Picklock-proof key slot for a lock device and a key thereof

A picklock-proof lock device having a key slot and a key fitting into the key slot, the lock device including a lock casing, a rotary cylinder in the lock casing movable between locked and unlocked positions, a plurality of first tumbler grooves in the lock casing and a plurality of second tumbler grooves in the rotary cylinder, the first and second tumbler grooves being aligned with each other when the rotary cylinder is in the locked position, a plurality of first tumblers located in the first tumbler grooves, a plurality of second tumblers located in the second tumbler grooves, and comprising:

• a) a key plate on the key, the key plate including two spaced apart U-shaped ribs, the U-shaped ribs facing in opposite directions with a connection plate connecting the two U-shaped ribs together, each U-shaped rib including two spaced apart parallel guide plates defining a guide slot therebetween, and a bottom plate connecting the parallel guide plates, the two spaced apart parallel guide plates having a plurality of different depth tumbler slots;
• the connection plate being spaced inwardly from outer edges of the guide plates to be free of tumbler engaging slots;
• and,
• b) a key slot in the rotary cylinder including two spaced apart, U-shaped grooves configured to accommodate therein the two U-shaped ribs, and salient plates located in the U-shaped grooves to engage the guide slots of the key when the key is inserted into the key slot.