Another possibility: timestamps. For convenience, split the 40-character hash into four parts, convert each part into an integer, and use it as a unix millis value. The first hash given in the example, f7f05111ddb22b58fdad8bee63a3cd2bcea43398, becomes<p><pre><code> 2003-09-30 02:26:06.941
1994-04-01 20:17:11.085
1989-01-17 00:26:01.549
1975-12-18 16:01:01.336</code></pre>