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/* $OpenBSD: key.c,v 1.98 2011/10/18 04:58:26 djm Exp $ */
/*
* Copyright (c) 2000, 2001 Markus Friedl. All rights reserved.
* Copyright (c) 2008 Alexander von Gernler. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "gnutls_int.h"
#include "errors.h"
#include "randomart.h"
/*
* 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.
*/
/*
* Field sizes for the random art. Have to be odd, so the starting point
* can be in the exact middle of the picture, and FLDBASE should be >=8 .
* Else pictures would be too dense, and drawing the frame would
* fail, too, because the key type would not fit in anymore.
*/
#define FLDBASE 8
#define FLDSIZE_Y (FLDBASE + 1)
#define FLDSIZE_X (FLDBASE * 2 + 1)
char *_gnutls_key_fingerprint_randomart(uint8_t *dgst_raw,
unsigned int dgst_raw_len,
const char *key_type,
unsigned int key_size,
const char *prefix)
{
/*
* Chars to be used after each other every time the worm
* intersects with itself. Matter of taste.
*/
const char augmentation_string[] = " .o+=*BOX@%&#/^SE";
char *retval, *p;
uint8_t field[FLDSIZE_X][FLDSIZE_Y];
char size_txt[16];
unsigned int i, b;
int x, y;
const size_t len = sizeof(augmentation_string) - 2;
unsigned int prefix_len = 0;
if (prefix)
prefix_len = strlen(prefix);
retval = gnutls_calloc(1,
(FLDSIZE_X + 3 + prefix_len) * (FLDSIZE_Y + 2));
if (retval == NULL) {
gnutls_assert();
return NULL;
}
/* initialize field */
memset(field, 0, FLDSIZE_X * FLDSIZE_Y * sizeof(char));
x = FLDSIZE_X / 2;
y = FLDSIZE_Y / 2;
/* 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 */
if (field[x][y] < len - 2)
field[x][y]++;
input = input >> 2;
}
}
/* mark starting point and end point */
field[FLDSIZE_X / 2][FLDSIZE_Y / 2] = len - 1;
field[x][y] = len;
if (key_size > 0)
snprintf(size_txt, sizeof(size_txt), " %4u", key_size);
else
size_txt[0] = 0;
/* fill in retval */
if (prefix_len)
snprintf(retval, FLDSIZE_X + prefix_len, "%s+--[%4s%s]", prefix,
key_type, size_txt);
else
snprintf(retval, FLDSIZE_X, "+--[%4s%s]", key_type, size_txt);
p = strchr(retval, '\0');
/* output upper border */
for (i = p - retval - 1; i < FLDSIZE_X + prefix_len; i++)
*p++ = '-';
*p++ = '+';
*p++ = '\n';
if (prefix_len) {
memcpy(p, prefix, prefix_len);
p += prefix_len;
}
/* output content */
for (y = 0; y < FLDSIZE_Y; y++) {
*p++ = '|';
for (x = 0; x < FLDSIZE_X; x++)
*p++ = augmentation_string[MIN(field[x][y], len)];
*p++ = '|';
*p++ = '\n';
if (prefix_len) {
memcpy(p, prefix, prefix_len);
p += prefix_len;
}
}
/* output lower border */
*p++ = '+';
for (i = 0; i < FLDSIZE_X; i++)
*p++ = '-';
*p++ = '+';
return retval;
}
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