You can fix your example by using `salt || MD5(grade || salt || secret)` as the code on the lockers.

`salt` is just a random value which makes sure that every hash will be different.

`secret` is a secret value which only teachers know. This prevents that students can just try every grade and compare hashes.

With `||` I mean concatenation.

This may be too complicated for 8 graders now though.



If you have any suggestions I would appreciate another analogy

02fa90fd41

bitcoin

I have been asked to ELI5 cryptographic hashes to kids (grade 8).. Is this ok?

Ah, okay, now I see.

However, two things:

1. Any student with the same grade will have the same hash

2. A smart child may realize they can just put every grade into the Hasher machine and compare the hashes. This assumes that the Hasher machine is publicly accessible (which should be the case if you want to have a good analogy to hash functions).

Because of this, I would say this example is not a good use case for hashing, to be honest.
Non-deterministic encryption with a secret key should be used here. 