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PA2AGA > HDDIG 09.01.00 12:36l 256 Lines 6612 Bytes #-9622 (0) @ EU
BID : HD_2000_3C
Read: DL6KCF GUEST
Subj: HamDigitalDigest 2000/3C
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Date: Sun, 09 Jan 00 01:04:14 MET
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From: pa2aga
To: hd_broadcast@pa2aga
Subject: HamDigitalDigest 2000/3C
X-BBS-Msg-Type: B
</HEAD>
<BODY>
<DIV>Why the writer is looking for a software implementation is =
the</DIV>
<DIV>real question? Does he already have the other parts of =
the</DIV>
<DIV>software, or is he just starting at the scrambler part?</DIV>
<DIV> </DIV>
<DIV>Here's a software scrambler for the Covox audio card :-)</DIV>
<DIV> </DIV>>>Here, scrambling generally refers to=20
"mixing-up"<BR>>>for the purpose of making something=20
un-intelligible.. <BR>><BR>>Not in the context of amateur =
digital=20
communications. There it is often<BR>>used in the way Hamish used=20
it:<BR></BODY></HTML>
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Content-Type: application/octet-stream;
name="vp.c"
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment;
filename="vp.c"
/*
* vp.c
*
* Voice Privacy
* Public Domain (p) 1990, S. R. Sampson
*
* Written for Turbo-C or Borland-C
*
* Notice it doesn't say "Secure Voice" :-)
*
* This program demonstrates scrambling of digitized voice input.
* It is designed to work with the Covox Audio Digitizer sound board
* as a validation tool. The algorithm used is the Time-Division
* Multiplex (TDM) method with an 8 kHz sample rate and 32 ms time
* segments. Producing 256 samples per segment. There are 8
* segments in a packet.
*
* The application to which this study is being performed, is that of
* a rural County Sheriff, who must travel a large territory, and doesn't
* always have access to a nearby phone. A cellular phone is one answer,
* but it can be easily monitored. This application would allow the
* Sheriff to use the dispatch radio. Currently an inversion scrambler is
* most often used, but this is very unsecure as well. The principle used
* in this design, is that the Sheriff would use it infrequently, and
* change the code on a daily basis. Most scanner listeners will think the
* scrambling method is more complex than it is, because the audio sounds
* very much like the Military Narrow Band Voice Scramblers.
*
* This is a "tactical" scrambler. That is, the breaking of the code would
* take longer than the operation being undertaken.
*/
#include <stdio.h>
#include <stdlib.h>
#include <dos.h>
#include <conio.h>
#define SAMPLE (short)(1193167L / 8000L) & 0x00FF
#define PORT 0x022F /* Hardware 8-bit input/output */
#define TCADRC 0x43 /* PC timer chip */
#define TCADRD 0x40
#define TCMODE 0x36
#define PPIADR 0x61
#define PPI0 0x48
void interrupt (far *oldvec)();
void init(void);
void breakout(void);
/*
* These are codes that would be enabled by a front panel
* thumbswitch. By using a different code each day, it would make
* analysis a little harder. Each of the 10 codes is different
* for different groups. The codes would be stored in EEPROM memory.
*/
static unsigned char codetable[11][8] = {
/* scrambled voice */
{ 7, 0, 2, 4, 1, 3, 5, 6},
{ 6, 2, 5, 0, 7, 3, 4, 1},
{ 1, 7, 4, 5, 3, 6, 2, 0},
{ 4, 3, 1, 2, 6, 7, 5, 0}, /* These are the segments */
{ 2, 0, 5, 6, 4, 1, 3, 7}, /* that are moved around */
{ 7, 5, 3, 0, 2, 6, 4, 1},
{ 4, 5, 3, 6, 1, 2, 0, 7},
{ 3, 0, 4, 6, 7, 2, 5, 1},
{ 5, 7, 2, 6, 4, 3, 1, 0},
{ 6, 3, 2, 1, 4, 0, 5, 7},
/* clear voice */
{ 0, 1, 2, 3, 4, 5, 6, 7}
};
static unsigned kkey[8]; /* scrambled table */
static unsigned ckey[8]; /* clear table */
static unsigned char samples[4096]; /* the working packet frames. input */
/* to the second half, take from */
/* the first half, then vice versa */
/*
* Interrupt routine to sample Digitizer Board
* This routine runs every 125 usec. It must be quick.
*/
void interrupt timer()
{
static unsigned char Segment = 0;
static unsigned char Counter = 0;
static int Delay = 2048;
static int NoDelay = 0;
int Temp, t1, t2;
/* Get input sample into random delayed position */
t1 = kkey[Segment] + Counter;
t2 = ckey[Segment] + Counter;
samples[t1 + Delay] = inportb(PORT);
outportb(PORT, samples[t2 + NoDelay]);
/* 8 Segments of 256 byte samples */
/* Note: Unsigned Characters roll over from 255 to 0 */
if (++Counter == 0) {
if (++Segment == 8) {
Segment = 0;
Temp = Delay;
Delay = NoDelay;
NoDelay = Temp;
}
}
/* reset interrupt timer */
outportb(0x20, 0x20);
}
void init(void)
{
/* get vector of current timer interrupt */
oldvec = getvect(8);
/* mask timer interrupt */
disable();
outportb(0x21, (1 | inportb(0x21)));
/* local timer interrupt routine */
setvect(8, timer);
/* rev up timer */
outportb(TCADRC, TCMODE);
outportb(TCADRD, SAMPLERATE); /* 8 kHz */
outportb(TCADRD, 0); /* 8 bit numbers */
/* unmask timer interrupt */
outportb(0x21, 0xFE & inportb(0x21));
enable();
}
void breakout(void)
{
/*
* Quit, restore computer to default setup
*/
/* mask timer interrupt */
disable(); /* disable interrupts */
outportb(0x21, (1 | inportb(0x21)));
outportb(TCADRC, TCMODE);
outportb(TCADRD, 0);
outportb(TCADRD, 0); /* divide by normal 65536 again */
setvect(8, oldvec); /* Reset original interrupt vector */
/* unmask timer interrupt */
outportb(0x21, (0xFE & inportb(0x21)));
outportb(PPIADR, PPI0);
enable(); /* enable interrupts */
exit(0);
}
void main(int argc, char **argv)
{
register short rn, i;
if (argc != 2) {
puts("Usage: scramble [0 - 10]\n");
exit(1);
}
rn = atoi(argv[1]);
if ((rn > 10) || (rn < 0)) {
puts("Code key is 0 to 9, 10 for Clear Voice\n");
exit(1);
}
for (i = 0; i < 2048; i++)
samples[i] = 0;
/*
* Get 8 code key numbers into the scramble table.
* (8 factorial permutations, 40,320)
*/
for (i = 0; i < 8; i++) {
kkey[i] = codetable[rn][i] * 256;
ckey[i] = codetable[10][i] * 256;
}
init();
/* process the interrupts. Break out with any key */
while (!kbhit())
;
breakout();
}
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>.
------------------------------
End of Ham-Digital Digest V2000 #3
******************************
Both my XYL and myself wish you a very
happy and prosperous New Year. Adam PA2AGA.
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