GATE (Graduate Aptitude Test in Engineering) Computer Science & IT (CS) Computer Networks-Network Security - Public Key and Private Key Cryptography Study Material (Page 5 of 9)
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Design of Block Cipher
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Number of Rounds
- More number of rounds, difficult for cryptanalytic attack.
- Even if function F is easy to break, a greater number of rounds make cipher strength high.
Function F Design
- F adds confusion. F must be difficult to evaluate through linear equations.
- F must produce avalanche effect. One-bit change produces change in several bits. F must follow bit independence criteria. Bit i is flipped for any i, j, k then output bit j and k should be changed independently.
Key Generation
- Generate one subkey for each round.
- Subkeys should be derived in such way that individual subkeys cannot be det…
… (12 more words) …
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DES (Data Encryption Standard)
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- DES was issued in 1977 by the National Bureau of Standards Now National Institute of Standards and Technology (NIST)
- In Data Encryption Algorithm, Data is encrypted in the block of 64 bits and key length is 56 bits. The output is of 64 bits.
- For Decryption, the same keys are used in reverse.
DES Encryption
Overview of Encryption Process
- 64-bit plaintext passes through an Initial Permutation (IP) . The input bits are rearranged and permuted input is generated.
- Then 16 rounds are performed with same function involving permutation and substitution.
- The output is of 64 bits. The left and right halves are swa…
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