Data Encryption Standard DES

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Definition: Data Encryption Standard DES

Data Encryption Standard is a standard encryption algorithm used to encrypt and decrypt electronic data. It was developed during 1970’s in the United States by IBM and submitted to a request for proposal floated by National Bureau of Standards (NBS) to protect official government data.


The algorithm used for encryption is available in public, but the key used is secret. The method processes 64 bit block of data at a time. The DES works on the basis of the Fiestel block cipher in the following way:


  • There are 2 inputs – the 64 bit data block to be encrypted and a 56 bit secret key
  • Initial permutation is done on both the inputs
  • The input 64 bit data is then divided into two 32 bit data and similarly the 56 bit key is also divided into two 28 bit parts. A left cyclical shift on the both the key parts is performed after which they are permuted together and compressed to produce a 48 bit number. This 48 bit number along with one of the two 32 bit input data undergoes a series of functions (permutation, XOR and substitution). The output is two 32-bit data.
  • The above mentioned step is performed 16 times
  • Final permutation (inverse of initial permutation) is done on the data
  • The Output is 64 bit encrypted data

In DES, the same key is used for both encryption as well as decryption. Hence it is a symmetric type method.

However after the development of DES, lot of issues regarding the security of the application came up due to the small size of the secret key. Now the DES has been replaced with AES (Advanced Encryption Standard).


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