Chapter 1: Introduction to Cryptography
(University-Level Detailed Notes)
1.1 Definition & Scope
Cryptography is the science and art of
securing communication in the presence of
adversaries.
It involves techniques for encrypting
(concealing) information, ensuring only
authorized parties can read it.
Core Goals of Cryptography:
1. Confidentiality – Ensures information is
readable only by intended recipient.
2. Integrity – Ensures information is not
altered during transmission.
, 3. Authentication – Confirms the identities
of the communicating parties.
4. Non-repudiation – Prevents sender from
denying sending a message.
Basic Concepts:
Term Meaning
Plain Original readable
text message
Encr Process of converting
yptio plaintext into ciphertext
n
Ciph Encrypted, unreadable
ertex message
t
Decr Process of converting
yptio ciphertext back to
n plaintext
,Key Secret information used
to encrypt/decrypt
Visual Diagram Idea (University Lecture
Style):
Plaintext ──[Encryption using
Key]──> Ciphertext ──[Decryption
using Key]──> Plaintext
Example:
●Plaintext: HELLO
●Key: 3 (Caesar Cipher)
●Ciphertext: KHOOR
1.2 Historical Background
Cryptography has evolved through centuries:
, 1.2.1 Ancient Ciphers
●Caesar Cipher: Shift each letter by a fixed
number.
○Example: Shift 3 → A becomes D
●Atbash Cipher: Alphabet reversed (A→Z,
B→Y, …)
1.2.2 Mechanical Encryption
●Enigma Machine (WWII): Rotor-based
machine used by Germans for military
communications.
●Complexity: Millions of possible keys →
required advanced cryptanalysis.
1.2.3 Modern Digital Cryptography
●Digital systems require mathematical
algorithms for secure communication.
(University-Level Detailed Notes)
1.1 Definition & Scope
Cryptography is the science and art of
securing communication in the presence of
adversaries.
It involves techniques for encrypting
(concealing) information, ensuring only
authorized parties can read it.
Core Goals of Cryptography:
1. Confidentiality – Ensures information is
readable only by intended recipient.
2. Integrity – Ensures information is not
altered during transmission.
, 3. Authentication – Confirms the identities
of the communicating parties.
4. Non-repudiation – Prevents sender from
denying sending a message.
Basic Concepts:
Term Meaning
Plain Original readable
text message
Encr Process of converting
yptio plaintext into ciphertext
n
Ciph Encrypted, unreadable
ertex message
t
Decr Process of converting
yptio ciphertext back to
n plaintext
,Key Secret information used
to encrypt/decrypt
Visual Diagram Idea (University Lecture
Style):
Plaintext ──[Encryption using
Key]──> Ciphertext ──[Decryption
using Key]──> Plaintext
Example:
●Plaintext: HELLO
●Key: 3 (Caesar Cipher)
●Ciphertext: KHOOR
1.2 Historical Background
Cryptography has evolved through centuries:
, 1.2.1 Ancient Ciphers
●Caesar Cipher: Shift each letter by a fixed
number.
○Example: Shift 3 → A becomes D
●Atbash Cipher: Alphabet reversed (A→Z,
B→Y, …)
1.2.2 Mechanical Encryption
●Enigma Machine (WWII): Rotor-based
machine used by Germans for military
communications.
●Complexity: Millions of possible keys →
required advanced cryptanalysis.
1.2.3 Modern Digital Cryptography
●Digital systems require mathematical
algorithms for secure communication.
