1. Cryptography and Network Security

2. Web Security Web now widely used by business, government, individuals
but Internet & Web are vulnerable
have a variety of threats
integrity
confidentiality
denial of service
authentication
need added security mechanisms

3. SSL (Secure Socket Layer)
transport layer security service
originally developed by Netscape
version 3 designed with public input
subsequently became Internet standard known as TLS (Transport Layer Security)
uses TCP to provide a reliable end-to-end service
SSL has two layers of protocols
SSL probably most widely used Web security mechanism. Its implemented at the Transport layer; cf IPSec at Network layer; or various Application layer mechanisms eg. S/MIME & SET (later).

4. Where SSL Fits HTTP SMTP POP3 80 25 110 HTTPS SSMTP SPOP3 443 465 995
HTTPS SSMTP SPOP3
Secure Sockets Layer
Transport
Network
Link

5. Uses Public Key Scheme Each client-server pair uses 2 public keys
one for client (browser)
created when browser is installed on client machine
one for server (http server)
created when server is installed on server hardware
2 private keys
one for client browser

6. SSL Architecture
Stallings Fig 17-2.

7. SSL Architecture SSL session SSL connection
an association between client & server
created by the Handshake Protocol
define a set of cryptographic parameters
may be shared by multiple SSL connections
SSL connection
a transient, peer-to-peer, communications link
associated with 1 SSL session

8. SSL Record Protocol confidentiality message integrity
using symmetric encryption with a shared secret key defined by Handshake Protocol
IDEA, RC2-40, DES-40, DES, 3DES, Fortezza, RC4-40, RC4-128
message is compressed before encryption
message integrity
using a MAC (Message Authentication Code) created using a shared secret key and a short message
SSL Record Protocol defines these two services for SSL connections.

9. SSL Change Cipher Spec Protocol
one of 3 SSL specific protocols which use the SSL Record protocol
a single message
causes pending state to become current
hence updating the cipher suite in use

10. SSL Alert Protocol conveys SSL-related alerts to peer entity severity
warning or fatal
specific alert
unexpected message, bad record mac, decompression failure, handshake failure, illegal parameter
close notify, no certificate, bad certificate, unsupported certificate, certificate revoked, certificate expired, certificate unknown
compressed & encrypted like all SSL data

11. SSL Handshake Protocol
allows server & client to:
authenticate each other
to negotiate encryption & MAC algorithms
to negotiate cryptographic keys to be used
comprises a series of messages in phases
Establish Security Capabilities
Server Authentication and Key Exchange
Client Authentication and Key Exchange
Finish

12. SSL Handshake Protocol
Stallings Fig 17-6.

13. TLS (Transport Layer Security)
IETF standard RFC 2246 similar to SSLv3
with minor differences
in record format version number
uses HMAC for MAC
a pseudo-random function expands secrets
has additional alert codes
some changes in supported ciphers
changes in certificate negotiations
changes in use of padding

14. TLS: Transport Layer Security
formerly known as SSL: Secure Sockets Layer
Addresses issues of privacy, integrity and authentication
What is it?
How does it address the issues?
How is it used
Will discuss changes later
SSL created at Netscape, TLS is IETF draft standard
SSL 3.0 -> TLS 3.1

15. What is TLS? Protocol layer
Requires reliable transport layer (e.g. TCP)
Supports any application protocols IP
TCP
TLS
HTTP
Telnet
FTP
LDAP
Reliable transport layer delivers data without duplicates or missing data, and in order.
Not really transparent to applications
Application must understand desired security level and if TLS cannot
provide that must not assume a secure connection
Application must communicate security parameters to TLS
Application may introduce security issues
e.g. HTTP 1.0 connection close with empty Content-Length

16. TLS: Privacy Encrypt message so it cannot be read
Use conventional cryptography with shared key
DES, 3DES
RC2, RC4
IDEA
Most block ciphers (64 bit blocks) except for RC4 stream cipher
CBC cipher block chaining
use IV (initialization vector)
XOR previous encrypted block with block then encrypt … A
Message B

17. TLS:Key Exchange Need secure method to exchange secret key
Use public key encryption for this
“key pair” is used - either one can encrypt and then the other can decrypt
slower than conventional cryptography
share one key, keep the other private
Choices are RSA or Diffie-Hellman

18. TLS: Integrity Compute fixed-length Message Authentication Code (MAC)
Includes hash of message
Includes a shared secret
Include sequence number
Transmit MAC with message
Secret is used so that someone cannot replace both message and MAC, putting a new matching MAC in place of the original

19. TLS: Integrity Receiver creates new MAC TLS allows MD5, SHA-1
should match transmitted MAC
TLS allows MD5, SHA-1 A B
Message’
MAC’
MAC =?
Message

20. TLS: Authentication Verify identities of participants
Client authentication is optional
Certificate is used to associate identity with public key and other attributes A
Certificate B

21. TLS: Overview Establish a session Transfer application data
Agree on algorithms
Share secrets
Perform authentication
Transfer application data
Ensure privacy and integrity

22. TLS: Architecture
TLS defines Record Protocol to transfer application and TLS information
A session is established using a Handshake Protocol
Operational and pending states
TLS Record Protocol
Handshake Protocol
Alert Protocol
Change
Cipher Spec

23. TLS: Record Protocol Currently no compression defined but could be
client boundaries are not preserved
2^14 bytes or less in protocol unit
md5, sha-1, none MAC
des, 3des, des40, rc2, rc4, idea none encryption

24. Secure Electronic Transactions (SET)
open encryption & security specification
to protect Internet credit card transactions
developed in 1996 by Mastercard, Visa etc
not a payment system, rather a set of security protocols & formats
secure communications amongst parties
trust from use of X.509v3 certificates
privacy by restricted info to those who need it

25. SET Components
Stallings Fig 17-8.

26. SET Transaction customer opens account customer receives a certificate
merchants have their own certificates
customer places an order
merchant is verified
order and payment are sent
merchant requests payment authorization
merchant confirms order
merchant provides goods or service
merchant requests payment

27. Dual Signature customer creates dual messages
order information (OI) for merchant
payment information (PI) for bank
neither party needs details of other
but must know they are linked
use a dual signature for this
signed concatenated hashes of OI & PI

28. Purchase Request – Customer
Stallings Fig

29. Purchase Request – Merchant
Stallings Fig

30. Purchase Request – Merchant
verifies cardholder certificates using CA sigs
verifies dual signature using customer's public signature key to ensure order has not been tampered with in transit & that it was signed using cardholder's private signature key
processes order and forwards the payment information to the payment gateway for authorization (described later)
sends a purchase response to cardholder

31. Payment Gateway Authorization
verifies all certificates
decrypts digital envelope of authorization block to obtain symmetric key & then decrypts authorization block
verifies merchant's signature on authorization block
decrypts digital envelope of payment block to obtain symmetric key & then decrypts payment block
verifies dual signature on payment block
verifies that transaction ID received from merchant matches that in PI received (indirectly) from customer
requests & receives an authorization from issuer
sends authorization response back to merchant

32. Payment Capture
merchant sends payment gateway a payment capture request
gateway checks request
then causes funds to be transferred to merchants account
notifies merchant using capture response

33. Summary have considered: need for web security
SSL/TLS transport layer security protocols
SET secure credit card payment protocols