Prerequisites & Notation

Before You Begin

This chapter introduces secrecy — defending against an external eavesdropper during delivery — as distinct from the demand-privacy model of Chapter 12. Prerequisites: MAN basics, information- theoretic secrecy, and Shamir secret sharing.

MAN coded caching (Ch 2)(Review ch02)
Self-check: Can you state the MAN rate and cache placement?
Demand privacy (Ch 12)(Review ch12)
Self-check: What is the Wan-Caire demand-privacy model?
Information-theoretic secrecy / wiretap channels(Review ch20)
Self-check: What is the secrecy capacity of the Wyner wiretap channel?
Shamir secret sharing
Self-check: How does a $(t, n)$ -threshold secret sharing work?
One-time pad cryptography
Self-check: What is the key-size requirement for perfect secrecy via OTP?

Notation for This Chapter

Symbols for secure delivery and secrecy in coded caching.

Symbol	Meaning	Introduced
$\mathcal{E}$	External eavesdropper observing the broadcast	s01
$Y_\mathcal{E}$	Eavesdropper's observation of the delivery message $X$	s01
$R_\text{sec}$	Secure delivery rate (files per channel use)	s02
$M_\text{sec}$	Minimum cache size for secure delivery (typically $\geq 1$ )	s02
$\mathcal{K}_k$	Secret key material at user $k$ (shared randomness)	s03
$(t, n)$	Shamir threshold scheme parameters	s03
$I(\cdot; \cdot)$	Mutual information (measuring leakage)	s01

← Ch 16 Security Model: Eavesdropper on the Broadcast