Mouse Trap Bubble Light Entropy Engine

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Most natural sources of random numbers, including radioactive decay, have a non-random bias, which may make the numbers unsuitable for many applications. Common sources of natural random numbers include Geiger counters recording the decay of radioactive elements; electronic amplifiers set to amplify thermal noise; cameras recording lava lamps; and the motion of a computer mouse. None of these produce good random numbers without a little bit of extra work. Sources of biased natural randomness can be fed into a randomness extractor which removes the bias to generate a stream of random numbers better suited to a given application. A cryptographically secure pseudo-random number generator (CSPRNG) is often used with a randomness extractor. John von Neumann created one of the earliest randomness extractors.

Here I present a very simple and cheap source of natural random numbers. This source requires almost no tools or expertise besides a screw-driver. What I have done is remove the sensor board from a USB mouse and attach it to the side of an Xmas tree bubble light. Wikipedia tells you all about Bubble Lights. The bubbles from the light trigger the motion sensor of the mouse, which is fed into a custom Python program I wrote. In principle this is similar to Lava Lamp random number generators; however, the construction is significantly simpler.

Bubble lights consist of a sealed glass vial filled with Methylene chloride. The bottom of the glass vial is placed against a small incandescent light bulb. The heat from the bulb causes the Methylene chloride to boil and bubble. The bubbles float to the top of the vial where the vapor condenses back into liquid. The high vapor pressure of Methylene chloride allows it to maintain a continuous process of boiling and condensation in a very small tube. The heat of a human hand is enough to drive continuous boiling. Other solvents with high vapor pressures would work, but Methylene chloride has the added advantage that it is relatively non-toxic and it is one of the few volatile solvents which is non-flammable, so it is safe to attach the bubble-lights to a tree, as opposed to hanging tubes of boiling gasoline or acetone on your Xmas tree.

tests

Tests run with a sample data file size of 12054570 bytes.

cat mtblee.bin | ent
Entropy = 7.999902 bits per byte.

Optimum compression would reduce the size
of this 12054570 byte file by 0 percent.

Chi square distribution for 12054570 samples is 1637.35, and randomly
would exceed this value 0.01 percent of the times.

Arithmetic mean value of data bytes is 127.5186 (127.5 = random).
Monte Carlo value for Pi is 3.144743280 (error 0.10 percent).
Serial correlation coefficient is 0.000179 (totally uncorrelated = 0.0).
cat mtblee.bin | rngtest
rngtest 2-unofficial-mt.12
Copyright (c) 2004 by Henrique de Moraes Holschuh
This is free software; see the source for copying conditions.  There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

rngtest: starting FIPS tests...
rngtest: entropy source exhausted!
rngtest: bits received from input: 96436560
rngtest: FIPS 140-2 successes: 4771
rngtest: FIPS 140-2 failures: 50
rngtest: FIPS 140-2(2001-10-10) Monobit: 1
rngtest: FIPS 140-2(2001-10-10) Poker: 7
rngtest: FIPS 140-2(2001-10-10) Runs: 47
rngtest: FIPS 140-2(2001-10-10) Long run: 1
rngtest: FIPS 140-2(2001-10-10) Continuous run: 0
rngtest: input channel speed: (min=416.889; avg=116061.408; max=1027960.526)Kibits/s
rngtest: FIPS tests speed: (min=323.520; avg=15329.371; max=18962.379)Kibits/s
rngtest: Program run time: 6990261 microseconds

code

There are two files. The main script is entropy-source. It imports a custom module called bandwidth.py. Both code files are listed below, but check https://github.com/noahspurrier/mtee for the latest, canonical version of this software.

entropy-source

#!/usr/bin/env python
# vim:set ft=python fileencoding=utf-8 sr et ts=4 sw=4 : See help 'modeline'

"""
SYNOPSIS

    entropy-source [-h,--help] [-v,--verbose] [--version] INPUT_DEVICE

DESCRIPTION

    This application produces entropy from the coordinates
    of mouse events. This should be a good source of truly
    random numbers. The raw entropy from the mouse may be
    filtered in various ways to eliminate bias. By default
    Von Neumann's debiasing method is used. This script is
    intended for education and experimentation. It is not
    intended to be a fast source of entropy. In fact, it is
    rather slow.

