The F-function splits the 32-bit input into four 8-bit quarters and uses the quarters as input to the S-boxes. The S-boxes accept 8-bit input and produce 32-bit output. The outputs are added modulo 232 and XORed to produce the final 32-bit output (see image in the upper right corner).[6] After the 16th round, undo the last swap, and XOR L with K18 and R with K17 (output whitening). Decryption is e