Lecture III : Communication Security, Services & Mechanisms

1. Lecture III : Communication Security,Services & Mechanisms Internet Security: Principles & Practices John K. Zao, PhD SMIEEE National Chiao-Tung University Fall 2005

2. Internet Security - ComSec Services & Mechanisms What is Communication Security? To provide safe communication over unsafe medium Alice Bob Eve • Safe Communication • Alice can send a message to Bob that only Bob can understand Confidentiality • Nobody can tamper with message content during communication Integrity • Bob can know for sure it was Alice who sent the message Authentication • Unsafe Medium • Medium over which passive and active attacks are possible

3. Internet Security - ComSec Services & Mechanisms Outline • What types of services do we need to protect communication? • What kinds of mechanisms do we use to protect communication?

4. Internet Security - ComSec Services & Mechanisms ISO 7498-2 : Security Framework Architecture • Security Services • Service Types • Service Layer Mapping • Security Mechanisms • Mechanism Definition • Service - Mechanism Mapping

5. Primary Services Internet Security - ComSec Services & Mechanisms Communication Security Services • Confidentiality • Data Confidentiality • Traffic Confidentiality • Data Integrity • Authentication • Data Origin Authentication • Peer Authentication • Access Control • Non-Repudiation • Non-Repudiation of Origin • Non-Repudiation of Reception • Audit • Availability – an after-thought but increasingly important Note: all services are defined here in context of Communication Security

6. Service Types Data Confidentiality / Disclosure Protection Connection Oriented Connectionless Selective Field Traffic Flow Confidentiality Origin Destination Association Message Size Transmission Patterns Accompanied with Data Integrity Protection Mechanisms Data Encryption Symmetric (Secret-Key) Asymmetric (Public-Key) Internet Security - ComSec Services & Mechanisms Confidentiality Protection of information from disclosure to unauthorized entities (organizations, people, machines, processes). Information includes data contents, size, existence, communicationcharacteristics, etc.

7. Service Types Message Integrity Associated with connectionless communication Message Stream Integrity Associated with connection oriented communication Protection Mechanisms Message Digests (Hashing) Sequence Numbers Nonce ID (Random Number) Time Stamps Internet Security - ComSec Services & Mechanisms Integrity Protection of data against creation, alteration, deletion, duplication, re-ordering by unauthorized entities (organizations, people, machines, processes). Integrity violation is always caused by active attacks.

8. Service Types Data Origin Authentication Associated with Connectionless Communication Peer Entity Authentication Associated withConnection Oriented Communication Fundamental for access controlhence, confidentiality & integrity Protection Mechanisms Password Manual One-Time Password Key Sharing Manual Symmetric Key (Tickets) Asymmetric Key (Certificates) Challenge – Response Nonce Based Zero Knowledge Proof Internet Security - ComSec Services & Mechanisms Authentication Communicating entities are provided with assurance & information of relevant identities of communicating partners (people, machines, processes). Personnel Authentication requires special attention.

9. Service Types Subject Based Typing Identity Based Role Based Enforcement Based Typing Mandatory Access Control ― Management Directed Discretionary Access Control ― Resource Owner Directed Protection Mechanisms Access Control Lists (ACLs) Object Based SpecificationEx.: UNIX File System Capabilities Subject Based Specification Issue Tickets/Certificates Internet Security - ComSec Services & Mechanisms Access Control • Protection of information resources or services from access or use by unauthorizedentities (organizations, people, machines, processes). • Privileges – rights to access or use resources or services • Principles – entities own access control privileges • Subjects – entities exercise access control privileges • Objects / Targets – resources or services accessed/used by subjects • Delegation – transfer of access control privileges among principals • Authorization – transfer of access control privileges from principals to subjects

10. Service Types Non-Repudiation of Origin Non-Repudiation of Reception Protection Mechanisms Notarization Time Stamp Digital Signature Internet Security - ComSec Services & Mechanisms Non-Repudiation Protection against denial of participation by communicating entities in all or part of a communication.

