Define steganography. Which parameters and design choice determine the actual algorithm of a Feistel Cipher ?
Subject Computer and Network Security
NU Year Set: 2.(b) Marks: 1+3 Year: 2014

Steganography (pronounced STEHG-uh-NAH-gruhf-ee, from Greek steganos, or "covered," and graphic, or "writing") is the hiding of a secret message within an ordinary message and the extraction of it at its destination. Steganography takes cryptography a step farther by hiding an encrypted message so that no one suspects it exists. Ideally, anyone scanning your data will fail to know it contains encrypted data.

Block size: Larger block sizes mean greater security but reduced encryption/decryption speed. A block size of 64 bits is a reasonable tradeoff and has been nearly universal in block cipher design. However, the new AES uses a 128-bit block size.

Key size: Larger key size means greater security but may decrease encryption/decryption speed. Key sizes of 64 bits or less are now widely considered being inadequate and 128 bits has become a common size.

A number of rounds: The essence of the Feistel cipher is that a single round offers inadequate security but that multiple rounds offer increased security. A typical size is 16 rounds.


Subkey generation algorithm: Greater complexity in this algorithm should lead to greater difficulty of cryptanalysis.

Round function: Again, greater complexity generally means greater resistance to cryptanalysis.

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