Sample proof of work in Ruby, what am I doing wrong?

A few things that need to be fixed here:

Endianness - The data given to you in JSON is almost completely in big endian but bitcoin uses little endian to serialize block headers before hashing.
You need to double hash the result with SHA256, meaning apply it once on the header and then apply the algorithm again on the result of the first hash.
Conversion to binary before hashing. You can't just hash the ascii characters, as those are just an encoding for the underlying binary, which is what is meant to be hashed.

I'm not very familiar with Ruby, but I made a short python script that you can use as a reference.

import hashlib
import binascii

def rev(string):
    revsed = ""
    for i in range(int(len(string)/2)):
        revsed = string[2*i : 2*i+2] + revsed
    return revsed

def DoubleHash(string):
    bin = binascii.unhexlify(string)
    hash = hashlib.sha256(hashlib.sha256(bin).digest()).digest()
    raw = str(binascii.hexlify(hash))[2:-1]
    return rev(raw)


# Straight from JSON

version = "02000000"
prev    = "000000000000000007c464352935f12c3695f7de4eee8390f444233682abf8aa"
merkle  = "14b2c974a4f9ab92a68f03a491965063d1f8a2e8b2268fdb4cbce92262bb09c0"
time    = "55078076" # hex(1426554998)
bits    = "18172ec0"
nonce   = "c3c1e61f" # hex(3284264479)

header = version + rev(prev) + rev(merkle) + rev(time) + rev(bits) + rev(nonce)

print(header)
print(DoubleHash(header))

The results:

02000000aaf8ab82362344f49083ee4edef795362cf135293564c4070000000000000000c009bb6222e9bc4cdb8f26b2e8a2f8d163509691a4038fa692abf9a474c9b21476800755c02e17181fe6c1c3
00000000000000001354e21fea9c1ec9ac337c8a6c0bda736ec1096663383429

morsecoder

Posted 2015-03-17T11:34:36.747

Reputation: 12 624

Thanks for this, it looks like either your prev didn't reverse properly or I'm misunderstanding what you're doing: last 5 of prev: bf8aa your rev of prev in header: aaf8a – user1130176 – 2015-03-17T15:31:02.687

You have to list the bytes in reverse order. Each byte is two hex characters. The previous block is 0000...f8aa. You just have to list the bytes in the reverse order as aaf8...0000. i.e. 1234 byte-reversed is 3412. – morsecoder – 2015-03-17T17:36:19.640

ok, i see, so it's both byte reversed and Endian reversed? – user1130176 – 2015-03-18T00:32:48.410

Endian reversed just means you need to list the bytes in the opposite order. Remember to mark answers as correct if they answered your question. – morsecoder – 2015-03-18T12:32:12.340

sorry for not being clear, i understand what endian reversed meant, i was attempting get confirmation that two distinct processing steps are required 1) reverse endian (swap the hex bytes) and 2) reverse the string – user1130176 – 2015-03-19T03:12:18.303

Reversing the endianness is the same thing as reversing the bytes in the string. – morsecoder – 2015-03-30T15:24:24.260

Sample proof of work in Ruby, what am I doing wrong?

Answers