Editing Data Encryption Standard (section)

=== Key schedule ===
<imagemap>
File:DES-key-schedule.png|thumb|250px|''[[:File:DES-key-schedule.png|Figure 3]]''— The key-schedule of DES
rect 96 28 298 58 [[DES supplementary material#Permuted choice 1 (PC-1)|Permuted choice 1]]
rect 127 122 268 155 [[DES supplementary material#Permuted choice 2 (PC-2)|Permuted choice 2]]
rect 127 216 268 249 [[DES supplementary material#Permuted choice 2 (PC-2)|Permuted choice 2]]
rect 127 357 268 390 [[DES supplementary material#Permuted choice 2 (PC-2)|Permuted choice 2]]
rect 127 451 268 484 [[DES supplementary material#Permuted choice 2 (PC-2)|Permuted choice 2]]
rect 96 91 127 116 [[DES supplementary material#Rotations in the key-schedule|Left shift by 1]]
rect 268 91 299 116 [[DES supplementary material#Rotations in the key-schedule|Left shift by 1]]
rect 96 185 127 210 [[DES supplementary material#Rotations in the key-schedule|Left shift by 1]]
rect 268 185 299 210 [[DES supplementary material#Rotations in the key-schedule|Left shift by 1]]
rect 96 326 127 351 [[DES supplementary material#Rotations in the key-schedule|Left shift by 2]]
rect 268 326 299 351 [[DES supplementary material#Rotations in the key-schedule|Left shift by 2]]
rect 96 419 127 444 [[DES supplementary material#Rotations in the key-schedule|Left shift by 1]]
rect 268 419 299 444 [[DES supplementary material#Rotations in the key-schedule|Left shift by 1]]
</imagemap>
Figure 3 illustrates the ''key schedule'' for encryption—the algorithm which generates the subkeys. Initially, 56 bits of the key are selected from the initial 64 by ''Permuted Choice 1'' (''PC-1'')—the remaining eight bits are either discarded or used as [[parity bit|parity]] check bits. The 56 bits are then divided into two 28-bit halves; each half is thereafter treated separately. In successive rounds, both halves are rotated left by one or two bits (specified for each round), and then 48 subkey bits are selected by ''Permuted Choice 2'' (''PC-2'')—24 bits from the left half, and 24 from the right. The rotations (denoted by "<<<" in the diagram) mean that a different set of bits is used in each subkey; each bit is used in approximately 14 out of the 16 subkeys.

The key schedule for decryption is similar—the subkeys are in reverse order compared to encryption. Apart from that change, the process is the same as for encryption. The same 28 bits are passed to all rotation boxes.