An LZ77 dictionary coder is a compression method that replaces repeated data with references to earlier text, or a sliding dictionary, instead of storing the same bytes again. It is efficient on structured or repetitive input, which is why it has long been used in general-purpose compression and in some secure protocols.
In cyber security, the risk is not the coder itself but the state it creates. If attacker-controlled data and secret data share the same compression context, the size of the compressed output can reveal patterns about the secret. That makes LZ77-style compression relevant to side-channel attacks, especially in multiplexed or interactive sessions. Defenders may disable compression, isolate contexts, or avoid sharing compression state across trust boundaries to reduce leakage.