Abstract: A hierarchical encryption device for decrypting a ciphertext and outputting a plaintext is disclosed in the invention, wherein the ciphertext comprises an encrypted block and a plurality of ciphertext blocks. The device comprises a first decryption unit, a generator and a second decryption unit. The second decryption unit is for decrypting the encrypted block by a secret key with a second decryption method to generate at least one index block and a plurality of confusion blocks. The generator is for generating a plurality of mask blocks according to the plurality of confusion blocks and the index block, wherein the number of the plurality of mask blocks is the same as that of the plurality of ciphertext blocks. The first decryption unit is for decrypting the plurality of ciphertext blocks by the plurality of mask blocks with a first decryption method to generate a plurality of plaintext blocks, wherein the number of the plurality of plaintext blocks is the same as that of the plurality of ciphertext blocks.