# Does a Feistel cipher structure have to be reversible? [duplicate]

• Sep 18, 2022 at 1:20
• TL;DR: the Feistel structure always yields a reversible transformation, regardless of if the round functions are reversible or not.
– fgrieu
Sep 18, 2022 at 16:26

No, not necessarily however by design it has an inverse. Even the $$F$$ function doesn't have an inverse, the Feistel network has its inverse by the design.