1. Introduction to Security
Chapter 9 Security
Introduction to Security

2. Overview Why study security Types of Threats Security mechanisms
Design issues
Cryptography

3. Why study Security

4. Why study Security Computers and mobile phones are used extensively
Malicious intentions of “bad” folks
Manipulate data or watch data exchanged
Imperative to understand Security of Distributed Systems
What mechanisms to apply and where to use them

5. Why study Security Security in Distributed systems
Secure channel for communication
Access control of users
What does a secure computer mean
Available
Reliable
Dependable
Maintains integrity
Confidential

6. Types of Threats

7. Types of Threats Interception Interruption Modification Fabrication
Gains access to service or data - Eavesdropping
Interruption
Service or data becomes unavailable
Modification
Tampering of service or changing data in the system
Fabrication
Additional data or activity generated and inserted in system

8. Security Mechanisms Encryption Authentication Authorization Auditing
Transform data to make it unrecognizable to attacker
Can check if the data is modified
Authentication
Verify identify the user, client, server, host
Authorization
Verify authorization to perform
Auditing
Audit logs help in analyze breach

9. Design Issues

10. Focus of Control - 3 approaches for protection
Protection of data against invalid operations

11. 2. Control which operation may be invoked

12. 3. Protection against unauthorized users

13. Layering of Security Mechanisms
At which level should security mechanisms be placed

14. Distribution of Security Mechanisms
Trusted Computing Base – set of all security mechanisms

15. Simplicity Designing is generally difficult
Simple mechanism is not sufficient

16. Cryptography

17. Cryptography It is fundamental to security Secures communication
Encrypt the data into something unintelligible
Those meant to receive can decipher the data
C = EK(P)
P = DK(C)
P – Plain text C – Cipher text K – Key
E and D – Encryption and Decryption algorithms

18. 3 types of cryptographic systems
3 types of attacks
Eavesdropping
Modification of messages
Insertion of messages
3 types of cryptographic systems
Symmetric
Asymmetric
Hash Functions

20. Symmetric Cryptograms
Secret key or shared key systems
Sender and Receiver share the secret key before hand
Example DES
Operates on 64 bit block of data
An initial round of permutation
Block is broken into two parts , Right and Left
16 rounds of identical operations, f
After the 16 rounds, the halves are joined
A final permutation(inverse of the initial)

21. DES

22. DES – Key Generation

23. DES
Difficult is break using analytical methods
Key search can break it
Triple DES encrypt – decrypt – encrypt (message)
Design not known, so harder to break
Latest algorithms use larger blocks and larger keys

24. Asymmetric Cryptograms
2 different keys, public key and private key
Encryption and decryption use different keys
Encryption function is hard, one way function
Mathematically not feasible for the attacker to calculate private key from private key
Public key is usually ‘signed’ by a third party

25. RSA
Named after the Ron, Shamir, Adleman
Each person communicating needs to generate public and private keys
Public key:
Select two large prime numbers p, q
Let n = p*q
Choose e such that it 1 < e < (p -1)(q – 1) and
e and (p -1)(q -1) are coprime
(n ,e) form the public key

26. Private key: Encryption C = P e mod n Decryption
It is calculated from p, q, e. There is a unique number d for given n, e.
d is the inverse of e ≡ (p-1)(q-1)
or de ≡ 1 mod (p - 1)(q - 1)
d is the private key
Encryption
C = P e mod n
Decryption
P = C d mod n

27. Strong collision resistance, cannot find m’ such that
Hash Functions
takes an arbitrary length input m and produces a bit string of fixed length h
h = H(m)
They are one way functions, computationally infeasible to find m knowing h
Strong collision resistance, cannot find m’ such that
H(m) = H(m’)
Often used to authenticate digital signatures

28. MD5 Message Digest Algorithm
MD5 hashes are 128-bits in length and are normally shown in their 32 digit hexadecimal value equivalent
it has been found to suffer from extensive vulnerabilities
MD5 is neither encryption nor encoding
Most U.S. government applications now require the SHA-2 family of hash functions
In 2012, the Flame malware exploited the weaknesses in MD5 to fake a Microsoft digital signature.

30. MD5
The message m is padded to make it congruent to 448 modulo 512, made 64 bits less than
A 64 bit representation of m is appended to the result of the above step
A four word buffer (A,B,C,D) is used to compute the message digest
A,B,C,D are 32 bit registers
word A :
word B : 89 ab cd ef
word C : fe dc ba 98
word D :

31. MD5
There are 4 functions that take each take 3 32-bit words as input and produce one 32-bit word as output
F (X, Y, Z) = XY or not (X) Z
G (X, Y, Z) = XZ or Y not (Z)
H (X, Y, Z) = X xor Y xor Z
I (X, Y, Z) = Y xor (X or not (Z))

32. MD5
[abcd k s i] denote the operation a = b + ((a + F (b, c, d) + X [k] + T [i]) <<< s).
Do the following 16 operations.
[ABCD ] [DABC ] [CDAB ] [BCDA ]
[ABCD ] [DABC ] [CDAB ] [BCDA ]
[ABCD ] [DABC ] [CDAB ] [BCDA ]
[ABCD ] [DABC ] [CDAB ] [BCDA ]

33. MD5
The message digest produced as output is
A, B, C, D.
That is, output begins with the low-order byte
of A, and end with the high-order byte of D

34. Current Research MD5 DES
Increasing the data structure size and the key length ensure the strength of the encryption algorithm.
RSA
It can be made more secure by using 4 prime numbers instead of 4
MD5

35. References
Tanenbaum, Andrew S., and Maarten van Steen. Distributed Systems:
Principles and Paradigms. Maarten Van Steen, 2016.
A hybrid security algorithm for RSA cryptosystem
Prabhat K. Panda; Sudipta Chattopadhyay
2017 4th International Conference on Advanced Computing and Communication Systems (ICACCS)
Extended DES algorithm to Galois Fields
Luminiţa Scripcariu; Petre-Daniel Mătăsaru; Felix Diaconu
2017 International Symposium on Signals, Circuits and Systems (ISSCS)