Embedding information in random bit sequences while maintaining certified randomness

Jim Cheetham jim at gonzul.net
Wed Sep 15 05:41:40 BST 2021

> Anybody else ever get an errno 28 (no space left on device) when trying
to post? I made a custom SIRDS for the list but if I attach it I always get
errno 28. Oh well...

I have concerns for the platform that our discussion group is on; your
error is hopefully a relatively simple back-end operational problem that
I've now notified the owner of; but more fundamentally the whole software
stack was written in Python2 and there is no route forwards for it ... :-(

I'll be switching to a simpler mailman replacement sometime soon I think.
It just takes some external interrupt to get this done!

The stereogram is misleading in a "random" context - given the two images
of the simple example there absolutely is a deterministic relationship
between them :-) even where the original left base-image may well have been
randomly populated. Once you start to stitch the images together to
generate the single image variation, there's a horizontal repeat that must
be based on the expected distance of the eyes from the image when being

All you'd have to do would be to grab the top line of pixels and look for
repeats. Start with a split into two pieces (for a simple stereogram), and
then three, four etc. (actually a success for 4 pieces would actually be
picked up by the two pieces test, so we can exclude multiples and stick to
primes only). Keep on checking until you're down close to 2 pixels I guess.

So from that perspective, it should be easy to detect an autostereogram by
testing only a very small chunk of data ...

(I also use the same stereogram eye convergence trick on
spot-the-difference images that are side-to-side, which works very well)
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