Exercise 1: Why a Co-Located Key Repeats Chapter 3's Own Mistake — Possible Solution ==================================================================== WHAT CHAPTER 3 ORIGINALLY ESTABLISHED ------------------------------ Per Chapter 3, "a backup stored right next to what it protects only guards against one specific kind of disaster ... it does nothing against a disaster that reaches both at once." A copy sitting beside the original only protects against the original being individually lost - not against anything capable of reaching both locations at once. WHY A CO-LOCATED KEY FAILS FOR THE IDENTICAL REASON ------------------------------ Per this chapter, "a key stored alongside the data it protects doesn't provide real protection, since anything that reaches the backup also reaches the key sitting right next to it." If an attacker (or a disaster) gains access to the backup's storage location, and the decryption key is stored in that same location, the attacker gains both the encrypted data and the means to decrypt it in a single step - the encryption provides no actual barrier at all, because whatever defeated the storage location's protection also delivered the key. WHY THIS IS THE SAME STRUCTURAL MISTAKE, JUST APPLIED TO A DIFFERENT OBJECT ------------------------------ Chapter 3's version: a data copy next to the original data provides no protection against whatever reaches both. This chapter's version: a key next to the data it decrypts provides no protection against whatever reaches both. In both cases, the failure isn't in the object itself (the backup copy, or the encryption) - it's in placing a supposed safeguard within reach of the exact threat it's meant to defend against. WHY RECOGNIZING THIS AS THE SAME PRINCIPLE MATTERS ------------------------------ Understanding this as one general rule - "a safeguard co-located with what it protects isn't a real safeguard" - rather than two unrelated facts to memorize, makes it possible to recognize the same mistake in other forms elsewhere (as this chapter does again later with backup deletion permissions on a broadly-trusted admin account). WHY THIS WORKS AS AN ANSWER ------------------------------ It restates Chapter 3's original reasoning about co-located backups, shows the parallel reasoning this chapter applies to encryption keys, and explains why both are the same underlying structural mistake rather than two separate, coincidentally similar rules.