Modern Cryptography Data Encryption Standard 1977 New Directions

Modern Cryptography Data Encryption Standard 1977 “New Directions in Cryptography” 1976

Ciphers �Symmetric key block ciphers �Public key ciphers �Stream ciphers �Post-quantum ciphers

Data Encryption Standard 1977 Horst Feistel (1915 – 1990) Simplified DES: Wade Trapp and Lawrence Washington

Data Encryption Standard 1976

DES Simplified DES 64 -bit block 56 -bit key (8 parity bits) 8 S-boxes 6 x 4 16 rounds Feistel cipher 12 -bit block 9 -bit key 2 S-boxes 4 x 3 4 rounds Feistel cipher

Simplified DES – Feistel Cipher

Key and Message

Key Schedule 9 bits of key 111 010 110 Use the 8 bits on the left for k 1 1110 1011 Rotate to the left one bit 110 101 Use the 8 bits on the left for k 12 1101 0110 Rotate to the left 1 bit 101 011 Use the 8 bits on the left for k 3 1010 1101 Rotate to the left 1 bit 010 111 Use the 8 bits on the left for k 4 0101 1011

Expansion Function and XOR

S-Box

DES Encryption

DES Decryption Encryption Decryption

DES Decryption Encryption Decryption

Secrecy of Algorithm Backdoor?

3 DES 112 -bit security

Security Level Perfect Security Random key, as long as the message, and used only once. Computational Security Today 112

Block Cipher Modes

Block Cipher Modes

64 -bit block 80 -bit key 32 rounds Unbalanced Feistel cipher Skipjack/Clipper Chip Skipjack declassified 1998 Clipper Chip 1993 -1996

Substitution-Permutation Networks Claude Shannon (1916 – 2001)

Claude Shannon “A Mathematical Theory of Communication” 1948 “The Theory of Secrecy Systems” 1949

“The Theory of Secrecy Systems 1949 Diffusion: “… the statistical structure of [the message] which leads to its redundancy is dissipated into long range statistics. ” Wire crossing, P-box Confusion: “… make the relation between the simple statistics of [the ciphertext] and the simple description of [the key] a very complex and involved one. ” S-box

SPN

PRESENT 2007 Many

PRESENT 64 -bit block 80 - or 128 -bit key 1 S-box 4 31 Rounds Substitution-Permutation Network

Substitution Layer

Permutation Layer

Substitution and Permutation

Key Schedule

Do Cryptographers Sleep Well? How do they know it’s secure?

Advanced Encryption Standard 2001 Joan Daemen and Vincent Rijmen Simplified AES: Mohammad Musa, Edward Schaefer, and Stephen Wedig

AES (Rijandael) AES Simplified AES 128 -bit block 128 -bit, 192 -bit, or 256 -bit key 10, 12, or 14 rounds SPN 16 -bit block 16 -bit key 2 rounds SPN

S-Box

S-Box

Add Key

SN, SR, MC

S-AES