[12425] in cryptography@c2.net mail archive
Re: [IP] Master Key Copying Revealed (Matt Blaze of ATT Labs)
daemon@ATHENA.MIT.EDU (Arnold G. Reinhold)
Wed Jan 29 10:36:43 2003
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In-Reply-To: <u1fsbbwb.fsf@optushome.com.au>
Date: Wed, 29 Jan 2003 05:20:02 -0500
To: cryptography@wasabisystems.com
From: "Arnold G. Reinhold" <reinhold@world.std.com>
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
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