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:
“There’s no art
To find the mind’s construction in the face.”
—William Shakespeare (1564–1616)
“Different persons growing up in the same language are like different bushes trimmed and trained to take the shape of identical elephants. The anatomical details of twigs and branches will fulfill the elephantine form differently from bush to bush, but the overall outward results are alike.”
—Willard Van Orman Quine (b. 1908)