MODULE 20 — CRYPTOGRAPHY (CEHv13)

SOURCE: CEHv13 – Module 20 – Cryptography

LEARNING OBJECTIVES (EXAM-MANDATORY)

You must be able to:

# Learning Objective
01 Explain cryptography concepts
02 Understand different encryption algorithms
03 Use different cryptography tools
04 Apply applications of cryptography
05 Describe cryptography attacks
06 Use cryptanalysis tools

MEMORY HOOK:
Concepts → Algorithms → Tools → Applications → Attacks → Analysis

OBJECTIVE 01 — CRYPTOGRAPHY CONCEPTS AND ENCRYPTION ALGORITHMS

WHAT IS CRYPTOGRAPHY (DEFINITION — EXACT CEH MEANING)

Term Definition
Cryptography The practice of concealing information by converting readable data into an unreadable format using encryption

ORIGIN (EXAM FACT):

  • Greek kryptos = hidden

  • Greek graphia = writing

MEMORY HOOK:
Crypto = hidden writing

WHAT ENCRYPTION DOES

Action Description
Encryption Converts plaintext into ciphertext
Decryption Converts ciphertext back into plaintext

CRYPTOGRAPHY PROCESS (LOGIC FLOW)

Step
Plaintext
Encryption algorithm + key
Ciphertext
Transmission
Decryption algorithm + key
Plaintext

EXAM TRAP:
Encryption does not remove data, it only transforms representation.

OBJECTIVES OF CRYPTOGRAPHY (VERY HIGH YIELD)

Objective Meaning
Confidentiality Only authorized users can access information
Integrity Data is not altered improperly
Authentication Identity of sender/receiver is verified
Non-repudiation Sender cannot deny sending the message

MEMORY HOOK:
CIA + N

EXAM TRAP:
Encryption alone ≠ authentication or integrity.

BASIC CRYPTOGRAPHY TERMINOLOGY

Term Meaning
Plaintext Readable original data
Ciphertext Encrypted unreadable data
Cipher Algorithm used to encrypt/decrypt
Key Secret value controlling encryption
Cryptanalysis Breaking encryption
Cryptosystem Algorithms + keys + protocols

TYPES OF CRYPTOGRAPHY (TOP-TIER EXAM CONTENT)

Cryptography is classified based on number of keys used.

1. SYMMETRIC KEY CRYPTOGRAPHY

Property Description
Keys used Same key for encryption and decryption
Speed Fast
Security issue Key distribution problem
Also called Secret-key cryptography

LOGIC:

  • Sender encrypts using shared secret key

  • Receiver decrypts using same key

MEMORY HOOK:
One key → fast → hard to share

2. ASYMMETRIC KEY CRYPTOGRAPHY

Property Description
Keys used Public key + private key
Speed Slow
Security Solves key distribution problem
Also called Public-key cryptography

LOGIC:

  • Public key encrypts

  • Private key decrypts

MEMORY HOOK:
Two keys → secure sharing → slower

ASYMMETRIC ENCRYPTION MESSAGE FLOW (EXAM LOGIC)

Step Description
1 Sender finds receiver’s public key
2 Sender encrypts message using public key
3 Only receiver’s private key can decrypt
4 Ensures confidentiality
5 Digital signatures ensure authentication

EXAM TRAP:
Public key cannot decrypt what it encrypts.

STRENGTHS & WEAKNESSES (VERY COMMON MCQs)

SYMMETRIC ENCRYPTION

Strengths Weaknesses
Fast Key distribution problem
Efficient Difficult key management
Less CPU usage No authentication

ASYMMETRIC ENCRYPTION

Strengths Weaknesses
Secure key exchange Slow
Digital signatures High CPU usage
Authentication Not suitable for bulk data

MEMORY HOOK:
Symmetric = fast, Asymmetric = trust

GOVERNMENT ACCESS TO KEYS (GAK) — EXAM CONCEPT

Term Explanation
GAK Government-mandated access to encryption keys
Purpose Lawful interception
Method Key escrow
Risk Weakens privacy

MEMORY HOOK:
Key escrow = third party holds keys

EXAM TRAP:
Key escrow ≠ backdoor (but effect is similar).

WHAT IS A CIPHER

Definition
A cipher is a set of mathematical steps used to encrypt or decrypt data

TYPES OF CIPHERS

CLASSICAL CIPHERS

Type Description
Substitution Replace characters
Transposition Rearrange characters

EXAMPLES (EXAM):

  • Caesar cipher

  • Hill cipher

  • Rail fence cipher

MEMORY HOOK:
Classical = letters

MODERN CIPHERS

Classified by:

A. TYPE OF KEY USED

Type
Symmetric
Asymmetric

B. TYPE OF INPUT DATA

Type Description
Block cipher Encrypts fixed-size blocks
Stream cipher Encrypts data bit-by-bit

MEMORY HOOK:
Block = chunks, Stream = flow

OBJECTIVE 01 — MEMORY CHECKLIST

You must remember:

  • Cryptography goals = CIA + N

  • Symmetric vs Asymmetric differences

  • Encryption ≠ authentication

  • Public key encrypts, private key decrypts

  • Block vs Stream cipher difference

  • Key distribution problem

  • Key escrow definition

STATUS

Module 20
Objective 01: COMPLETE