Python os.random() Examples

def test_urandom_failure(self):
        # Check urandom() failing when it is not able to open /dev/random.
        # We spawn a new process to make the test more robust (if getrlimit()
        # failed to restore the file descriptor limit after this, the whole
        # test suite would crash; this actually happened on the OS X Tiger
        # buildbot).
        code = """if 1:
            import errno
            import os
            import resource

            soft_limit, hard_limit = resource.getrlimit(resource.RLIMIT_NOFILE)
            resource.setrlimit(resource.RLIMIT_NOFILE, (1, hard_limit))
            try:
                os.urandom(16)
            except OSError as e:
                assert e.errno == errno.EMFILE, e.errno
            else:
                raise AssertionError("OSError not raised")
            """
        assert_python_ok('-c', code) 

def test_urandom_failure(self):
        # Check urandom() failing when it is not able to open /dev/random.
        # We spawn a new process to make the test more robust (if getrlimit()
        # failed to restore the file descriptor limit after this, the whole
        # test suite would crash; this actually happened on the OS X Tiger
        # buildbot).
        code = """if 1:
            import errno
            import os
            import resource

            soft_limit, hard_limit = resource.getrlimit(resource.RLIMIT_NOFILE)
            resource.setrlimit(resource.RLIMIT_NOFILE, (1, hard_limit))
            try:
                os.urandom(16)
            except OSError as e:
                assert e.errno == errno.EMFILE, e.errno
            else:
                raise AssertionError("OSError not raised")
            """
        assert_python_ok('-c', code) 

def web2py_uuid(ctokens=UNPACKED_CTOKENS):
    """
    This function follows from the following discussion:
    http://groups.google.com/group/web2py-developers/browse_thread/thread/7fd5789a7da3f09

    It works like uuid.uuid4 except that tries to use os.urandom() if possible
    and it XORs the output with the tokens uniquely associated with this machine.
    """
    rand_longs = (random.getrandbits(64), random.getrandbits(64))
    if HAVE_URANDOM:
        urand_longs = _struct_2_long_long.unpack(fast_urandom16())
        byte_s = _struct_2_long_long.pack(rand_longs[0] ^ urand_longs[0] ^ ctokens[0],
                                          rand_longs[1] ^ urand_longs[1] ^ ctokens[1])
    else:
        byte_s = _struct_2_long_long.pack(rand_longs[0] ^ ctokens[0],
                                          rand_longs[1] ^ ctokens[1])
    return str(uuid.UUID(bytes=byte_s, version=4)) 

def fromEntropy(entropy, public=False):
        "Create a BIP32Key using supplied entropy >= MIN_ENTROPY_LEN"
        if entropy == None:
            entropy = os.urandom(MIN_ENTROPY_LEN/8) # Python doesn't have os.random()
        if not len(entropy) >= MIN_ENTROPY_LEN/8:
            raise ValueError("Initial entropy %i must be at least %i bits" %
                                (len(entropy), MIN_ENTROPY_LEN))
        I = hmac.new("Bitcoin seed", entropy, hashlib.sha512).digest()
        Il, Ir = I[:32], I[32:]
        # FIXME test Il for 0 or less than SECP256k1 prime field order
        key = BIP32Key(secret=Il, chain=Ir, depth=0, index=0, fpr='\0\0\0\0', public=False)
        if public:
            key.SetPublic()
        return key 

def AES_new(key, IV=None):
    """ Returns an AES cipher object and random IV if None specified """
    if IV is None:
        IV = fast_urandom16()

    return AES.new(key, AES.MODE_CBC, IV), IV 

def initialize_urandom():
    """
    This function and the web2py_uuid follow from the following discussion:
    http://groups.google.com/group/web2py-developers/browse_thread/thread/7fd5789a7da3f09

    At startup web2py compute a unique ID that identifies the machine by adding
    uuid.getnode() + int(time.time() * 1e3)

    This is a 48-bit number. It converts the number into 16 8-bit tokens.
    It uses this value to initialize the entropy source ('/dev/urandom') and to seed random.

    If os.random() is not supported, it falls back to using random and issues a warning.
    """
    node_id = uuid.getnode()
    microseconds = int(time.time() * 1e6)
    ctokens = [((node_id + microseconds) >> ((i % 6) * 8)) %
               256 for i in range(16)]
    random.seed(node_id + microseconds)
    try:
        os.urandom(1)
        have_urandom = True
        try:
            # try to add process-specific entropy
            frandom = open('/dev/urandom', 'wb')
            try:
                if python_version == 2:
                    frandom.write(''.join(chr(t) for t in ctokens)) # python 2
                else:
                    frandom.write(bytes([]).join(bytes([t]) for t in ctokens)) # python 3
            finally:
                frandom.close()
        except IOError:
            # works anyway
            pass
    except NotImplementedError:
        have_urandom = False
        logger.warning(
            """Cryptographically secure session management is not possible on your system because
your system does not provide a cryptographically secure entropy source.
This is not specific to web2py; consider deploying on a different operating system.""")
    if python_version == 2:
        packed = ''.join(chr(x) for x in ctokens) # python 2
    else:
        packed = bytes([]).join(bytes([x]) for x in ctokens) # python 3
    unpacked_ctokens = _struct_2_long_long.unpack(packed)
    return unpacked_ctokens, have_urandom