PNG ICO ICNS MORE
Desktop apps
Smooth
One bit
Unlock, Lock
DarkGray
48x48
Lock, Blue, secure
Pixel
Diagona Icons
security, password, Lock
16x16
Photography & graphic design
3D
Dark Glass
Lock, Key, password
128x128
UI
Fugue Icons
Lock, disable
Mixed
Carpelinx
password, secure, Lock
File, Lock
Lock
64x64
Silk
Go, Lock