Is there a SHA1 match for g000

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Hi All,

I have been searching for a SHA1 hash where the first 4 bytes equal g000.

I have been searching for 48 hours and tried every 7 digit combination

I am just wondering if there is a match for this set of chars, surely there must be at some point?

Thanks George

Posted 6-Mar-11 23:56pm

grwithey

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OriginalGriff · Accepted Answer · 2011-03-07T00:07:00

Solution 1

Yes, there will be, lots, but given that the shortest SHA is 160 bits, the odds on you finding one by randomly putting just 7 digits into the hashing algorithm are too small to list. How big is 2^160?

That is kind of the idea of SHA: That you can't predict the value from the start data, and you can't work out the data from the value... :laugh:

Posted 7-Mar-11 0:07am

OriginalGriff

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grwithey 7-Mar-11 10:41am

Ha yes true, i have already tried every possible combination from 0 up to "zzzzzzz" which has taken a few days to get there, which is several billion combinations if i understand correctly.

Yes 2 ^ 160 would be pretty huge. I will have to continue to let it run and see what happens as i found a match for the range from 0000 to f000

OriginalGriff 7-Mar-11 10:48am

1 match in only several days? You were lucky! :laugh:

OriginalGriff 7-Mar-11 10:53am

Oh, and I don't want to worry you unduly, but which version of SHA are you checking? Because I normally use SHA512 (which predicatably has 512 bits) and they are due to release the SHA1024 specification early next year...

grwithey 8-Mar-11 2:35am

I think it is 160 bit value that is produced

Sergey Alexandrovich Kryukov 7-Mar-11 12:23pm

I wonder, are your experimenting blind-folded or perhaps you estimated the probability or math.expectation of your results. And why that heroic effort? :-)
--SA

Sergey Alexandrovich Kryukov 7-Mar-11 12:24pm

Griff, you're right, of course, my 5.
--SA

grwithey 8-Mar-11 2:32am

I was assigned the task of creating a table containing a possible match for every first 4 bytes of the SHA1 hash so every value from 0000 to zzzz although i only need to produce the first 64 entries. I will probably have to skip this value if it is not found today as this is due for thursday.

OriginalGriff 8-Mar-11 3:18am

I really hate to disappoint you further, but "0000" to "zzzz" is nowhere near the full range of values: If you are actually comparing against the first four bytes of the raw SHA (and there are a total of 20 bytes in 160 bits), then each byte can have 256 different values, not limited to just 0-9, A-Z and a-z.
So there are 256*256*256*256 different possible first four bytes...

grwithey 8-Mar-11 5:09am

The solution is that it cannot be done in the context i am using it:

As each char is not a byte it is 4 bits. so the max value for each char is f (1111) meaning it wont get further than f000. The next value would be 0100 and ffff as the maximum for the first 4 chars of the hashed string. For this example i am lucky in that the chars can only be 0-9 and a-f so should be feasible. Thanks for the pointers. i now have a better understanding of what is going on. =)

OriginalGriff 8-Mar-11 5:14am

Those are called nibbles, not bytes or chars! http://en.wikipedia.org/wiki/Nibble
The sequence 0-9A-F is called Hex (or hexadecimal) and is often represented by prefixing it with "0x". So 0xff or 0xFF would be 255 in decimal.