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Re: bike locks and encryption

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On 2014-10-07, RichD <r_delaney2001@yahoo.com> wrote:
> On October 6, RichD wrote:
>> bicycle locks as examples of one way function...
>> Specifically, the combination type: 4 dials,
>> numbered 0..9, the cylinder mates with the receptacle 
>> with the correct combination. 
>
> To be precise, the cable type, with the ends 
> that mate, not the U lock.

There is less difference between these than you think.  With a cable lock, you
manually arrange some dials into a configuration.

With a keyed U-lock, there is still a combination: that combination is
imprinted as a machined pattern on the key. When the key is inserted, it moves
some pins into a configuration, which is equivalent to turning the dials,
except that since you have only one key, you can only express one combination.

Ordinary residential entrance keys are also combinations. The keys have
teeth, and these teeth arise because "valleys" between the teeth are machined
to different depths. The depths are quantized, typically to 10 possibilities,
which can be represented by the digits 0 to 9.  So a key with four "valleys"
between five teeth represents a combination somewhere between 0000 and 9999.

If you know the combination number, you can machine a key which will open the
lock, and in principle, you could have all 10,000 keys made which match
that lock's "key way", and do a brute force by trying them one by one.

When you buy a lock re-keying kit which consists of replacement tumblers for
the lock, together with matching keys, you will probably see that there is a
combination number written on the packaging. That number could be used to order
additional matching tumblers, which, if installed into additional locks, will
all work with the same key.

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bike locks and encryption RichD <r_delaney2001@yahoo.com> - 2014-10-06 23:28 -0700
  Re: bike locks and encryption Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-10-07 11:39 +0100
    Re: bike locks and encryption Richard Heathfield <invalid@see.sig.invalid> - 2014-10-07 11:53 +0100
      Re: bike locks and encryption Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-10-07 16:24 +0100
        Re: bike locks and encryption Richard Heathfield <invalid@see.sig.invalid> - 2014-10-07 21:26 +0100
          Re: bike locks and encryption Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-10-08 01:34 +0100
          Re: bike locks and encryption RichD <r_delaney2001@yahoo.com> - 2014-10-07 23:16 -0700
      Re: bike locks and encryption RichD <r_delaney2001@yahoo.com> - 2014-10-07 23:27 -0700
  Re: bike locks and encryption RichD <r_delaney2001@yahoo.com> - 2014-10-07 13:57 -0700
    Re: bike locks and encryption Kaz Kylheku <kaz@kylheku.com> - 2014-10-07 21:21 +0000
      Re: bike locks and encryption "BartC" <bc@freeuk.com> - 2014-10-07 22:33 +0100
        Re: bike locks and encryption Jongware <jongware@no-spam.plz> - 2014-10-08 15:51 +0200
  Re: bike locks and encryption Kaz Kylheku <kaz@kylheku.com> - 2014-10-07 21:10 +0000
    Re: bike locks and encryption RichD <r_delaney2001@yahoo.com> - 2014-10-07 23:34 -0700
      Re: bike locks and encryption Kaz Kylheku <kaz@kylheku.com> - 2014-10-08 14:10 +0000
        Re: bike locks and encryption RichD <r_delaney2001@yahoo.com> - 2014-10-10 18:33 -0700

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