SYMMETRIC ENCRYPTION

Process of converting one binary string to another binary stringINPUT - sequence of plaintext bitsPROCESS - perform series of operationsOUTPUT - series of cyphertext bits

STREAM CIPHERINPUT - one bit of plaintext, keyPROCESS - perform series of operationsOUTPUT - one bit of cyphertext bitsSome stream ciphers process blocks of one byte and can be called Block ciphersKEY - > Key is much shorter than the length of the plaintextKEY STREAM GENERATOR -> Generates the keystream used for encryptionBoth sides have the same key and the key stream generatorKEYSTREAM has to be as long as the plaintextPsuedoRandom generator should be unpredictable to make cipher secure

BLOCK CIPHERINPUT - a block of plaintext bits, keyPROCESS - perform series of operationsOUTPUT - a block of cyphertext bitsPropertiesPlaintext Block size is fixedCyphertext Blocksize is also fixedBlock size too short (dictionary attacks) and too large can cause issues like padding of spaces unused in the blackVersatility - widely used, primitives like MAC and hash functionsCompatibility - since used in many places, easily compatible like AES AdaptabilityPROBLEMS of PADDINGintroduces inefficiency, e.g. padding 8 bit in a 128-bit AES schemecan cause security issue if a proper padding scheme is not chosenDES -> 64 bits blockAEX -> 128 bits block

Vernam Cipher applies one-time pad on binary strings. INPUT - sequence of plaintext bitsPROCESS - perform one-time pad operations (XOR)OUTPUT - series of cyphertext bitsUses pseudo random Key generator to generate a key streamLength of the Key same as the PlaintextKey >= PlaintextDESAESIDEASERPENTTWOFISH

IMPACT OF ERRORTransmission Error bit flip, 0 becomes 1 and 1 becomes 0Transmission Loss bits gets droppedComputational Error incorrectly computed 1 became 0 and 0 became 1

Properties of STREAM CIPHERSNo Error PropagationSpeedOn the fly encryption

Examples of STREAM CIPHERRC-4 (TLS/SSL), A5/1 (GSM), E0 (BLUETOOTH)

DES (Data Encryption Standard)is also known as Feistel Cypherblock size is 64 bit

Technical Control - hardware to store the keys and protocol used to secure exchange the keysProcess Control - policies, practice & procedures for key managementEnvironmental Control - physical location plays very important roleHuman Control - Managing keys is a human

SIMPLE HIERARCHYMaster key top level keys, longest lifetime, use Hardware security module to store the keysKey encryption key long lifetimeData Keys shortest lifetime

Definitions

Cipher

DES

Key Management