About a week ago I posted my (Don Mitchell's really) truerand() routine
for Unix. truerand() needs some post-processing before use; it cannot
be used directly. Here's a more complete version; the main interface is
randbyte(), which returns (in about a third of a second) one really
random byte (based on 64 truerand() bits) that can be used directly.
As an added bonus, the library also throws in a shs-2 function and the
basic truerand() code.
The basic idea is that you exploit randomness in the drift between
the processor clock and the rate at which interval timer interrupts
occur. Such drift occurs even on idle processors. randbyte() assumes
that there's at least about .4 bits of "entropy" per interrupt, which is
(probably) a safe assumption on modern processors. Randomness introduced
by the OS (scheduler, etc.) can add to the overall entropy, but shouldn't
be relied upon by itself.
An advantage to this approach (using clock skew) is that the randomness
doesn't depend on external events like user input, network traffic or
processor load. That makes it especially attractive for generating keys
on unattended servers, e.g., for generating Diffie-Hellman exponents.
Note, however, that very (very) slow and heavily-loaded processors may
not provide enough cycles to the truerand process between interrupts for
these assumptions to hold. Also, all bets are off on processors that use
a single clock source for both interval timing and CPU clocking.
This code is very BSD/SunOS-centric and is completely untested elsewhere.
Read the comments for scary warnings about testing on your own platform
before using it for anything serious like generating keys.
-matt
=======================cut here==============
#!/bin/sh
# This is a shell archive (produced by GNU sharutils 4.1).
# To extract the files from this archive, save it to some FILE, remove
# everything before the `!/bin/sh' line above, then type `sh FILE'.
#
# Existing files will *not* be overwritten unless `-c' is specified.
#
# This shar contains:
# length mode name
# ------ ---------- ------------------------------------------
# 1270 -rw-r--r-- makefile
# 1246 -rw-r--r-- randbyte.c
# 2886 -rw-r--r-- truerand.c
# 7142 -rw-r--r-- shs.c
# 149 -rw-r--r-- randtest.c
#
touch -am 1231235999 $$.touch >/dev/null 2>&1
if test ! -f 1231235999 && test -f $$.touch; then
shar_touch=touch
else
shar_touch=:
echo
echo 'WARNING: not restoring timestamps. Consider getting and'
echo "installing GNU \`touch', distributed in GNU File Utilities..."
echo
fi
rm -f 1231235999 $$.touch
#
# ============= makefile ==============
if test -f 'makefile' && test X"$1" != X"-c"; then
echo 'x - skipping makefile (file already exists)'
else
echo 'x - extracting makefile (text)'
sed 's/^X//' << 'SHAR_EOF' > 'makefile' &&
# makefile for librand
# tested on Sparc-20 (SunOS 4.x) and P100 (BSDI) only.
# You're on your own elsewhere. Read the comments for scary warnings.
#
# Usage: int randbyte();
#
#* The authors of this software are Don Mitchell, Matt Blaze & Jack Lacy.
#* Copyright (c) 1995 by AT&T.
#* Permission to use, copy, and modify this software without fee
#* is hereby granted, provided that this entire notice is included in
#* all copies of any software which is or includes a copy or
#* modification of this software and in all copies of the supporting
#* documentation for such software.
#*
#* This software may be subject to United States export controls.
#*
#* THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
#* WARRANTY. IN PARTICULAR, NEITHER THE AUTHORS NOR AT&T MAKE ANY
#* REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
X
SRCS=randbyte.c truerand.c shs.c
OBJS=randbyte.o truerand.o shs.o
CC=gcc
CFLAGS=
# No -O in CFLAGS! On some compilers, this optimizes out the counter...
X
librand.a: $(OBJS)
X ar rcv librand.a $(OBJS)
X ranlib librand.a
X
randtest: randtest.c $(SRCS)
X cc -DDEBUGRND randtest.c $(SRCS) -o randtest
X
librand.shar: makefile $(SRCS) randtest.c
X shar makefile $(SRCS) randtest.c > librand.shar
SHAR_EOF
$shar_touch -am 0930150995 'makefile' &&
chmod 0644 'makefile' ||
echo 'restore of makefile failed'
shar_count="`wc -c < 'makefile'`"
test 1270 -eq "$shar_count" ||
echo "makefile: original size 1270, current size $shar_count"
fi
# ============= randbyte.c ==============
if test -f 'randbyte.c' && test X"$1" != X"-c"; then
echo 'x - skipping randbyte.c (file already exists)'
else
echo 'x - extracting randbyte.c (text)'
sed 's/^X//' << 'SHAR_EOF' > 'randbyte.c' &&
/*
X * Random byte interface to truerand()
X * Matt Blaze 5/95
X * eight really random bits
X * usage:
X * unsigned char r; int randbyte();
X * r=randbyte();
X * randbyte() takes about .3 seconds on most machines.
