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Cryptography / Declassified

Julius Caesar protected military dispatches with a substitution so simple a soldier could memorize it: shift every letter of the plaintext forward by three...

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Julius Caesar protected military dispatches with a substitution so simple a soldier could memorize it: shift every letter of the plaintext forward by three positions in the alphabet. Key sections include: Cryptography / Declassified; ~ 50 BC: The Caesar Cipher; 9th c.: Al-Kindi & Frequency Analysis; 1466: Alberti's Cipher Disk; 1939–45: Enigma & the Bombe; 1976: Diffie-Hellman Key Exchange; 1977: RSA — Public Keys for Everyone; 1991: PGP — Pretty Good Privacy; 2001: AES — The Modern Standard; Elliptic Curves & TLS 1.3.

Key sections

01Cryptography / Declassified
02~ 50 BC: The Caesar Cipher
039th c.: Al-Kindi & Frequency Analysis
041466: Alberti's Cipher Disk
051939–45: Enigma & the Bombe
061976: Diffie-Hellman Key Exchange
071977: RSA — Public Keys for Everyone
081991: PGP — Pretty Good Privacy
092001: AES — The Modern Standard
10Elliptic Curves & TLS 1.3
112008: Bitcoin — Cryptography for Money
12The Post-Quantum Threat
13Further Reading
14Video Dispatches

Topics covered

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Slide outline

01Cryptography / Declassified
02~ 50 BC: The Caesar Cipher
039th c.: Al-Kindi & Frequency Analysis
041466: Alberti's Cipher Disk
051939–45: Enigma & the Bombe
061976: Diffie-Hellman Key Exchange
071977: RSA — Public Keys for Everyone
081991: PGP — Pretty Good Privacy
092001: AES — The Modern Standard
10Elliptic Curves & TLS 1.3
112008: Bitcoin — Cryptography for Money
12The Post-Quantum Threat
13Further Reading
14Video Dispatches

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Presentation Transcript

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Slide 01

Cryptography / Declassified

CENTRAL ARCHIVE // CRYPTANALYSIS BUREAU
A Thirteen-Slide History of Secrets
CASE FILE: 1947-K // CLEARANCE LEVEL OMEGA
Top Secret
Eyes Only
03 NOV 2026

Slide 02

~ 50 BC: The Caesar Cipher

// File 02 — Antiquity
Julius Caesar protected military dispatches with a substitution so simple a soldier could memorize it: shift every letter of the plaintext forward by three positions in the alphabet.
A → D, B → E, C → F
Plaintext: VENI VIDI VICI
Ciphertext: YHQL YLGL YLFL
Key space: only 25 shifts — trivial for a modern attacker, unbreakable to most Roman enemies.
Suetonius records the technique in The Lives of the Twelve Caesars.
Substitution ciphers dominate cryptography for the next eighteen centuries.
02 / 13

Slide 03

9th c.: Al-Kindi & Frequency Analysis

// File 03 — Baghdad, House of Wisdom
In 9th-century Baghdad, the polymath Abu Yusuf al-Kindi wrote Risala fi Istikhraj al-Mu'amma — "A Manuscript on Deciphering Cryptographic Messages."
Observation: in any natural language, letter frequencies are stable.
In English text, E appears ~12.7% of the time; in Arabic, alif and lam dominate.
By counting symbols in a ciphertext, the cryptanalyst maps the most common ciphertext letter to E, and so on.
A monoalphabetic cipher's 26! key space collapses to a puzzle solvable with pencil & paper.
The first known systematic cryptanalysis. Codebreaking is born.
03 / 13

Slide 04

1466: Alberti's Cipher Disk

// File 04 — Renaissance Italy
Architect, organist, art theorist — Leon Battista Alberti also gave the world polyalphabetic cryptography.
Two concentric copper disks, one rotating, lettered around their rims.
The sender shifts the disk mid-message, switching cipher alphabets.
Frequency analysis fails — the most common letter is no longer constant.
A descendant of this idea, the Vigenere cipher, was called "le chiffre indechiffrable" for 300 years.
Fig. 4-A — Alberti disk (reconstruction)
04 / 13

Slide 05

1939–45: Enigma & the Bombe

// File 05 — Bletchley Park, Buckinghamshire
Germany's Enigma machine encrypted Wehrmacht traffic with three (later four) rotating rotors and a plugboard — an estimated 158,962,555,217,826,360,000 daily settings.
Polish cryptographers (Rejewski, Rozycki, Zygalski) cracked early Enigma in the 1930s.
At Bletchley Park, Alan Turing & Gordon Welchman built the Bombe, an electromechanical engine that brute-forced rotor settings using cribs.
Intelligence gleaned, codenamed ULTRA, is credited with shortening WWII by an estimated two years.
Fig. 5-A — Enigma rotor wiring
Ultra
05 / 13