    This script must be run as root.

    The INPUT_DEVICE must be a file in the directory
    '/etc/input/', such as '/etc/input/event4'.
    Do not use the '/etc/input/mouse*' devices.

    Use the '--list' and '--detect'' options to help
    figure out which input device to use.

    == Disable the entropy mouse under X11 ==

    You may wish to disable the mouse being used for entropy
    under X11 to prevent the mouse pointer from wiggling
    around the screen. Disabling the mouse under X11 will
    not disable it under /dev/input, so it will still be a
    source of entropy.

    First identify which mouse you wish to disable.
        xinput --list
    Next find the ID of the 'Device Enabled' property of the mouse.
        xinput --list-props 16
    Finally, set the 'Device Enabled' property to zero.
        xinput --set-prop 16 145 0

    == Bugs ==

    Some of the constants used when working with Linux input
    event are not generated in a portable way under Python.
    This seems to mostly be a problem on big-endian
    platforms like the PowerPC. To work around this, you can
    hard-code the constants used in this script. To find the
    constant values compile and run the following C program
    which will print out the value of the constants.
    Save this snippet as "ev-print.c":

    /* Build with
     *     make ev-print
     * or
     *     gcc ev-print.c -o ev-print
     */
    #include <stdio.h>
    #include <linux/input.h>
    int main (int argc, char *argv[]) {
        printf("EVIOCGNAME(255): %u\n", EVIOCGNAME(255));
        printf("EVIOCGBIT(0, 255): %u\n", EVIOCGBIT(0, 255));
        printf("EVIOCGID: %u\n", EVIOCGID);
        printf("EVIOCGVERSION: %u\n", EVIOCGVERSION);
    }

EXAMPLES

    Most of the operations require root permissions. In
    these examples the 'sudo' command is used when
    necessary.

    First you need to know the name of the input device you
    want to use as a source of entropy. To find the name you
    use the '--detect' option to display the name of the
    next input device that is plugged into the system. Start
    this command before you plug in the mouse, then as soon
    as you plug it in its name will be printed. Note that
    some mice create more than one name, so you will have to
    try each name to see which one works.

        $ ./entropy-source --detect
        /dev/input/event4

    The default operation with no options is to output 8-bit
    bytes of entropy from the given input device. In this
    example the bytes are piped into 'od' to display them in
    hex. Sudo is used to run the command with root
    permissions.

        $ sudo ./entropy-source /dev/input/event4 | od -x
        0000000 0bbd b360 4887 5b06 213e 53e3 becc bd08
        0000020 4552 056f 6698 be45 2e67 f78a 43b1 44ee

    The following example will show the raw bits, with bias,
    as they are pulled from the input device. This is useful
    to see how fast the device is generating bits.

    $ sudo ./entropy-source --raw /dev/input/event4
    011000001110010000010001011001100110111011010111101111111
    100000100110011001000101110001000100100101101011011000110

    In this example the entropy-source script is run in
    the background and its output is sent to a file. Then
    the GNU Plotutils command, graph, is used to visualize
    the random data.

    $ sudo ./entropy-source /dev/input/event4 >> entropy-source.bin &
    [1] 4711
    $ ./histogram.py entropy-source.bin |
      egrep -v "^\s*#" | awk '{print $2}' |
      graph --auto-abscissa 1.0 -r 0.1 -u 0.1 -h 0.8 -w 0.8
      --bitmap-size 1024x768 -F HersheySans -T png | display -

EXIT STATUS

    This exits with status 0 on success and 1 otherwise.
    This exits with a status greater than 1 if there was an
    unexpected run-time error.

