We all know the ASCII randomart generated by ssh-keygen when creating or validating ssh public keys.

We also know you can generate hashes of any file with sha1sum or md5sum.

But, is it possible to generate randomart "ssh-keygen-style" from any file that is not a public ssh key?

That would be a funnier way of visually comparing the checksum of two files.

2 Answers

You can generate random art of any file with this little C program made by nirejan:

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#define XLIM 17
#define YLIM 9
#define ARSZ (XLIM * YLIM)
#define DEBUG 0
static uint16_t array[ARSZ];
const char symbols[] = { ' ', '.', 'o', '+', '=', '*', 'B', 'O', 'X', '@', '%', '&', '#', '/', '^', 'S', 'E'
};
void print_graph(void)
{ uint8_t i; uint8_t j; uint16_t temp; printf("+--[ RandomArt ]--+\n"); for (i = 0; i < YLIM; i++) { printf("|"); for (j = 0; j < XLIM; j++) { temp = array[j + XLIM * i]; printf("%c", symbols[temp]); } printf("|\n"); } printf("+-----------------+\n");
}
static char string[256];
static int ishex (char c)
{ if ((c >= '0' && c <= '9') || (c >= 'A' && c <= 'F') || (c >= 'a' && c <= 'f')) { return 1; } return 0;
}
/* * The hexval function expects a hexadecimal character in the range * [0-9], [A-F] or [a-f]. Passing any other character will result in * undefined behaviour. Make sure you validate the character first. */
static uint8_t hexval (char c)
{ if (c <= '9') { return (c - '0'); } else if (c <= 'F') { return (c - 'A' + 10); } else if (c <= 'f') { return (c - 'a' + 10); } return 0;
}
int convert_string(char *arg)
{ uint16_t i; char c; i = 0; while (*arg && i < 255) { c = *arg; if (!ishex(c)) { printf("Unrecognized character '%c'\n", c); return 1; } arg++; string[i] = hexval(c) << 4; if (!*arg) { printf("Odd number of characters\n"); return 1; } c = *arg; if (!ishex(c)) { printf("Unrecognized character '%c'\n", c); return 1; } arg++; string[i] |= hexval(c); i++; } // Add the terminating null byte string[i] = '\0'; return 0;
}
uint8_t new_position(uint8_t *pos, uint8_t direction)
{ uint8_t newpos; uint8_t upd = 1; int8_t x0; int8_t y0; int8_t x1; int8_t y1; x0 = *pos % XLIM; y0 = *pos / XLIM; #if DEBUG printf("At position (%2d, %2d)... ", x0, y0); #endif switch (direction) { case 0: // NW #if DEBUG printf("Moving NW... "); #endif x1 = x0 - 1; y1 = y0 - 1; break; case 1: // NE #if DEBUG printf("Moving NE... "); #endif x1 = x0 + 1; y1 = y0 - 1; break; case 2: // SW #if DEBUG printf("Moving SW... "); #endif x1 = x0 - 1; y1 = y0 + 1; break; case 3: // SE #if DEBUG printf("Moving SE... "); #endif x1 = x0 + 1; y1 = y0 + 1; break; default: // Should never happen #if DEBUG printf("INVALID DIRECTION %d!!!", direction); #endif x1 = x0; y1 = y0; break; } // Limit the range of x1 & y1 if (x1 < 0) { x1 = 0; } else if (x1 >= XLIM) { x1 = XLIM - 1; } if (y1 < 0) { y1 = 0; } else if (y1 >= YLIM) { y1 = YLIM - 1; } newpos = y1 * XLIM + x1; #if DEBUG printf("New position (%2d, %2d)... ", x1, y1); #endif if (newpos == *pos) { #if DEBUG printf("NO CHANGE"); #endif upd = 0; } else { *pos = newpos; } #if DEBUG printf("\n"); #endif return upd;
}
void drunken_walk(void)
{ uint8_t pos; uint8_t upd; uint16_t idx; uint8_t i; uint8_t temp; pos = 76; for (idx = 0; string[idx]; idx++) { temp = string[idx]; #if DEBUG printf("Walking character index %d ('%02x')...\n", idx, temp); #endif for (i = 0; i < 4; i++) { upd = new_position(&pos, temp & 3); if (upd) { array[pos]++; } temp >>= 2; } } array[pos] = 16; // End array[76] = 15; // Start
}
int main(int argc, char *argv[])
{ if (argc != 2) { printf("Usage: bishop <hex string>\n"); return 1; } if (convert_string(argv[1])) { printf("String conversion failed!\n"); return 1; } drunken_walk(); print_graph(); return 0;
}

---

To use it, follow these steps:

1. Put the source code in a file:
   • Open gedit or your favorite text editor.
   • Paste the above source code.
   • Save it as bishop.c.
2. Compile the code running gcc bishop.c -o bishop.

3. View the random art of any file (where myfile is the file):

   ./bishop $(sha512sum myfile | cut -f1 -d ' ')

4. Create a custom script to view the random art of any file:

   • Create the local binaries folder if doesn't exists:

     sudo mkdir -p /usr/local/bin

   • Create a file on that folder with the script:

     sudo touch /usr/local/bin/randomart

   • Give permissions to the file:

     sudo chmod 777 /usr/local/bin/randomart

   • Run gedit /usr/local/bin/randomart to edit the file and paste this on it:

     #!/bin/bash
     bishop $(sha512sum "$@" | cut -f1 -d ' ')

   • Save the file.

   • Copy the program that we built on the previous step to the local binaries folder:

     sudo cp bishop /usr/local/bin/

   • Give run permission to the binary:

     sudo chmod a+x /usr/local/bin/bishop

5. Use the newly-created program running randomart myfile where myfile is the file.

1

The page OpenSSH Keys and The Drunken Bishop gives a good introduction to how the algorthm works.

The details of it can be found in
The drunken bishop: An analysis of the OpenSSH fingerprint visualization algorithm.

The topic is discussed in a more general form in the 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)".

2

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