The invention provides a diffusion function working on a multidimensional diffusion-area (plaintext/ciphertext), in which a multidimensional medium is meanwhile overlapped to the diffusion-area; accordingly, repeating the diffusion function for at least one time thus brings about the multilayer effect. FIG. 1 shows an embodiment of the present invention in flow chart diagram form, comprising of: inputting a plaintext in encryption or a ciphertext in decryption 100; inputting a series of password data forward in encryption or backward in decryption 200; further, by the password data, converting the dimensions of the plaintext 300, and implementing with a diffusion function, repeated TE times in encryption, TD times in decryption 400; outputting the ciphertext in encryption or the plaintext in decryption 600 if completing all password data 500.