Extra: Encryption and Signing

[bhuvy2]

Is your feature request related to a problem? Please describe.
Most students coming in have a vague idea of encryption and signing, but we should introduce them to the bare minimum in the book.

Describe the solution you'd like

• Talk about Symmetric and Asymmetric Cryptography in the Abstract
• Diffie Helman Key Exchange? May be too advanced
• Talk about GnuPG to manage keys
• Talk about Encryption, its benefits and drawbacks
• Talk about Signing, its benefits and drawbacks

Describe alternatives you've considered
Nope

Additional context
Nope