Outline Operational model of encryption Symmetric

Outline

Operational model of encryption

Symmetric key encryption

One-time pad – theoretical vs. practical security

DES – Data Encryption Standard Initial Permutation

DES round function F

DES key scheduler

AES – Advanced Encryption Standard

General structure of Rijndael encryption/decryption plaintext w[0. . 3] w[4. . 7] w[36. . 39] w[40. . 43] ciphertext

Rijndael – Shift row and mix column 2311 1231 x 1123 3112 =

Rijndael – Key expansion

RC 4 stream cipher

Asymmetric key encryption

RSA (Rivest, Shamir, Adleman, 1978)

Proof of RSA decryption

Proof of RSA decryption cont’d

Cryptographic hash functions message of arbitrary length hash function fix length message digest / hash value / fingerprint

How long should a hash value be?

General structure of hash functions

SHA 1 – Secure Hash Algorithm 64 bits length 512 bits

SHA 1 compression function f A B C D E

SHA 1 compression function f cont’d

SHA 1 compression function f cont’d

Block cipher operation modes – ECB

Block cipher operation modes – CBC

Block cipher operation modes – CFB initialized with IV shift register (n) select s bits

Block cipher operation modes – OFB initialized with IV shift register (n) select s bits

Block cipher operation modes – CTR

Enveloping plaintext message bulk encryption key public key of the receiver

Message Authentication Codes (MAC)

HMAC

Digital signatures

“Hash and sign” paradigm private key of sender message hash message signature hash signature public key of sender yes/no

El. Gamal signature scheme

El. Gamal signature scheme cont’d

How to establish a shared symmetric key?

The Wide-Mouth-Frog protocol

The Needham-Schroeder protocol (1978)

Public-key Needham-Schroeder (1978)

Diffie-Hellman key exchange (1976)

Man-in-the-middle attack

Public-key certificates

Single CA CA

Certificate chains

CA structures

CA structures cont’d

CA structures cont’d