[IP] Master Key Copying Revealed (Matt Blaze of ATT Labs)

[Arnold G. Reinhold]

I took a look at the "MIT Guide to Lock Picking"  August 1991 revision at
http://www.lysator.liu.se/mit-guide/mit-guide.html

It says:

"9.10 Master Keys
Many applications require keys that open only a single lock and keys 
that open a group of locks. The keys that open a single lock are 
called change keys and the keys that open multiple locks are called 
master keys. To allow both the change key and the master key to open 
the same lock, a locksmith adds an extra pin called a spacer to some 
of the pin columns. See Figure 9.8. The effect of the spacer is to 
create two gaps in the pin column that could be lined up with the 
sheer line. Usually the change key aligns the top of the spacer with 
the sheer line, and the master key aligns the bottom of the spacer 
with the sheer line (the idea is to prevent people from filing down a 
change key to get a master key). In either case the plug is free to 
rotate."

The parenthetical comment suggests awareness of the general 
vulnerability Matt exploited, but I suspect that had the authors 
known the multiple partial copy trick Matt described, they would have 
published it.

Arnold Reinhold

---------------------------------------------------------------------
The Cryptography Mailing List
Unsubscribe by sending "unsubscribe cryptography" to majordomo at wasabisystems.com