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TUCoPS :: Unix :: General :: time_qua.txt

Simple Unix Time Quantization Package - prevents certain hacks




/*
X * Simple Unix time quantization package
X * {mab,lacy}@research.att.com
X * v0.5 - 12/95
X *
X * TESTED ONLY UNDER SUNOS 4.x and BSDI 2.0.  This is unsupported
X * software.  Use at own risk.  Test carefully on new platforms.
X */
/*
X * The authors of this software are Matt Blaze and Jack Lacy
X *              Copyright (c) 1995 by AT&T Bell Laboratories.
X *
X * Permission to use, copy, and modify this software without fee is
X * hereby granted, provided that this entire notice is included in all
X * copies of any software which is or includes a copy or modification
X * of this software and in all copies of the supporting documentation
X * for such software.
X *
X * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR
X * IMPLIED WARRANTY.  IN PARTICULAR, NEITHER THE AUTHORS NOR AT&T MAKE
X * ANY REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE
X * MERCHANTABILITY OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR
X * PURPOSE.
X */
X
/*
X * WARNING: This package will provide quantized cpu consumption only
X * subject to the limitations of the OS on which it is run.  It will
X * fail in extreme cases (e.g., very very heavy load and very slow
X * machines (e.g., .001 MIPS).  Understand its limits before you use
X * it.
X *
X * Note that start_quantize takes MILLISECONDS, not microseconds.  See
X * quantize.3 for details.
X *
X * To prevent timing attacks (e.g., Kocher) in most PK crypto
X * applications in most applications on most cpus, surrounding the
X * call to the functions that use the secret with
X *	start_quantize(100);
X * and
X *	end_quantize();
X * will do reasonably well.
X */
X
#ifndef NO_QUANTIZE
#include <signal.h>
#include <setjmp.h>
#include <sys/time.h>
#include <stdio.h>
X
static jmp_buf quant_end;
static long quant_quantum=0;
X
static void quant_interrupt()
{
X	long nquantum;
X
X	nquantum = quant_quantum;
X	if (nquantum != 0)
X		set_quant_interrupt(nquantum);
X	else
X		longjmp(quant_end, 1);
X
}
X
static set_quant_interrupt(microsecs)
X     long microsecs;
{
X	struct itimerval it, oit;
X	
X	timerclear(&it.it_interval);
X	it.it_value.tv_sec = microsecs/1000000;
X	it.it_value.tv_usec = microsecs%1000000;
X	(void) signal(SIGVTALRM, quant_interrupt);
X	return setitimer(ITIMER_VIRTUAL, &it, &oit);
}
X
int start_quantize(quantum)
X     int quantum;	/* millisecs */
{
X	if (quantum <= 0)
X		return -1;
X	quant_quantum = (quantum * 1000) + 1; /* microsecs */
X	return set_quant_interrupt(quant_quantum);
}
X
int end_quantize()
{
X	if (setjmp(quant_end))
X		return 0;
X	if (quant_quantum == 0)
X		return -1; /* start_quantize never called */
X	quant_quantum = 0; /* we return at next quantum */
X	while (1)
X		;
X	return -1; /* should never happen */
}
X
#else /* NO_QUANTIZE */
#include <stdio.h>
X
int start_quantize(quantum)
X     int quantum;
{
X	fprintf(stderr,"Warning: QUANTIZE not available\n");
X	fflush(stderr);
X	return -1;
X
}
X
int end_quantize()
{
X	return -1;
}
X
#endif


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