Encryption/Cryptography-General Flashcards
Goals of Cryptography
Confidentiality
Integrity
Authentication
Nonrepudiation
Kerckhoff’s Principle
A crypto system should remain secure if everyone about it is known (except the key)
AND logical operation function
^ Symbol: (X^Y) and the value is true when both values (X and Y) are true.
OR logical operation function
V Symbol: (X v Y): The output is true when at least 1 input is true.
NOT logical operation function
~ Symbol: ~X or ~Y: It reverses the input value.
Exclusive OR logical operation function
O with cross symbol: It outputs true when only 1 of the inputs is true.
Modulo function
The remainder left over from division
Work function
Amount time/cost to brute force through a crypto system.
Codes versus Ciphers
Code: Crypto graphic system of symbols used to represent words/phrases, but not designed to ensure confidentiality. Example is the 10 system used by law enforcement
Cypher: Specifically designed to generate confidential cipher text from input and using algorithm to scramble input.
Transposition Cipher
Rearranges the plaintext characters to create the cipher text using a secret key.
Substitution Ciphers
Uses algorithm to replace plaintext characters with cipher text characters. Example Caesar Cipher where each character is just shifted three positions to the right. Also known is ROT3 cipher.
Caesar Cypher formula
C= (P+3) mod 26
One-time Pads
Uses a different substitution alphabet for each character of plain text. The Pad is at least as long as the original message. Unbreakable if used correctly. Must be generated randomly. The pad must be physical protected. AKA Vernam Ciphers.
Vigenère cipher.
Substitution cipher that uses multiple alphabets
Running Key Ciphers
Uses text from a book or newspaper as the cipher key. Prevents having to exchange physical lengthy one-time pads.
