miner.py

#!/usr/bin/env python
# coding=utf-8

import hashlib
import os
import subprocess
import sys
import time

if len(sys.argv) < 3:
	print """Usage: ./miner.py <clone_url> <public_username>

Arguments:

<clone_url> is the string you’d pass to `git clone` (i.e.
  something of the form `username@hostname:path`)

<public_username> is the public username provided to you in
  the CTF web interface."""
	sys.exit(1)

clone_spec = sys.argv[1]
public_username = sys.argv[2]

def solve():

	# Start with a number with lots of digits so that the length of the commit
	# object can be predicted and is unlikely to ever increase (because we’ll
	# _probably_ have found a coin by then).
	nonce = 1000000000000000 # length=16

	#difficulty = '000001'
	with open('difficulty.txt', 'r') as f:
		difficulty = f.read().strip()

	tree = subprocess.check_output(['git', 'write-tree']).strip()
	with open('.git/refs/heads/master', 'r') as f:
		parent = f.read().strip()
	timestamp = int(time.time())
	print 'Mining…'
	base_hasher = hashlib.sha1()
	# The length of all such commit messages is 233, as long as the nonce is 16
	# digits long.
	header = "commit 233\x00"
	base_content = """tree %s
parent %s
author CTF user <me@example.com> 1333333337 +0000
committer CTF user <me@example.com> 1333333337 +0000

Give me a Gitcoin

""" % (tree, parent)
	base_hasher.update(header + base_content)

	while True:
		nonce = nonce + 1
		hasher = base_hasher.copy()
		noncestr = str(nonce)
		hasher.update(noncestr)
		content = base_content + noncestr
		sha1 = hasher.hexdigest()
		#print '>>%s<<' % sha1
		if sha1 < difficulty:
			with open('commit.txt', 'w') as f:
				f.write(content)
			print 'Mined a Gitcoin! The SHA-1 is:'
			os.system('git hash-object -t commit commit.txt -w')
			os.system('git reset --hard %s' % sha1)
			break

def prepare_index():
	os.system('perl -i -pe \'s/(%s: )(\d+)/$1 . ($2+1)/e\' LEDGER.txt' % public_username)
	os.system('grep -q "%s" LEDGER.txt || echo "%s: 1" >> LEDGER.txt' % (public_username, public_username))
	os.system('git add LEDGER.txt')

def reset():
	os.system('git fetch origin master >/dev/null 2>/dev/null')
	os.system('git reset --hard origin/master >/dev/null')

while True:
	prepare_index()
	solve()
	if os.system('git push origin master') == 0:
		print 'Success :)'
		break
	else:
		print 'Starting over :('
		reset()