X */
/*
X * The author of this software is Matt Blaze.
X * Copyright (c) 1995 by AT&T.
X * Permission to use, copy, and modify this software without fee
X * is hereby granted, provided that this entire notice is included in
X * all copies of any software which is or includes a copy or
X * modification of this software and in all copies of the supporting
X * documentation for such software.
X *
X * This software may be subject to United States export controls.
X *
X * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
X * WARRANTY. IN PARTICULAR, NEITHER THE AUTHORS NOR AT&T MAKE ANY
X * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
X * OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
X */
X
int randbyte()
{
X unsigned long truerand();
X unsigned char *shs();
X unsigned long r[2];
X unsigned char *hash;
X
X r[0]=truerand(); r[1]=truerand();
X hash = shs(r,sizeof(r));
#ifdef DEBUGRND
X printf("%011o %011o %02x\n",r[0],r[1],*hash & 0xff);
#endif
X return ((int) (*hash)) & 0xff;
}
SHAR_EOF
$shar_touch -am 0930145795 'randbyte.c' &&
chmod 0644 'randbyte.c' ||
echo 'restore of randbyte.c failed'
shar_count="`wc -c < 'randbyte.c'`"
test 1246 -eq "$shar_count" ||
echo "randbyte.c: original size 1246, current size $shar_count"
fi
# ============= truerand.c ==============
if test -f 'truerand.c' && test X"$1" != X"-c"; then
echo 'x - skipping truerand.c (file already exists)'
else
echo 'x - extracting truerand.c (text)'
sed 's/^X//' << 'SHAR_EOF' > 'truerand.c' &&
/*
X * Physically random numbers (very nearly uniform)
X * D. P. Mitchell
X * Modified by Matt Blaze 2/95
X */
/*
X * The authors of this software are Don Mitchell and Matt Blaze.
X * Copyright (c) 1995 by AT&T.
X * Permission to use, copy, and modify this software without fee
X * is hereby granted, provided that this entire notice is included in
X * all copies of any software which is or includes a copy or
X * modification of this software and in all copies of the supporting
X * documentation for such software.
X *
X * This software may be subject to United States export controls.
X *
X * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
X * WARRANTY. IN PARTICULAR, NEITHER THE AUTHORS NOR AT&T MAKE ANY
X * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
X * OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
X */
X
/*
X * WARNING: depending on the particular platform, truerand() output may
X * be biased or correlated. In general, you can expect about 16 bits of
X * "pseudo-entropy" out of each 32 bit word returned by truerand(),
X * but it may not be uniformly diffused. You should therefore run
X * the output through some post-whitening function (like MD5 or DES or
X * whatever) before using it to generate key material. (RSAREF's
X * random package does this for you when you feed truerand() bits to the
X * seed input function.)
X *
X * Test these assumptions on your own platform before fielding a system
X * based on this software or these techniques.
X *
X * This software seems to work well (at 16 bits per truerand() call) on
X * a Sun Sparc-20 under SunOS 4.1.3 and on a P100 under BSDI 2.0. You're
X * on your own elsewhere.
