Cryptography Contact Information Professor Ann Dooms Ann Doomsvub
Cryptography
Contact Information Professor Ann Dooms Ann. Dooms@vub. ac. be Assistant Adriaan Barri Adriaan. Barri@vub. ac. be Office Pleinlaan 9, 2. 29 Webpage http: //homepages. vub. ac. be/~andooms (Education) Course • Johanes A. Buchmann. Text Introduction to Cryptography, Springer, 2000. • Richard Mollin, Codes: The Guide to Secrecy From Ancient to Modern Times, Chapman & Hall, 2005. • Alfred J. Menezes, Paul C. van Oorschot and Scott A. Vanstone Handbook of Applied Cryptography, CRC Press, 1996. Cryptography 3/6/2021 | pag. 2
INTRODUCTION Introduction 3/6/2021 | pag. 3
Cryptology Cryptography A form of communication which is primarily concerned with the secure transmission (through encryption) of a secret message over an insecure channel. + Cryptanalysis Deals with attacks on encrypted intercepted messages to recover the secret message. = Introduction 3/6/2021 | pag. 4 Cryptology
Cryptosystem Introduction 3/6/2021 | pag. 5
Example: Ceasar Cipher Cryptography 3/6/2021 | pag. 6
Example: Ceasar Cipher Hence the number of keys should be large! Introduction 3/6/2021 | pag. 7
BASIC CONCEPTS Introduction 3/6/2021 | pag. 8
Symmetric vs Asymmetric Cryptosystems Introduction 3/6/2021 | pag. 9
Cryptanalysis Kerckhoff’s principle Introduction 3/6/2021 | pag. 10
Attacks Introduction 3/6/2021 | pag. 11
Example: Attacks Introduction 3/6/2021 | pag. 12
Alphabet Introduction 3/6/2021 | pag. 13
Alphabet Introduction 3/6/2021 | pag. 14
Words Introduction 3/6/2021 | pag. 15
Permutations Introduction 3/6/2021 | pag. 16
Permutations Cryptography 3/6/2021 | pag. 17
SYMMETRIC CRYPTOSYSTEMS Symmetric Cryptosystems 3/6/2021 | pag. 18
Block Ciphers Symmetric Cryptosystems 3/6/2021 | pag. 19
Block Ciphers Symmetric Cryptosystems 3/6/2021 | pag. 20
Block Ciphers: Permutation Cipher Symmetric Cryptosystems 3/6/2021 | pag. 21
Block Ciphers: Multiple Encryption Symmetric Cryptosystems 3/6/2021 | pag. 22
Block Ciphers: Modes of Use • ECB: Electronic Codebook • CBC: Cipherblock Chaining • CFB: Cipher Feedback • OFB: Output Feedback Cryptography 3/6/2021 | pag. 23
Block Ciphers – ECB: Electronic Codebook Mode Cryptography 3/6/2021 | pag. 24
Block Ciphers – ECB: Electronic Codebook Mode Cryptography 3/6/2021 | pag. 25
Block Ciphers – ECB: Electronic Codebook Mode Cryptography 3/6/2021 | pag. 26
Example: Block Ciphers – ECB Cryptography 3/6/2021 | pag. 27
Drawback: Block Ciphers – ECB Cryptography 3/6/2021 | pag. 28
Example: Block Ciphers – ECB Cryptography 3/6/2021 | pag. 29
Block Ciphers – CBC: Cipherblock Chaining Mode Cryptography 3/6/2021 | pag. 30
Block Ciphers – CBC: XOR Cryptography 3/6/2021 | pag. 31
Block Ciphers – CBC: Cipherblock Chaining Mode Cryptography 3/6/2021 | pag. 32
Block Ciphers – CBC: Cipherblock Chaining Mode Cryptography 3/6/2021 | pag. 33
Block Ciphers – CBC: Cipherblock Chaining Mode Cryptography 3/6/2021 | pag. 34
Example: Block Ciphers – CBC Cryptography 3/6/2021 | pag. 35
Block Ciphers – CBC: Cipherblock Chaining Mode Cryptography 3/6/2021 | pag. 36
Example: Block Ciphers – CBC Cryptography 3/6/2021 | pag. 37
Drawback: Block Ciphers – CBC Cryptography 3/6/2021 | pag. 38
Block Ciphers – CFB: Cipher Feedback Mode Cryptography 3/6/2021 | pag. 39
Block Ciphers – CFB: Cipher Feedback Mode Cryptography 3/6/2021 | pag. 40
Block Ciphers – CFB: Cipher Feedback Mode Cryptography 3/6/2021 | pag. 41
Example: Block Ciphers – CFB Cryptography 3/6/2021 | pag. 42
Drawback: Block Ciphers – CFB The smaller the block length r, the shorter the ciphertext blocks. This means on the hand that transmission is faster, but on the other hand that the block encryption function must be applied more frequently. The optimal choice of r depends on a tradeoff between transmission and computation speed. Cryptography 3/6/2021 | pag. 43
Block Ciphers – OFB: Output Feedback Mode Cryptography 3/6/2021 | pag. 44
Block Ciphers – OFB: Output Feedback Mode Cryptography 3/6/2021 | pag. 45
Block Ciphers – OFB: Output Feedback Mode Cryptography 3/6/2021 | pag. 46
Example: Block Ciphers – OFB Cryptography 3/6/2021 | pag. 47
Drawback: Block Ciphers – OFB Cryptography 3/6/2021 | pag. 48
- Slides: 48