© UCL Crypto group – October 2004 – DIMACS - Smart Theory Meets Smartcard Practice Smart Theory...

© UCL Crypto group – October 2004 – DIMACS - Smart Theory Meets Smartcard Practice

Smart Theory Meets Smartcard Practice

Jean-Jacques Quisquater [email protected]

Research Director CNRS, France andUniversité catholique de Louvain, Louvain-la-Neuve,

BelgiumUCL Crypto Group http://uclcrypto.org

Part of this work done while visiting scientist at MIT-CSAIL

© UCL Crypto group DIMACS talk - 2004 2

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CONTENTSCONTENTSCONTENTSCONTENTS

• Introduction• Smart cards• IBC• Remote integrity• Using bad primitives • Conclusion

• Introduction• Smart cards• IBC• Remote integrity• Using bad primitives • Conclusion


Goal of the talk

• Show by examples that thinking with tamperproof and doing crypto with constrained objects is interesting for theoretical and practical purposes.

© UCL Crypto group – October 2004 – DIMACS - Smart Theory Meets Smartcard Practice

Short Story of Smart Cards• René Barjavel (1966) « La nuit des temps » (Gondas) • several inventors in USA (IBM - 1968), Japan, Germany,

France• Roland Moreno (F) pushed the right version (1974)• Michel Ugon and Louis Guillou were the technical

inventors (~ 1977)• SPOM: single chip (security): 1981: first crypto algo

and protocol (secret key): tests in France• first DES: 1985 (TRASEC, Belgium,TB100 -> Proton)• first RSA: CORSAIR (Philips): 1989 (coprocessor)• ... • in some sense smart angel-in-the-box (Shai Halevi,

yesterday).


Ring by Moreno (1974) and first smart card (1980)


The chip (IC)

ROMROM EEPROMflash memory

EEPROMflash memory

CPUCPU I/OI/O coprocessorDES – RSA -ECC

coprocessorDES – RSA -ECC

securitylogic

securitylogic

RAMRAM

sensorssensorsfirewall

Reset Ground Volt Clock


A complete computer


Passive attacks

ChipChipChipChip

CLK

GRD

VCC

RST

I/O

2. SPA-DPA2. SPA-DPA1. timing1. timing

3. probing3. probing4. measuresof radiations

4. measuresof radiations


Active fault attacks(Bellcore attack)

Key=1010110...

© UCL Crypto group DIMACS talk - 2004

SENDER k (Alice)E(m)


RECEIVER k(Bob)

D(E(m))=m

RECEIVER k(Bob)

D(E(m))=m

encrypted message

E(m)=10010100111

Tamperproof modelTamperproof model




RECEIVER k(Bob)

D(E(m))=m

RECEIVER k(Bob)

D(E(m))=m

E(m)=10010100111

Tamperproof model => asymmetric crypto(DH-RSA – 1980 public)

Tamperproof model => asymmetric crypto(DH-RSA – 1980 public)

Only able to encryptOnly able to encryptOnly able to decryptOnly able to decrypt


Identification with identity-based crypto(Shamir 1984Guillou 1984

Fiat-Shamir 1986)

PROVER kId

E(r) = R

PROVER kId

E(r) = R

VERIFIER KE(Id) = kE(r) = ? R

VERIFIER KE(Id) = kE(r) = ? R

Id

Surprise r

Response R

Authority KE(Id) = k

Authority KE(Id) = k

IdIdkk


Identity-Based Encryption

• Adi Shamir: Identity-Based Cryptosystems and Signature Schemes. CRYPTO 1984: 47-53.

• Yvo Desmedt, Q.: Public-Key Systems Based on the Difficulty of Tampering (Is There a Difference Between DES and RSA?). CRYPTO 1986: 111-117.

• Dan Boneh, Matthew K. Franklin: Identity-Based Encryption from the Weil Pairing. CRYPTO 2001: 213-229.

• Clifford Cocks: An Identity Based Encryption Scheme Based on Quadratic Residues Source LNCS, Proc. of the 8th IMA Intern. Conf. on Cryptography and Coding 2001: 360-363.


Hierarchical IBC?

• Was done also in 1984• The easy way: you iterate the

process with cards being mother, daughter, granddaughter, aso.


Tamperproof model useful?

• Sometimes proof of concept• Sometimes useful to simulate

public-key crypto in closed systems• Yes, but we don’t know how to

translate tamperproof into trapdoor in a crypto function.


First smart card (1980)


Security with two chips or with a unsecure server?

• One chip is tamperproof but slow,• The other one is a unsecure memory or a

fast unsecure processor, …• Philippe Béguin, Q.: Secure Acceleration of DSS Signatures

Using Insecure Server. ASIACRYPT 1994: 249-259 • Possible for El gamal signatures with small memory• RSA? • See Philippe Béguin, Q.: Fast Server-Aided RSA Signatures

Secure Against Active Attacks. CRYPTO 1995: 57-69 • but parameters need to be changed due to an attack by

Nguyen–Stern (Asiacrypt 1998). Better?• Work in progress


New problem: “remote integrity”(better than Tripwire®?)

IICIS 2003: Deswarte,Q, Saïdane

PROVERSmart card

IdM (secret)

PROVERSmart card

IdM (secret)

VERIFIER

r! A!h(M)

f(r,h(M))=R?

VERIFIER

r! A!h(M)

f(r,h(M))=R?

Id

Surprise A

Response R

A lot of smart cardsA lot of smart cards


Protocol for remote integrity• GENERAL INIT: Let M = (content of the file), integer

n = pq (RSA modulus, 1024 bits) public: factorisation is secret a = a random number, 1 <a <n-1, secret (chosen by verifier)

• INIT for ONE FILE: h = aM mod n precomputed by verifier

• Verifier generates a random number r and computes challenge A = ar mod n

• Smart card computes response: R = AM mod n and send R (or a part of it)

• Verifier computes C = hr mod n and checksif R = C = aMr mod n

• Diffie-Hellman protocol• Problem: Proof!

• Work in progress (optimisations)


Using bad primitives?

PROVER kh(), r1!

E(r1+r2) = R

PROVER kh(), r1!

E(r1+r2) = R

VERIFIER kE(r1+r2) = R ?

VERIFIER kE(r1+r2) = R ?

h(r1) (weak commitment)

r2

Response R, r1

• Bad random generator • Breakable hash function h()• E: resists to linear crypto, • E: bad for differential crypto

• Bad random generator • Breakable hash function h()• E: resists to linear crypto, • E: bad for differential crypto


General conclusion

Thinking theoretically with strongly constrained objects set interesting problems with practical results.

Many open problems.

UCL©

© UCL Crypto group – October 2004 – DIMACS - Smart Theory Meets Smartcard Practice Smart Theory...

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