X */
X
#include <signal.h>
#include <setjmp.h>
#include <sys/time.h>
#include <math.h>
#include <stdio.h>
X
static jmp_buf env;
static unsigned count;
static unsigned ocount;
static unsigned buffer;
X
static int
tick()
{
X struct itimerval it, oit;
X
X timerclear(&it.it_interval);
X it.it_value.tv_sec = 0;
X it.it_value.tv_usec = 16665;
X if (setitimer(ITIMER_REAL, &it, &oit) < 0)
X perror("tick");
}
X
static void
interrupt()
{
X if (count)
X longjmp(env, 1);
X (void) signal(SIGALRM, interrupt);
X tick();
}
X
static unsigned long
roulette()
{
X
X if (setjmp(env)) {
X count ^= (count>>3) ^ (count>>6) ^ ocount;
X count &= 0x7;
X ocount=count;
X buffer = (buffer<<3) ^ count;
X return buffer;
X }
X (void) signal(SIGALRM, interrupt);
X count = 0;
X tick();
X for (;;)
X count++; /* about 1 MHz on VAX 11/780 */
}
X
unsigned long
truerand()
{
X
X count=0;
X (void) roulette();
X (void) roulette();
X (void) roulette();
X (void) roulette();
X (void) roulette();
X (void) roulette();
X (void) roulette();
X (void) roulette();
X (void) roulette();
X (void) roulette();
X return roulette();
}
X
int
n_truerand(n)
int n;
{
X int slop, v;
X
X slop = 0x7FFFFFFF % n;
X do {
X v = truerand() >> 1;
X } while (v <= slop);
X return v % n;
}
X
X
X
SHAR_EOF
$shar_touch -am 0930143395 'truerand.c' &&
chmod 0644 'truerand.c' ||
echo 'restore of truerand.c failed'
shar_count="`wc -c < 'truerand.c'`"
test 2886 -eq "$shar_count" ||
echo "truerand.c: original size 2886, current size $shar_count"
fi
# ============= shs.c ==============
if test -f 'shs.c' && test X"$1" != X"-c"; then
echo 'x - skipping shs.c (file already exists)'
else
echo 'x - extracting shs.c (text)'
sed 's/^X//' << 'SHAR_EOF' > 'shs.c' &&
/*
X * The authors of this software are Jim Reeds and Jack Lacy
X * Copyright (c) 1992, 1994 by AT&T.
X * Permission to use, copy, and modify this software without fee
X * is hereby granted, provided that this entire notice is included in
X * all copies of any software which is or includes a copy or
X * modification of this software and in all copies of the supporting
X * documentation for such software.
X *
X * This software may be subject to United States export controls.
X *
X * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
X * WARRANTY. IN PARTICULAR, NEITHER THE AUTHORS NOR AT&T MAKE ANY
X * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
X * OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
X */
X
/*
X * Secure Hash Standard
X * proposed NIST SHS
X * coded for byte strings: number of bits is a multiple of 8
X *
X * Copyright (c) 1992, 1994 AT&T Bell Laboratories
X * Coded by Jim Reeds 5 Feb 1992
X * Enhanced by Jack Lacy 1993, 1994
X */
X
/*
X * unsigned char * shs(char *s, int n);
X *
X * input:
X * s character array to be hashed
X * n length of s in BYTES
X * output:
X * return value: address of 5 unsigned longs holding hash
X *
X * machine dependencies:
X * assumes a char is 8 bits
X */
X
/*
X * passes test on:
X * gauss (vax)
X * 3k (cray)
X * slepian (MIPS)
X * bird (sparcstation II)
X */
X
#include <sys/types.h>
#include <stdio.h>
X
typedef struct {
X long totalLength;
X unsigned long h[5];
X unsigned long w[80];
} SHS_CTX;
X
unsigned char *shs();
#ifdef SOLARIS2X
