A general way of cryptography

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)