason hashing can't be reversed is simply because data is lost. Many different inputs can give the same hash.
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Combrad is not online. Combrad
Joined: 18 Jul 2009
Total Posts: 11025
08 Jul 2012 03:40 AM
749854
7+4+9+8+5+4=27
2+7 = 9

9 to 749854
Try to figure it out :)
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Avolition is not online. Avolition
Joined: 20 Apr 2011
Total Posts: 708
08 Jul 2012 04:27 AM
I don't think it's impossible to crack a hashing algorithm, just very very very hard. As Anaminus said, it wouldn't be IMPOSSIBLE to get a list of numbers that would fit the hash, just very very very hard.

There's an onion site where you can buy "credits" and exchange them with other hackers in return for them to try and bruteforce your hash. They usually use their botnet's slave's GPUs to do this. That's what I've always used when I've needed to crack a hash, and it's a quite neat system.
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Silvu is not online. Silvu
Joined: 05 Mar 2011
Total Posts: 19434
08 Jul 2012 05:13 AM
Ok

Thanks guys

I get it now

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popinman322 is not online. popinman322
Joined: 04 Mar 2009
Total Posts: 5184
08 Jul 2012 06:52 AM
Pfft, huge chain of thousand core servers with 1TB ram on each. They will get the job done. x3
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RA2lover is not online. RA2lover
Joined: 09 Nov 2008
Total Posts: 1254
08 Jul 2012 07:48 AM
no. just hit the guy with a $5 wrench until he tells the pass, instead of building a million-dollar cluster to crack it.
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Avolition is not online. Avolition
Joined: 20 Apr 2011
Total Posts: 708
08 Jul 2012 07:59 AM
If I used my personal computer as well as my Bitcoin rigs to bruteforce a SHA-256 hash, I could easily do millions per second. It wouldn't cost anywhere near a million dollars.
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popinman322 is not online. popinman322
Joined: 04 Mar 2009
Total Posts: 5184
08 Jul 2012 12:25 PM
@Avo

I'm talking about billions per second. :/
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Roundel is not online. Roundel
Joined: 20 Mar 2010
Total Posts: 469
08 Jul 2012 12:26 PM
decrypting any hash is the same as decrypting any other hash

you just have to get a dictionary of known words correlating with known hashes

avolition is right cause all you'd need to do is try a bunch of combinations of letters and numbers and you'd be able to get most pwrds within a day
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Merely is not online. Merely
Joined: 07 Dec 2010
Total Posts: 17266
08 Jul 2012 12:34 PM
with current computing power it would take millions of years

in a few years pretty much all methods that rely on time/memory as the safeguard will be easy to crack
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pwnedu46 is not online. pwnedu46
Joined: 23 May 2009
Total Posts: 7534
08 Jul 2012 01:36 PM
"Pfft, huge chain of thousand core servers with 1TB ram on each. They will get the job done. x3"


Google compute engine? It gives you access to 771,886 cores.
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