Constant-Time Data Processing & QUIC Privacy

NCC Group Cryptography Services analyzed QUIC implementations and found recurrent timing side channels caused by processing data that begins at a secret offset (e.g., variable-length QUIC packet numbers). The report explains the leakage risk (revealing packet number length and inferred payload size), presents constant-time primitives and full proof-of-concept code in Rust and Common Lisp to extract/process data at secret offsets without branching, and discusses practical costs, limitations, and deployment considerations for maintaining constant-time behavior.