Cryptography Flashcards
Draw a cryptographic block diagram:
What is a code system?
Use of codewords.
Cipher Systems
Use a secret key on the characters.
Classical Ciphers: Transposition
Rearranges the letters.
Classic Ciphers: Substitution Cipher
Replaces characters with alternate characters.
Classic Cipher: Product Cipher
Combination of transposition and substitution ciphers.
Will both rearrange AND use a different character set.
Classic vs. Modern ciphers
Classic: Act on characters and words.
Modern: Act on data bits representing information.
Modern Cipher: Block Cipher
Devites the PT into fixed size chunks and operates on each chunk individually IOT produce CT.
Modern Cipher: Stream Cipher
Uses an algorpith to produce a stream of binary digits called the cryptographic bit stream. The cryptographic bit stream is combined with the plain text bit stream through the use of an XOR operation to produce the CT bit stream.
Two types of key management:
Public Key
Private Key
Private Key
Same key for encryption and decryption.
Public Key
Two different keys: A public one for encryption and a private one for decryption. Only the receiver has the decryption key but everyone has the one for encryption.
Data Encryption Standards (DES)
Symmetric Encryption algorithm using a 56 bit key. Not computationally secure.
Advanced Encryption Standard (AES)
Symmetric Encryption algorithm, 256 bit key, computationally secure.
Public Key Signature
The sender uses a private key to encrypt a block chain in a method unique to her key. The decryption key is public and by decrypting it, you verify that only the sender could have encrypted it with their private key.
