Elliptic curve cryptography and LDPC codes are two that come to mind. Though afaik the latter hasn't really been improved since ~1960 and were only patented af

Elliptic curve cryptography and LDPC codes are two that come to mind. Though afaik the latter hasn't really been improved since ~1960 and were only patented after rediscovering them in 1993, and I have no clue whether progress in elliptic curve cryptography stalled due to patents or because they don't offer any practical benefits over RSA.