From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Fri, 27 Jan 2012 23:11:34 +0000 (-0800)
Subject: cochran: do a partial header de-scramble
X-Git-Url: http://git.tdb.fi/?p=ext%2Fsubsurface.git;a=commitdiff_plain;h=1a66a74e8a35c1fd85060060ba61bb1b67d6eb44

cochran: do a partial header de-scramble

This descrambles at least parts of the header data.  Some of it has the
same pattern of data 4kB apart, it may be that there is a dive hiding in
there too (ie what I currently call a "header" may in fact be a header
_plus_ a dive).

But the 4kB thing may well be an artifact of the crazy scrambling code
itself.  Who knows what kind of chunking the Cochran Analyst
"encryption" uses.

As with the dive data, there seems to be some offset differences between
different CAN files.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/cochran.c b/cochran.c
index e5beea9..650a479 100644
--- a/cochran.c
+++ b/cochran.c
@@ -79,7 +79,7 @@ static int figure_out_modulus(const unsigned char *decode, const unsigned char *
 
 #define hexchar(n) ("0123456789abcdef"[(n)&15])
 
-static void show_line(unsigned offset, const unsigned char *data, unsigned size)
+static int show_line(unsigned offset, const unsigned char *data, unsigned size, int show_empty)
 {
 	unsigned char bits;
 	int i, off;
@@ -105,18 +105,51 @@ static void show_line(unsigned offset, const unsigned char *data, unsigned size)
 		asc[1] = 0;
 	}
 
-	if (bits)
+	if (bits) {
 		puts(buffer);
+		return 1;
+	}
+	if (show_empty)
+		puts("...");
+	return 0;
 }
 
-static void cochran_debug_write(const char *filename, int dive, const unsigned char *data, unsigned size)
+static void cochran_debug_write(const char *filename, const unsigned char *data, unsigned size)
 {
-	int i;
-	printf("\n%s, dive %d\n\n", filename, dive);
+	int i, show = 1;
 
-	for (i = 0; i < size; i += 16) {
-		show_line(i, data + i, size - i);
-	}
+	for (i = 0; i < size; i += 16)
+		show = show_line(i, data + i, size - i, show);
+}
+
+static void parse_cochran_header(const char *filename,
+		const unsigned char *decode, unsigned mod,
+		const unsigned char *in, unsigned size)
+{
+	char *buf = malloc(size);
+
+	/* Do the "null decode" using a one-byte decode array of '\0' */
+	partial_decode(0    , 0x0b14, "", 0, 1, in, size, buf);
+
+	/*
+	 * The header scrambling is different form the dive
+	 * scrambling. Oh yay!
+	 */
+#if 0 // Alex
+	partial_decode(0x058c, 0x0b14, decode, 0, mod, in, size, buf);
+#else // Don
+	partial_decode(0x05a0, 0x0b14, decode, 0, mod, in, size, buf);
+#endif
+	partial_decode(0x0b14, 0x1b14, decode, 0, mod, in, size, buf);
+	partial_decode(0x1b14, 0x2b14, decode, 0, mod, in, size, buf);
+	partial_decode(0x2b14, 0x3b14, decode, 0, mod, in, size, buf);
+	partial_decode(0x3b14, 0x5414, decode, 0, mod, in, size, buf);
+	partial_decode(0x5414,   size, decode, 0, mod, in, size, buf);
+
+	printf("\n%s, header\n\n", filename);
+	cochran_debug_write(filename, buf, size);
+
+	free(buf);
 }
 
 static void parse_cochran_dive(const char *filename, int dive,
@@ -150,7 +183,8 @@ static void parse_cochran_dive(const char *filename, int dive,
 	partial_decode(0x4a14, 0xc9bd, decode, 0, mod, in, size, buf);
 	partial_decode(0xc9bd,   size, decode, 0, mod, in, size, buf);
 
-	cochran_debug_write(filename, dive, buf, size);
+	printf("\n%s, dive %d\n\n", filename, dive);
+	cochran_debug_write(filename, buf, size);
 
 	free(buf);
 }
@@ -172,6 +206,8 @@ int try_to_open_cochran(const char *filename, struct memblock *mem, GError **err
 
 	mod = figure_out_modulus(decode, mem->buffer + dive1, dive2 - dive1);
 
+	parse_cochran_header(filename, decode, mod, mem->buffer + 0x40000, dive1 - 0x40000);
+
 	for (i = 0; i < 65534; i++) {
 		dive1 = offsets[i];
 		dive2 = offsets[i+1];
@@ -179,7 +215,7 @@ int try_to_open_cochran(const char *filename, struct memblock *mem, GError **err
 			break;
 		if (dive2 > mem->size)
 			break;
-		parse_cochran_dive(filename, i, decode, mod, mem->buffer + dive1, dive2 - dive1);
+		parse_cochran_dive(filename, i+1, decode, mod, mem->buffer + dive1, dive2 - dive1);
 	}
 
 	exit(0);