Encryption apparatus

1. An encryption apparatus comprising:

an idle data inserting unit that takes an input of a frame including a fixed-length header and a variable-length payload; and

an encrypting unit that receives an output of the idle data inserting unit,

wherein, if a first length of the frame is less than a predetermined value which corresponds to a predetermined time period for encrypting the variable-length payload by the encrypting unit, the idle data inserting unit appends at least one fixed-length idle data following the variable-length payload to make a second length of the frame greater than or equal to the predetermined value and transmits the frame including the at least one fixed-length idle data to the encrypting unit.

2. The encryption apparatus according to claim 1 , wherein the idle data inserting unit, upon detecting stop of receiving the frame, transmits the at least one fixed-length idle data to the encrypting unit.

3. The encryption apparatus according to claim 1 , wherein, if the frame is to be non-encrypted, the idle data inserting unit transmits the frame as it is to the encrypting unit.

4. The encryption apparatus according to claim 1 , wherein:

the frame is configured to position one header byte of a processing sequence in an upper byte position and another one byte following the one header byte in a lower byte position, and is a 16-bit sequence parallel for each two bytes; and

if the frame has an odd joint in which a final byte of the frame is located in the upper byte position, the idle data inserting unit appends the at least one fixed-length idle data to make a predetermined pattern and transmits the frame padded with the at least one fixed-length idle data to the encrypting unit.

5. The encryption apparatus according to claim 1 , wherein:

the variable-length payload includes first and second blocks to be processed, which are independently encrypted,

the predetermined time period is a time period for encrypting one of the blocks by the encrypting unit,

the encrypting unit includes first and second cryptographic calculation planes,

the first cryptographic calculation plane encrypts the first block, and

the second cryptographic calculation plane encrypts the second block.

6. The encryption apparatus according to claim 1 , wherein the at least one fixed-length idle data includes a fixed pattern of five bytes.

7. The encryption apparatus according to claim 1 , wherein:

the frame consists of an at minimum six-byte-length of data including a header having a five-byte-length and a payload having a one-byte-length,

the encrypting unit includes two cryptographic calculation planes which independently encrypt N bytes in one clock,

if the predetermined time period is less than or equal to 6×2÷N clocks, the predetermined value is obtained by time periods of greater than a first value which is equal to the predetermined time period divided by 2, and

if the predetermined time period is greater than or equal to 6×2÷N clocks, the predetermined value is obtained by time periods of greater than a second value which is equal to the predetermined time period subtracted by 6.

8. The encryption apparatus according to claim 1 , wherein:

the frame consists of an at minimum six-byte-length of data including a header having a five-byte-length and a payload having a one-byte-length,

the encrypting unit includes three cryptographic calculation planes which independently encrypt N bytes in one clock,

if the predetermined time period is less than or equal to 6×3÷N clocks, the predetermined value is obtained by time periods of greater than a first value which is equal to the predetermined time period divided by 3, and

if the predetermined time period is greater than or equal to 6×3÷N clocks, the predetermined value is obtained by time periods of greater than a second value which is equal to the predetermined time period subtracted by 6 and then divided by 2.