Best SFIC Core Parts Breakdown

SFIC core parts. The plug (left) in SFIC locks consists of two parts: an inner plug (which has the two holes in the back that mate with the housing fingers) surrounded by a control sleeve (which has the retaining tab). In this photo, the inner plug has been pulled out (by two pin positions). There are two separate shear lines formed by this arrangement. Operating keys line up pin stack cuts at the inner shear line (which allows 360 degree rotation of the plug), while control keys line up pin stack cuts at the outer shear line (which allows retraction of the retaining tab).

Because the two shear lines are separated by slightly more than the maximum bitting height of a key, any given cut can only reach one of the two shear positions. Each pin stack must therefore have two sets of cuts -- one for each shear line -- stacked one on top of the other. Each shear line is keyed (and can be mastered) separately, and a key that lines up cuts for some pins at the operating shear line and cuts for other pins at the control shear line will not operate the lock at all. (In this respect, SFIC locks are similar to "master ring" cylinder designs). Note that the bitting of a control key at any given position might be higher, lower, or the same as an operating key; the only requirement is that the complete control key bitting cannot also be used as an operating key.

The two shear lines can make SFIC locks difficult to manipulate (pick) with conventional tools, because the attacker will usually set some of the pin stacks at the operating shear line and others at the control shear line. In fact, assuming randomly distributed keys, equal friction on the plug and control sleeve, and no mastering, a six pin core will only be expected to pick successfully an average of one out of 64 times, and a seven pin core only one out of 128 times. (In practice it is somewhat easier, due to unequal friction and mastering of the operating keyspace, but it is still usually difficult). Compounding the difficulty are the small and heavily warded keyways and the tight manufacturing tolerances. Somewhat surprisingly, spool, serrated, and other "security" pin designs are not typically used (though Best now offers them as an option).

Image taken with a Nikon D-100 digital camera with a Nikkor 85mm 1:2.8D tilt/shift macro lens (with Kenko extension tube). Lit by electronic flash and various reflectors.

Copyright © 2003 by Matt Blaze. All rights reserved. You may not copy, modify or use this image for any commercial or non-commercial purpose without permission.

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