Randomizer.cpp

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/* 
------- Strong random data generation on a Macintosh (pre - OS X) ------
        
--  GENERAL: We aim to generate unpredictable bits without explicit
    user interaction. A general review of the problem may be found
    in RFC 1750, "Randomness Recommendations for Security", and some
    more discussion, of general and Mac-specific issues has appeared
    in "Using and Creating Cryptographic- Quality Random Numbers" by
    Jon Callas (www.merrymeet.com/jon/usingrandom.html).

    The data and entropy estimates provided below are based on my
    limited experimentation and estimates, rather than by any
    rigorous study, and the entropy estimates tend to be optimistic.
    They should not be considered absolute.

    Some of the information being collected may be correlated in
    subtle ways. That includes mouse positions, timings, and disk
    size measurements. Some obvious correlations will be eliminated
    by the programmer, but other, weaker ones may remain. The
    reliability of the code depends on such correlations being
    poorly understood, both by us and by potential interceptors.

    This package has been planned to be used with OpenSSL, v. 0.9.5.
    It requires the OpenSSL function RAND_add. 

--  OTHER WORK: Some source code and other details have been
    published elsewhere, but I haven't found any to be satisfactory
    for the Mac per se:

    * The Linux random number generator (by Theodore Ts'o, in
      drivers/char/random.c), is a carefully designed open-source
      crypto random number package. It collects data from a variety
      of sources, including mouse, keyboard and other interrupts.
      One nice feature is that it explicitly estimates the entropy
      of the data it collects. Some of its features (e.g. interrupt
      timing) cannot be reliably exported to the Mac without using
      undocumented APIs.

    * Truerand by Don P. Mitchell and Matt Blaze uses variations
      between different timing mechanisms on the same system. This
      has not been tested on the Mac, but requires preemptive
      multitasking, and is hardware-dependent, and can't be relied
      on to work well if only one oscillator is present.

    * Cryptlib's RNG for the Mac (RNDMAC.C by Peter Gutmann),
      gathers a lot of information about the machine and system
      environment. Unfortunately, much of it is constant from one
      startup to the next. In other words, the random seed could be
      the same from one day to the next. Some of the APIs are
      hardware-dependent, and not all are compatible with Carbon (OS
      X). Incidentally, the EGD library is based on the UNIX entropy
      gathering methods in cryptlib, and isn't suitable for MacOS
      either.

    * Mozilla (and perhaps earlier versions of Netscape) uses the
      time of day (in seconds) and an uninitialized local variable
      to seed the random number generator. The time of day is known
      to an outside interceptor (to within the accuracy of the
      system clock). The uninitialized variable could easily be
      identical between subsequent launches of an application, if it
      is reached through the same path.

    * OpenSSL provides the function RAND_screen(), by G. van
      Oosten, which hashes the contents of the screen to generate a
      seed. This is not useful for an extension or for an
      application which launches at startup time, since the screen
      is likely to look identical from one launch to the next. This
      method is also rather slow.

    * Using variations in disk drive seek times has been proposed
      (Davis, Ihaka and Fenstermacher, world.std.com/~dtd/;
      Jakobsson, Shriver, Hillyer and Juels,
      www.bell-labs.com/user/shriver/random.html). These variations
      appear to be due to air turbulence inside the disk drive
      mechanism, and are very strongly unpredictable. Unfortunately
      this technique is slow, and some implementations of it may be
      patented (see Shriver's page above.) It of course cannot be
      used with a RAM disk.

--  TIMING: On the 601 PowerPC the time base register is guaranteed
    to change at least once every 10 addi instructions, i.e. 10
    cycles. On a 60 MHz machine (slowest PowerPC) this translates to
    a resolution of 1/6 usec. Newer machines seem to be using a 10
    cycle resolution as well.
    
    For 68K Macs, the Microseconds() call may be used. See Develop
    issue 29 on the Apple developer site
    (developer.apple.com/dev/techsupport/develop/issue29/minow.html)
    for information on its accuracy and resolution. The code below
    has been tested only on PowerPC based machines.

    The time from machine startup to the launch of an application in
    the startup folder has a variance of about 1.6 msec on a new G4
    machine with a defragmented and optimized disk, most extensions
    off and no icons on the desktop. This can be reasonably taken as
    a lower bound on the variance. Most of this variation is likely
    due to disk seek time variability. The distribution of startup
    times is probably not entirely even or uncorrelated. This needs
    to be investigated, but I am guessing that it not a majpor
    problem. Entropy = log2 (1600/0.166) ~= 13 bits on a 60 MHz
    machine, ~16 bits for a 450 MHz machine.

