AES and IDEA Encryption Algorithms


The subbytes step of AES encryption.

AES Encryption

Because of the small key size of 56 bits, DES can’t withstand coordinated brute-force attacks using modern cryptanalysis; dedicated machines can now break DES within a day. Consequently, The National Institute of Standards and Technology (NIST) selected the Advanced Encryption Standard (AES) as the authorized Federal Information Processing Standard (FIPS) 197 for all non-secret communications by the U.S. government, which became effective in May 2002. AES is included in the ISO/IEC 18033-3 standard. AES has the following important characteristics:

  • Private key symmetric block cipher (similar to DES)
  • Stronger and faster than 3DES
  • Life expectancy of at least 20 to 30 years
  • Supports key sizes of 128 bits, 192 bits, and 256 bits
  • Freely available to all; royalty free, non-propriety, and not patented
  • Small footprint: AES can be used effectively in memory and in central processing unit (CPU) limited environments such as smart cards

It should be noted that the AES (Rjindael) algorithm was selected by NIST from a group that included four other finalists: MARS, RC6, Serpent, and Twofish. It was developed by Belgian cryptographers Dr. Joan Daemen and Dr. Vincent Rijmen. (The name Rjindael is a play on the names of the two inventors, Daemen and Rijmen.) It seems resistant to side-channel attacks such as power- and timing-based attacks, which are attacks against a hardware implementation, not against a particular algorithm. For example, power-and timing-based attacks measure the time it takes to encrypt a message or the minute echanges in power consumption during the encryption and decryption process. Occassionally, these attacks are sufficient enough to allow hackers to recover keys used by the device.

Unlike DES, which uses Feistel cycles in each round, Rijindael uses iterative rounds like International Data Encryption Algorithm (IDEA). It is a minor revision of an earlier cipher, Proposed Encryption Standard (PES). Data operates on 128-bit chunks, which are grouped into four groups of 4 bytes each. The number of rounds is also dependent on the key size, such that 128-bit keys have 9 rounds, 192-bit keys have 11 rounds, and 256-bit keys have 13 rounds. Each round consists of a substitution step of one S-box per data bit, followed by a pseudo-permutation step in which bits are shuffled between groups. Then each group is multiplied out in a matrix fashion and the results are added to the subkey for the round.

IDEA Encryption

The European counterpart to the DES algorith is the IDEA. Unlike DES, which it was intended as a replacement for, it is a considerably faster and more secure. IDEA’s enhanced speed is due to the fact that each round consists of simpler operations than in the Feistel cycle in DES. IDEA uses simple operations like exclusive or (XOR), addition and multiplication, which are more efficient to implement in software than the substitution and permutation operations of DES. Addition and multiplication are the two simplest binary calculations for a computer to perform, and XOR is also a simple operation.

IDEA operates on 64-bit blocks with a 128-bit key, and the encryption/decryption process uses eight rounds with six 16-bit subkeys per round. The IDEA algorithm is patented both in the U.S. and in Europe, but free non-commercial use is also permitted. IDEA is widely recognized as one of the components of Pretty Good Privacy (PGP) version 2.0. It is also an optional algorithm in the OpenPGP standard. IDEA was developed in the early 1990s by cryptographers James Masey and Xuejia Lai as part of a combined research project between Ascom and the Swiss Federal Institute of Technology. The algorithm was patented in a number of countries, but was freely available for non-commercial use. “IDEA” is also a trademark. The last patents expired in 2012, and IDEA is now free to use for both commercial and non-commercial purposes.

External Links:

Advanced Encryption Standard (AES) at Wikipedia

International Data Encryption Algorithm (IDEA) at Wikipedia

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