Video Content Lesson 3 Flashcards
Julius Caesar’s Cryptography was known as
ROT3 (Rotate 3 characters)
Famous German Encryption Machine
Enigma
Japanese Encryption Machine
Purple Machine
Current Goals of Cryptography
Ensure Confidentiality (private messages stay private even during transmission) Provide Integrity (ensure message hasn't been changed in transmission--digital signature does this) Provide Authentication (Validates claimed identity of message's sender, uses encrypted challenge phrases to ensure other party knows appropriate key--similar to non-repudiation) Provides Nonrepudiation (provides assurance that message came from who it says it came from, validates that message has not been spoofed)
Cryptographic Uses
Email
Protocols and standards (PGP Pretty Good Privacy; S/MIME Secure/Multipurpose Internet Mail Extension; IPSec Internet connection security; SSL/TLS Secure Socket Layer/Transport Layer Security)
Concepts and Methodologies
Cryptography Terms Tranposition Cipher Subtitution Cipher Cipher Categories Cipher Process Symmetric Algorithms Asymmetric Algorithms Message Authentication
Cryptography Terms
plaintext-Original message- readable
Ciphertext-encrypted message- only readable if first decrypted
Cipher-process of rearranging or altering a plantext message so it is unreadable
Tranposition Cipher
Start with a keyword
List the ordinal values, based on a letter’s position in the alphabet
Write plaintext message in tabular form
Read individual columns
Substitution Cipher
replaces each character of a plaintext message
All that is needed is a table of plaintext characters and their associated substitute characters
A simple algorithm can be created
Both sender and receiver must use same
One-Time Pad (OTP) (only known unconditionally secure cipher)
Never reuse a OTP
Cipher Categories
Stream Cipher (each character is encrypted-example substitution cipher) Block Cipher (works on a chunk/block of plaintext-example transposition cipher)
Cipher Process
One-way function (function that is relatively easy to use to produce output values AND impossible (or nearly so) to deduce the input values from the output values)
Algorithm is sequence of steps used to encrypt plaintext
Key is some value used by the algorithm to encrypt plaintext
Symmetric Algorithms
Secret Key Algorithm (same key used to encrypt and decrypt a message
Weaknesses (Key Distribution, lacking nonrepudiation, not scalable (to lots of people)
Main Strength (Fast)
Asymmetric Algorithms
Public Key Algorithm (public and private key)
Sender encrypts the message with the receiver’s public key
Receiver decrypts the message with his own private key
Strengths (user maintenance and key management is easy, supports nonrepudiation, key distribution is simple)
Weakness (Slow)
Message Authentication
Hashing (mathmatical process that produces a digest of a message (similar to checksums); when the message changes, the digest changes as well; extremely unlikely for two messages to produce the same digest
Hashing allows the receiver to verify authenticity of the message
Digital signatures are used to verify the authenticity of a message
Cryptopraphic Algorithms
Binary math used in most cryptographic algorithms (AND, OR, XOR) (most typically used XOR) DES Triple DES IDEA-Blowfish-Skipjack AES RSA-El Gamal Hashing Algorithms Other Hashing Algorithms
DES
Symetrical Coding
Data Encryption Standard (DES)
Published in 1977
Adopted by US government as a standard for all data communications
64-bit block cipher
Key is 56-bit key (remaining 8 bits are parity bits)
4 DES modes
1-Electronic Codebook (ECB) (each 64-bit plaintext block is encrypted with the key)
2-Cipher Block Chaining (CBC) (the XOR operator is used to combine each plaintext block and the preceeding block before encryption)
3-Cipher Feedback (CFB) (the XOR operator is used to combine each plaintext block and the preceeding block after encryption)
4-Output Feedback (OFB) (similart to CFB, but the plaintext is combined with a seed value using the XOR operator
Triple DES
Double DES (2DES)--No stronger than DES Triple DES (3DES) More secure implementation of the DES algorithm Exists in three versions (all versions are equally secure) Ecryption algorithm is the same as DES E(K1,E(K2,E(K3,P))) 168 bits E(K1,E(K2,E(K1,P))) 112 bits E(K1,D(K2,E(K1,P))) 112 bits E-encryption algorithm D-decryption algormithm K1, K2, K3-encryption keys P-plaintext
IDEA
IDEA - International Data Encryption Algorithm (stronger alternative to DES)
Works on 64-bit blocks
Key starts at 128-bits
Key is broken into 52 16-bit subkeys
Subkeys are used to encrypt the plaintext
Very secure (used in commercial business)
Blowfish
Developed by Bruce Schneider as an alternative to DES and IDEA
Operates on 64-bit blocks
Key can vary from 32 bits to 448 bits