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Chapter 7 Web Security

Chapter 7 Web Security. MSc. NGUYEN CAO DAT Dr. TRAN VAN HOAI . 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

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Chapter 7 Web Security

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  1. Chapter 7Web Security MSc. NGUYEN CAO DAT Dr. TRAN VAN HOAI

  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 • Transport Layer Security (SSL/TLS) • Secure Electronic Transactions (SET)

  3. SSL (Secure Socket Layer) • Reliable end-to-end secure service • Provides a “secure TCP socket” • Usually used with Web browsers • Can be used for other applications too • Introduced by Netscape in 1995 • Provided options for 40 and 128 bit keys • Submitted to IETF standards • Result – TLS (RFC 2246)

  4. SSL Architecture

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

  6. SSL Record Protocol Services • message integrity • using a MAC with shared secret key • similar to HMAC but with different padding • confidentiality • using symmetric encryption with a shared secret key defined by Handshake Protocol • AES, IDEA, RC2-40, DES-40, DES, 3DES, Fortezza, RC4-40, RC4-128 • message is compressed before encryption

  7. SSL Record Protocol Operation

  8. 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

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

  10. 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

  11. SSL Handshake Protocol

  12. 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 types & negotiations • changes in crypto computations & padding

  13. Client Authentication • SSL/TLS, IE, Netscape, Firefox all support client certs • Rarely used outside of corporate settings • Peoplesoft ISIS? Nope • HTTP Basic authentication within SSL session • Cleartext password stored on server, but hidden on wire • Could use Digest authentication instead

  14. Performance • SSL is slow • Crypto • Latency (in addition to TCP) • Session resumption • Servers have it rough, signing with private key to prove identity

  15. HTTPS and Web Servers • HTTP over SSL usually port 443 • 443 means "use SSL" • No substantial HTTP awareness of SSL underneath • Web pages typically include a lot of embedded content • potentially fetched over different TCP connections • session resumption is critical for performance • HTTP persistent connections are very helpful • Proxies • A proxy is a man-in-the-middle • HTTP "CONNECT" method just relays data; proxy can't examine • Possible to reconfigure clients so that a real man-in-the-middle "attack" on https is possible • Set up your own Certificate Authority and issue a server cert for name * • Apache / OpenSSL / mod_ssl very common combination • Fairly complicated setup • Plenty of commercial server support

  16. 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

  17. SET Components

  18. 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

  19. 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

  20. Dual Signature Construction • DS=E(PRc, [H(H(PI)||H(OI))])

  21. SET Purchase Request • SET purchase request exchange consists of four messages • Initiate Request - get certificates • Initiate Response - signed response • Purchase Request - of OI & PI • Purchase Response - ack order

  22. Purchase Request – Customer

  23. 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

  24. Purchase Request – Merchant

  25. 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

  26. 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

  27. Summary • have considered: • Transport layer security (SSL/TLS) • Secure Electronic Transactions (SET)

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