another term you might look for (used in physical security and
financial controls) is dual custody or sometimes double custody.
(if you're searching, add -child or security for better search
i don't see why the analogies are not apt.
one question is whether the two people can both perform their
respective act independently
or whether they need to perform their act within a bounded time.
in the case of auditcon locks, for example, often used on the money
safe part of atms:
these features are called
Allows access by a subordinate only after being enabled by a
supervisory combination. Once enabled, a subordinate user has access
to the lock during any valid opening time.
[for example, this would be used in a supermarket if a manager wants
to allow a subordinate to open the safe the next morning]
Two Person Integrity, which requires two users to open the lock.
the x-09 (approved for use in us top secret) has three modes:
A-single combination code
b-Dual combination mode which allows access only when two different
three number combinations are dialed within 10 seconds of one another
On Jan 28, 2008, at 2:56 PM, John Denker wrote:
Hi Folks --
I have been asked to opine on a system that requires a
two-person login. Some AIX documents refer to this as
a common method of increasing login security
However, I don't think it is very common; I get only five hits
By way of not-very-apt analogy:
-- I am aware of business checks that require two signatures;
-- I am aware that purchase orders are commonly signed by
two persons (the initiator and the approver);
-- I am aware of missile-launch procedures that require two
persons using two keys;
-- I am aware of software development procedures where a patch
is submitted (and signed) by one person, tested (and signed
off) by another, and committed to the official repository by
a third person.
-- et cetera.
However, it is important to note that the aforementioned examples
all share an important property, as we see from the following:
*) The parties give their approval _after_ the semantics has
been fully determined. It would defeat all security if two
signatures were attached to a blank check or a blank PO.
*) As a related point, the approval is attached to a particular
transaction. The approver is not merely certifying that Joe
is really Joe, and is generally allowed to write checks
(mere identification); the approver is certifying that this
particular check is OK.
*) To say the same thing another way, there is no pretexting.
There is no pretext for turning the keys on the missile launcher
unless you intend to launch a missile. The semantics of the
keys is clear.
We need to talk about threat models:
a) The purveyors of the system in question don't have any clue
as to what their threat model is. I conjecture that they might
be motivated by the non-apt analogies itemized above.
b) In the system in question, there are myriad reasons why Joe
would need to log in. If Joe wanted to do something nefarious,
it would take him less than a second to come up with a seemingly
non-nefarious pretext. When the approver approves Joe's login,
the approver has no idea what the consequences of that approval
will be. The two-person login requires the approver to be
present at login time, but does not require the approver to
remain present, let alone take responsibility what Joe does
c) The only threat model I can come up with is the case where
Joe's password has been compromised, and nobody else's has.
Two-person login would provide an extra layer of security
in this case. This threat is real, but there are other ways
of dealing with this threat (e.g. two-factor authentication)
... so this seems like quite a lame justification for the
d) Or have I overlooked something?
From the foregoing, you might conclude that the two-person login
system is worthless security theater ... but harmless security
theater, and therefore not worth worrying about either way.
But the plot thickens. The purveyors have implemented two-person
login in a way that manifestly /reduces/ security. Details
available on request.
So now I throw it open for discussion. Is there any significant
value in two-person login? That is, can you identify any threat
that is alleviated by two-person login, that is not more wisely
alleviated in some other way?
If so, is there any advice you can give on how to do this right?
Any DOs and DONTs?
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