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HC-256 is a stream cipher designed to provide bulk encryption in software at high speeds while permitting strong confidence in its security. A 128-bit variant was submitted as an eSTREAM cipher candidate and has been selected as one of the four final contestants in the software profile. The algorithm is designed by Hongjun Wu, and was first published in 2004. It is not patented. ==Function== HC-256 has a 256 bit key and an initialization vector (nonce) of 256 bits.〔 Internally, it consists of two secret tables (P and Q). Each table contains 1024 32-bit words. For each state update one 32-bit word in each table is updated using a non-linear update function. After 2048 steps all elements of the tables have been updated. It generates one 32-bit word for each update step using a 32-bit to 32-bit mapping function similar to the output function of the Blowfish cipher. Finally a linear bit-masking function is applied to generate an output word. It uses the two message schedule functions in the hash function SHA-256 internally, but with the tables P and Q as S-boxes. HC-128 is similar in function, and reduces each of key length, nonce, number of words in the tables P and Q, and number of table updating steps by half.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「HC-256」の詳細全文を読む スポンサード リンク
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