> 3. For some historical reasons, many people feel the need to change keys regularly. This is rather misguided: key rotation makes sense in an army or spy network where there are many keys, and partial compromissions are the normal and expected situation, so a spy network must, by necessity, be in permanent self-cleansing recovery mode; when there is a single key and the normal situation is that the key is NOT compromised, changing it brings no tangible advantage.

This is a really strange advice from Thomas Pornin. People rotate keys because not doing so weakens most symmetric encryption schemes. For example while using AES-GCM with 96-bit nonces one needs to rotate keys after encrypting roughly 2^32 ~ 4 billion messages; otherwise the IV collision probability will be higher than 2^(-32), which is already high enough in most large scale systems (and really bad things happen when the IV is repeated).