IT5703 Cryptography
and Network Security
Dr.G.Geetha M.E.,Ph.D
Women scientist
Qualified Patent Agent, IP Consultant
Deputy Director -Centre for Intellectual Property Rights
Associate Professor,
Department of Information Science and Technology,
College of Engineering, Guindy,
Anna University, CEG Campus, Chennai
UNIT I : INTRODUCTION TO SECURITY AND
NUMBER THEORY
Basics of Security – CIA Triad – Threats, Attacks and Services –
Classical Cryptography –Substitution – Transposition – One-time
Pad – Cryptanalysis – Number Theory – Modular Arithmetic –
Euclidean Theorem – Extended Euclidean Theorem – Algebraic
Structures –Galois Field – Prime Numbers – Fermat’s Theorem –
Euler’s Phi function – Euler's Theorem– Chinese Remainder theorem
– Modular Exponentiation –Logarithms – Elliptic Curve Arithmetic.
UNIT II: SYMMETRIC CRYPTOGRAPHY
Modern Cryptography – Symmetric Cipher – Block and Stream
Cipher – Feistel Ciphers –Data Encryption Standard (DES) – DES
Structure – Key Generation – Simplified DES –Linear and
Differential cryptanalysis –Triple DES – Advanced Encryption
Standard (AES) – Basic Structure – Transformations – Key
Expansions Process – Analysis of AES – Modes of operation –
RC4
UNIT III: ASYMMETRIC KEY
CRYPTOGRAPHY
Public Key Cryptosystems – RSA Algorithm – ElGamal
Cryptosystems – Diffie-Hellman key exchange – Elliptic curve
cryptography – Hash functions – Hash algorithms – Secure Hash
Algorithm SHA – MD5 – Message Authentication Codes –
Quantum Cryptography –Quantum Key Distribution – Threshold
Cryptography
UNIT IV: SECURITY APPLICATIONS
Digital Signatures Schemes– Digital Certificate – Key
Management – Kerberos – Key Agreement and Distribution – PKI
– X.509 Certificate – E-Mail Security – PGP – S/MIME –IP
security – Virtual Private Network (VPN) – Web Security –
Secure Socket Layer (SSL) –Transport Layer Security – Secure
Electronic Transaction (SET) – Blockchain
UNIT V: FIREWALL & WIRELESS SECURITY
Buffer Overflow and Malicious Software – Password
Management – Introduction to Firewall – Firewall Generations –
Intrusion Detection System – Types of IDS – Intrusion Prevention
System – Wireless LAN – Wireless LAN Security – Network
Access Control and Cloud Security.
UNIT III: ASYMMETRIC KEY
CRYPTOGRAPHY
Public Key Cryptosystems – RSA Algorithm – ElGamal
Cryptosystems – Diffie-Hellman key exchange – Elliptic curve
cryptography – Hash functions – Hash algorithms – Secure Hash
Algorithm SHA – MD5 – Message Authentication Codes –
Quantum Cryptography –Quantum Key Distribution – Threshold
Cryptography
Public Key Cryptosystems
Public Key Cryptosystems
Hash Algorithms
• see similarities in the evolution of hash functions & block
ciphers
– increasing power of brute-force attacks
– leading to evolution in algorithms
– from DES to AES in block ciphers
– from MD4 & MD5 to SHA-1 & RIPEMD-160 in hash algorithms
• likewise tend to use common iterative structure as do
block ciphers
MD5
• designed by Ronald Rivest (the R in RSA)
• latest in a series of MD2, MD4
• produces a 128-bit hash value
• until recently was the most widely used hash algorithm
– in recent times have both brute-force & cryptanalytic concerns
• specified as Internet standard RFC1321
MD5 Overview
1. pad message so its length is 448 mod 512
2. append a 64-bit length value to message
3. initialise 4-word (128-bit) MD buffer (A,B,C,D)
4. process message in 16-word (512-bit) blocks:
– using 4 rounds of 16 bit operations on message block & buffer
– add output to buffer input to form new buffer value
5. output hash value is the final buffer value
MD5 Overview
MD5 Compression Function
• each round has 16 steps of the form:
a = b+((a+g(b,c,d)+X[k]+T[i])<<<s)
• a,b,c,d refer to the 4 words of the buffer, but used in
varying permutations
– note this updates 1 word only of the buffer
– after 16 steps each word is updated 4 times
• where g(b,c,d) is a different nonlinear function in each
round (F,G,H,I)
• T[i] is a constant value derived from sin
MD5 Compression Function
MD4
• precursor to MD5
• also produces a 128-bit hash of message
• has 3 rounds of 16 steps vs 4 in MD5
• design goals:
– collision resistant (hard to find collisions)
– direct security (no dependence on "hard" problems)
– fast, simple, compact
– favours little-endian systems (eg PCs)
Strength of MD5
• MD5 hash is dependent on all message bits
• Rivest claims security is good as can be
• known attacks are:
– Berson 92 attacked any 1 round using differential cryptanalysis (but can’t
extend)
– Boer & Bosselaers 93 found a pseudo collision (again unable to extend)
– Dobbertin 96 created collisions on MD compression function (but initial
constants prevent exploit)
• conclusion is that MD5 looks vulnerable soon