AUTHOR

    Noah Spurrier <noah@noah.org>

LICENSE

    This license is approved by the OSI and FSF as GPL-compatible.
        http://opensource.org/licenses/isc-license.txt

    Copyright (c) 2013, Noah Spurrier <noah@noah.org>
    PERMISSION TO USE, COPY, MODIFY, AND/OR DISTRIBUTE THIS SOFTWARE FOR ANY
    PURPOSE WITH OR WITHOUT FEE IS HEREBY GRANTED, PROVIDED THAT THE ABOVE
    COPYRIGHT NOTICE AND THIS PERMISSION NOTICE APPEAR IN ALL COPIES.
    THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
    WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
    MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
    ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
    ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

VERSION

    Version 1
"""

import sys
import os
import struct
import time
import fcntl
import time
import traceback
import optparse
import bandwidth

# ioctl constants from from pycopia.OS.Linux.IOCTL by
# Keith Dart <keith@kdart.com> and from
# /usr/include/asm-generic/ioctl.h via /usr/include/ioctl.h
#
# ioctl command encoding: 32 bits total, command in lower 16 bits,
# size of the parameter structure in the lower 14 bits of the
# upper 16 bits.
# Encoding the size of the parameter structure in the ioctl request
# is useful for catching programs compiled with old versions
# and to avoid overwriting user space outside the user buffer area.
# The highest 2 bits are reserved for indicating the ``access mode''.
# NOTE: This limits the max parameter size to 16kB -1 !
#
# The following is for compatibility across the various Linux
# platforms.  The i386 ioctl numbering scheme doesn't really enforce
# a type field.  De facto, however, the top 8 bits of the lower 16
# bits are indeed used as a type field, so we might just as well make
# this explicit here.  Please be sure to use the decoding macros
# below from now on.
INT = "i"
INT2 = "ii"
INT5 = "iiiii"
SHORT = "h"
USHORT = "H"
SHORT4 = "hhhh"

sizeof = struct.calcsize

_IOC_NRBITS = 8
_IOC_TYPEBITS = 8
_IOC_SIZEBITS = 14
_IOC_DIRBITS = 2
_IOC_NRMASK = ((1 << _IOC_NRBITS) - 1)
_IOC_TYPEMASK = ((1 << _IOC_TYPEBITS) - 1)
_IOC_SIZEMASK = ((1 << _IOC_SIZEBITS) - 1)
_IOC_DIRMASK = ((1 << _IOC_DIRBITS) - 1)
_IOC_NRSHIFT = 0
_IOC_TYPESHIFT = (_IOC_NRSHIFT + _IOC_NRBITS)
_IOC_SIZESHIFT = (_IOC_TYPESHIFT + _IOC_TYPEBITS)
_IOC_DIRSHIFT = (_IOC_SIZESHIFT + _IOC_SIZEBITS)
IOCSIZE_MASK = (_IOC_SIZEMASK << _IOC_SIZESHIFT)
IOCSIZE_SHIFT = (_IOC_SIZESHIFT)

# direction bits
_IOC_NONE = 0
_IOC_WRITE = 1
_IOC_READ = 2


def _IOC(dir, type, nr, FMT):
    return int((((dir) << _IOC_DIRSHIFT) |
               ((type) << _IOC_TYPESHIFT) |
               ((nr) << _IOC_NRSHIFT) |
               ((FMT) << _IOC_SIZESHIFT)) & 0xffffffff)


# used to create numbers
# type is the assigned type from the kernel developers
# nr is the base ioctl number (defined by driver writer)
# FMT is a struct module format string.
def _IO(type, nr):
    return _IOC(_IOC_NONE, (type), (nr), 0)


def _IOR(type, nr, FMT):
    return _IOC(_IOC_READ, (type), (nr), sizeof(FMT))


def _IOW(type, nr, FMT):
    return _IOC(_IOC_WRITE, (type), (nr), sizeof(FMT))


def _IOWR(type, nr, FMT):
    return (_IOC(_IOC_READ | _IOC_WRITE,
            (type), (nr), sizeof(FMT)))


# used to decode ioctl numbers
def _IOC_DIR(nr):
    return (((nr) >> _IOC_DIRSHIFT) & _IOC_DIRMASK)


def _IOC_TYPE(nr):
    return (((nr) >> _IOC_TYPESHIFT) & _IOC_TYPEMASK)


def _IOC_NR(nr):
    return (((nr) >> _IOC_NRSHIFT) & _IOC_NRMASK)


def _IOC_SIZE(nr):
    return (((nr) >> _IOC_SIZESHIFT) & _IOC_SIZEMASK)


