Editing Data Encryption Standard (section)

=== Overall structure ===
{{more citations needed section|date=August 2009}}
The algorithm's overall structure is shown in Figure 1: there are 16 identical stages of processing, termed ''rounds''. There is also an initial and final [[permutation]], termed ''IP'' and ''FP'', which are [[inverse function|inverses]] (IP "undoes" the action of FP, and vice versa). IP and FP have no cryptographic significance, but were included in order to facilitate loading blocks in and out of mid-1970s 8-bit based hardware.<ref>{{Cite book|last=Schneier|title=Applied Cryptography|edition=1st|page=271}}</ref>

Before the main rounds, the block is divided into two 32-bit halves and processed alternately; this criss-crossing is known as the [[Feistel scheme]]. The Feistel structure ensures that decryption and encryption are very similar processes—the only difference is that the subkeys are applied in the reverse order when decrypting. The rest of the algorithm is identical. This greatly simplifies implementation, particularly in hardware, as there is no need for separate encryption and decryption algorithms.

The ⊕ symbol denotes the [[XOR|
exclusive-OR]] (XOR) operation. The ''F-function'' scrambles half a block together with some of the key. The output from the F-function is then combined with the other half of the block, and the halves are swapped before the next round. After the final round, the halves are swapped; this is a feature of the Feistel structure which makes encryption and decryption similar processes.