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Cryptography. Contact Information. Introduction. Cryptology. A form of communication which is primarily concerned with the secure transmission (through encryption ) of a secret message over an insecure channel. Cryptography. +. - PowerPoint PPT Presentation
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Contact Information
Cryptography 22/04/23 | pag. 2
Professor
Assistant
Office
Webpage
Course Text
Adriaan [email protected]
Pleinlaan 9, 2.29
http://homepages.vub.ac.be/~andooms (Education)
• Johanes A. Buchmann. 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.
Introduction
Introduction22/04/23 | pag. 3
Cryptology
Introduction22/04/23 | pag. 4
Cryptology
+
A form of communication which is primarily concerned with the secure transmission (through encryption) of a secret message over an insecure channel.
Deals with attacks on encrypted intercepted messages to recover the secret message.
=
Cryptography
Cryptanalysis
Cryptosystem
Introduction22/04/23 | pag. 5
Example: Ceasar Cipher
Cryptography 22/04/23 | pag. 6
Example: Ceasar Cipher
Introduction22/04/23 | pag. 7
Hence the number of keys should be large!
Basic Concepts
Introduction22/04/23 | pag. 8
Symmetric vs AsymmetricCryptosystems
Introduction22/04/23 | pag. 9
Cryptanalysis
Introduction22/04/23 | pag. 10
Kerckhoff’s principle
Attacks
Introduction22/04/23 | pag. 11
Example: Attacks
Introduction22/04/23 | pag. 12
Alphabet
Introduction22/04/23 | pag. 13
Alphabet
Introduction22/04/23 | pag. 14
Words
Introduction22/04/23 | pag. 15
Permutations
Introduction22/04/23 | pag. 16
Permutations
Cryptography 22/04/23 | pag. 17
Symmetric Cryptosystems
Symmetric Cryptosystems22/04/23 | pag. 18
Block Ciphers
Symmetric Cryptosystems22/04/23 | pag. 19
Block Ciphers
Symmetric Cryptosystems22/04/23 | pag. 20
Block Ciphers:Permutation Cipher
Symmetric Cryptosystems22/04/23 | pag. 21
Block Ciphers:Multiple Encryption
Symmetric Cryptosystems22/04/23 | pag. 22
Block Ciphers:Modes of Use
Cryptography 22/04/23 | pag. 23
• ECB: Electronic Codebook
• CBC: Cipherblock Chaining
• CFB: Cipher Feedback
• OFB: Output Feedback
Block Ciphers – ECB:Electronic Codebook Mode
Cryptography 22/04/23 | pag. 24
Block Ciphers – ECB:Electronic Codebook Mode
Cryptography 22/04/23 | pag. 25
Block Ciphers – ECB:Electronic Codebook Mode
Cryptography 22/04/23 | pag. 26
Example:Block Ciphers – ECB
Cryptography 22/04/23 | pag. 27
Drawback:Block Ciphers – ECB
Cryptography 22/04/23 | pag. 28
Example:Block Ciphers – ECB
Cryptography 22/04/23 | pag. 29
Block Ciphers – CBC:Cipherblock Chaining Mode
Cryptography 22/04/23 | pag. 30
Block Ciphers – CBC:XOR
Cryptography 22/04/23 | pag. 31
Block Ciphers – CBC:Cipherblock Chaining Mode
Cryptography 22/04/23 | pag. 32
Block Ciphers – CBC:Cipherblock Chaining Mode
Cryptography 22/04/23 | pag. 33
Block Ciphers – CBC:Cipherblock Chaining Mode
Cryptography 22/04/23 | pag. 34
Example:Block Ciphers – CBC
Cryptography 22/04/23 | pag. 35
Block Ciphers – CBC:Cipherblock Chaining Mode
Cryptography 22/04/23 | pag. 36
Example:Block Ciphers – CBC
Cryptography 22/04/23 | pag. 37
Drawback:Block Ciphers – CBC
Cryptography 22/04/23 | pag. 38
Block Ciphers – CFB:Cipher Feedback Mode
Cryptography 22/04/23 | pag. 39
Block Ciphers – CFB:Cipher Feedback Mode
Cryptography 22/04/23 | pag. 40
Block Ciphers – CFB:Cipher Feedback Mode
Cryptography 22/04/23 | pag. 41
Example:Block Ciphers – CFB
Cryptography 22/04/23 | pag. 42
Drawback:Block Ciphers – CFB
Cryptography 22/04/23 | pag. 43
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.
Block Ciphers – OFB:Output Feedback Mode
Cryptography 22/04/23 | pag. 44
Block Ciphers – OFB:Output Feedback Mode
Cryptography 22/04/23 | pag. 45
Block Ciphers – OFB:Output Feedback Mode
Cryptography 22/04/23 | pag. 46
Example:Block Ciphers – OFB
Cryptography 22/04/23 | pag. 47
Drawback:Block Ciphers – OFB
Cryptography 22/04/23 | pag. 48