In this lesson, we introduce basic building blocks of product cipher for symmetric key algorithm, and the old Data Encryption Standard, we call it DES. Here we show the basic building blocks, P-box and S-box, corresponding to the transposition cipher and substitution cipher in simple hardware representation. Here we show an 8-bit P-box or permutation box. It takes a input, either 0 or 1 signal can be sent into those port. And it can be send out and direct to different output port. It basically shuffles a 0 and 1 in different position. The shuffling is decided by the nine patterns shown inside of the P-box here, they connect the port. For example here, 10010001 will come out through the P-box as 10110000. Note that the number of 1 stays the same as the number of 0. We have three 1 here. The lower diagram is a 3 bit substitution box called S-box. It compose of a decoder, 3-bit to 8 output decoder, followed by a P-box, followed by 8 to 3 encoder. Here with 101 the pattern coming in to the 3 port. The decoder will select or activate the 5th output port. Here we use 0 index, the 6th line, what we call it FIPS port. The top output port is a 0 port. The 5th line signal will be coming out and then you will drive the P-box and the resulting of that is 7th output port will be triggered. And that trigger will send a signal to the last input port of the encoder and the encoder will produce 111 equivalent of 7 decimal output pattern. In summary, the S-box can substitute the incoming 101 bit pattern as 111 output pattern in a very fast manner with the hardware permutation. We can also simulate all these operation using the software. Also we can verify the bit pattern with the equivalent of 0123456 decimal coming in each of them will produce the value of equivalent bit pattern of 24506713 decimal value coming up. A product cipher combines two or more transformations to make it more secure and resistant to cryptanalysis. Figure c on the right hand side here is a product cipher utilize four P-box. In between is 12 S-box to construct a 12 bit cipher. Note that each of the p1 and p4 P-box and P-box inside each of those 12 S-box could have different permutation pattern inside. You can envision that we can easily construct by stack up all these 12 bit pattern into a 16 bit product cipher with the same design. c has a block size of 64 bits. Here we show the basic design of DES. DES stand for Data Encryption Standard. It is a symmetric key algorithm developed by IBM, early 1970. National Bureau of Standard, NBS, after consulting with NSA, adopt it as an official federal information processing standard. We typically call it F-I-P-S, FIPS, for United States in 1977. Due to the involvement of NSA, it often nourished the suspicion that there is a back door brewing in DES. It has a block size of 64 bits, basic version has 56 bit key. It goes through 16 iteration as shown here on the left hand side with an initial transposition and later output, inverse transposition. In each iteration shown on the right side here, the right 32 bit is sent directly to form that left output 32 bit. The same right 32 bit and the key are then fit into S-box through some substitutions. The output is then equal with the left hand side 32 bit to form the right side output 32 bit. DES is considered to be insecure now because it was broken by organizations in a distributed decryption effort on Internet. It is organized by distributed.net and EFF, early January 1999. And that was broken in just 22 hour 15 minutes. And since then, NIST has withdrawn it as a standard. To extend the life of DES and the related hardware and software, triple DES was proposed and developed. The same DES encryption and decryption box are concatenated showing here to extend the key lenghts, and at the same time make it compatible with old DES processing if the user chooses to do so. A ciphertext is encrypt plaintext with the DES encryption function where ends a key number one. And then the result is encrypt with key number two, finally encrypt with the key number three. It use the same 64 bit block size and has two options. The first option is using three key equivalent to 168 bit key. The second option using K1, K2, and repeat the K1, the K3 key and therefore it has 112 bit key. It has limited usage based on the analysis right now. Most of people already move to use a new AES standard already. Many new operating system nowaday already stop using and accept the three DES and DES as a cyber switch in accepting the SSL secure connection.