The Data Encryption Standard (DES) is a data encryption algorithm, which was put forth by Federal Information Processing Standard (FIPS) 36-3. This algorithm has a block size of 64 bits and makes use of 56 bits when executing where 8 bits are used for parity; the parity bits are taken away from the full 64 bits. The algorithm is symmetric cryptosystem and is a 16-round Feistel cipher in specific. In cases where the algorithm is used for communication, the same secret must be known by both eth sender and the receiver. The secret is used to decrypt and encrypt message; it can also be used to have verification for Message Authentication Code (MAC). DES can also be utilized for single-user encryption, for example, file storage in the hard disk in a form that is encrypted.
DES algorithm has different modes of operation. One of the modes is Electronic Code Book (ECB) where data is divided into blocks of 64 bits and that the encryption of the blocks is done one by one. The encryption of different blocks is discrete. In this case, if there is some error that is experienced in sending blocks in a network, it will only mean that any error that is experienced in the block will affect that block alone. In this mode also, there is the rearrangement of blocks, which will make the data get scrambled. This action can go without anyone noticing. Another mode is that of Cipher Block Chaining (CBC) where each block, which has been encrypted using cipher text, is XORed with the plaintext that will be encrypted next; in this case, all blocks will depend on their previous blocks. Another mode includes Cipher Feedback and Output Feedback.
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Pfleeger, C., & Pfleeger, S. (2003). Security in computing. London: Prentice Hall Professional.