Break-Open One-Shot Password Stores

Mark Lomas ukcrypto at
Mon Feb 27 13:32:27 GMT 2012

The last time I inquired about buying PIN envelopes they were sealed in the
factory but completed using a dot matrix printer on the outside of the
Note that these don't protect you against an insider with access to unused

The boxes that Ian asked about are sold as 'evidence boxes'. The police use
them to prove that that they didn't misuse something in custody. I have
used these in the past to protect keys. For example we kept an alarm
override key in such a box in case it was needed in the middle of the night.

Evidence boxes are better than PIN envelopes because the tab that seals it
shut has a serial number. It has a ratchet mechanism like a cable tie so
you have to cut it to open the box. Having cut the tab it is difficult to
obtain a replacement with the same number.

A slight design flaw is that the boxes are clear. We used to wrap keys in
card before putting them in the box.


On 27 February 2012 11:00, Paul Barnfather <lists at> wrote:

> On 27 February 2012 07:42, Ian Batten <igb at> wrote:
> > Has anyone seen such devices for sale?
> How about the way banks issue PIN codes for ATM and credit cards? They
> come in the form of a printed letter with a neat little plastic
> tear-off tab which makes it very clear if the PIN has been read by
> someone else.
> They seem to be a cheap and effective way of storing and communicating
> a "read once" password.
> I assume they are fairly resistant to casual tampering.
> Does anyone know if they are printed with a conventional printer, or
> do they require specialised hardware to produce?
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