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syster.c
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syster.c
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/* Nagravision Syster encoder for hacktv */
/*=======================================================================*/
/* Copyright 2018 Alex L. James */
/* Copyright 2018 Philip Heron <[email protected]> */
/* */
/* This program is free software: you can redistribute it and/or modify */
/* it under the terms of the GNU General Public License as published by */
/* the Free Software Foundation, either version 3 of the License, or */
/* (at your option) any later version. */
/* */
/* This program is distributed in the hope that it will be useful, */
/* but WITHOUT ANY WARRANTY; without even the implied warranty of */
/* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the */
/* GNU General Public License for more details. */
/* */
/* You should have received a copy of the GNU General Public License */
/* along with this program. If not, see <http://www.gnu.org/licenses/>. */
/* -=== Nagravision Syster encoder ===-
*
* These functions implement the image scrambler for Nagravision Syster.
* This system uses line shuffling to obscure the image.
*
* This does not yet produce any VBI line data so is not compatible
* with real hardware.
*
*/
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include "video.h"
/* The standard syster substitution table */
const static uint8_t _key_table[256] = {
10, 11, 12, 13, 16, 17, 18, 19, 13, 14, 15, 16, 0, 1, 2, 3,
21, 22, 23, 24, 18, 19, 20, 21, 23, 24, 25, 26, 26, 27, 28, 29,
19, 20, 21, 22, 11, 12, 13, 14, 28, 29, 30, 31, 4, 5, 6, 7,
22, 23, 24, 25, 5, 6, 7, 8, 31, 0, 1, 2, 27, 28, 29, 30,
3, 4, 5, 6, 8, 9, 10, 11, 14, 15, 16, 17, 25, 26, 27, 28,
15, 16, 17, 18, 7, 8, 9, 10, 17, 18, 19, 20, 29, 30, 31, 0,
24, 25, 26, 27, 20, 21, 22, 23, 1, 2, 3, 4, 6, 7, 8, 9,
12, 13, 14, 15, 9, 10, 11, 12, 2, 3, 4, 5, 30, 31, 0, 1,
24, 25, 26, 27, 2, 3, 4, 5, 31, 0, 1, 2, 7, 8, 9, 10,
13, 14, 15, 16, 26, 27, 28, 29, 14, 15, 16, 17, 18, 19, 20, 21,
22, 23, 24, 25, 5, 6, 7, 8, 19, 20, 21, 22, 12, 13, 14, 15,
17, 18, 19, 20, 27, 28, 29, 30, 10, 11, 12, 13, 11, 12, 13, 14,
6, 7, 8, 9, 1, 2, 3, 4, 0, 1, 2, 3, 4, 5, 6, 7,
3, 4, 5, 6, 8, 9, 10, 11, 15, 16, 17, 18, 23, 24, 25, 26,
29, 30, 31, 0, 25, 26, 27, 28, 9, 10, 11, 12, 21, 22, 23, 24,
20, 21, 22, 23, 30, 31, 0, 1, 16, 17, 18, 19, 28, 29, 30, 31
};
static void _update_field_order(ng_t *s)
{
int i, j;
int b[32];
/* This function generates the scrambled line order for the
* next field based on _key_table, s->s and s->r parameters.
*
* Based on work by Markus G. Kuhn from his publication
* 'Analysis of the Nagravision Video Scrambling Method', 1998-07-09
*/
for(i = 0; i < 32; i++)
{
b[i] = -32 + i;
}
for(i = 0; i < 287; i++)
{
j = i <= 254 ? _key_table[(s->r + (2 * s->s + 1) * i) & 0xFF] : i - 255;
b[j] = s->order[b[j] + 32] = i;
}
}
int ng_init(ng_t *s, vid_t *vid)
{
int i;
memset(s, 0, sizeof(ng_t));
s->vid = vid;
/* Initial seeds. Updated every field. */
s->s = 0;
s->r = 0;
_update_field_order(s);
/* Allocate memory for the delay */
s->delay = calloc(2 * vid->width * NG_DELAY_LINES, sizeof(int16_t));
if(!s->delay)
{
return(VID_OUT_OF_MEMORY);
}
/* Setup the delay line pointers */
for(i = 0; i < NG_DELAY_LINES; i++)
{
s->delay_line[i] = &s->delay[2 * vid->width * i];
}
return(VID_OK);
}
void ng_free(ng_t *s)
{
free(s->delay);
}
void ng_render_line(ng_t *s)
{
int j = 0;
int x, f, i;
int line;
int16_t *dline;
/* Calculate which line is about to be transmitted due to the delay */
line = s->vid->line - NG_DELAY_LINES;
if(line < 0) line += s->vid->conf.lines;
/* Calculate the field and field line */
f = (line < NG_FIELD_2_START ? 1 : 2);
i = line - (f == 1 ? NG_FIELD_1_START : NG_FIELD_2_START);
if(i >= 0 && i < NG_LINES_PER_FIELD)
{
/* Adjust for the decoder's 32 line delay */
i += 32;
if(i >= NG_LINES_PER_FIELD)
{
i -= NG_LINES_PER_FIELD;
f = (f == 1 ? 2 : 1);
}
/* Reinitialise the seeds if this is a new field */
if(i == 0)
{
s->s = rand() & 0x7F;
s->r = rand() & 0xFF;
_update_field_order(s);
}
/* Calculate which line in the delay buffer to copy image data from */
j = (f == 1 ? NG_FIELD_1_START : NG_FIELD_2_START) + s->order[i];
if(j < line) j += s->vid->conf.lines;
j -= line;
if(j < 0 || j >= NG_DELAY_LINES)
{
/* We should never get to this point */
fprintf(stderr, "*** Nagravision Syster scrambler is trying to read an invalid line ***\n");
j = 0;
}
}
/* Swap the active line with the oldest line in the delay buffer,
* with active video offset in j if necessary. */
for(x = 0; x < s->vid->width * 2; x += 2)
{
int16_t t = s->vid->output[x];
s->vid->output[x] = s->delay_line[x >= s->vid->active_left * 2 ? j : 0][x];
s->delay_line[0][x] = t;
}
/* Advance the delay buffer */
dline = s->delay_line[0];
for(x = 0; x < NG_DELAY_LINES - 1; x++)
{
s->delay_line[x] = s->delay_line[x + 1];
}
s->delay_line[x] = dline;
}