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Churning is an encryption function used to scramble downstream user data of the ATM passive optical network system defined by the ITU G.983.1 standard. The standard states that churning "offers a low level of protection for data confidentiality". Cryptanalysis had shown that "the churning cipher is robustly weak". ==Algorithm== Churning uses 24 bits of the key, designated X1..X8 and P1..P16. Ten static K bits are generated from the key: K1 = (X1 *P13 *P14) + (X2 *P13 *not P14) + (X7 *not P13 *P14) + (X8 *not P13 *not P14) K2 = (X3 *P15 *P16) + (X4 *P15 *not P16) + (X5 *not P15 *P16) + (X6 *not P15 *not P16) K3 = (K1 *P9) + (K2 *not P9) K4 = (K1 *not P9) + (K2 *P9) K5 = (K1 *P10) + (K2 *not P10) K6 = (K1 *not P10) + (K2 *P10) K7 = (K1 *P11) + (K2 *not P11) K8 = (K1 *not P11) + (K2 *P11) K9 = (K1 *P12) + (K2 *not P12) K10 = (K1 *not P12) + (K2 *P12) The churning transforms eight Y bits into eight Z bits: (Z1..Z4) = TransformNibble(Y1..Y4, K1, P1, K3, K2, P2, K4, K1, K3, K5, K2, P4, K6) (Z5..Z8) = TransformNibble(Y5..Y8, K1, P5, K7, K2, P6, K8, K1, P7, K9, K2, P8, K10) 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「Churning (cipher)」の詳細全文を読む スポンサード リンク
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