With Elliptic Curves, we can compute the order of any point (and, in particular, the point $nP$; this is especially easy on the curves we actually use for ECC, because those curves typically have an order $hq$, for a small $h$ and a large prime $q$ (and the order of any point is a divisor of $hq$).
So, if $q$ is the order of the point $nP$, and if $n$ is ...
There is the idea of a fuzzy vault, a coding theory based idea first proposed by Juels,
developed for biometric applications, it warrants a look.
Start at Wikipedia. These notes below are excellent:
Actually, lecturers/professors build simplified version of block ciphers and hash functions so that the students can understand better.
For Block ciphers there are;
Simplified DES by Edward Schaefer in 96. You can also set it in Stinson's book Appendix G.
Simplified AES is first appeared on Cryptologia, 2003 by Musa, Schaefer, and Wedig.