[manwe150]

Recent timing attacks rely on the observation that modern CPUs send some messages faster than other messages, based on predicting what they might contain, so some delays get magnified (those that deviate from expectations) while other delays (those that match prior data) get minimized as you go down. An encrypted payload leaks this same information too (the process is independent of what data is being transferred), although that leaked information is (hopefully) not useful since it just leaks the encrypted data, which (hopefully) looks like random noise. But that data has to be encrypted and decrypted at some point somewhere, which gives a point to attack.