Complex sentence: A lot of research was done in the past but the most significant contributions were the PGP (Pretty Good Privacy) and the trust based security but none of the protocols made a decent trade off between security and performance.
Split into simpler sentences: A lot of research has been done in the past but the most significant contributions have been the PGP (Pretty Good Privacy) and trust based security. None of the protocols have made a decent trade off between security and performance.