The invention is, firstly, a cryptographic apparatus for encrypting unencrypted data, comprising an input module for inputting the unencrypted data and an output module for outputting encrypted data, and a key automaton (44) adapted for converting the unencrypted data into the encrypted data, and the key automaton (44) is an composition of automata said composition of automata having a set of states and a set of input signals identical to each other and being implemented as a permutation automaton without output signals, said composition of automata comprises at least one factor automaton without output signals, each of the unencrypted data and the encrypted data has a character set identical to each other, and the set of states and the set of input signals, respectively, consist of blocks obtained from all possible combinations of said character set, wherein the blocks are of a predetermined block length. The invention is, furthermore, a cryptographic apparatus for decrypting encrypted data. The invention is, thirdly, a cryptographic method for encrypting unencrypted data. The invention is, fourthly, a cryptographic method for decrypting encrypted data.
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