1. CIM3681 - Introduction 1 Introduction Based on Cryptography and Network Security by William Stallings, 3rd Edition

2. CIM3681 - Introduction 2 Introduction The art of war teaches us to rely not on the likelihood of the enemy's not coming, but on our own readiness to receive him; not on the chance of his not attacking, but rather on the fact that we have made our position unassailable. —The Art of War, Sun Tzu

3. CIM3681 - Introduction 3 Contents Introduction ( 介紹 ) Services( 服務 ), Mechanisms( 機制 ), and Attacks( 攻擊 ) The OSI Security Architecture ( 保衛結構 ) A Model ( 模型 ) for Network Security

4. CIM3681 - Introduction 4 Background Information Security requirements ( 必要條件 ) have changed in recent ( 近代的 ) times Traditionally ( 傳統, 慣例 ) provided by physical and administrative ( 管理的, 行政的 ) mechanisms computer use requires automated tools to protect files and other stored information use of networks and communications links ( 鏈 ) requires measures ( 措施 ) to protect data during transmission

5. CIM3681 - Introduction 5 Definitions Computer ( 電子計算機 )Security - generic name for the collection of tools designed to protect data and to thwart hackers Network ( 網絡 ) Security - measures to protect data during their transmission Internet ( 互聯網絡 ) Security - measures to protect data during their transmission over a collection of interconnected ( 互連 ) networks Our focus is on Internet Security

6. CIM3681 - Introduction 6 Services, Mechanisms, and Attacks systematic ( 有系統的 ) way to define requirements consider three aspects ( 方向 ) of information ( 資訊 ) security:  security attack  security mechanism  security service

7. CIM3681 - Introduction 7 Security Service enhances the security of the data processing systems and the information transfers of an organization intended to counter security attacks make use of one or more security mechanisms to provide the service replicate functions normally associated with physical documents  eg. have signatures, dates; need protection from disclosure, tampering, or destruction; be notarized or witnessed; be recorded or licensed

8. CIM3681 - Introduction 8 Security Mechanism a mechanism that is designed to detect, prevent, or recover from a security attack no single mechanism that will support all functions required however one particular element underlies many of the security mechanisms in use: cryptographic techniques hence our focus on this area

9. CIM3681 - Introduction 9 Security Attacks any action that compromises ( 危害 ) the security of information owned by an organization information security is about how to prevent ( 預防, 防 止, 避免, 阻止 ) attacks, or failing that, to detect attacks on information-based systems have a wide range of attacks can focus of generic ( 一般的, 普通的 ) types of attacks note: often threat ( 威脅, 恐嚇, 造成威脅的事物 )& attack mean same

10. CIM3681 - Introduction 10 The OSI Security Architecture ITU-T X.800 Security Architecture for OSI defines a systematic way of defining and providing security requirements for us it provides a useful, if abstract, overview of concepts we will study Treat ITU-T X.800 with security service, security mechanism, and security attack

11. CIM3681 - Introduction 11 X.800 Security Services X.800 defines it as: a service provided by a protocol layer of communicating open systems, which ensures adequate ( 足夠的, 充 分的 ) security of the systems or of data transfers RFC 2828 defines it as: a processing or communication service provided by a system to give a specific ( 特定的, 具體的 ) kind of protection to system resources

12. CIM3681 - Introduction 12 X.800 Security Services (5) Authentication ( 鑑定, 鑑別 ) - assurance that the communicating entity is the one claimed Access Control ( 存取控制 ) - prevention of the unauthorized use of a resource Data Confidentiality ( 數據機密性 ) –protection of data from unauthorized disclosure Data Integrity ( 數據完整性 ) - assurance that data received is as sent by an authorized entity Non-Repudiation( 不得否認 ) - protection against denial by one of the parties in a communication Refer to Table 1.4 Security Services (X.800)

13. CIM3681 - Introduction 13 Security Mechanisms (X.800) specific security mechanisms:  Encipherment ( 加密 ), digital signatures ( 數位簽字 ), access controls, data integrity, authentication exchange, traffic padding ( 填補 ), routing ( 選路 ) control, notarization ( 公証 ) Pervasive ( 滲透的 ) security mechanisms:  trusted functionality ( 功能性 ), security labels ( 標簽 ), event detection, security audit trails ( 蹤跡 ), security recovery ( 恢復 ) Refer to Table 1.5 Security Mechanisms (X.800)

14. CIM3681 - Introduction 14 Security Attacks (X.800) passive ( 消極的, 被動的 ) attacks - eavesdropping on, or monitoring of, transmissions to:  obtain message contents, or  monitor traffic flows active ( 積極的 ) attacks – modification of data stream to:  Masquerade ( 偽裝, 假裝 ) of one entity as some other  Replay ( 重演 ) previous messages  modify messages in transit ( 運輸 )  Denial ( 拒絕 ) of service

15. CIM3681 - Introduction 15 Model for Network Security A security-related transformation on the information to be sent. E.g. Encryption Some secret information shared by the two principals, unknown to the opponent. E.g. A trusted ( 信任 ) third party is responsible for distributing the secret information to the principals ( 負責人 ).

16. CIM3681 - Introduction 16 Model for Network Security Four basic tasks in designing a security service  design a suitable algorithm( 運演算法則 ) for the security transformation  generate the secret information (keys) used by the algorithm  develop methods to distribute and share the secret information  specify a protocol enabling the principals to use the transformation and secret information for a security service

17. CIM3681 - Introduction 17 Methods for handling threats in the SM  select appropriate gatekeeper functions to identify users  implement security controls to ensure only authorised ( 授權的 ) users access designated information or resources

18. CIM3681 - Introduction 18 Summary Introduction Services, Mechanisms, and Attacks The OSI Security Architecture A Model for Network Security http://WilliamStallings.com/Crypto3e.html