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Understanding Web Security and SSL/TLS Protocols

Explore web security challenges, SSL/TLS protocols, and approaches in e-commerce, with a focus on TCP/IP layers and SSL architecture.

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Understanding Web Security and SSL/TLS Protocols

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  1. Web Security

  2. Web Security Introduction • Need for security on the Transport Control Protocol (TCP) Layer • Uses Secure Socket Layer (SSL) and Internet standard SSL called Transport Layer Service • Allows TCP users to indentify security mechanisms • Particularly concerted with E – commerce security: Secure Electronic Transaction (SET)

  3. Web Security Considerations • Room for nearly all levels of security in the Web • E.g. previous considerations • Nevertheless: Web presents unique challenges • All communication two way thus doubling the opportunity for attack • Web integrated into business: high losses if security compromised • Security flaws in complex software • Web Servers may provide access to local intranet • Users not aware of security risks

  4. Threats Classifications

  5. Web Security Approaches • Different ways of implementing security • Similar in services and (to an extent) mechanisms • Differ with respect to scope and location with TCP/IP stack • Simple security: Use IP Security! IPSec runs over TCP • Another solution: Run security just above TCP, below IP • Basis of SSL and TLS • Choice: Make SSL/TLS transparent or integrate into applications? (advantage: tailored to needs, disadvantage: complexity)

  6. SSL and TLS • Current version is SSL v3. TLS is essentially SSLv3.1 • Not a “successor” exactly, just a different standard • SSL Architecture • Make TCP reliable/secure • Higher level protocols operate (HTTP for instance) on SSL • SSL uses three protocols: Handshake Protocol, Change Cipher Spec Protocol, Alter Protocol • Also a special “record” protocol • Used in management of SSL exchanges

  7. 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

  8. SSL Architecture

  9. SSL Architecture • SSL connection • A transient, peer-to-peer, communications link • Associated with 1 SSL session • SSL session • An association between client & server • Created by the handshake protocol • Define a set of cryptographic parameters • May be shared by multiple SSL connections

  10. Session and Connection States • Session state has following parameters • Session Identifier, Peer certificate (X509, etc) • Compression Method • Cipher spec (data encryption) and hash • Master secret • Is resumable? • Connection state: • Server and client randomness • Keys: Server/Client MAC, Server/Client Write • Initialization vectors • Sequence numbers

  11. 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

  12. SSL Record Appearance

  13. SSL Record Protocol Operation

  14. 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

  15. 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

  16. 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

  17. SSL Handshake Protocol

  18. 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

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