Keep Your Enemies Close:Distance Bounding Against Smartcard Relay Attacks

Authors: Saar Drimer and Steven J. MurdochPresented in: Usenix Security Symposium 2007

Kishore Padma Raju

Today’s Talk

• Smart Card• Relay Attacks• Defenses• Distance Bounding

Smart Card

• Sheet of plastic – integrated circuit(microcontroller) – Eight contact pads • Ground • Power• Reset• Clock• Bidirectional I/O signal

Payment system

is fully deployed in the UK since 2006, with banks making grand claims of security

uses the EMV (Europay MasterCard Visa) protocol

1066 requires a correct 4 digit PIN input for authorizing transactions

uses RSA for Static Data Authentication (SDA)

Payment Environment

• Four parties– Cardholder– merchant: control the payment terminal– Issuer bank• Contractual relation with cardholder

– Acquirer bank• Contractual relation with merchant

A simplified smartcard transaction

Authentication

• Dynamic data authentication– Merchant • Verify signature with public key

• Static data authentication– Merchant are not trusted• Data is static• Authorization is done online

RELAY ATTACK

IMPLEMENTATION

• Counterfeit Terminal– Chip and pin terminals($10)– Xilinx Spartan($200)– USB GemPC twin reader($40)

IMPLEMENTATION

• Counterfeit Card– Ground down the chip to card’s pad– Maxim 1740/1 transistor($2)

• Controlling software– Software developed in python

$500 worth of off-the-shelf hardware, two laptops and moderateengineering skill is all it takes.

Results

• VASCO Chip authentication program(CAP)• Merchant in UK

Previously proposed defenses

Tamper resistant terminalsProtects banks by erasing keys upon

tampering, cardholders aren’t trained to tell the difference

Impose timing constraints on terminal-card interactionA good start, but short timing advantages translateinto long distances; most interactions are predictable

Distance Bounding

• Parameters– Prover P(Smart card)– Verifier V(terminal)

Distance Bounding

Distance Bounding–initialization phase

Used Hancke-Kuhn N(v) and N(p) provide freshness to the transaction and prevent from replay attacks

Distance Bounding

– MACs are computed under shared key– verifier loads a shift register with random bits– prover splits MAC into two shift registers

Distance Bounding – bit exchange phase

Timing critical phase:– single bit challenge-response pairs are exchanged– response bit is the next bit from the shift register corresponding to thechallenge bit’s content– response bit is deleted at prover and stored at verifier

Distance Bounding – Verify Phase

The verifier checks that the responses are correct and concludes, based on its timing settings, the maximum distance the prover is away

Experimental Setup

Example of Rapid Bit-exchange phase

A 3 8 F 6 D 7 5challenger 1010 0011 1000 1111 0110 1101 0111 0101

Register0 x0x0 11xx x011 xxxx 0xx1 xx1x 1xxx 1x0x

Register1 1x0x xx10 1xxx 0001 x10x 01x0 x111 x1x0

Response 1000 1110 1011 0001 0101 0110 1111 1100

8 E B 1 5 6 F C

A single bit-pair exchange:challenge=1, response=0

Waveform

Possible attacks on distance bounding

• Guessing attack– Initiate bit-exchange phase– 50% of challenges and 50% of responses– Totally 75% success– Probability (3/4)^64 using 64 bits

• Replay– Revealing both response registers by running the

protocol twice• Delay line manipulation– Manipulate delay lines to expose both registers’ state

Future work

Working towars providing secure distance bounding protection for RFID.

STRENGTHS

• Low Cost• Robust

Weakness

• Gave idea to attack their system