Cryptography Chapter 7 Part 2 Pages 781 to 812

Symmetric Cryptography Secret Key Figure 7-10 on page 782 Key distribution problem – Secure courier Many keys – N(N-1)/2 – N=100, 4,950 keys

Symmetric Cryptography Provides only confidentiality Very fast. Hard to break. Data Encryption Standard (DES) Triple-DES (3DES) Advanced Encryption Standard (AES)

Asymetric Cryptography Public Key/Private Key Figure 7-11 on page 784 Alice, Bob, and Evil Eve Very slow Manageable key distribution Authentication and Non-repudiation – Bob encrypts with his private key

Asymetric Cryptography Bob sends message to Alice S= Private[Bob](Public[Alice]){Message} Alice authenticates that it came from Bob A = Public[Bob]{S} Alice decrypt – confidentiality M = Private[Alice]{A}

Asymetric Cryptography Rivest-Shamir-Adleman (RSA) Elliptic curve cryptosystem (ECC)

Comparison Table 7-1 on page 786

Block Ciphers 32, 64, or 128 bit blocks Figure on page 787 Confusion – substitution Diffusion – transposition Avalanche effect – slight change to input causes significant change to output IV – initialization vector – Don’t get same result

Stream Cipher Figure 7-13 on page 789 Figure 7-14 on page 790 Streaming communications – such as VoIP

Hybrid Encryption Figure page 794

Session Keys Figure 7-16 on page 797

DES Data Encryption Standard Data Encryption Algorithm (DEA) 56-bit keys 64-bit blocks 16 rounds of transpositions and substitution functions

DES ANSI (American National Standards Institute) standard in : Electronic Frontier Foundation broke DES in 3 days with brute force attack against keyspace using 1,536 microprocessors

DES Modes Electronic Code Book (EBC) 64-bit block encrypted by the key Can be done in parallel Can disclose patterns

Cipher Block Chaining (CBC) Figure 7-17 IV – 64-bit initialization vector Previous Ciphtertest XOR next Plaintext Errors persist

Cipher Feedback (FRB) Mode Figure 7-18 on page 805 For small text such as keystrokes or mouse movements Plaintext XOR Keystream

Output Feedback (OFB) Mode Figure 7-19 on page 806 Errors in data do not persist For video or VoIP

Counter (CTR) Mode Figure page 807 No IV Can encrypt in parallel

Triple DES DES-EEE3 DES-EDE2 48 rounds is slow Used while NIST adopted a new standard

AES Advanced Encryption Standard Rijndael Block & Key lengths: 128, 192, 256 NIST standard