Re: Master Key crack
From: Richard Herring (junk_at_[127.0.0.1)
Date: 07/30/03
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Date: Wed, 30 Jul 2003 09:55:31 +0100
In message <3f26c2b3$1_2@news.vic.com>, John E. Hadstate
<nospam@null.nil> writes
>
>"Richard Herring" <junk@[127.0.0.1]> wrote in message
>news:KO4eUTtVapJ$EwcG@baesystems.com...
>> In message <3f2677e9$1_2@news.vic.com>, John E. Hadstate
>> <nospam@null.nil> writes
>> >
>> >"Stuart Green" <greens80@hotmail.com> wrote in message
>> >news:1761049f.0307290239.28dd7f11@posting.google.com...
>> >> I remeber reading an article about a guy who utilised a master key
>> >> hack, known to locksmiths, to identify pin placements on a key and
>> >> grind them down progressively to build a masterkey for a lock.
>>
>> [...]
>>
>> >In a simple system producing one Master and one Owner key for each lock,
>> >each pin position in the lock has two short pins inserted. The length of
>> >the first pins in each pin position establish the cut heights for the
>Owner
>> >keys. The sum of the lengths of the first and second pins in each
>position
>> >establish the cut heights for the Master key. The pins come in standard
>> >lengths, and there are constraints on the maximum height differences
>between
>> >adjacent pins. Typical locks come with 4, 5, or 6 pin positions.
>> >
>> >There are a finite number of combinations of pins that make up each
>Master
>> >series. Thus, one might enumerate all the possible pin placements for
>owner
>> >keys for each Master series. Then, given a few owner keys known to be
>part
>> >of one Master series, one might search the entire tree of pin
>combinations
>> >until one established which Master series included all the given owner
>keys.
>> >This would establish the cut lengths for the Master key for that series.
>> >
>> >I suspect that for any decent system, you would need a lot more than 4
>owner
>> >keys to establish which Master series they belong to (although there are
>> >some Master series for 4-pin tumblers that produce a very small number of
>> >usable owner keys).
>> >
>> I think the "master key hack" mentioned by the OP is the one where one
>> sequentially varies the height of a single pin on one known Owner key to
>> determine the Master height at that pin. In principle, given one Owner
>> key and access to the keyhole, that will yield the complete Master
>> heights using as many blanks as there are pin positions, plus a lot of
>> filing.
> s
> s
> s
> s
>gggpggggg
> p
> 1
> 1
> 1
> 2
> 2
> k
> k
> k
>
>To make this Owner key work, "k" has to push p up by 1 unit (so it aligns
>with "g").
>
>To make the Master key work, "k" has to push p up by 4 units (so the lowest
>"1" aligns with "g").
>
>Thus, the Owner key has to be cut more deeply at each pin position than the
>Master key.
>
>So, other than showing a maximum cutting depth for each pin position, how
>does the Owner key reveal the Master key?
(Not just the Owner key, the Owner key plus access to the keyhole with a
set of test blanks:)
1. By indicating which of the two possible depths of each pin is _not_
that of the Master.
2 By providing a known working depth for all the other pins.
-- Richard Herring
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