# Cryptography / Declassified

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Category: Technology
Slides: 14
Updated: 2026-05-17T20:55:46.557Z
Tags: catalog, tech, cryptography

## Summary

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.

## Slide Outline

1. Cryptography / Declassified
2. ~ 50 BC: The Caesar Cipher
3. 9th c.: Al-Kindi & Frequency Analysis
4. 1466: Alberti's Cipher Disk
5. 1939–45: Enigma & the Bombe
6. 1976: Diffie-Hellman Key Exchange
7. 1977: RSA — Public Keys for Everyone
8. 1991: PGP — Pretty Good Privacy
9. 2001: AES — The Modern Standard
10. Elliptic Curves & TLS 1.3
11. 2008: Bitcoin — Cryptography for Money
12. The Post-Quantum Threat
13. Further Reading
14. Video Dispatches

## Slide Transcript

### Slide 1: 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 2: ~ 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 3: 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 4: 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 5: 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 6: 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 7: 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 8: 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 9: 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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