Regarding the Guest User Security update, I am following the guide here: https://www.learnexperiencecloud.com/s/article/Guest-User-Record-Access-Development-Best-Practices

The examples for moving DML statements to a without sharing class make a lot of sense, but I am struggling to understand the examples for the encryption/decryption concepts.

The guide makes a lot of assumptions regarding the developer's  understanding of encryption/decryption, and doesn't explain that part as much. My follow up questions after reading this:

1) Are there any other resources regarding the concept of " encryption / decryption " we could reference to understand better what the examples in the guide are doing?

2) Do I need to apply encryption/decryption to be compliant with the Guest User Security update, or is it just a best practice suggestion? I'm struggling to understand how the Guest User Security update necessitates encrypt/decrypt. 

The need to abstract DML statements to a without sharing class makes a lot of sense, but I am lacking context for the encryption/decryption requirement/recommendation.