Abstract: A cylinder (10) which is highly pick-resistant and also highly resistant to other means of forced entry is provided. The cylinder is of a unique hemispherical construction, involving a hemispherical shell (12), hemispherical plug (13) and hemispherical plug insert (14). In a preferred embodiment, the keyway (28) includes two keyways (23, 25). The key is of a correspondingly complex configuration including a generally circular handle portion (28) and two generally semicircular tumbler pin actuating portions (36 and 37). The hemispherical configuration and the multiplicity of keyways renders it particularly difficult to pick the lock.