    User-launched application startup times will have a variance of
    a second or more relative to machine startup time. Entropy >~22
    bits.

    Machine startup time is available with a 1-second resolution. It
    is predictable to no better a minute or two, in the case of
    people who show up punctually to work at the same time and
    immediately start their computer. Using the scheduled startup
    feature (when available) will cause the machine to start up at
    the same time every day, making the value predictable. Entropy
    >~7 bits, or 0 bits with scheduled startup.

    The time of day is of course known to an outsider and thus has 0
    entropy if the system clock is regularly calibrated.

--  KEY TIMING: A  very fast typist (120 wpm) will have a typical
    inter-key timing interval of 100 msec. We can assume a variance
    of no less than 2 msec -- maybe. Do good typists have a constant
    rhythm, like drummers? Since what we measure is not the
    key-generated interrupt but the time at which the key event was
    taken off the event queue, our resolution is roughly the time
    between process switches, at best 1 tick (17 msec). I  therefore
    consider this technique questionable and not very useful for
    obtaining high entropy data on the Mac.

--  MOUSE POSITION AND TIMING: The high bits of the mouse position
    are far from arbitrary, since the mouse tends to stay in a few
    limited areas of the screen. I am guessing that the position of
    the mouse is arbitrary within a 6 pixel square. Since the mouse
    stays still for long periods of time, it should be sampled only
    after it was moved, to avoid correlated data. This gives an
    entropy of log2(6*6) ~= 5 bits per measurement.

    The time during which the mouse stays still can vary from zero
    to, say, 5 seconds (occasionally longer). If the still time is
    measured by sampling the mouse during null events, and null
    events are received once per tick, its resolution is 1/60th of a
    second, giving an entropy of log2 (60*5) ~= 8 bits per
    measurement. Since the distribution of still times is uneven,
    this estimate is on the high side.

    For simplicity and compatibility across system versions, the
    mouse is to be sampled explicitly (e.g. in the event loop),
    rather than in a time manager task.

--  STARTUP DISK TOTAL FILE SIZE: Varies typically by at least 20k
    from one startup to the next, with 'minimal' computer use. Won't
    vary at all if machine is started again immediately after
    startup (unless virtual memory is on), but any application which
    uses the web and caches information to disk is likely to cause
    this much variation or more. The variation is probably not
    random, but I don't know in what way. File sizes tend to be
    divisible by 4 bytes since file format fields are often
    long-aligned. Entropy > log2 (20000/4) ~= 12 bits.
    
--  STARTUP DISK FIRST AVAILABLE ALLOCATION BLOCK: As the volume
    gets fragmented this could be anywhere in principle. In a
    perfectly unfragmented volume this will be strongly correlated
    with the total file size on the disk. With more fragmentation
    comes less certainty. I took the variation in this value to be
    1/8 of the total file size on the volume.

--  SYSTEM REQUIREMENTS: The code here requires System 7.0 and above
    (for Gestalt and Microseconds calls). All the calls used are
    Carbon-compatible.
*/

/*------------------------------ Includes ----------------------------*/

#include "Randomizer.h"

// Mac OS API
#include <Files.h>
#include <Folders.h>
#include <Events.h>
#include <Processes.h>
#include <Gestalt.h>
#include <Resources.h>
#include <LowMem.h>

// Standard C library
#include <stdlib.h>
#include <math.h>

/*---------------------- Function declarations -----------------------*/

// declared in OpenSSL/crypto/rand/rand.h
extern "C" void RAND_add (const void *buf, int num, double entropy);

unsigned long GetPPCTimer (bool is601); // Make it global if needed
                    // elsewhere

/*---------------------------- Constants -----------------------------*/

#define kMouseResolution 6      // Mouse position has to differ
                    // from the last one by this
                    // much to be entered
#define kMousePositionEntropy 5.16  // log2 (kMouseResolution**2)
#define kTypicalMouseIdleTicks 300.0    // I am guessing that a typical
                    // amount of time between mouse
                    // moves is 5 seconds
#define kVolumeBytesEntropy 12.0    // about log2 (20000/4),
                    // assuming a variation of 20K
                    // in total file size and
                    // long-aligned file formats.
#define kApplicationUpTimeEntropy 6.0   // Variance > 1 second, uptime
                    // in ticks  
#define kSysStartupEntropy 7.0      // Entropy for machine startup
                    // time


