Easy to remember fingerprints for data?

Question

I need to create fingerprints for RSA keys that users can memorize or at least easily recognize. The following ideas have come to mind:

• Break the SHA1 hash into portions of, say 4 bits and use them as coordinates for Bezier splines. Draw the splines and use that picture as a fingerprint.
• Use the SHA1 hash as input for some fractal algorithm. The result would need to be unique for a given input, i.e. the output can't be a solid square half the time.
• Map the SHA1 hash to entries in a word list (as used in spell checkers or password lists). This would create a passphrase consisting of real words.
• Instead of a word list, use some other large data set like Google maps (map the SHA1 hash to map coordinates and use the map region(s) as a fingerprint)

Any other ideas? I'm sure this has been implemented in one form or another.

Answer 1

OpenSSH contains something like that, under the name "visual host key". Try this:

ssh -o VisualHostKey=yes somesshhost

where somesshhost is some machine with a SSH server running. It will print out a "fingerprint" of the server key, both in hexadecimal, and as an ASCII-art image which may look like this:

+--[ RSA 2048]----+
|   .+            |
|   + o           |
|  o o +          |
|   + o +         |
|  . o E S        |
|   + * .         |
|    X o .        |
|   . * o         |
|   .o .          |
+-----------------+

or like this:

+--[ RSA 1024]----+
|        .*BB+    |
|       . .++o    |
|        = oo.    |
|       . =o+..   |
|        So+..    |
|        ..E.     |
|                 |
|                 |
|                 |
+-----------------+

Apparently, this is inspired from techniques described in this article. OpenSSH is opensource, with a BSD-like license, so chances are that you could simply reuse their code (it seems to be in the key.c file, function key_fingerprint_randomart()).

Answer 2

I found something called random art which generates an image from a hash. There is a Python implementation available for download: http://www.random-art.org/about/

There is also a paper about using random art for authentication: http://sparrow.ece.cmu.edu/~adrian/projects/validation/validation.pdf

It's from 1999; I don't know if further research has been done on this.