# taken from /usr/include/linux/input.h
EVIOCGVERSION = _IOR(69, 0x01, INT)  # get driver version
EVIOCGID = _IOR(69, 0x02, SHORT4)  # get device ID
EVIOCGREP = _IOR(69, 0x03, INT2)  # get repeat settings
EVIOCSREP = _IOW(69, 0x03, INT2)  # set repeat settings
EVIOCGKEYCODE = _IOR(69, 0x04, INT2)  # get keycode
EVIOCSKEYCODE = _IOW(69, 0x04, INT2)  # set keycode
EVIOCGKEY = _IOR(69, 0x05, INT2)  # get key value
EVIOCGNAME = _IOC(_IOC_READ, 69, 0x06, 255)  # get device name
EVIOCGPHYS = _IOC(_IOC_READ, 69, 0x07, 255)  # get physical location
EVIOCGUNIQ = _IOC(_IOC_READ, 69, 0x08, 255)  # get unique identifier
EVIOCRMFF = _IOW(69, 0x81, INT)  # Erase a force effect
EVIOCSGAIN = _IOW(69, 0x82, USHORT)  # Set overall gain
EVIOCSAUTOCENTER = _IOW(69, 0x83, USHORT)  # Enable or disable auto-centering
EVIOCGEFFECTS = _IOR(69, 0x84, INT)  # number of effects at the same time
EVIOCGRAB = _IOW(69, 0x90, INT)  # Grab/Release device


# these take parameters.
def EVIOCGBIT(evtype, len=255):
    # get event bits
    return _IOC(_IOC_READ, 69, 0x20 + evtype, len)


def EVIOCGABS(abs):
    # get abs value/limits
    return _IOR(69, 0x40 + abs, INT5)


def EVIOCGSW(len):
    # get all switch states
    return _IOC(_IOC_READ, 69, 0x1b, len)


def EVIOCGLED(len):
    #  get all LED states
    return _IOC(_IOC_READ, 69, 0x19, len)

#struct input_event {
#        struct timeval time; = {long seconds, long microseconds}
#        unsigned short type;
#        unsigned short code;
#        unsigned int value;
#};

EVFMT = "llHHi"
EVsize = struct.calcsize(EVFMT)

EV_SYN = 0x00
EV_KEY = 0x01
EV_REL = 0x02
EV_ABS = 0x03
EV_MSC = 0x04
EV_SW = 0x05
EV_LED = 0x11
EV_SND = 0x12
EV_REP = 0x14
EV_FF = 0x15
EV_PWR = 0x16
EV_FF_STATUS = 0x17
EV_MAX = 0x1f
EV_NAMES = {
    EV_SYN: "Sync",
    EV_KEY: "Keys or Buttons",
    EV_REL: "Relative Axes",
    EV_ABS: "Absolute Axes",
    EV_MSC: "Miscellaneous",
    EV_SW: "Switches",
    EV_LED: "Leds",
    EV_SND: "Sound",
    EV_REP: "Repeat",
    EV_FF: "Force Feedback",
    EV_PWR: "Power Management",
    EV_FF_STATUS: "Force Feedback Status",
}


class Event(object):

    """This represents a kernel input event from a device in /dev/input/.
    This stores the event time, type, code, and value.
    See also: /sys/class/input/event*
    """

    def __init__(self):

        self.tv_sec = None
        self.tv_usec = None
        self.evtype = None
        self.code = None
        self.value = None
        self.tt = None

    def __str__(self):

        return ("tv_sec: %d, tv_usec: %6d, evtype: 0x%x," +
                "code: 0x%x, value: 0x%x" %
                (self.tv_sec, self.tv_usec, self.evtype,
                    self.code, self.value))

    def encode(self):

