Easy to remember fingerprints for data? - hash

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

For item 3 (entries in a word list), see RFC-1751 - A Convention for Human-Readable 128-bit Keys, which notes that
The authors of S/Key devised a system to make the 64-bit one-time
password easy for people to enter.
Their idea was to transform the password into a string of small
English words. English words are significantly easier for people to
both remember and type. The authors of S/Key started with a
dictionary of 2048 English words, ranging in length from one to four
characters. The space covered by a 64-bit key (2^64) could be covered
by six words from this dictionary (2^66) with room remaining for
parity. For example, an S/Key one-time password of hex value:
EB33 F77E E73D 4053
would become the following six English words:
TIDE ITCH SLOW REIN RULE MOT
You could also use a compound fingerprint to improve memorability, like english words followed (or preceeded) by one or more key-dependent images.
For generating the image, you could use things like Identicon, Wavatar, MonsterID, or RoboHash.
Example:
TIDE ITCH SLOW
REIN RULE MOT

Answer 3

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.

Answer 4

Your first suggestion (draw the path of splines for every four bytes, then fill using the nonzero fill rule) is exactly what I use for visualization in hashblot.