# Security of DES P_BOX

I'm curious about the design of the P_BOX of DES. I found a paper on this topic, but it dates back to 1989. This means the effect of p-box values of the cipher immunity against Differential Cryptanalysis and linear cryptanalyisis is not mentioned since they were Publicly discovered during the 90's (According to Bruce Schneier's book "Applied cryptography , the NSA and IBM knew about the attack since the 70s). I tried to look online, but it seemed to me that unlike the S-boxes which have considerable amount of literature, there are no good resources on the p_boxes.

The placement of the p_box in the Feistel function is shown here:

The permutation itself is shown here:

Previously on Crypto.SE, we explored the roles of the initial and final permutations and how they impact security. What about the permutation in the Feistel function? What impact (if any) does it have on security?

• Straight up reference requests are off-topic on this site. I edited your question to make it more on-topic. If I changed your original intent, please let me know or feel free to edit yourself. – mikeazo Dec 18 '14 at 12:42
• In ON THE DESIGN OF PERMUTATION P IN DES TYPE CRYPTOSYSTEMS You'll find reference to D. W. Davies, "Some Regular Properties of the Data Encryption Standard", also hinted in D.W. Davies book "Security for Computer Networks", 2nd, Hamiltonian cycles in the DES, P. 66. Also note other than E Perm bleed over the only way C key bits affect S Boxes 5-8 or D key bits affect S Boxes 1-4 outputs is through the P Permutation and successive rounds. – user1430 Dec 18 '14 at 19:21

For example, PBoxes which make some independent groups of sboes, do not provide full diffusion at all and are considered unsecure. Also, consider Pbox which matches sboxes like $(2, 3, 4, 5, 6, 7, 1)$ (e.g. 1 shift left). You need at least 7 rounds to provide full diffusion.