        #tv_sec, tv_usec = divmod(self.tt, 1.0)
        return struct.pack(EVFMT, self.tv_sec, self.tv_usec,
                           self.evtype, self.code, self.value)

    def decode(self, bev):

        self.tv_sec, self.tv_usec, self.evtype, self.code, self.value = \
            struct.unpack(EVFMT, bev)
        self.tt = self.tv_usec/1000000.0 + self.tv_sec


class EventDevice(object):

    def __init__(self, filename):

        self.filename = filename
        self.name = None
        self.driver_version = None
        self.idbus = None
        self.idvendor = None
        self.idproduct = None
        self.idversion = None
        self.caps = None
        self._eventq = []
        self._fd = os.open(self.filename, os.O_RDONLY)

        # The following try/except wrappers are a hack
        # to handle the following error:
        #     IOError: [Errno 22] Invalid argument
        # The way the ioctl constants are defined is not very portable.
        # For example, on some systems the EVIOCGNAME is defined incorrectly.
        # I need to fix how ioctl constants are defined. The constant
        # 1090536710 is one that "just works" on PowerPC where using
        # EVIOCGNAME fails. It's probably a big-endian vs.
        # little-endian thing. PowerPC is big endian.

        # device name
        try:
            name = fcntl.ioctl(self._fd, EVIOCGNAME, chr(0) * 256)
        except (IOError):
            name = fcntl.ioctl(self._fd, 1090471174, chr(0) * 256)
        self.name = name.strip(chr(0)).strip()
        # driver version
        try:
            ver = fcntl.ioctl(self._fd, EVIOCGVERSION, '\x00\x00\x00\x00')
        except (IOError):
            ver = fcntl.ioctl(self._fd, 1074021633, '\x00\x00\x00\x00')
        self.driver_version = struct.unpack(INT, ver)[0]
        # device ID info
        try:
            devid = fcntl.ioctl(self._fd, EVIOCGID,
                                '\x00\x00\x00\x00\x00\x00\x00\x00')
        except (IOError):
            devid = fcntl.ioctl(self._fd, 1074283778,
                                '\x00\x00\x00\x00\x00\x00\x00\x00')
        self.idbus, self.idvendor, self.idproduct, self.idversion = \
            struct.unpack(SHORT4, devid)
        # capabilities
        try:
            caps = fcntl.ioctl(self._fd, EVIOCGBIT(0), '\x00\x00\x00\x00')
        except (IOError):
            caps = fcntl.ioctl(self._fd, 1090471200, '\x00\x00\x00\x00')
        self.caps = struct.unpack(INT, caps)[0]

    def __del__(self):

        if hasattr(self, '_fd') and self._fd is not None:
            os.close(self._fd)

    def __str__(self):

        caps_names = []
        for (evtype, ev_name) in EV_NAMES.items():
            if self.has_feature(evtype):
                caps_names.append(ev_name)
        caps_names_str = ", ".join(caps_names)
        return ("%s : name='%s', driver_version=0x%x, bus=0x%x, " +
                "vendor=0x%04x, product=0x%04x, version=0x%x, " +
                "caps-bits=0x%02x, caps-names='%s'" %
                (self.filename, self.name, self.driver_version,
                    self.idbus, self.idvendor, self.idproduct,
                    self.idversion, self.caps, caps_names_str))

    def _fill(self):

        global EVsize
        try:
            raw = os.read(self._fd, EVsize * 32)
#            raw = os.read(self._fd, EVsize)
        except EOFError:
            self.close()
        else:
            if raw:
                for i in range(len(raw)/EVsize):
                    ev = Event()
                    ev.decode(raw[i*EVsize:(i+1)*EVsize])
                    self._eventq.append(ev)

    def read(self):

        if not self._eventq:
            self._fill()
        if len(self._eventq) < 1:
            print "read nothing"
            return None
        return self._eventq.pop()

    def has_feature(self, evtype):

        return self.caps >> evtype & 1


def mouse_events(input_device):

    ed = EventDevice(input_device)
    while ed:
        ev = ed.read()
        if ev.evtype == EV_REL:
            yield ev


def mouse_motion(input_device):

    """This generates the relative motion of the given input device."""

    ed = EventDevice(input_device)
    while ed:
        ev = ed.read()
        if ev.evtype == EV_REL:
            yield ev.value


def mouse_timing_delta(input_device):

    """This generates the timing of each mouse event."""

