Message to the Class

TSTEPHAAXLISLAESCEMQIYQ

Scytale

Image Source: Wikipedia

Message to the Class

TSTEPHAAXLISLAESCEMQIYQ

T    H    I    S    I

 S    A    S    C    Y

  T    A    L    E    Q

   E    X    A    M

    P    L    E    Q

Early Ciphers

• Substitution Ciphers
  • Cryptoquip - Easily Breakable
• Polyalphabetic Ciphers
  • First described by Al-Kindi in the 9^th century
  • Later explained by Leon Battista Alberti in 1467

Tabula Recta

Image Source: Wikipedia

Image Source: Wikipedia

Enigma Machine

Image Source: Wikipedia

Enigma Machine Rotors

Image Source: Wikipedia

Enigma Machine Rotors

Image Source: Wikipedia

Enigma Machine Ratchet

Image Source: Wikipedia

Image Source: Wikipedia

Enigma Machine Plugboard

Image Source: Wikipedia

Enigma Key

• Choice and order of rotors
• Initial position of rotors
• Ring setting on rotors
• Plug connections

Enigma Operation

• Set wheels to today's key from codebook
• Operator chooses message key
• Encode message key TWICE to avoid errors
• Set wheels to message key
• Encrypt and send message

Enigma Stengths

• Many factors to the encryption
• Had up to 8 different wheels to choose from by the end of the war
• 150 Trillion different setups

Enigma Weaknesses

• A letter would never encrypt to itself
• Plugboards were reciprocal
• Wheels were not similar enough (could determine which wheels were used)
• Poor policies and procedures

Marian Rejewski

Image Source: Wikipedia

Cracking Enigma

• 1932 - First cracked by Marian Rejewski of Poland
• 1938 - Germany added 2 wheels
• 1939 - Alan Turing creates Bombe
• 1945 - Almost every message deciphered within 2 days

Bombe

Image Source: Wikipedia

Impact

“My own conclusion is that it shortened the war by not less than two years and probably by four years … we wouldn't in fact have been able to do the Normandy Landings, even if we had left the Mediterranean aside, until at the earliest 1946, probably a bit later.”

-Sir Harry Hinsley
British Intelligence Historian

Claude Shannon

Image Source: Wikipedia

Symmetric Key Encryption

Image Source: Wikipedia

Public Key Encryption

Image Source: Askamathematician.com

RSA Encryption

• Developed in 1977
• Named for the 3 creators (Ron Rivest, Adi Shamir, Lenonard Adleman)
• Uses the product of 2 large prime numbers to generate a key
• Key strength depends on the difficulty of factoring large numbers

RSA Example

• Choose 2 distinct prime numbers
  p and q
• Compute their product n = pq
• Compute the totient t of n:
  t = (p - 1)(q - 1)

RSA Example

• Choose any number e less than t that is coprime to t (they share no common factors but 1)
• Calculate d as the modular multiplicative inverse of e (mod t)
  e * x = 1 (mod t)

RSA Keys

• Public Key : (n, e)
• Encode: c = m^e (mod n)
  
  
• Private Key : (n, d)
• Decode: m = c^d (mod n)
  

Assignments

• Read and be prepared to discuss:
  • Tubes Chapter 7: Where Data Sleeps
• Blog 8: TBD - Due 10/27 10:00 PM
• HTML & CSS Project - Due 10/21 10:00 PM
• Scratch Chaocipher - Due 10/28 10:00 PM

Blog 8: TBD

TBD

• TBD