#define bzero(b, l) memset(b, 0, l)
#define bcopy(s, d, l) memcpy(d, s, l)
#define bcmp(s, d, l) (memcmp(s, d, l)? 1 : 0)
#endif
X
static long nbits;
static unsigned long *h;
static unsigned long *w;
static void shs1();
/*
static void packl (unsigned long);
static void pack (unsigned char, unsigned char, unsigned char, unsigned char);
static void shs1(void);
static void opack(unsigned char);
*/
X
#define MASK (unsigned long)0xffffffffL /* in case more than 32
bits per long */
X
/*
X * stick one byte into the current block; process the block when full
X */
static void opack(c)
X unsigned char c;
{
X int n32, nd32, shiftbits;
X register unsigned long x, mask, y;
X
X nd32 = (int)(nbits >> 5); /* nbits/32 */
X n32 = (int)(nbits & 0x1f); /* nbits%32 */
X shiftbits = 24-n32;
X
X x = (unsigned long)(c<<shiftbits);
X mask = (unsigned long)(0xff << shiftbits);
X mask = ~mask;
X
X y = w[nd32];
X y = (y & mask) + x;
X w[nd32] = y;
X
X nbits += 8;
X if(nbits==512){
X nbits = 0;
X shs1();
X }
}
X
static void pack(c0, c1, c2, c3)
X unsigned char c0, c1, c2, c3;
{
X int nd32;
X
X nd32 = (int)(nbits >> 5);
X w[nd32] = (u_long)(((u_long)c0<<24) | ((u_long)c1<<16) | ((u_long)c2<<8) |
(u_long)c3);
X
X nbits += 32;
X if(nbits==512){
X nbits = 0;
X shs1();
X }
}
X
/*
X * stick a 4 byte number into the current block
X */
static void
packl(x)
X unsigned long x;
{
X pack((unsigned char)(x>>24), (unsigned char)(x>>16),
X (unsigned char)(x>>8), (unsigned char)(x>>0));
}
X
/*
X * process one block
X */
static void
shs1()
{
X unsigned long *wp;
X unsigned long temp;
X unsigned long A, B, C, D, E;
X int t;
X
#define S(n,x) (u_long)(((x)<<(n))|((MASK&(x))>>(32-(n))))
X
X wp = w;
X t = 8;
X do {
X wp[16] = S(1, (u_long)(wp[13]^wp[8]^wp[2]^wp[0]));
X wp[17] = S(1, (u_long)(wp[14]^wp[9]^wp[3]^wp[1]));
X wp[18] = S(1, (u_long)(wp[15]^wp[10]^wp[4]^wp[2]));
X wp[19] = S(1, (u_long)(wp[16]^wp[11]^wp[5]^wp[3]));
X wp[20] = S(1, (u_long)(wp[17]^wp[12]^wp[6]^wp[4]));
X wp[21] = S(1, (u_long)(wp[18]^wp[13]^wp[7]^wp[5]));
X wp[22] = S(1, (u_long)(wp[19]^wp[14]^wp[8]^wp[6]));
X wp[23] = S(1, (u_long)(wp[20]^wp[15]^wp[9]^wp[7]));
X wp += 8;
X t--;
X } while (t > 0);
X
X A = h[0];
X B = h[1];
X C = h[2];
X D = h[3];
X E = h[4];
X
X t = 0;
X while (t<20) {
X temp = S(5,A) + E + w[t++];
X temp += (unsigned long)0x5a827999L + ((B&C)|(D&~B));
X E = D; D = C; C = S(30,B); B = A; A = temp;
X }
X while (t<40) {
X temp = S(5,A) + E + w[t++];
X temp += (unsigned long)0x6ed9eba1L + (B^C^D);
X E = D; D = C; C = S(30,B); B = A; A = temp;
X }
X while (t<60) {
X temp = S(5,A) + E + w[t++];
X temp += (unsigned long)0x8f1bbcdcL + ((B&C)|(B&D)|(C&D));
X E = D; D = C; C = S(30,B); B = A; A = temp;
X }
X while (t<80) {
X temp = S(5,A) + E + w[t++];
X temp += (unsigned long)0xca62c1d6L + (B^C^D);
X E = D; D = C; C = S(30,B); B = A; A = temp;
X }
X h[0] = MASK&(h[0] + A);
X h[1] = MASK&(h[1] + B);
X h[2] = MASK&(h[2] + C);
X h[3] = MASK&(h[3] + D);
X h[4] = MASK&(h[4] + E);
}
X
#define CHARSTOLONG(wp,s,i) {*wp++ = (u_long)((((u_long)(s[i])&0xff)<<24)|(((u_
long)(s[i+1])&0xff)<<16)|(((u_long)(s[i+2])&0xff)<<8)|(u_long)(s[i+3]&0xff));}
X
X
void
shsInit(mdContext)
X SHS_CTX *mdContext;
{
X nbits = 0;