11. Service Types Off-line Analysis(Computer Forensic) On-line Analysis(Real-time Intrusion Detection) Protection Mechanisms “Syslog” Intrusion Monitors / Sensors Common Intrusion Detection Framework (CIDF) Common Information Model (CIM) Internet Security - ComSec Services & Mechanisms Audit Recording & analyses of participation, roles and actions in information communication by relevant entities.

12. Internet Security - ComSec Services & Mechanisms Layers of Protocol Protection Security Protection is provided in multiple protocol layers.

13. Internet Security - ComSec Services & Mechanisms Service vs. Layer Mapping

14. Internet Security - ComSec Services & Mechanisms ISO 7498-2 : Security Architecture • Security Services • Service Types • Service Layer Mapping • Security Mechanisms • Mechanism Definition • Service - Mechanism Mapping

15. Internet Security - ComSec Services & Mechanisms Security Mechanisms • Encipherment – with Secret / Public Key Cryptography • Data Integrity – with One-Way Hash Function • Authentication – with Public-Key Challenge/Response • Access Control • Digital Signature – with Public-Key Cryptography • Traffic Padding • Notarization

16. Random Number Generator Symmetric Key Symmetric Key Clear Text Cipher Text Clear Text Encryption Engine Decryption Engine Internet Security - ComSec Services & Mechanisms Symmetric / Secret Key Encipherment Algorithms use same keys for encryption & decryption : • Symmetric / Secret Key must be dispatched in secret • Used for bulk encryption / decryption Also used in following security services : • Authentication

17. PrivateKey Public Key Clear Text Cipher Text Clear Text Encryption Engine Decryption Engine Internet Security - ComSec Services & Mechanisms Asymmetric / Public Key Encipherment Algorithms use different keys for encryption & decryption • Public Key is disclosed but Private Key is kept secret • Computationally intensive - based on large prime numbers Also used in following security services : • Digital Signatures • Authentication • Key Exchange

18. Internet Security - ComSec Services & Mechanisms Data Encryption & Key Distribution Public Key Private Key Encryption Engine Decryption Engine { Symmetric Key Random Number Generator Symmetric Key Symmetric Key Clear Text Cipher Text Clear Text Encryption Engine Decryption Engine

19. Message MD5 Digest Internet Security - ComSec Services & Mechanisms Message Digest or Hash Message Originator Computes a fixed-length message digest from the message using a one-way hash transformation Message Recipient Validate message integrity by computing the message hash and comparing with the message digest

20. Random Number Generator Decryption Engine Private Key Challenge Response Challenge (Recovered) Encryption Engine Public Key = Same? Internet Security - ComSec Services & Mechanisms Challenge-Response Authentication • Challenger sends a challenge of random number to Responder • Responder creates a responsebydigitally signing the challenge with its private key and returns the response to the Challenger • Challenger processes the response with public key of legitimate Responder and compare it with original challenge

21. Message Message MD5 Internet Security - ComSec Services & Mechanisms Digital Signature Signature is public-key encrypted hash of a document and its relevant parameters Signed Document Private Key Digital Signature Decryption Engine Hash

22. Message MD5 Public Key Internet Security - ComSec Services & Mechanisms Digital Signature Validation Message recipients can validate the signature by “encrypting it” with the public key and comparing with document’s hash value Signed Document Hash = Digital Signature Valid? Encryption Engine Hash

23. Service: Data Confidentiality Mechanism [1]: Encipherment Symmetric (Secret-Key) Cipher Asymmetric (Public-Key) Cipher Mechanism [2]: Integrity Message Digest / Digital Hash Mechanism [3]: Key Management Key Distribution Centers (Secret-Key) Public Key Infrastructure(Public-Key) Manual Keying Service: Peer Authentication Mechanism [1]: Challenge+Response Nonce (Random Number) Based Zero-Knowledge Proof Mechanism [2] Integrity Message Digest / Digital Hash Internet Security - ComSec Services & Mechanisms Service - Mechanism Mapping Single security services may need to be implemented by multiple and different security mechanisms.