1 Introduction The State of the Art in Electronic Payment Systems, IEEE Computer, September 1997.

1

Introduction

The State of the Art in Electronic Payment Systems, IEEE Computer, September 1997

2

Requirements and Safeguards for ECommerce

• Entity authentication

• Message integrity

• Payment non-repudiation

• Effective audit mechanism

• Privacy

3

Safeguards and Security Mechanisms

• Cryptography– Private- and Public-key Cryptography– Cryptographic Certificates

4

Hello World and Welcome to The simple crypt

Key=23

_r{{x7@xe{s7vys7@r{txzr7cx7Cr7d�~zg{r7tengc

Private-key Cryptography

5

ALICE BOB

Eve

6

MessageThis is a big secret

MessageI?~jhYUWEKUia

The Internet

MessageThis is a big secret

MessageI?~jhYUWEKUia

Recipient’s private key

Recipient’s PUBLIC key

7PGP,Version 6.5.1 Manual, NetworkAssociates, 1999.

8

PGP,Version 6.5.1 Manual, NetworkAssociates, 1999.

9

Certificate Authorities

• The Certificate Authority (CA) is a trusted third party

• Provides the necessary authentication and security infrastructure

• The CA creates and issues certificates

10

PGP,Version 6.5.1 Manual, NetworkAssociates, 1999.

11Sondra Schneider, IFsec, June 11, 1999.

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Using the CA to Establish Trust

Customer Merchant

The CA1- Establisha Certificate

2- send signed requestand certificate

3- CheckSignature

4-Merchant can trust customerand may continue with trade

13Sondra Schneider, IFsec, June 11, 1999.

14

Sondra Schneider, IFsec, June 11, 1999.

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Authentication Protocols

• General-purpose secure messaging protocols include:– SSL– S/MIME

• Secure protocols for electronic commerce include:– EDI/MIME. – SET

16

SET

Byte, June 1997

17

June 1997

18

June 1997

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The Use of Smartcards

Byte, June 1997

20Minimal Key Lengths for Symmetric Ciphers, Matt Blaze and others, 1996.

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Avoiding bogus encryption products, Matt Curtin, 1998.

22

RSAfrom the RSA FAQ

• RSA is a public-key cryptosystem– take two large primes, p and q,– find their product n = pq; (n is called the

modulus)– Choose, e, less than n and relatively prime to (p-

1)(q-1), and find its inverse, d, mod (p-1)(q-1), which means that:

ed = 1 mod (p-1)(q-1);– e and d are called the public and private

exponents, respectively.– The public key is the pair (n,e);– the private key is d.– The factors p and q must be kept secret, or

destroyed.

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Two numbers are relatively prime when they share no factors in common other than 1. In other words, if the greatest common divisor of a and n is equal to 1. This is written:

gcd(a,n) = 1

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• It is difficult (presumably) to obtain the private key d from the public key (n,e).

• If one could factor n into p and q, however, then one could obtain the private key d.

• Thus the entire security of RSA is predicated on the assumption that factoring is difficult.

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RSA encryption:• suppose Alice wants to send a private

message, m, to Bob.• Alice creates the ciphertext

c = m^e mod n,• e and n are Bob's public key.• To decrypt, Bob computes:

m = c^d mod n, • and recovers the original message m; the

relationship between e and d ensures that Bob correctly recovers m. Since only Bob knows d, only Bob can decrypt.

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• public-key operations take O(k^2) steps,

• private key operations take O(k^3) steps,

• key generation takes O(k^4) steps

• where k is the number of bits in the modulus