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Why Cryptosystems Fail?. Ross Anderson Presented by Ananth Rajagopala-Rao. 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.
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Why Cryptosystems Fail? Ross Anderson Presented by Ananth Rajagopala-Rao
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.
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.
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.
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.
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!!!
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.
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??
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??
