initial commit

libpcp/randomart.c

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+/*
+ * Draw an ASCII-Art representing the fingerprint so human brain can
+ * profit from its built-in pattern recognition ability.
+ * This technique is called "random art" and can be found in some
+ * scientific publications like this original paper:
+ *
+ * "Hash Visualization: a New Technique to improve Real-World Security",
+ * Perrig A. and Song D., 1999, International Workshop on Cryptographic
+ * Techniques and E-Commerce (CrypTEC '99)
+ * sparrow.ece.cmu.edu/~adrian/projects/validation/validation.pdf
+ *
+ * The subject came up in a talk by Dan Kaminsky, too.
+ *
+ * If you see the picture is different, the key is different.
+ * If the picture looks the same, you still know nothing.
+ *
+ * The algorithm used here is a worm crawling over a discrete plane,
+ * leaving a trace (augmenting the field) everywhere it goes.
+ * Movement is taken from dgst_raw 2bit-wise.  Bumping into walls
+ * makes the respective movement vector be ignored for this turn.
+ * Graphs are not unambiguous, because circles in graphs can be
+ * walked in either direction.
+ */
+
+#include "randomart.h"
+
+#define	FLDSIZE_Y	8
+#define	FLDSIZE_X	FLDSIZE_Y * 2
+
+char *key_fingerprint_randomart(unsigned char *dgst_raw, unsigned int dgst_raw_len)
+{
+	/*
+	 * Chars to be used after each other every time the worm
+	 * intersects with itself.  Matter of taste.
+	 */
+	char	*augmentation_string = " .o+=*BOX@%&#/^";
+	char	*retval, *p;
+	char	 field[FLDSIZE_X][FLDSIZE_Y];
+	unsigned int	 i, b;
+	int	 x, y;
+
+	retval = ucmalloc((FLDSIZE_X + 3) * (FLDSIZE_Y + 2));
+
+	/* initialize field */
+	memset(field, ' ', FLDSIZE_X * FLDSIZE_Y * sizeof(char));
+	x = FLDSIZE_X / 2;
+	y = FLDSIZE_Y / 2;
+	field[x][y] = '.';
+
+	/* process raw key */
+	for (i = 0; i < dgst_raw_len; i++) {
+		int input;
+		/* each byte conveys four 2-bit move commands */
+		input = dgst_raw[i];
+		for (b = 0; b < 4; b++) {
+			/* evaluate 2 bit, rest is shifted later */
+			x += (input & 0x1) ? 1 : -1;
+			y += (input & 0x2) ? 1 : -1;
+
+			/* assure we are still in bounds */
+			x = MAX(x, 0);
+			y = MAX(y, 0);
+			x = MIN(x, FLDSIZE_X - 1);
+			y = MIN(y, FLDSIZE_Y - 1);
+
+			/* augment the field */
+			p = strchr(augmentation_string, field[x][y]);
+			if (*++p != '\0')
+				field[x][y] = *p;
+
+			input = input >> 2;
+		}
+	}
+
+	/* fill in retval */
+	p = retval;
+
+	/* output upper border */
+	*p++ = '+';
+	for (i = 0; i < FLDSIZE_X; i++)
+		*p++ = '-';
+	*p++ = '+';
+	*p++ = '\n';
+
+	/* output content */
+	for (y = 0; y < FLDSIZE_Y; y++) {
+		*p++ = '|';
+		for (x = 0; x < FLDSIZE_X; x++)
+			*p++ = field[x][y];
+		*p++ = '|';
+		*p++ = '\n';
+	}
+
+	/* output lower border */
+	*p++ = '+';
+	for (i = 0; i < FLDSIZE_X; i++)
+		*p++ = '-';
+	*p++ = '+';
+
+	return retval;
+}