# Merkle Tree hashing

I'm trying to implement my own Markle Tree, currently I'm working on getting the hashing done correctly.

I've used some hashes from http://blockexplorer.com/rawblock/000000000000a85d42610b292d2baebe54ff0c854847fe3d2ca37ac7d6e46b99

Example inputs (first two hashes from blockexplorer):

Ina: 3a459eab5f0cf8394a21e04d2ed3b2beeaa59795912e20b9c680e9db74dfb18c

Inb: be38f46f0eccba72416aed715851fd07b881ffb7928b7622847314588e06a6b7

Concatenated string (H1+H2): 3a459eab5f0cf8394a21e04d2ed3b2beeaa59795912e20b9c680e9db74dfb18cbe38f46f0eccba72416aed715851fd07b881ffb7928b7622847314588e06a6b7

Hash of concatenated string: Ans v1: b5916d6bc34bd4157aa73c3d799a6cfcef85e0659465734362d0cebb8901e93d

Final hash of concatenated string: Ans v2: 215f8397a3090a0bc8f4a2e98609a10d55fc7b939fa1ecf9803df20b1ee089a2

Result I got: 215f8397a3090a0bc8f4a2e98609a10d55fc7b939fa1ecf9803df20b1ee089a2

Checked my calculations "manually" using http://www.fileformat.info/tool/hash.htm?hex=b5916d6bc34bd4157aa73c3d799a6cfcef85e0659465734362d0cebb8901e93d and got the same results.

Am I doing someting wrong following this example: https://en.bitcoin.it/wiki/Protocol_specification#Merkle_Trees . I take my input hashes, concatenate them together, and double SHA256 that string. I also tried treating the input strings as a and b, that is, first double SHA256 them, and only then join them together, but the result was also wrong. Does anyone have a step-by-step example of proper hashing of the Merkle Tree?

As it was pointed out to me by ArtForz in this post: https://bitcointalk.org/index.php?topic=44707.msg534605#msg534605 the hashes are stored in little endian notation, so I first need to reverse them before double-hashing them, and then reverse the output back to get the proper result.

Added two cents. In excel VBA

Private Function Sha256String(ByVal a)
b = a
While Len(b) > 0
c = c + Right(b, 2)
b = Left(b, Len(b) - 2)
Wend
Sha256String = c
End Function


Run that on a and b hashes, concatenate them, double hash as hex bytes: http://www.fileformat.info/tool Then run the function on the sha-256 answer.