Why%20Cryptosystems%20Fail?

1
Why Cryptosystems Fail?

• Ross Anderson
• Presented by Ananth Rajagopala-Rao

2
Motivation

• 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.

3
Case Study ATM systems

• 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.

4
How ATM fraud takes place

• 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.

5
How ATM works?

• 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
• Given any card we can figure out the PIN.
• We can forge ATM cards with cheap off the shelf
  hardware.

6
Problems with encryption products

• 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!!!

7
Problems with encryption products (cont.)

• 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.

8
Problems with practices of banks

• 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??

9
The threat model is wrong

• 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??