| Summary: | 碩士 === 國立成功大學 === 電腦與通信工程研究所 === 94 === Advanced Encryption Standard (AES) was published in 2001 with Rijndael algorithm. Although AES is used in many different applications, the study of dedicated hardware implementation has become a hot topic in the past five years. Rijmen, one of the designer of Rijndael algorithm, had suggested the usage of subfield arithmetic in the critical path of computing an inverse of 256 elements. In particular, it is well-known that the computational cost of certain Galois Field operations is lower when field elements are mapped to an isomorphic composite field. On the other side, Barkan and Biham proposed the concept of dual ciphers in 2002. The emersion of dual ciphers has brought the discussion of AES to a wide region. Although the intermediate values of dual cipher during encryption or decryption are different from those of AES, the dual ciphers are equivalent to AES in all aspects. In this thesis, we map the field elements of AES to those of Dual AES first, and then translate the field elements of Dual AES to a composite field representation—Composite-Dual AES. Next, the Composite-Dual AES can be parameterized to become a configurable AES—Composite-Dual Cipher. The proposed Composite-Dual Cipher can provide more than 2^21 different AES block cipher schemes. Data can be encrypted not only with secret keys and initial vectors, but also by different block ciphers.
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