Slide 06

1976: Diffie-Hellman Key Exchange

// File 06 — Stanford, California
Two strangers stand in a crowded room of eavesdroppers. They speak only in public. Yet by the end of the conversation, they share a secret no listener can derive.
Whitfield Diffie & Martin Hellman, in "New Directions in Cryptography," publish the impossible.
Security rests on the discrete logarithm problem: given g, p, ga mod p, recovering a is computationally infeasible.
The 4,000-year-old assumption that secret communication requires a pre-shared key is overturned in fourteen pages.
(GCHQ's James Ellis & Clifford Cocks had reached similar ideas earlier — classified until 1997.)
06 / 13

Slide 07

1977: RSA — Public Keys for Everyone

// File 07 — MIT, Massachusetts
One year after Diffie-Hellman, Rivest, Shamir & Adleman turn the abstraction into a usable algorithm.
Pick two large primes p, q; let n = p·q. Publish n and exponent e.
Encrypt: c = me mod n. Decrypt with secret d: m = cd mod n.
Security: factoring n back into p, q is believed to be intractable at sufficient size.
Suddenly: digital signatures, certificates, and the future internet are mathematically possible.
Fig. 7-A — Asymmetric padlock
Confidential
07 / 13

Slide 08

1991: PGP — Pretty Good Privacy

// File 08 — Boulder, Colorado
Alarmed by Senate Bill 266, which would have compelled crypto backdoors, Phil Zimmermann released Pretty Good Privacy as freeware. Within weeks it had crossed every border.
RSA + IDEA + a "web of trust" key model, packaged for ordinary users.
The U.S. opened a three-year criminal investigation under arms-export law — PGP's source code was, technically, a munition.
Zimmermann famously published the source as a book — protected by the First Amendment — circumventing export controls.
The "Crypto Wars" of the 1990s end with strong cryptography in the hands of citizens.
08 / 13

Slide 09

2001: AES — The Modern Standard

// File 09 — NIST, Gaithersburg
After an open international competition, NIST selects Rijndael — designed by Belgian cryptographers Joan Daemen & Vincent Rijmen — as the Advanced Encryption Standard.
Replaces aging DES (1977), whose 56-bit key had become brute-forceable.
Block cipher; 128, 192, or 256-bit keys; substitution-permutation network over a finite field.
Hardware acceleration (Intel AES-NI, 2010) makes it nearly free on modern CPUs.
Today AES protects everything from disk encryption to classified government communications.
09 / 13

Slide 10

Elliptic Curves & TLS 1.3

// File 10 — The Modern Web
By the 2000s, RSA's key sizes balloon to keep pace with factoring advances. Elliptic Curve Cryptography (Koblitz & Miller, 1985) offers equivalent security at a fraction of the size.
Curve25519 & Ed25519 (Daniel J. Bernstein, 2005–2011): fast, side-channel-resistant, beloved by SSH, Signal, and the Tor project.
TLS 1.3 (RFC 8446, 2018) prunes legacy ciphers, mandates forward secrecy, and trims the handshake to a single round-trip.
Every padlock icon in your browser is now backed by ECDH key exchange + AES-GCM or ChaCha20-Poly1305.
Let's Encrypt (2016) makes that padlock free, automatic, and universal.
10 / 13

Slide 11

2008: Bitcoin — Cryptography for Money

// File 11 — cryptography-mailing-list.metzdowd.com
On 31 October 2008, a nine-page paper signed Satoshi Nakamoto appears on a cypherpunk mailing list: "Bitcoin: A Peer-to-Peer Electronic Cash System."
SHA-256 proof-of-work + ECDSA signatures + a Merkle-tree ledger = trustless settlement.
The genesis block (3 Jan 2009) embeds a Times of London headline: "Chancellor on brink of second bailout for banks."
Cryptography moves from securing communication to securing value itself.
Whether you love or loathe the consequences, the cryptographic ideas are durable: hash-linked ledgers underpin Git, Certificate Transparency, supply-chain attestation, and more.
11 / 13

Slide 12

The Post-Quantum Threat

// File 12 — Threat Assessment
In 1994, Peter Shor published an algorithm that — given a sufficiently large quantum computer — factors integers and computes discrete logarithms in polynomial time.
RSA, Diffie-Hellman, and ECC all collapse under Shor's algorithm.
"Harvest now, decrypt later": adversaries are believed to be archiving ciphertext today against future quantum capabilities.
NIST's PQC competition (2016–2024) selected lattice-based CRYSTALS-Kyber (key encapsulation) and CRYSTALS-Dilithium (signatures), plus hash-based SPHINCS+.
Migration is already underway in TLS, SSH, and Signal — the next decade is a quiet, global, cryptographic retrofit.
Top Secret
12 / 13

Slide 13

Further Reading

// File 13 — End of Dossier
The Code Book — Simon Singh. The single best popular history of cryptography.
Cryptonomicon — Neal Stephenson. Bletchley Park, fictional, glorious.
Applied Cryptography — Bruce Schneier. The classic working reference.
Real-World Cryptography — David Wong. Modern, practical, current.
NIST IR 8413 — Status Report on the Third Round of the PQC Standardization Process.
Video Dispatches
YouTube — Enigma Machine & Turing
YouTube — Public Key Cryptography Explained
// END OF DOSSIER — RETURN TO CENTRAL ARCHIVE //
Declassified
13 / 13

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