Download - Modern symmetric cipher
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Modern Symmetric Key
AlgorithmBy Prof : Rupesh Mishra
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Algorithm Type
Stream Cipher
Block Cipher
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Stream Cipher
• Bit by Bit encryption and Decryption
• Encoding and Decoding
• XOR Logic Operation
• RC4
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Block Cipher
• Block of text encrypted and decrypted
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Confusion
• Substitution Technique
• No clue about Key from ciphertext
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Diffusion
• No clue about plaintext from ciphertext
• Transposition Technique
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Modes of Algorithm
• Electronic Code Book (ECB)
• Cipher Block Chaining (CBC)
• Cipher Feedback Mode (CFB)
• Output Feedback Mode (OFB)
• Counter Mode
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Electronic Code Book
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Drawback of ECB
• Identical blocks of ciphertext.
• An eavesdropper notices that blocks 23 and
95 of the ciphertext are equal.
• If, in addition, he knows (or can guess) the
value of block 23 of plaintext, he can then
deduce the content of block 95 of the
plaintext
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Cipher Block Chaining
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Cipher Feedback Mode
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Cipher Feedback Mode
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Output Feedback Mode
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Counter Mode
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Counter Mode • A b-bit counter is initialized to a random value.
This value is encrypted with the secret key.
• Encrypted value is XORed with the first block of
plaintext
• The counter is then incremented.
• the incremented value is encrypted and XORed
with the next block of plaintext to create the
ciphertext and so on.
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Original ECB CBC
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DES
• Data Encryption Standard/Algorithm
• Adopted in 1977 by National Institute of
Standards and Technology (NIST)
• Plaintext 64 bit/Block
• Key 56 bit
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64 bit
Plaintext
DES
64 bit
Ciphertext
56 bit
Key
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L0 R0
F
L1 R1
𝑲𝒆𝒚
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Steps in DES1. Initial Permutation
2. 16 Round of Feistel Function
3. Final Permutation
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Feistel Function
1. Expansion Permutation
2. S – Box Substitution
3. P – Box Permutation
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Key Generation
• Key Discarding Process
• Key Transformation
• Sub - Key Generation
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• DES Decryption
• DES Cryptanalysis
o Keyspace
o Diffrential and Linear cryptanalysis
• Variations of DES
o Double DES
o Triple DES
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Advanced Encryption Standard (AES)
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Introduction
• Regular DES is not very secure and triple
DES is slow. The block size in both is 64 bits
• A more secure secret key algorithm with a
larger block size is desirable
• In 2001, Rijndael was selected by NIST from
among 5 finalists as the new standard
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AES features
• Block size = 128 bits
• Key size = 128/192/256 bits
• No of rounds = 10, 12 or 14
• Does not have a Fiestal structure
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AES Encryption• Each round includes
– Byte substitution
– Row shift
– Column mixing
– Subkey Addition
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Byte Substitution
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S-Box Operation
B
(Input)
GF(28) Inverse
Affine Mapping
B’
(Output)
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Row Shift
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MixCol
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Mix Column
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Add Round Key
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Add Round Key
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Symmetric Key Cipher
• Single Shared Key is used for Encryption and
Decryption.
• Fast and Effective
• DES , AES , Salsa20
• Limitation
o Key Exchange
o Repetition of Key
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