F O U N D A T I O N S O F

Cryptography

History • The CIA Triad • Classical Encryption Techniques

A Visual Study Deck

Agenda

Three pillars of this presentation

01

History of Cryptography

From ancient scytales to modern computer-age algorithms

02

The CIA Triad

Confidentiality, Integrity, and Availability in cryptographic systems

03

Classical Encryption

The Caesar cipher and Vigenère cipher, in depth

Foundations of Cryptography

1

01

History of Cryptography

A five-thousand-year contest between codemakers and codebreakers

SECTION 1 · ERA 1

Ancient Cryptography (1900 BCE – 500 CE)

1

Egyptian hieroglyphs (~1900 BCE): non-standard symbols used for mystique, one of the earliest recorded uses of concealment writing

Hebrew Atbash cipher: a simple substitution scheme that reverses the alphabet

Spartan scytale (~5th century BCE): a wooden rod device that realigns transposed letters — one of the first cryptographic tools

Roman Caesar cipher (~58 BCE): a fixed-shift substitution cipher used by Julius Caesar for military orders

Polybius square: converts letters into numeric coordinate pairs for transmission

History of Cryptography

2

SECTION 1 · ERA 2

Medieval Cryptography (500 – 1400 CE)

2

Al-Kindi's frequency analysis (~800 CE): the single most important breakthrough in early cryptanalysis

The core insight: letters occur with predictable frequency in any language, creating a statistical fingerprint

Consequence: monoalphabetic substitution ciphers became fundamentally insecure, regardless of key choice

European monasteries: used symbol-substitution ciphers to protect religious and diplomatic manuscripts

Early bureaus: Venice and the Vatican developed some of the first dedicated cipher clerks

History of Cryptography

3

SECTION 1 · ERA 3

Renaissance Cryptography (1400 – 1800 CE)

3

Alberti's cipher disk (1467): the first polyalphabetic cipher mechanism, using two rotating alphabets

Trithemius's tabula recta (1508): a systematic table of shifted alphabets

Bellaso / Vigenère cipher (1553): a keyword-driven polyalphabetic cipher, later misattributed to Blaise de Vigenère

‘Le chiffre indéchiffrable’: considered unbreakable for nearly three centuries

The Great Cipher of Louis XIV: a syllable-based cipher protecting French royal correspondence

History of Cryptography

4

SECTION 1 · ERA 4

Mechanical & Wartime Era (1800 – 1945)

4

Playfair cipher (1854): digraph substitution cipher used by the British military

ADFGVX cipher (1918): German WWI field cipher combining substitution and transposition

Enigma machine (1920s–1945): German electromechanical rotor cipher with an astronomical key space

Bletchley Park & the Bombe: Alan Turing's team mechanized the search for daily Enigma settings

Legacy: codebreaking efforts here are credited with shortening WWII and seeding modern computing

History of Cryptography

5

SECTION 1 · ERA 5

The Modern Computer Era (1945 – Present)

5

Shannon's secrecy theory (1949): established confusion and diffusion as pillars of cryptographic design

DES (1977): first publicly available, government-approved symmetric block cipher

Diffie–Hellman (1976) & RSA (1977): introduced public-key cryptography, solving the key-distribution problem

AES (2001): current U.S. federal standard and the world's dominant symmetric cipher

Today: elliptic-curve cryptography, blockchain, and post-quantum research define the frontier

History of Cryptography

6

SECTION 1 · SUMMARY

Five Eras at a Glance

1900 BCE

– 500 CE

Ancient

Scytale, Atbash,

Caesar cipher

500

– 1400 CE

Medieval

Al-Kindi's

frequency analysis

1400

– 1800 CE

Renaissance

Polyalphabetic

ciphers

1800

– 1945

Mechanical

Rotor cipher

machines (Enigma)

1945

– Present

Modern

DES, RSA,

AES

Cryptographic progress is cyclical: long periods of confidence are repeatedly broken by sudden cryptanalytic breakthroughs, which then drive the invention of stronger schemes.

History of Cryptography

7

SECTION 1 · CASE STUDIES

Famous Historical Incidents

!

The Babington Plot (1586): Mary, Queen of Scots' cipher was broken by Thomas Phelippes, producing evidence used at her trial

The Zimmermann Telegram (1917): British cryptanalysts decrypted a German proposal to Mexico, helping draw the U.S. into WWI

Navajo Code Talkers (WWII): an unwritten language plus military substitutions created a code Japan never broke

History of Cryptography

8

02

The CIA Triad

Confidentiality, Integrity, and Availability — the three pillars of secure systems

SECTION 2 · OVERVIEW

The Three Pillars

C

Confidentiality

Only authorized parties can read the information

Encryption (symmetric & asymmetric)

I

Integrity

Data has not been altered without detection

Hash functions, MACs, digital signatures

A

Availability

Systems and data remain accessible when needed

Redundancy, secure key management

The CIA Triad

9

SECTION 2 · PILLAR 1

Confidentiality

C

Definition: ensures information is accessible only to authorized parties

Mechanism: encryption transforms plaintext into unreadable ciphertext using a key

Advantages: protects data from eavesdroppers; supports regulatory compliance (healthcare, finance)

Disadvantages: doesn't guarantee data hasn't been altered; poor key management undermines it; adds performance overhead

