Cryptology

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Underlying principles

• Information theory
• Random numbers
• Statistical characteristics of language
• Computationally intractable problems

Methods of proving information is correct or has been transferred

Authentication

Sender authentication

Key management

• PKI
• PGP

Methods of concealing information

Cryptography

• Ciphers and codes, including basic methods
• Symmetric, asymmetric, and both
• Key management protocols

Specific cipher implementations

Manual

• Monoalphabetic substitutions
• Polyalphabetic substitutions
  • Straddling methods
• Transposition
• Superencipherment

Mechanical/Electromechanical

• Jefferson/Bazeries cylinder, strip ciphers
• Vernam
• Rotor and rotor-like: Hagelin, Enigma, Purple, SIGABA/Typex

Computer (general purpose and chip) implementations

• General characteristics of military (KG vs KW, etc.)
• Non-text/data: secure voice, video, fax
• DES
• PGP
• AES

Steganography

• Invisible ink methods?
• Classic covert channel
• Masking with graphics
• Spread spectrum, frequency agility, {{seealso|electronic warfare))

Methods of obtaining partial or full information

See also: communications intelligence for things including traffic analysis and direction finding

• Man-in-the-middle attack
• Various general scenarios: brute force, chosen plaintext
• Basic mathematical cryptanalysis: frequency analysis, index of coincidence, Kappa test
• Advanced mathematical cryptanalysis
• Red/black engineering and other COMSEC supporting measures

See also: communications intelligence

• "Practical cryptanalysis" (black bag job), radiofrequency MASINT#Unintentional Radiation MASINT (TEMPEST/Van Eck, etc.), acoustic cryptanalysis
• "rubber hose cryptanalysis"