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 construction stiff working overtime takes more stress and straining than we did just to stay high.”
—Gus Van Sant, U.S. screenwriter and director, and Dan Yost. Bob Hughes (Matt Dillon)
“Anyone can see that to write Uncle Toms Cabin on the knee in the kitchen, with constant calls to cooking and other details of housework to punctuate the paragraphs, was a more difficult achievement than to write it at leisure in a quiet room.”
—Anna Garlin Spencer (18511931)