cryptography

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Applications and Uses of Cryptography


What Is Cryptography
Cryptography is the science of hiding information in plain sight, in order to conceal it from unauthorized parties.
• Substitution cipher first used by Caesar for battlefield communications


Encryption methodologies

Substitution Cipher
Plaintext characters are substituted to form ciphertext
• “A” becomes “R”, “B” becomes “G”, etc.
• Character rotation
• A table or formula is used
• ROT13 is a Caesar cipher
• Image from Wikipedia (link Ch 5a)
• Subject to frequency analysis attack


Polyalphabetic Cipher
Two or more substitution alphabets
CAGED becomes RRADB
Not subject to frequency attack

One-time Pad
Works like running key cipher, except that key is length of plaintext, and is used only once
Highly resistant to cryptanalysis


Block Cipher
Encrypt and decrypt a block of data at a time
• Typically 128 bits
Typical uses for block ciphers
• Files, e-mail messages, text communications, web
Well known encryption algorithms
• DES, 3DES, AES, CAST, Twofish, Blowfish, Serpent
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Applications and Management of Cryptography


Uses for Cryptography
File encryption
• PGP and GPG
• WinZip (version 9 uses AES)
• EFS (encrypting file system) for Windows
• Crypt tool for Unix
Encrypted volumes and disks
• Truecrypt for Windows, Mac, Unix
• Bitlocker for Windows Vista
• PGP Disk
• SafeBoot