Timing attack
Power analysis (DPA)
A "server" compares your guess against a hidden secret with the age-old naive comparison: byte by byte, bailing out on the first mismatch. The time it takes — here counted in operations, never a real clock — leaks how many characters you got right, without ever saying whether you got the whole secret.
The hardware thread:the transistor and the CMOS inverterthe clock path and its delayhow that same delay — and that same power draw — turn into an information leak (you are here)