25-08-2017, 09:32 PM
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Introduction
Apart from the actual Rijndael proposal [11], it is common to come across several other modified proposals and implementations of the same when compared to the implementation of standardized version of AES on various platforms. In this paper, we summarize some of such implementations and proposals. A summary of several implementations and modifications presented till date as per our knowledge is a take away from this paper. Optimization over area, performance is one part of the implementation story whereas modifications aim at presenting or improving the existing version of a design. In Rijndael’s case, modifications presented span from one to every transformation of the algorithm. Most proposals concentrate on reducing the hardware resources used and improving the performance and throughput. There are proposals available to increase the complexity of the algorithm against certain tradeoffs.
1. A Modified Rijndael Algorithm and its Implementation using FPGA
A modified Rijndael algorithm capable of encrypting a 128 bit input/ output key is presented in [1]. The introduced architecture was implemented by VHDL, schematic and core generator – Based Design which are synthesized, placed and routed in Virtex XCV800-6bg432. Implementation resulted in an optimized area (7148) slices and (44) MHz clock speed. Below is a result table from
A Modified Version of Rijndael Algorithm Implemented to analyze the Ciphertexts Correlation for Switched S-Boxes
The modified version of Rijndael [2] analyzes random changes the accessing order of SBoxes implemented in the source code of the original algorithm, due to affine transformation and inverse matrix properties. The goal of [6] was to obtain two different cipher texts. A PRNG designed by Gorge Marsaglia was made use in the software solution. The proposed method in [2] is that when the number generated by the PRNG- Psuedo Random Number Generator is 0, the S-boxes is accessed for encryption and Inverse S-box is accessed for decryption i.e., regular Rijndael method. If the number generated by the PRNG is 1, then Inverse S-box is accessed for encryption and S-box is accessed for decryption i.e., the Reverse of the actual Rijndael method. Such an approach is termed as Switched S-box variant of RIjndael in [2].
. Implementation of Stronger AES by Using Dynamic S-Box Dependent of Master Key.
A modification proposed in [5] is to convert the static Rijndael S-box into a dynamic S-box that depends on the Master key. Two S-box designs are presented in [5]. The first design exclusively ORs any one byte of the Master key chosen randomly with every cell of Static S-box. Such a dynamic S-box can be denoted as (S-box XOR Onebyte(hex)).
Another proposed design of S-box also involves Exclusively ORing all the cells of the S-box, but this time, it isn’t limited to just the first byte of the Cipher key. Instead, every byte of the Cipher key is bitwise EXORed with the next consecutive byte until all 16 bytes of the cipher key are exhausted. The resulting 1 byte hexadecimal value is then EXORed with every cell of Static S-box. Such an S-box can be denoted as (S-Box XOR ResByte(hex)) where ResByte is given by Ci[15] XOR Ci[14] XOR…. Ci[0]. An example S-box design for both the above proposals can be observed in [5]. In general, the representation of S-box is SBOXxor_key[i]