>  is critical understanding why public-private key pair cryptography works

Kinda sorta... the thing is, few use RSA anymore exactly because factoring is too easy. It's all elliptic curves nowadays which do not require any secret prime numbers. 

Yes. I was tired and misread it. They'll definitely understand that factoring primes is a lot harder than multiplying them. I think this aspect is critical understanding why public-private key pair cryptography works, rather than just stating "these are the pieces and what they look like in action".

DiracDelta

Wait... Grade 8 in the UK is 13/14 year old. 

02fa90fd41

bitcoin

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

8 year olds know basic arithmetic. You can explain the notion of multiplication being easier than factoring without getting into any discussion of field theory.

You can even time them on multiplication vs factoring to show the challenge of brute force.