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