Feistel Cipher - Construction Details

Construction Details

Let be the round function and let be the sub-keys for the rounds respectively.

Then the basic operation is as follows:

Split the plaintext block into two equal pieces, (, )

For each round, compute

.

Then the ciphertext is .

Decryption of a ciphertext is accomplished by computing for

.

Then is the plaintext again.

One advantage of the Feistel model compared to a substitution-permutation network is that the round function does not have to be invertible.

The diagram illustrates both encryption and decryption. Note the reversal of the subkey order for decryption; this is the only difference between encryption and decryption.

Read more about this topic:  Feistel Cipher

Famous quotes containing the words construction and/or details:

    No real “vital” character in fiction is altogether a conscious construction of the author. On the contrary, it may be a sort of parasitic growth upon the author’s personality, developing by internal necessity as much as by external addition.
    —T.S. (Thomas Stearns)

    Then he told the news media
    the strange details of his death
    and they hammered him up in the marketplace
    and sold him and sold him and sold him.
    My death the same.
    Anne Sexton (1928–1974)