`Guess', a Mastermind clone from James Harvey. This checkin also

introduces a few new utility functions in misc.c, one of which is
the bitmap obfuscator from Mines (which has therefore been moved out
of mines.c).

[originally from svn r5992]

1 files changed, 0 insertions, 106 deletions

diff --git a/mines.c b/mines.c
index 388a7d5..6895b2e 100644
--- a/mines.c
+++ b/mines.c
@@ -1828,112 +1828,6 @@ static char *minegen(int w, int h, int n, int x, int y, int unique,
     return ret;
 }
 
-/*
- * The Mines game descriptions contain the location of every mine,
- * and can therefore be used to cheat.
- * 
- * It would be pointless to attempt to _prevent_ this form of
- * cheating by encrypting the description, since Mines is
- * open-source so anyone can find out the encryption key. However,
- * I think it is worth doing a bit of gentle obfuscation to prevent
- * _accidental_ spoilers: if you happened to note that the game ID
- * starts with an F, for example, you might be unable to put the
- * knowledge of those mines out of your mind while playing. So,
- * just as discussions of film endings are rot13ed to avoid
- * spoiling it for people who don't want to be told, we apply a
- * keyless, reversible, but visually completely obfuscatory masking
- * function to the mine bitmap.
- */
-static void obfuscate_bitmap(unsigned char *bmp, int bits, int decode)
-{
-    int bytes, firsthalf, secondhalf;
-    struct step {
-	unsigned char *seedstart;
-	int seedlen;
-	unsigned char *targetstart;
-	int targetlen;
-    } steps[2];
-    int i, j;
-
-    /*
-     * My obfuscation algorithm is similar in concept to the OAEP
-     * encoding used in some forms of RSA. Here's a specification
-     * of it:
-     * 
-     * 	+ We have a `masking function' which constructs a stream of
-     * 	  pseudorandom bytes from a seed of some number of input
-     * 	  bytes.
-     * 
-     * 	+ We pad out our input bit stream to a whole number of
-     * 	  bytes by adding up to 7 zero bits on the end. (In fact
-     * 	  the bitmap passed as input to this function will already
-     * 	  have had this done in practice.)
-     * 
-     * 	+ We divide the _byte_ stream exactly in half, rounding the
-     * 	  half-way position _down_. So an 81-bit input string, for
-     * 	  example, rounds up to 88 bits or 11 bytes, and then
-     * 	  dividing by two gives 5 bytes in the first half and 6 in
-     * 	  the second half.
-     * 
-     * 	+ We generate a mask from the second half of the bytes, and
-     * 	  XOR it over the first half.
-     * 
-     * 	+ We generate a mask from the (encoded) first half of the
-     * 	  bytes, and XOR it over the second half. Any null bits at
-     * 	  the end which were added as padding are cleared back to
-     * 	  zero even if this operation would have made them nonzero.
-     * 
-     * To de-obfuscate, the steps are precisely the same except
-     * that the final two are reversed.
-     * 
-     * Finally, our masking function. Given an input seed string of
-     * bytes, the output mask consists of concatenating the SHA-1
-     * hashes of the seed string and successive decimal integers,
-     * starting from 0.
-     */
-
-    bytes = (bits + 7) / 8;
-    firsthalf = bytes / 2;
-    secondhalf = bytes - firsthalf;
-
-    steps[decode ? 1 : 0].seedstart = bmp + firsthalf;
-    steps[decode ? 1 : 0].seedlen = secondhalf;
-    steps[decode ? 1 : 0].targetstart = bmp;
-    steps[decode ? 1 : 0].targetlen = firsthalf;
-
-    steps[decode ? 0 : 1].seedstart = bmp;
-    steps[decode ? 0 : 1].seedlen = firsthalf;
-    steps[decode ? 0 : 1].targetstart = bmp + firsthalf;
-    steps[decode ? 0 : 1].targetlen = secondhalf;
-
-    for (i = 0; i < 2; i++) {
-	SHA_State base, final;
-	unsigned char digest[20];
-	char numberbuf[80];
-	int digestpos = 20, counter = 0;
-
-	SHA_Init(&base);
-	SHA_Bytes(&base, steps[i].seedstart, steps[i].seedlen);
-
-	for (j = 0; j < steps[i].targetlen; j++) {
-	    if (digestpos >= 20) {
-		sprintf(numberbuf, "%d", counter++);
-		final = base;
-		SHA_Bytes(&final, numberbuf, strlen(numberbuf));
-		SHA_Final(&final, digest);
-		digestpos = 0;
-	    }
-	    steps[i].targetstart[j] ^= digest[digestpos++];
-	}
-
-	/*
-	 * Mask off the pad bits in the final byte after both steps.
-	 */
-	if (bits % 8)
-	    bmp[bits / 8] &= 0xFF & (0xFF00 >> (bits % 8));
-    }
-}
-
 static char *describe_layout(char *grid, int area, int x, int y,
                              int obfuscate)
 {