A symmetric encryption/decryption method includes the steps of selecting a
diffused mechanism, and the diffused mechanism includes at least one
selected from a shift point, a block and a frame; obtaining a plurality
of bits required for a cipher by the diffused mechanism and the element
number of each dimension of a plaintext; carrying out at least one
diffused operation for the plaintext; repeating the foregoing steps to
achieve the effect of encrypting the plaintext. Since the sum of the
encryption diffused times and the decryption diffused times equals to the
diffused cycle, the cipher can be read and at least one dimensional
diffused operation of the ciphertext can be carried out, and thus
achieving the effect of decrypting the ciphertext.