Cryptography: Block Cipher

 

In general, in a block cipher, we replace N bits from the plaintext with N bits of ciphertext. What defines an ideal block cipher?


An ideal block cipher is a type of block cipher in which it allows for the maximum for the maximum number of possible encryption mapping from plain text block. Ideal block cipher is defined by its encryption key which is its codebook itself, meaning that the table shows relation between the input and the output blocks and the relation between output and input block is random.



What makes ideal block cipher impractical?

The key size. The key size of the encryption key of ideal block cipher is given by n2^n. if n=64 key size is 10^21 bits. This is impractical for real time implementation.