Pseudorandom number generating apparatus or encryption or decryption apparatus using the same

A decryption apparatus comprising:

• a pseudorandom number generating apparatus for generating a pseudorandom number sequence having a length equal to that of plaintext data to be encrypted;
• and
• an operation section for conducting an exclusive OR-ing operation on the generated pseudorandom number sequence and the plaintext data, thereby calculating ciphertext data and outputting the ciphertext data, and
• said pseudorandom number generating apparatus comprises:
• a state storage section;
• a buffer;
• a state transformation section for conducting transformation using a storage content of said buffer and a storage content of said state storage section and outputting a result of the transformation;
• a state storage control section for updating an internal state of said state storage section by using the output of said state transformation section according to a clock;
• and
• a buffer control section for updating an internal state of said buffer by using the output of said buffer transformation section,
• said state storage section has a capacity of 3 blocks (where one block has n bits), and said buffer has a capacity of a plurality of blocks, and
• said state transformation section comprises:
• a nonlinear transformation section that uses the storage content of said buffer and the storage content of said state storage section as inputs;
• and
• an output section for outputting one block data included in said result of the transformation as a partial random number sequence.

A decryption apparatus comprising:

• a pseudorandom number generating apparatus for generating a pseudorandom number sequence having a length equal to that of ciphertext data, by using information for determining a random number sequence used when generating the ciphertext data to be decrypted;
• and
• an operation section for conducting exclusive OR-ing operation on the generated pseudorandom number sequence and the ciphertext data, and thereby calculating plaintext data, and outputting the plaintext data, and
• said pseudorandom number generating apparatus comprises:
• a state storage section;
• a buffer;
• a state transformation section for conducting transformation using a storage content of said buffer and a storage content of said state storage section and outputting a result of the transformation;
• a state storage control section for updating an internal state of said state storage section by using the output of said state transformation section according to a clock;
• and
• a buffer control section for updating an internal state of said buffer by using the output of said buffer transformation section,
• said state storage section has a capacity of 3 blocks (where one block has n bits), and said buffer has a capacity of a plurality of blocks, and
• said state transformation section comprises:
• a nonlinear transformation section that uses the storage content of said buffer and the storage content of said state storage section as inputs;
• and
• an output section for outputting one block data included in said result of the transformation as a partial random number sequence.

A pseudorandom number generating program that implements, in a computer including a storage device and a processor:

• a state storage section;
• a buffer;
• a state transformation section for conducting transformation using a storage content of said buffer and a storage content of said state storage section and outputting a result of the transformation;
• a state storage control section for updating an internal state of said state storage section by using the output of said state transformation section according to a clock;
• and
• a buffer control section for updating an internal state of said buffer by using the output of said buffer transformation section, wherein
• said state storage section has a capacity of 3 blocks (where one block has n bits), and said buffer has a capacity of a plurality of blocks, and
• said state transformation section comprises:
• a nonlinear transformation section that uses the storage content of said buffer and the storage content of said state storage section as inputs;
• and
• an output section for outputting one block data included in said result of the transformation as a partial random number sequence.