What Is the Data Encryption Standard?

Data Encryption Standard In 1977, the US National Bureau of Standards announced the symmetric key algorithm developed by IBM for electronic data encryption. DeDES is a prototype block cipher, which takes a fixed-length plaintext bit string and converts it into another ciphertext bit string of the same length through a series of complex operations. In the case of DES, the block size is 64 bits. DES also uses keys to customize the transformation so that decryption can be performed only by someone who knows the specific key used for encryption.

DeDES is a prototype block cipher, which takes a fixed-length plaintext bit string and converts it into another ciphertext bit string of the same length through a series of complex operations. In the case of DES, the block size is 64 bits. DES also uses keys to customize the transformation so that decryption can be performed only by someone who knows the specific key used for encryption. The keys apparently consist of 64 bits; however, only 56 of them are actually used by the algorithm. An additional 8 bits are used only for parity checking and are discarded thereafter. Therefore, the effective key length is 56 bits.

The keys are nominally stored or transmitted as 8 bytes, each with parity. According to ANSI X3.92-1981 (now called ANSI INCITS 92-1981) ^[1]

The algorithm is based on an earlier design by Horst Feistel.

The overall structure of the algorithm is shown in the figure: there are 16 identical processing stages, called loops. There are also initial and final permutations called IP and FP, which are reversals (IP "undo" actions of FP and vice versa). IP and FP have no encryption meaning, but it is included to facilitate the use of 8-bit hardware-based load blocks in the mid-1970s. ^[3]

Simplified DES (SDES)

Simplified DES (SDES) is used for educational purposes only to help students understand modern cryptanalysis techniques. SDES has similar attributes and structure to DES, but has been simplified to make it easier to perform encryption and decryption manually with pencil and paper. Some people think that learning SDES can understand the principles of DES and other block ciphers.

It was originally scheduled to serve for ten years. During this period, the encryption standard was not under real threat. It has been active in the international community for more than 20 years.

The biggest attack on DES is that its key length is only 56 bits. In 1990, S. Biham and A. Shamir proposed a differential attack method. The attack was performed by selecting the plaintext 247 attack and finally found a possible key. M.Matsui The linear analysis method, using 243 known plaintexts, successfully decoded the 16-round DES algorithm. So far, this is the most effective method of deciphering.

Since 1997, RSA has launched a competition called "Challenge the DES." In the first challenge, Rock Weisser spent 96 days cracking a piece of information encrypted with DES.

On December 22, 1999, RSA Corporation launched the "DES Challenge III". On January 19, 2000, the 250,000-dollar DES decryptor developed by the Electronic Frontier Foundation successfully cracked the DES encryption algorithm with a record of 22.5 hours. DES has gradually completed its historical mission.