```# This code is quite straightforward, one exception being the inclusion of a random string from the receiving party, Bob, in this case,
# in the hash. This gives Bob assurance that Alice didn't precompute two hashes, "heads random string" and "tails another random string",
# with the same hash value. This is really paranoia in the extreme as modern hashes are collision-free to a very high degree of probability.

# The following Python program is an implementation of coin-flipping using a cryptographic hash:

#!/usr/local/bin/python3

from hashlib import sha256
from random import random, randrange

MAX_S, CHARS, FIRST_ASCII = 55, 26, 97

alice_s = ''
for i in range(MAX_S):
alice_s += chr(randrange(CHARS) + FIRST_ASCII)
print("\nAlice's string is", alice_s)
bob_s = ''
for i in range(MAX_S):
bob_s += chr(randrange(CHARS) + FIRST_ASCII)
print("\nBob's   string is", bob_s)
if random() > 0.5:
else:
outcome = 'tails'
s_to_hash = outcome + ' ' + alice_s + ' ' + bob_s
hash_out = sha256(s_to_hash.encode('utf-8')).hexdigest()
print("""\

Alice chooses {0:s} and sends Bob the hash of {0:s} + ' ' + her string + ' ' +
Bob's string = {1:s}
""".format(outcome, hash_out))

if random() > 0.5:
else:
bob_guess = 'tails'

print('Bob chooses', bob_guess)
if bob_guess == outcome:
print('\nBob wins')
else:
print("""\

Alice wins

Alice sends Bob her string so that he can do the hash and confirm her choice.
""")

# End of Code

# Test Ouput 1 (Alice wins):

# Alice's string is bmqujztahsqwmwjeckcfrhqwnfcwvjrgrexjeobbbqmbenffdfqbxrn

# Bob's   string is zrcvoxpcfslphvjqacyptewditwjqixkejdlkvuejrisrtnujattshy

# Alice chooses tails and sends Bob the hash of tails + her string + ' ' + Bob's string = 28b287547f6f720dd239b0c322168f2a489481cead48fd40363be9edf4383fda

# Alice wins

# Alice sends Bob her string so that he can do the hash and confirm her choice.

# Test Output 2 (Bob wins):

# Alice's string is lpemcvcatlmbytzhkvmxukclwbzkelxpsusimakwuoxjdlhntneusux

# Bob's   string is zftwyecehvncmsnqclqutugpofepvtjlfiuovyjcmzvayihbdkaabae

# Alice chooses tails and sends Bob the hash of tails + her string + ' ' + Bob's string = 6337c3688ffc8fc77eebae69d4c420bb0cae633767d9faed7eac34a42cea1d9b

# Bob chooses tails

# Bob wins
```