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L0. Introduction

L0. Introduction. Rocky K. C. Chang , January 2013. The Internet is inherently insecure. Internet backbone infrastructure: DoS , worm Routing protocols (BGP): route hijacking DNS: poisoning, DoS

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L0. Introduction

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  1. L0. Introduction Rocky K. C. Chang, January 2013

  2. The Internet is inherently insecure. • Internet backbone infrastructure: DoS, worm • Routing protocols (BGP): route hijacking • DNS: poisoning, DoS • Core Internet protocols (e.g., IP, TCP/UDP, HTTP): eavesdropping, modification, authentication • LAN security: eavesdropping, modification, authentication • Host security (e.g., Web servers, database): DoS, authentication, phishing, malicious software implant, identity and data theft, data exfiltration, etc.

  3. Internet security is inherently complex. • A packet goes through many hops and links. • Involve from the physical layer and up. • Physical layer security • Network security • System security • Application security • Complexity in software and protocols • Software ages • Some protocol fields are never tested. • The weakest link • The human factor • The success of Internet makes things worse. • Security verses privacy (anonymity) • How to measure security?

  4. Internet security is more than cryptography. • Cryptography is not the solution to many security problems, e.g., software exploit, DoS. • The vulnerability could come from the implementations of the cryptographic algorithms. • Cryptography affects performance. • Ease of use

  5. Security involves • Threats: potential violation of security • Policies • Security policies: trust and access control • Confidentiality policies: The Bell-LaPadula model • Integrity policies: Clark-Wilson integrity model • Hybrid policies: Chinese Wall models • Design and implementation • Identity representation, access control lists, information flow, etc • Encryption and key management • Authentication (human, user account, machine, service)

  6. Security involves • How to ascertain how well a system meets its security goals? • Assurance, system evaluation (TCSEC) • Miscellaneous, e.g., • Viruses, worms, software security • Auditing • Intrusion detection • System security • Network security • User security

  7. This course is not about • Cryptography, the art of secret writing, • Writing computer viruses and worms, • Special techniques of attacking and defending, • The lower layer security measures, • System security, • Biometrics, • Application-specific security • …

  8. This course is about • Understand the 3 fundamental cryptographic functions used in network security. • Understand the issues involved when applying the cryptographic functions to the network protocols. • Understand the main elements in securing today’s Internet infrastructure. • Exposed to some current Internet security problems.

  9. Purposes of network security • Confidentiality (or secrecy): Prevent others from reading information shared between two participants. • Authentication: Verify someone’s or something’s identity. • Message integrity: Assure that the message received has not be altered since it was generated by a legitimate source. • Nonrepudiation: A sender should not be able to falsely deny later that he sent a message. • Legitimate (and authorized) usage: Ensure that the network and system resources are properly utilized.

  10. Possible threats • Obtaining information for … • Secrecy, authentication • Modifying information for … • Authentication, message integrity • Stealing information for … • Secrecy, authentication, legitimate usage • Lying electronically for … • Nonrepudiation • Backmail for … • Secrecy, legitimate usage, message integrity • Revenge for … • Legitimate usage, message integrity • Testing for … • Legitimate usage, message integrity • Contracted for … • Secrecy, authentication, legitimate usage, message integrity • Fun for … • Secrecy, authentication, legitimate usage, message integrity

  11. The goals of security • Prevention: • Confidentiality, source authentication, nonrepudiation, and legitimate usage • Active countermeasures • Detection: • Message authentication, nonrepudiation, and legitimate usage • Active and passive countermeasures • Recovery: • Legitimate usage • Rely on the detection. • Traceback: • Locate the actual attack source(s).

  12. Scope of considerations • Two cases • The secrecy, message integrity, authentication, and nonrepudiation services are provided by some cryptographic functions. • Denial-of-service, worms, viruses, etc • Scope: • Concern mainly communication between two parties (group communication security is another important topic). • Concern attacks against protocols, not those against cryptographic algorithms or cryptographic techniques used to implement the algorithms.

  13. Cryptography • Plaintext  (encryption)  ciphertext • Ciphertext  (decryption)  plaintext • What is the secret? • The cryptographic algorithm (restricted algorithm) • The cryptographic algorithm is not a secret, but the key is. • Level of security  the length of the key  the time of discovering the key using brute force • The security problem is reduced to the securing of the key.

  14. Types of attacks • Passive attacks (eavesdropping), e.g., • ciphertext-only attacks (recognizable plaintext attacks) • Fred has seen some ciphertext. • known-plaintext attacks • Fred has obtained some <plaintext, ciphertext> pairs. • chosen-plaintext attacks • Fred can choose any plaintext he wants. • Active attacks, e.g., • pretend to be someone else • introduce new messages in the protocol • delete existing messages • substituting one message for another • replay old messages

  15. Three cryptographic functions • Hash functions: require 0 key • Secret key functions: require 1 key • Public key functions: require 2 keys

  16. Secret key (symmetric) cryptography • Given: • Alice and Bob agree on a secret key cryptosystem. • Alice and Bob agree on a key (secret) K. • Encryption and decryption using the key. • Alice encrypts M with K: K{M} • Bob decrypts K{M} with K  M • Problems: • Keys must be distributed in secret. • Compromising keys means compromising all aspects of security. • The number of keys is not scalable to the user population size.

  17. Usages of the secret key cryptography • Transmitting over an insecure channel • Secure storage on insecure media • Authentication: • Challenge-response authentication with shared secret • Message integrity check

  18. Public key (asymmetric) cryptography • Given: • Alice and Bob agree on a public key cryptosystem. • Alice owns a pair of public key and private key, and Bob knows Alice’s public key, which is not a secret. • Encryption using the public key and decryption using the private key. • Alice encrypts M with Bob’s public key: {M}Bob • Bob decrypts {M}Bob with its private key  M • Generate a digital signature on a message: • Alice signs M with its private key: [M]Alice. • Bob verifies Alice’s signature on [M]Alice with Alice’s public key.

  19. Usages of the public key cryptography • Problems: • Public-key algorithms are slow. Secret key algorithms are at least 1,000 times faster. • Obtain the public key reliably. • Usages: • Transmitting over an insecure channel • Secure storage on insecure media (difference as compared with the secret key cryptography?) • Authentication: • Nonrepudiation with the digital signatures.

  20. Hash functions • A hash (message digest or one-way function) produces a short, fixed-sized output h(m) for a message m. • Properties: • One-way functions are relatively easy to compute, i.e., given x and compute h(x). • However, given h(x), it is significantly harder to compute x. • It is computationally infeasible to find two inputs that hash to the same value.

  21. Usages of hash functions • Password hashing • Message integrity • Keyed hash: compute h(message | key) and send the result with the message. • Message fingerprinting • Downline load security • Digital signature efficiency

  22. Securing the Internet • IP Security (IPSec) • TCP and UDP insecurity • SSL/TLS • DNS security • Firewalls • DoS attacks and the countermeasures • Buffer overflow attacks and the countermeasures • Wireless LAN security

  23. Acknowledgments • This set of notes is based on • C. Kaufman, R. Perlman, and M. Speciner, Network Security: Private Communication in Public World, Second Edition, Prentice Hall PTR, 2002. • L. Peterson and B. Davie, Computer Networks: A Systems Approach, Morgan Kaufmann, 2000. • B. Schneier. Applied Cryptography, Second Edition, Wiley, 1996. • M. Bishop, Introduction to Computer Security, Addison Wesley, 2005.

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