    ed = mouse_events(input_device)
    t1 = ed.next().tt
    while ed:
        tt = ed.tv_usec/1000000.0 + ed.tv_sec


def entropy_bit(input_device):

    """This takes the relative motion of the given input device
    and generates raw bits based on whether the motion is
    odd or even. See mouse_motion(). """

    motion = mouse_motion(input_device)
    while motion:
        bit = motion.next() % 2
        yield bit


def entropy_bit_unbias_vonneumann(input_device):

    """This takes the raw bits from entropy_bit() and
    removes simple bias using Von Neumann's method.
    This is the preferred alternative to using
    entropy_bit_unbias_xor(). """

    bits = entropy_bit(input_device)
    while bits:
        bit1 = bits.next()
        bit2 = bits.next()
        if bit1 == bit2:
            continue
        else:
            yield bit1


def entropy_bit_unbias_xor(input_device):

    """This takes the raw bits from entropy_bit() and
    removes simple bias using xor. This is an alternative
    debiasing method to entropy_bit_unbias_vonneumann(). """

    motion = entropy_bit(input_device)
    while motion:
        bit1 = motion.next()
        bit2 = motion.next()
        yield bit1 ^ bit2


def entropy_bit_unbias_vonneumann2(input_device):

    """This is a second order version of entropy_bit_unbias_vonneumann().
    This basically applies the Von Neumann method twice. """

    bits = entropy_bit_unbias_vonneumann(input_device)
    while bits:
        bit1 = bits.next()
        bit2 = bits.next()
        if bit1 == bit2:
            continue
        else:
            yield bit1


def entropy_bytes(input_device):

    """This is a generator for an entropy source of 8-bit bytes with
    Von Neumann bias filtering. This calls entropy_bit_unbias_vonneumann
    8 times to generate a byte. """

    bit_source = entropy_bit_unbias_vonneumann(input_device)
    #bit_source = entropy_bit_unbias_xor(input_device)
    while bit_source:
        byte = 0x00
        for nn in range(8):
            byte = byte << 1
            bit = bit_source.next()
            byte = byte | bit
        yield byte


def byte_generator(bit_source):

    while bit_source:
        byte = 0x00
        for nn in range(8):
            byte = byte << 1
            bit = bit_source.next()
            byte = byte | bit
        yield byte


def list_devices(evtype=None):

    """This returns a list all input event devices with the given evtype. By
    default (evtyype=None) all input devices are listed. Set evtype to 'EV_REL'
    to list mouse devices. """

    devices = []
    for nn in range(0, 100):
        filename = "/dev/input/event%d" % nn
        if os.path.exists(filename):
            ed = EventDevice(filename)
            if evtype is None or ed.has_feature(evtype):
                devices.append(ed)
        else:
            break
    return devices


def detect_hotplug(dev_path='/dev/input', timeout=30, idle_time=0.250):

    """This waits and returns a list of new devices created
    under /dev/input/. Only device files named 'event*' are returned.
    If no device is created before the timeout then None is returned.
    This may return an empty list if something changed under /dev/input, but
    an 'event*' device file was not found.
    """

    before_timestamp = os.stat(dev_path).st_mtime
    timeout_mark = time.time() + timeout
    before_list = os.listdir(dev_path)
    while True:
        time.sleep(idle_time)
        after_timestamp = os.stat(dev_path).st_mtime
        if after_timestamp != before_timestamp:
            break
        if time.time() > timeout_mark:
            return None
    after_list = os.listdir(dev_path)
    new_files = [ii for ii in after_list if ii not in before_list and ii[0:5]
                 == 'event']
    return new_files


def xor_strings(str_a, str_b):

    return ''.join([chr(ord(aa) ^ ord(bb)) for aa, bb in zip(str_a, str_b)])


def main(options, args):

    try:
        if options.list:
            for dev in list_devices(EV_REL):
                print(dev)
            return 0
    except Exception, ee:
        sys.stderr.write('ERROR: Read permission denied.\n')
        sys.stderr.write('Perhaps you forgot to use "sudo".\n')
        return 1

    if options.detect:
        new_devices = detect_hotplug()
        if new_devices is None:
            sys.stderr.write('ERROR: No device found before timeout.\n')
            return 1
        for dev_name in sorted(new_devices):
            print '/dev/input/%s' % dev_name
        return 0

