Distributed Security Issues: Network Design and Threats

1. Distributed Security Issues • CP3397 • Design of Networks and Security

2. Objectives • To transfer the concepts from a single Computer to a Network • How can basic issues be viewed in a Network Environment • How can we present security so its not perceived as Big Brother?

3. Distributed Security is Different • In a centralised environment, all security is necessarily managed at one point • We can not have users controlling local security at the Work Station • There must be a Policy on Security Administered from a central point

4. Distributed Issues • In a distributed environment, local security is not practical due to scalability problems • In security terms a user or system entity (e.g., a process) is referred to as a principal • Principals request operations by sending message to system objects

5. Categories defined for Security Concern • Loss of Confidentiality • information is revealed to one or more unauthorised principals • Loss of Integrity • information is corrupted, accidentally or maliciously

6. Security Concerns • Loss of Accountability • information or actions cannot be accurately attributed • Loss of Service • services are denied to authorised principals

7. Potential Security Breaches common to Distributed systems • Physical damage, Forgery, Interception • Masquerading, Modification, Replay • Spoofing, Repudiation, Infiltration • Viruses, Trojan Horses, Logic Bombs, etc

8. Distributed Concepts: The 3 ‘A’s • Authentication • Establishing the validity of a claimed identity • Authorisation • Establishing the credentials of authenticated principal and their access rights • Accountability • Establishing proof of origin of actions i.e who sent a message, who edited a file (and when)

9. Distributed Concepts: The 5 ‘S’s • Secret • cannot be interpreted by unauthorised principal • Sealed • tampering can be detected • Signed • identity of principal can be guaranteed • Stamped • confirmation of receipt can be guaranteed • Sequence • duplication and replay are prevented

10. Security Policy • Security is concerned with more than just technical systems • A security policy is a set of rules that define • Procedures - relevant to security management • e.g. what constitutes authorised activity, appropriate monitoring mechanisms? • Responsibilities - who is responsible for what? • Reporting - what, when and to whom? • Enforcement - how to ensure the policy is enacted

11. Basic Security Policy • Assumes all clients are untrustworthy until trustworthiness can be proved • Assumes all services are untrustworthy • Assumes all networks are completely untrustworthy • Clients and servers must be trusted to some degree • within the context of a security policy • Concept of Security Domain • each domain has its own security policy

12. Basic Security Mechanisms • Data Confidentiality • Authentication • Authorisation • Non-repudiation • Administration

13. Data Confidentiality • The process of ensuring message contents are only revealed to authorised principals • Main technique is cryptography • Two related aspects: • Encryption • conversion of Plaintext to Ciphertext • Decryption • the reverse • Uses a key, K,and can be represented as: Ciphertext = K(Plaintext)

14. Encryption • The art of secret writing • Trust in the honesty of each end of the encrypted channel. • Using paper based systems this trust was implicate. • Both parties agreed not to divulge the Key

15. Electronic Encryption • There is now the possibility of a dispute between parties, for instance in an e - commerce transaction. • Trust is lost and protocol techniques are required with normally the inclusion of a third party the .. Trusted Third Party.(TTP)

16. Encryption • Old paradigm • New paradigm Intruder TTP

17. Encryption - Symmetric • Also known as Shared or Secret Key Encryption • Uses a shared secret key Ks to encrypt a message, M. If Ciphertext = Ks(M) Then M = Ks(Ciphertext) • Requires a key distribution service • The Trusted Third Party • Example is Data Encryption Standard (DES), developed for US DoD.

18. Key Distribution Service Secret Key, K Secret Key, K Ciphertext Plaintext Encryption Decryption Plaintext Symmetrical Key Encryption

19. Bit-level cipher • XOR • Truth table • A B F • 0 0 0 • 0 1 1 • 0 1 • 1 1 1 • Used to encrypt any type of data – not just text based • Encryption key is just a bit pattern • Apply an XOR between the data and key • Forward the result • Decryption – repeat the process using the same key

20. 0101110111010011 M Plaintext 1000110101110101 Ks Shared Key (encryption key) C Ciphertext plain text XORed With the key 1101000010100110 1000110101110101 Ks Shared Key (same key) Bit-level cipher 0101110111010011M Plaintext C = Ks( M ) and so M = Ks ( C )

21. Problems with symmetric keys • If key broken/compromised then all data can be intercepted or bogus messages sent • Distribution of keys can be difficult either by hand or across various channels • Short keys may result in repeated substrings – easy to break pattern • Longer keys more secure but key distribution more difficult • Use shorter keys but more complicated algorithms

22. DES • Message is divided into 64 packets and a 56 bit key is applied • Produces 64 encrypted data from complex algorithm XORs, substitutions, transpositions etc. • Has around 25 steps (calculations) in the algorithm • Some of the parts of the algorithms involving swaps were seen as illogical • Developed by a team from IBM but with input from the American National Security Agency who persuaded 56 bit key instead of the proposed 128 bits. • Seen as a weak encryption technique with political reasons as to why • 256 = 1016 possible key values • Brute force attack breaks it within hours or even less

23. Improved Symmetrical algorithms • Triple-DES • DES algoritm applied three times with 2 differing keys • Was used to extend the life of DES • International Data Encryption Algorithm • Block encryption algoritm (1990) • 128 bit key and still yet to be broken – but weak keys that will allow an attack have been identified

24. Encryption - Asymmetric • Asymmetric • Uses a key-pair - two different keys: • one private, Kpriv - for encryption • one public, Kpub - for decryption M = Kpub( Kpriv(M)) • Distribution - either • Public key can be freely distributed • or a Key Distribution Service can be used • Hard to generate efficient key pairs • Example is RSA algorithm

25. Public-Private Key Encryption • “Give me the public • key for . . . . .” Key Distribution Service Public Key, Kpub Ciphertext Plaintext Plaintext Encryption Decryption Public Key, Kpub Private Key, Kpriv

26. Asymmetric • Asymmetric - e.g. RSA • Key pairs based on factors of prime numbers • Difficult to calculate effective key pairs • Extremely difficult to crack (billions of years) • Slower in operation than DES (100-10,000 times) • Provides a signature that can not reproduced • Keys for commercial level security are 1024 bits long and are typically 1024–2048 bits long • Brute force attack not applicable

27. Why use symmetric keys? • typically faster 100 to 1,000 times than public key encryption, places a much heavier computational load on computer processors than symmetric key encryption. • symmetric key technology is generally used to provide secrecy for the bulk encryption and decryption of information. • Symmetric keys are commonly used by security protocols as session keys for confidential online communications. • Transport Layer Security (TLS) and Internet Protocol security (IPSec) protocols use symmetric session keys with standard encryption algorithms to encrypt and decrypt confidential communications between parties. • Different session keys are used for each confidential communication session and session keys are sometimes renewed at specified intervals.

28. Transmission Checksums • Checksums are widely used in computing for error detection • Can also be used to check integrity of messages • based on the fact that it is difficult to modify message without altering checksum • Cheap and quick • But only useful when confidentiality is not important but non-modification is crucial

29. Summary • So we can map single user to network security issues • Need a Policy • Need someone responsible for the policy • Confidentiality • Encryption • Private / Public