Ciphers

Evolution of Technology

Manual

• Simple transposition or substitution algorithms.

Mechanic

• From XIX cent.

  • Enigma machine.

  • M-209 Converter.

• More complex substitution algorithms.

Informatics

• Appear with computers.

• Highly complex substitution algorithms.

• Mathematical algorithms.

Basic Types

Transposition

• The original cleartext is scrambled

• Block permutations.

Substitution

Each original symbol is replaced by another.

• Original symbols were letters, digits, and punctuation.

• Actually, they are blocks of bits.

Substitution strategies

• Mono-alphabetic (one -> one).

• Polyalphabetic (many one -> one).

• Homophonic (one -> many).