    # The following options require args[0] to be defined.

    input_device = args[0]
    if not os.access(input_device, os.R_OK):
        sys.stderr.write('ERROR: Read permission denied: %s\n' % input_device)
        sys.stderr.write('Perhaps you forgot to use "sudo".\n')
        return 1

    if options.raw:
        # Remember, this is BIASED, so it is expected to give
        # more of one value of bit than another.
        entropy_source = entropy_bit(input_device)
        for bit in entropy_source:
            sys.stdout.write('%d' % bit)
            sys.stdout.flush()

    if options.rawvn:
        entropy_source = entropy_bit_unbias_vonneumann(input_device)
        for bit in entropy_source:
            sys.stdout.write('%d' % bit)
            sys.stdout.flush()

    if options.rawvn2:
        entropy_source = entropy_bit_unbias_vonneumann2(input_device)
        for bit in entropy_source:
            sys.stdout.write('%d' % bit)
            sys.stdout.flush()

    if options.rawxor:
        entropy_source = entropy_bit_unbias_xor(input_device)
        for bit in entropy_source:
            sys.stdout.write('%d' % bit)
            sys.stdout.flush()

    if options.events:
        event_source = mouse_events(input_device)
        for ev in event_source:
            print str(ev)

    if options.bytes:
        bw = bandwidth.bandwidth()
        last_bandwidth_report = time.time()
        entropy_source_bits = entropy_bit_unbias_vonneumann(input_device)
        entropy_source = byte_generator(entropy_source_bits)
        for byte in entropy_source:
            sys.stdout.write(chr(byte))
            sys.stdout.flush()
            bw.update(1)
            if time.time() - last_bandwidth_report > 10:
                last_bandwidth_report = time.time()
                sys.stderr.write('1 minute bandwidth: %f bytes per second\n'
                                 % bw.bandwidth_covering(60.0))
                sys.stderr.flush()

if __name__ == "__main__":
    try:
        start_time = time.time()
        parser = optparse.OptionParser(
            formatter=optparse.TitledHelpFormatter(),
            usage=globals()['__doc__'],
            version='1'
        )
        parser.add_option('-v', '--verbose', action='store_true',
                          default=False, help='verbose output')
        parser.add_option('--bytes', action='store_true',
                          default=True, help='dump binary stream (default)')
        parser.add_option('--hex', action='store_true',
                          default=False, help='dump ASCII hex stream')
        parser.add_option('--raw', action='store_true',
                          default=False, help='dump raw bits with bias')
        parser.add_option('--rawvn', action='store_true',
                          default=False, help='dump raw bits with' +
                          ' von Neumann debiasing')
        parser.add_option('--rawvn2', action='store_true',
                          default=False, help='dump raw bits with' +
                          ' 2-pass von Neumann debiasing')
        parser.add_option('--rawxor', action='store_true',
                          default=False, help='dump raw bits with' +
                          ' xor debiasing')
        parser.add_option('--events', action='store_true',
                          default=False, help='dump raw mouse events')
        parser.add_option('--list', action='store_true',
                          default=False, help='list input devices')
        parser.add_option('--detect', action='store_true',
                          default=False, help='detect when input device' +
                          ' is newly plugged.')
        (options, args) = parser.parse_args()
        if not options.list and not options.detect and len(args) < 1:
            msg = """Missing input device argument. The mouse device is
usually something like '/dev/input/event3' or '/dev/input/event4'."""
            parser.error(msg)
        if options.verbose:
            print(time.asctime())
        exit_code = main(options, args)
        if exit_code is None:
            exit_code = 0
        if options.verbose:
            print (time.asctime())
            print ('TOTAL TIME IN MINUTES: %f' %
                   ((time.time()-start_time)/60.0))
        sys.exit(exit_code)
    except KeyboardInterrupt as e:  # The user pressed Ctrl-C.
        sys.exit(0)
    except SystemExit as e:  # The script called sys.exit() somewhere.
        raise e
    except Exception as e:
        print ('ERROR: Unexpected Exception')
        print (str(e))
        traceback.print_exc()
        os._exit(2)

bandwidth.py

#!/usr/bin/env python
# vim:set ft=python fileencoding=utf-8 sr et ts=4 sw=4 : See help 'modeline'
"""Bandwidth calculator.