/*------------------------ Function definitions ----------------------*/

CRandomizer::CRandomizer (void)
{
    long    result;
    
    mSupportsLargeVolumes =
        (Gestalt(gestaltFSAttr, &result) == noErr) &&
        ((result & (1L << gestaltFSSupports2TBVols)) != 0);
    
    if (Gestalt (gestaltNativeCPUtype, &result) != noErr)
    {
        mIsPowerPC = false;
        mIs601 = false;
    }
    else
    {
        mIs601 = (result == gestaltCPU601);
        mIsPowerPC = (result >= gestaltCPU601);
    }
    mLastMouse.h = mLastMouse.v = -10;  // First mouse will
                        // always be recorded
    mLastPeriodicTicks = TickCount();
    GetTimeBaseResolution ();
    
    // Add initial entropy
    AddTimeSinceMachineStartup ();
    AddAbsoluteSystemStartupTime ();
    AddStartupVolumeInfo ();
    AddFiller ();
}

void CRandomizer::PeriodicAction (void)
{
    AddCurrentMouse ();
    AddNow (0.0);   // Should have a better entropy estimate here
    mLastPeriodicTicks = TickCount();
}

/*------------------------- Private Methods --------------------------*/

void CRandomizer::AddCurrentMouse (void)
{
    Point mouseLoc;
    unsigned long lastCheck;    // Ticks since mouse was last
                    // sampled

#if TARGET_API_MAC_CARBON
    GetGlobalMouse (&mouseLoc);
#else
    mouseLoc = LMGetMouseLocation();
#endif
    
    if (labs (mLastMouse.h - mouseLoc.h) > kMouseResolution/2 &&
        labs (mLastMouse.v - mouseLoc.v) > kMouseResolution/2)
        AddBytes (&mouseLoc, sizeof (mouseLoc),
                kMousePositionEntropy);
    
    if (mLastMouse.h == mouseLoc.h && mLastMouse.v == mouseLoc.v)
        mMouseStill ++;
    else
    {
        double entropy;
        
        // Mouse has moved. Add the number of measurements for
        // which it's been still. If the resolution is too
        // coarse, assume the entropy is 0.

        lastCheck = TickCount() - mLastPeriodicTicks;
        if (lastCheck <= 0)
            lastCheck = 1;
        entropy = log2l
            (kTypicalMouseIdleTicks/(double)lastCheck);
        if (entropy < 0.0)
            entropy = 0.0;
        AddBytes (&mMouseStill, sizeof (mMouseStill), entropy);
        mMouseStill = 0;
    }
    mLastMouse = mouseLoc;
}

void CRandomizer::AddAbsoluteSystemStartupTime (void)
{
    unsigned long   now;        // Time in seconds since
                    // 1/1/1904
    GetDateTime (&now);
    now -= TickCount() / 60;    // Time in ticks since machine
                    // startup
    AddBytes (&now, sizeof (now), kSysStartupEntropy);
}

void CRandomizer::AddTimeSinceMachineStartup (void)
{
    AddNow (1.5);           // Uncertainty in app startup
                    // time is > 1.5 msec (for
                    // automated app startup).
}

void CRandomizer::AddAppRunningTime (void)
{
    ProcessSerialNumber PSN;
    ProcessInfoRec      ProcessInfo;
    
    ProcessInfo.processInfoLength = sizeof (ProcessInfoRec);
    ProcessInfo.processName = nil;
    ProcessInfo.processAppSpec = nil;
    
    GetCurrentProcess (&PSN);
    GetProcessInformation (&PSN, &ProcessInfo);

    // Now add the amount of time in ticks that the current process
    // has been active

    AddBytes (&ProcessInfo, sizeof (ProcessInfoRec),
            kApplicationUpTimeEntropy);
}

void CRandomizer::AddStartupVolumeInfo (void)
{
    short           vRefNum;
    long            dirID;
    XVolumeParam    pb;
    OSErr           err;
    
    if (!mSupportsLargeVolumes)
        return;
        
    FindFolder (kOnSystemDisk, kSystemFolderType, kDontCreateFolder,
            &vRefNum, &dirID);
    pb.ioVRefNum = vRefNum;
    pb.ioCompletion = 0;
    pb.ioNamePtr = 0;
    pb.ioVolIndex = 0;
    err = PBXGetVolInfoSync (&pb);
    if (err != noErr)
        return;
        
    // Base the entropy on the amount of space used on the disk and
    // on the next available allocation block. A lot else might be
    // unpredictable, so might as well toss the whole block in. See
    // comments for entropy estimate justifications.

