This document discusses information security, including types of attacks, security services, mechanisms, and cryptography concepts. It covers passive and active attacks such as interception and modification. Cryptography techniques include substitution and transposition ciphers using keys known only to the sender and receiver. The document also discusses cryptanalysis methods like known-plaintext analysis and man-in-the-middle attacks, as well as stream ciphers that generate a keying stream from a secret seed.

1. Introduction
Information Transferring: In information transfer there are several
problems may occur like
Attack
Interruption
Interception
Modification
Fabrication

2. Attacks, Services and Mechanisms
Security Attacks :Action compromises the information security
Security Services: Enhances the security of data processing
and transferring.
Security mechanism :Detect, prevent and recover from a
security attack

3. Types of Attack
Passive attacks
Interception
 Release of message contents
 Traffic analysis
Active attacks
Interruption, modification, fabrication
 Masquerade
 Replay
 Modification
 Denial of service

4. Network Security Model
• Trusted Third Party
• principal
• Security transformation
• opponent

5. Basic Concepts of Cryptography
Cryptography is the study of
 Secret(crypto) writing(graphy)
Concerned with developing algorithms:
 Conceal the context of some message from all except the sender and
recipient (privacy or secrecy), and/or
 Verify the correctness of a message to the recipient (authentication)

6. Continued……
 Plaintext : The original intelligible message
 Ciphertext : The transformed message
Cipher :An algorithm for transforming an intelligible message into
unintelligible by transposition and/or substitution.
Key : Some critical information used by the cipher, known only to the
sender & receiver

7. Classical Cryptographic Techniques
Two basic components of classical ciphers:
 Substitution:letters are replaced by other letters
 Transposition:letters are arranged in a different order
 Monoalphabetic: only one substitution/ transposition is
Polyalphabetic:where several substitutions/ transpositions are used

8. Steganography
Conceal the existence of message
 Character marking
 Invisible ink
 Pin punctures
 Typewriter correction ribbon

9. Cryptanalysis
It’s the way of breaking the codes

10. • Known-Plaintext Analysis (KPA): Attacker decrypt ciphertexts with known
partial plaintext.
• Chosen-Plaintext Analysis (CPA): Attacker uses ciphertext that matches
arbitrarily selected plaintext via the same algorithm technique.
• Ciphertext-Only Analysis (COA): Attacker uses known ciphertext collections.
• Man-in-the-Middle (MITM) Attack: Attack occurs when two parties use
message or key sharing for communication via a channel that appears
secure but is actually compromised. Attacker employs this attack for the
interception of messages that pass through the communications channel.
Hash functions prevent MITM attacks.
• Adaptive Chosen-Plaintext Attack (ACPA): Similar to a CPA, this attack uses
chosen plaintext and ciphertext based on data learned from past
encryptions.

11. Stream Ciphers
• Start with a secret key (“seed”)
• Generate a keying stream
• i-th bit/byte of keying stream is a function of the key and the first i-1
ciphertext bits.
• Combine the stream with the plaintext to produce the ciphertext
(typically by XOR)