DESCRIPTION

    This module is used to keep track of the amount of data
    passing through a system. After you create the bandwidth
    object you call update() on the object with the number of
    bytes being handled at any point in time. Presumably this
    would be inside a loop processing bytes. The object will
    keep a history of the time and number of bytes processed.
    When you want to know the instantaneous bandwidth you call
    bandwidth_covering() with the range of seconds you want the
    bandwidth calculation to cover. It will return the bytes per
    second over that time period.

    To reduce the size of the history log size the byte counts
    and times are aggregated into 10 second bins. This effects
    the granularity of the bandwidth calculations. If bandwidth
    in your application changes significantly on a smaller time
    scale than 10 seconds, then you may want to adjust the object
    property, bin_length_secs. The byte_count_history_max_secs
    object property also may be adjusted to set the limits of the
    history log.

AUTHOR

    Noah Spurrier <noah@noah.org>

LICENSE

    This license is approved by the OSI and FSF as GPL-compatible.
        http://opensource.org/licenses/isc-license.txt

    Copyright (c) 2013, Noah Spurrier
    PERMISSION TO USE, COPY, MODIFY, AND/OR DISTRIBUTE THIS SOFTWARE FOR ANY
    PURPOSE WITH OR WITHOUT FEE IS HEREBY GRANTED, PROVIDED THAT THE ABOVE
    COPYRIGHT NOTICE AND THIS PERMISSION NOTICE APPEAR IN ALL COPIES.
    THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
    WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
    MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
    ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
    ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

VERSION

    Version 1
"""

import os
import sys
import time


class bandwidth:

    def __init__(self):

        self.byte_count_history = [[0.0, 0]]
        self.byte_count_history_max_secs = 15 * 3600
        self.bin_length_secs = 10.0

    def __str__(self):

        ss = ''
        ss += '1 minute bandwidth: %f\n' % self.bandwidth_covering(60.0)
        ss += '5 minute bandwidth: %f\n' % self.bandwidth_covering(300.0)
        ss += 'history length: %d\n' % len(self.byte_count_history)
        ss += 'log of update times and byte counts:\n'
        ss += '    ' + str(self.byte_count_history)
        return ss

    def update(self, byte_count):

        now_time = time.time()
        # Add byte_count to history. Aggregate into bins of bin_length_secs.
        if (len(self.byte_count_history) > 0 and
                now_time - self.byte_count_history[-1][0] <
                self.bin_length_secs):
            self.byte_count_history[-1][1] += byte_count
        else:
            self.byte_count_history.append([now_time, byte_count])
        # Drop byte_counts that are older than byte_count_history_max_secs.
        # FIXME: Yes, I know lists are inefficient as dequeues.
        while (len(self.byte_count_history) > 0 and
                (now_time - self.byte_count_history[0][0]) >
                self.byte_count_history_max_secs):
            self.byte_count_history.pop(0)

    def bandwidth_covering(self, timespan_secs):

        if len(self.byte_count_history) < 1:
            return 0.0
        now_time = time.time()
        # Find the point in history newer than timespan_secs.
        for ii in range(len(self.byte_count_history)):
            if now_time - self.byte_count_history[ii][0] <= timespan_secs:
                break
        # Calculate total_time from point in history previously found.
        time_total = now_time - self.byte_count_history[ii][0]
        # Get the sum of byte counts starting from the point previously found.
        byte_total = 0
        for ii in range(ii, len(self.byte_count_history)):
            byte_total += self.byte_count_history[ii][1]
        return byte_total / time_total


if __name__ == '__main__':

    print('Initializing bandwidth counts...')
    bw = bandwidth()

    for ii in range(60):
        bw.update(1)
        print(bw)
        time.sleep(1)
    for ii in range(60):
        bw.update(2)
        print(bw)
        time.sleep(1)
    for ii in range(10000):
        bw.update(1)
        print(bw)
        time.sleep(1)