Download Why Cryptosystems Fail?

Why Cryptosystems Fail?
Ross Anderson
Presented by Ananth Rajagopala-Rao
Motivation
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Designers of cryptosystems are at a
disadvantage as compared to other engineers
as they receive no feedback on their systems.
Governments, banks and military are very
secretive about their mistakes.
The emphasis on research in cryptosystems
today is misplaced because of this.
Case Study – ATM systems
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In USA, banks are required to
reimburse all disputed transactions
unless they can prove a fraud by the
customer, as a result banks lose approx.
$15,000 a year.
In the UK, there have been several
accusations of fraud by banks which
later turned out to be clerical errors.
How ATM fraud takes place
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Most cases till 1994 were extremely
simple, nobody used any cryptanalysis
or other advanced techniques.
A design goal of the the ATM system is
that any fraud requires the cooperation
of a minimum of two persons, most
frauds indicate elementary design flaws
that violate this goal.
How ATM works?
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The account no and the an offset is stored on
the card.
The PIN is a cryptographic function of the a/c
number + the offset stored on the card.
The management of the keys for this
cryptographic function is where a lot of
problems arise.
If we know the PIN key
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Given any card we can figure out the PIN.
We can forge ATM cards with cheap off the shelf
hardware.
Problems with encryption
products
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All hardware that stores important keys must
be physically tamper resistant.
Of the 10,000 member banks of VISA and
Mastercard, only about 1,000 have invested
in such hardware.
All these security modules are manufactured
by IBM, and the IBM manual actually tells
how any programmer can recover the keys
for debugging purposes!!!
Problems with encryption
products (cont.)
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Key entry into these security modules is
through obsolete IBM 3178 serial terminals.
The key is usually distributed between two
high ranked officials in the bank.
These officials are mostly reluctant to use a
keyboard, and simple give the key to the
technician.
Even if they do type it in, they use emulation
s/w on the service technicians laptop, which
can record the key strokes.
Problems with practices of
banks
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Some banks subcontract their ATM system to
‘facilities management’ firms. No back
officials have any idea about the security
implications of this.
Most keys are exchanged in open
correspondence.
Some banks place the encryption module
inside the branch, and transmit PINs in
plaintext to ATMs.
Point of sale systems at stores??
The threat model is wrong
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Designers concentrate on what possible to
happen than on what is likely to happen.
We overestimate the sophistication of both
the users of the cryptosystem as well as that
of the attacker.
Grossly underestimate “internal” threats.
Hangover from military applications, DOD
funding, WW II etc. where the entities in
question are nations??