X mdContext->h[0] = (unsigned long)0x67452301L;
X mdContext->h[1] = (unsigned long)0xefcdab89L;
X mdContext->h[2] = (unsigned long)0x98badcfeL;
X mdContext->h[3] = (unsigned long)0x10325476L;
X mdContext->h[4] = (unsigned long)0xc3d2e1f0L;
X mdContext->totalLength = 0;
}
X
X
void
shsUpdate(mdContext, s, n)
X SHS_CTX *mdContext;
X unsigned char *s;
X unsigned int n;
{
X register unsigned long *wp;
X long nn = n;
X long i;
X
X w = mdContext->w;
X h = mdContext->h;
X mdContext->totalLength += n;
X
X nbits = 0;
X n = n/(u_long)64;
X wp = w;
X
X while(n>0){
X CHARSTOLONG(wp,s,0);
X CHARSTOLONG(wp,s,4);
X CHARSTOLONG(wp,s,8);
X CHARSTOLONG(wp,s,12);
X CHARSTOLONG(wp,s,16);
X CHARSTOLONG(wp,s,20);
X CHARSTOLONG(wp,s,24);
X CHARSTOLONG(wp,s,28);
X CHARSTOLONG(wp,s,32);
X CHARSTOLONG(wp,s,36);
X CHARSTOLONG(wp,s,40);
X CHARSTOLONG(wp,s,44);
X CHARSTOLONG(wp,s,48);
X CHARSTOLONG(wp,s,52);
X CHARSTOLONG(wp,s,56);
X CHARSTOLONG(wp,s,60);
X n--;
X wp = w;
X s = (s + 64);
X shs1();
X }
X i=nn%64;
X while(i>3) {
X CHARSTOLONG(wp,s,0);
X s = (s + 4);
X nbits += (u_long)32;
X i -= 4;
X }
X while (i) {
X opack((unsigned char)*s++);
X i--;
X }
}
X
void
shsFinal(mdContext)
X SHS_CTX *mdContext;
{
X long nn = mdContext->totalLength;
X w = mdContext->w;
X h = mdContext->h;
X
X opack(128);
X while(nbits != 448)opack(0);
X packl((unsigned long)(nn>>29));
X packl((unsigned long)(nn<<3));
X
X /* if(nbits != 0)
X handle_exception(CRITICAL,"shsFinal(): nbits != 0\n");*/
}
X
unsigned char *
shs(s, n)
X unsigned char *s;
X long n;
{
X SHS_CTX *mdContext;
X static SHS_CTX mdC;
X static unsigned char ret[20];
X int i;
X
X mdContext = &mdC;
X
X shsInit(mdContext);
X shsUpdate(mdContext, s, n);
X shsFinal(mdContext);
X for (i=0; i<5; i++) {
X ret[i*4] = (mdContext->h[i]>>24)&0xff;
X ret[i*4+1] = (mdContext->h[i]>>16)&0xff;
X ret[i*4+2] = (mdContext->h[i]>>8)&0xff;
X ret[i*4+3] = (mdContext->h[i])&0xff;
X }
X
X return ret;
}
X
/*int fread(char *, int, int, FILE *);*/
X
unsigned long *
fShsDigest(in)
X FILE *in;
{
X SHS_CTX *mdContext;
X SHS_CTX mdC;
X unsigned char buffer[1024];
X long length, total;
X
X mdContext = &mdC;
X
X bzero(buffer, 1024);
X
X total = 0;
X shsInit(mdContext);
X while ((length = fread(buffer, 1, 1024, in)) != 0) {
X total += length;
X shsUpdate(mdContext, buffer, length);
X }
X shsFinal(mdContext);
X
X return mdContext->h;
}
X
X
X
SHAR_EOF
$shar_touch -am 0930142495 'shs.c' &&
chmod 0644 'shs.c' ||
echo 'restore of shs.c failed'
shar_count="`wc -c < 'shs.c'`"
test 7142 -eq "$shar_count" ||
echo "shs.c: original size 7142, current size $shar_count"
fi
# ============= randtest.c ==============
if test -f 'randtest.c' && test X"$1" != X"-c"; then
echo 'x - skipping randtest.c (file already exists)'
else
echo 'x - extracting randtest.c (text)'
sed 's/^X//' << 'SHAR_EOF' > 'randtest.c' &&
main(argc,argv)
int argc; char **argv;
{
X int count;
X
X if (argc==1)
X count = 0;
X else
X count = atoi(argv[1]) + 1;
X while (--count)
X randbyte();
}
SHAR_EOF
$shar_touch -am 0930150095 'randtest.c' &&
chmod 0644 'randtest.c' ||
echo 'restore of randtest.c failed'
shar_count="`wc -c < 'randtest.c'`"
test 149 -eq "$shar_count" ||
echo "randtest.c: original size 149, current size $shar_count"
fi
exit 0