Applications: encrypted messaging, online banking, corporate VPNs

The CIA Triad

10

SECTION 2 · PILLAR 2

Integrity

I

Definition: ensures information has not been altered without authorization

Mechanism: hash functions, MACs, and digital signatures detect tampering

Advantages: detects accidental corruption and deliberate forgery; computationally efficient

Disadvantages: weak hash algorithms (MD5, SHA-1) can suffer collisions; requires secure key/certificate distribution

Applications: software update verification, digital signatures, blockchain transactions

The CIA Triad

11

SECTION 2 · PILLAR 3

Availability

A

Definition: ensures authorized users can access systems and data when needed

Mechanism: redundancy, failover, and secure authentication keep systems resilient

Advantages: supports business continuity; reduces disruption from unauthorized access

Disadvantages: lost keys can themselves cause outages; DDoS attacks bypass cryptography entirely

Applications: redundant cloud backups, content delivery networks, high-availability SSO

The CIA Triad

12

SECTION 2 · BEYOND THE TRIAD

Authentication, Non-Repudiation & Kerckhoffs's Principle

+

Authentication: verifies that a message truly originates from its claimed sender

Non-repudiation: prevents a sender from later denying they sent a message (via digital signatures)

Kerckhoffs's Principle (1883): a system should stay secure even if everything except the key is public

Why it matters: modern algorithms like AES and RSA are published openly and battle-tested; classical ciphers relied on secrecy of method — a weaker strategy

The CIA Triad

13

SECTION 2 · SUMMARY

CIA Triad at a Glance

A single real system often layers multiple mechanisms together — a strategy known as defense in depth.

The CIA Triad

14

03

Classical Encryption

The Caesar cipher and the Vigenère cipher — foundations of substitution cryptography

SECTION 3 · CAESAR CIPHER

How the Caesar Cipher Works

C

Type: monoalphabetic substitution cipher, named after Julius Caesar

Formula: C = (P + k) mod 26 for encryption; P = (C − k) mod 26 for decryption

Key: a single fixed shift value k, between 1 and 25

Example: with shift k = 3, 'A' becomes 'D', 'B' becomes 'E', wrapping 'X' → 'A'

Key space: only 25 possible non-trivial keys — extremely small by modern standards

Classical Encryption

15

SECTION 3 · CAESAR CIPHER

Worked Example & Brute Force

H

E

L

L

O

shift +3 ▼

K

H

O

O

R

Plaintext ‘HELLO’ → Ciphertext ‘KHOOR’ (shift = 3)

Brute-force weakness

Only 25 possible shifts exist.�An attacker can try every shift value in a fraction of a second and flag the one producing valid dictionary words — no key needed.��Example: ‘PHHW PH DW GDZQ’ only becomes readable (‘MEET ME AT DAWN’) at shift 3 — every other shift produces gibberish.

Classical Encryption

16

SECTION 3 · CAESAR CIPHER

Caesar Cipher — Pros, Cons & Applications

C

Advantages: extremely simple to implement and teach; fast to encrypt/decrypt by hand

Disadvantages: trivially broken by brute force (25 keys) and frequency analysis; provides no real modern security

Applications: cryptography education, ROT13 for hiding spoilers online, historical reference

Key takeaway: a fixed single shift makes this the weakest class of substitution cipher

Classical Encryption

17

SECTION 3 · VIGENÈRE CIPHER

How the Vigenère Cipher Works

Type: polyalphabetic substitution cipher using a repeating keyword��Formula: Ci = (Pi + Ki) mod 26, where Ki is the keyword letter at that position��Mechanism: the keyword repeats to match plaintext length; each letter uses a different shift

Plaintext

A

T

T

A

C

K

Key

L

E

M

O

N

L

Cipher

L

X

F

O

P

V

Keyword ‘LEMON’ encrypts ‘ATTACK...’ → ‘LXFOPV...’

Classical Encryption

18

SECTION 3 · VIGENÈRE CIPHER

Cryptanalysis: Breaking the ‘Unbreakable’

V

Kasiski examination (1863): searches for repeated ciphertext sequences to estimate keyword length

Index of coincidence (1922): William Friedman's statistical measure — English text ≈ 0.067, random text ≈ 0.038

Process: once keyword length is known, each subsequence is broken with ordinary frequency analysis

Historical result: Charles Babbage and Friedrich Kasiski independently ended three centuries of confidence in this cipher

Classical Encryption

19

SECTION 3 · VIGENÈRE CIPHER

Vigenère Cipher — Pros, Cons & Applications

V

Advantages: far stronger than monoalphabetic ciphers; flattens letter-frequency patterns

Disadvantages: vulnerable to Kasiski examination and index-of-coincidence attacks; weak with short/repeated keywords

Applications: historical diplomatic & military communication; teaching polyalphabetic substitution

Legacy: conceptual ancestor of the one-time pad, proven unbreakable by Claude Shannon in 1949

Classical Encryption

20

SECTION 3 · COMPARISON

Caesar vs. Vigenère

Classical Encryption

21

Key Takeaways

1

Cryptography evolved from simple manual ciphers to a rigorous mathematical science, driven by a continuous cycle of codemaking and codebreaking

2

The CIA triad — confidentiality, integrity, and availability — remains the universal framework for evaluating any cryptographic or security system

3

The Caesar and Vigenère ciphers, though insecure today, remain foundational teaching tools for substitution, keys, and cryptanalysis

4

Modern cryptography still faces the same core challenge classical cryptographers faced: secure key distribution

Foundations of Cryptography

22

Thank You

Questions & Discussion