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Soumyadipta Majumder asked: What is the difference between Data Encryption Standard (DES) & Advanced Encryption Standard (AES)?

Arul R. replies: Encryption standards are used to secure data and communication. With advancement in computational processing power, encryption standards too evolved, replacing the old with more effective new ones. The Data Encryption Standard (DES) was an excellent encryption standard for nearly two decades, from 1970s to 1990s. However, with the emergence of faster super computers that could break the then encryption standard like DES in hours, the latter was replaced by Triple DES for a while and thereafter completely replaced by Advanced Encryption Standard (AES). The current computational power and costs would take years to break AES. However, in another three decades, AES too would be replaced by better and stronger encryption standards.

Both DES and AES use Block Cipher – a symmetric key encryption. The plain text gets encrypted into cipher text through block cipher encryption process using a certain Bit Key. The process also includes a combination of cipher operations like substitution, transposition and bitwise operation (XOR). However, the plain texts, segregated as blocks before the process of encryption, differ in the case of DES and AES. The block size for DES is 64 bits, whereas for AES it is 128 bits.

Similarly, while DES uses a 56 Bit Key, AES uses a minimum of 128 Bit Key. AES also uses 192 and 256 Bit Keys for stronger encryption. Triple DES is a variant of DES, where the operation of DES happens for three times consecutively, using three different keys, thereby making an effective key length of 168 bits (56*3=168). Another variation of Triple DES is 112 Bit Key (56*2=112), where two keys are used three times with one key used again for the third time. If a brute force attack is tried, the possible key combination for DES would be 256 (2^56) and for AES it would be 2128 (2^128), 2192 (2^192) and 2256 (2^256) based on the key size.

The key and block size combination thus maintains the strength of the encryption standard in relation to the changing computational power of the processors.

Posted on August 19, 2016

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