    AddBytes (&pb, sizeof (pb),
        kVolumeBytesEntropy +
        log2l (((pb.ioVTotalBytes.hi - pb.ioVFreeBytes.hi)
                * 4294967296.0D +
            (pb.ioVTotalBytes.lo - pb.ioVFreeBytes.lo))
                / pb.ioVAlBlkSiz - 3.0));
}

/*
    On a typical startup CRandomizer will come up with about 60
    bits of good, unpredictable data. Assuming no more input will
    be available, we'll need some more lower-quality data to give
    OpenSSL the 128 bits of entropy it desires. AddFiller adds some
    relatively predictable data into the soup.
*/

void CRandomizer::AddFiller (void)
{
    struct
    {
        ProcessSerialNumber psn;    // Front process serial
                        // number
        RGBColor    hiliteRGBValue; // User-selected
                        // highlight color
        long        processCount;   // Number of active
                        // processes
        long        cpuSpeed;   // Processor speed
        long        totalMemory;    // Total logical memory
                        // (incl. virtual one)
        long        systemVersion;  // OS version
        short       resFile;    // Current resource file
    } data;
    
    GetNextProcess ((ProcessSerialNumber*) kNoProcess);
    while (GetNextProcess (&data.psn) == noErr)
        data.processCount++;
    GetFrontProcess (&data.psn);
    LMGetHiliteRGB (&data.hiliteRGBValue);
    Gestalt (gestaltProcClkSpeed, &data.cpuSpeed);
    Gestalt (gestaltLogicalRAMSize, &data.totalMemory);
    Gestalt (gestaltSystemVersion, &data.systemVersion);
    data.resFile = CurResFile ();
    
    // Here we pretend to feed the PRNG completely random data. This
    // is of course false, as much of the above data is predictable
    // by an outsider. At this point we don't have any more
    // randomness to add, but with OpenSSL we must have a 128 bit
    // seed before we can start. We just add what we can, without a
    // real entropy estimate, and hope for the best.

    AddBytes (&data, sizeof(data), 8.0 * sizeof(data));
    AddCurrentMouse ();
    AddNow (1.0);
}

//-------------------  LOW LEVEL ---------------------

void CRandomizer::AddBytes (void *data, long size, double entropy)
{
    RAND_add (data, size, entropy * 0.125); // Convert entropy bits
                        // to bytes
}

void CRandomizer::AddNow (double millisecondUncertainty)
{
    long time = SysTimer();
    AddBytes (&time, sizeof (time), log2l (millisecondUncertainty *
            mTimebaseTicksPerMillisec));
}

//----------------- TIMING SUPPORT ------------------

void CRandomizer::GetTimeBaseResolution (void)
{   
#ifdef __powerc
    long speed;
    
    // gestaltProcClkSpeed available on System 7.5.2 and above
    if (Gestalt (gestaltProcClkSpeed, &speed) != noErr)
        // Only PowerPCs running pre-7.5.2 are 60-80 MHz
        // machines.
        mTimebaseTicksPerMillisec =  6000.0D;
    // Assume 10 cycles per clock update, as in 601 spec. Seems true
    // for later chips as well.
    mTimebaseTicksPerMillisec = speed / 1.0e4D;
#else
    // 68K VIA-based machines (see Develop Magazine no. 29)
    mTimebaseTicksPerMillisec = 783.360D;
#endif
}

unsigned long CRandomizer::SysTimer (void)  // returns the lower 32
                        // bit of the chip timer
{
#ifdef __powerc
    return GetPPCTimer (mIs601);
#else
    UnsignedWide usec;
    Microseconds (&usec);
    return usec.lo;
#endif
}

#ifdef __powerc
// The timebase is available through mfspr on 601, mftb on later chips.
// Motorola recommends that an 601 implementation map mftb to mfspr
// through an exception, but I haven't tested to see if MacOS actually
// does this. We only sample the lower 32 bits of the timer (i.e. a
// few minutes of resolution)

asm unsigned long GetPPCTimer (register bool is601)
{
    cmplwi  is601, 0    // Check if 601
    bne _601        // if non-zero goto _601
    mftb    r3      // Available on 603 and later.
    blr         // return with result in r3
_601:
    mfspr r3, spr5      // Available on 601 only.
                // blr inserted automatically
}
#endif