Cfm mode system

摘要

A method for producing at least one ciphertext block from at least one plaintext block using a block cipher E and a key K, the method including receiving n plaintext blocks, wherein n is an integer greater than 0, setting Q₀ equal to an initial value, and for each plaintext block of the n plaintext blocks: computing Q_i=E_K(Q_i-1) XOR P_i; and computing C_i=M(P_i, Q_i), thereby producing n ciphertext blocks, wherein 0i denotes an i-th plaintext block of the n plaintext blocks, and C_i denotes an i-th ciphertext block of the n ciphertext blocks, and M is a selector function which, for each bit C_ij of block C_i, selects a first argument of M if bit P_ij is not to be encrypted, and selects a second argument of M if bit P_ij is to be encrypted. Related apparatus and methods are also provided.