Write a Python program that tries to find a collision by using SHA-256 as in the

Question

Write a Python program that tries to find a collision by using SHA-256 as in the Python sample code below. Let your program generate ten hash values of random fraudulent messages (i.e., sets of three composite numbers) and report whether a collision was found.

Sample Code

from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import hashes digest = hashes.Hash(hashes.SHA256(), backend=default_backend())
digest.update(b"251")
digest.update(b"157")
digest.update(b"191")
digest.finalize()

Explanation / Answer

from __future__ import absolute_import, division, print_function

import abc

import six

from cryptography import utils
from cryptography.exceptions import (
AlreadyFinalized, UnsupportedAlgorithm, _Reasons
)
from cryptography.hazmat.backends.interfaces import HashBackend

@six.add_metaclass(abc.ABCMeta)
[docs]class HashAlgorithm(object):
@abc.abstractproperty
def name(self):
"""
A string naming this algorithm (e.g. "sha256", "md5").
"""

@abc.abstractproperty
def digest_size(self):
"""
The size of the resulting digest in bytes.
"""

@abc.abstractproperty
def block_size(self):
"""
The internal block size of the hash algorithm in bytes.
"""

@six.add_metaclass(abc.ABCMeta)
[docs]class HashContext(object):
@abc.abstractproperty
def algorithm(self):
"""
A HashAlgorithm that will be used by this context.
"""

@abc.abstractmethod
[docs] def update(self, data):
"""
Processes the provided bytes through the hash.
"""

@abc.abstractmethod
[docs] def finalize(self):
"""
Finalizes the hash context and returns the hash digest as bytes.
"""

@abc.abstractmethod
[docs] def copy(self):
"""
Return a HashContext that is a copy of the current context.
"""

@utils.register_interface(HashContext)
[docs]class Hash(object):
def __init__(self, algorithm, backend, ctx=None):
if not isinstance(backend, HashBackend):
raise UnsupportedAlgorithm(
"Backend object does not implement HashBackend.",
_Reasons.BACKEND_MISSING_INTERFACE
)

if not isinstance(algorithm, HashAlgorithm):
raise TypeError("Expected instance of hashes.HashAlgorithm.")
self._algorithm = algorithm

self._backend = backend

if ctx is None:
self._ctx = self._backend.create_hash_ctx(self.algorithm)
else:
self._ctx = ctx

algorithm = utils.read_only_property("_algorithm")

[docs] def update(self, data):
if self._ctx is None:
raise AlreadyFinalized("Context was already finalized.")
if not isinstance(data, bytes):
raise TypeError("data must be bytes.")
self._ctx.update(data)

[docs] def copy(self):
if self._ctx is None:
raise AlreadyFinalized("Context was already finalized.")
return Hash(
self.algorithm, backend=self._backend, ctx=self._ctx.copy()
)

[docs] def finalize(self):
if self._ctx is None:
raise AlreadyFinalized("Context was already finalized.")
digest = self._ctx.finalize()
self._ctx = None
return digest

@utils.register_interface(HashAlgorithm)
[docs]class SHA1(object):
name = "sha1"
digest_size = 20
block_size = 64

@utils.register_interface(HashAlgorithm)
[docs]class SHA224(object):
name = "sha224"
digest_size = 28
block_size = 64

@utils.register_interface(HashAlgorithm)
[docs]class SHA256(object):
name = "sha256"
digest_size = 32
block_size = 64

@utils.register_interface(HashAlgorithm)
[docs]class SHA384(object):
name = "sha384"
digest_size = 48
block_size = 128

@utils.register_interface(HashAlgorithm)
[docs]class SHA512(object):
name = "sha512"
digest_size = 64
block_size = 128

@utils.register_interface(HashAlgorithm)
[docs]class RIPEMD160(object):
name = "ripemd160"
digest_size = 20
block_size = 64

@utils.register_interface(HashAlgorithm)
[docs]class Whirlpool(object):
name = "whirlpool"
digest_size = 64
block_size = 64

@utils.register_interface(HashAlgorithm)
[docs]class MD5(object):
name = "md5"
digest_size = 16
block_size = 64

@utils.register_interface(HashAlgorithm)
[docs]class BLAKE2b(object):
name = "blake2b"
_max_digest_size = 64
_min_digest_size = 1
block_size = 128

def __init__(self, digest_size):
if (
digest_size > self._max_digest_size or
digest_size < self._min_digest_size
):
raise ValueError("Digest size must be {0}-{1}".format(
self._min_digest_size, self._max_digest_size)
)

self._digest_size = digest_size

digest_size = utils.read_only_property("_digest_size")

@utils.register_interface(HashAlgorithm)
[docs]class BLAKE2s(object):
name = "blake2s"
block_size = 64
_max_digest_size = 32
_min_digest_size = 1

def __init__(self, digest_size):
if (
digest_size > self._max_digest_size or
digest_size < self._min_digest_size
):
raise ValueError("Digest size must be {0}-{1}".format(
self._min_digest_size, self._max_digest_size)
)

self._digest_size = digest_size

digest_size = utils.read_only_property("_digest_size")

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