JP2003263106A - Padding system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the load of a network due to the increase of data volume in padding system for block encryption processing. <P>SOLUTION: In the padding system for shaping a block of unit length by interpolating (padding) data of prescribed length in order to compensate the shortage of a block less than the unit length when executing transformation/ inverse transformation processing based on a block cipher by dividing target data into blocks of the unit length, a part of another block to which the transformation/inverse transformation processing has already been applied is segmented and used for padding data for the block less than the unit length. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of dividing communication data of the Internet or the like into blocks each having a unit length and performing block cipher processing. And a padding method for interpolating data of a predetermined length and shaping the data into blocks of unit length. 2. Description of the Related Art In recent years, the speed and cost of communication infrastructure have been increasing, and encryption processing has become more important for the Internet in order to ensure security in online shopping, content distribution, and the like. As an example of the encryption process, there is a block encryption process in which communication data is divided into fixed unit lengths (blocks) and a conversion / reverse conversion process (encryption / decryption) is performed for each unit length. What is block cipher processing?
The continuous data is divided into fixed unit lengths (blocks), and conversion / inversion processing is performed for each block.
If continuous data is divided into unit lengths from the beginning of the data, a case may occur where the last block is less than the unit length. In this case, the shortage is interpolated (padded) with data of a predetermined length, shaped into a unit length, and then subjected to conversion / inversion processing. FIG. 5 is a diagram showing an example of a padding method in the block cipher processing. According to this figure, the data length is N bytes (1 byte is 8 bits), the unit length is L bytes,
A description will be given of the conversion / inversion processing procedure in the case of N ≠ mL (N, L, and m are integers). FIG. 5A shows encryption target data having a data length of N bytes. Next, FIG.
As shown in the figure, the data to be encrypted is divided into blocks B1, B2, B3, and B4 each having a unit length of L bytes.
The last block less than bytes is B5. Next, FIG.
As shown in (c), a block to which a data α byte of a predetermined length is added to make the last block B5 a unit length of L bytes is referred to as a block C. After all the blocks have a unit length of L bytes, each block is subjected to conversion processing to obtain encrypted blocks b1, b2, b3, b4, and c. The data obtained by combining the blocks b1, b2, b3, b4, and c has a data length (N + α) bytes as shown in FIG. 5D. [0004] However, since data of a predetermined length is added to the last block less than the unit length and shaped into the unit length, the data is compared with the data before conversion and converted. Is increased by the added data of a predetermined length. In the case of Ethernet (registered trademark) used for data communication such as the Internet, the datagram per packet is specified as a maximum of 1500 bytes.
When the data of one packet is encrypted by the block cipher processing and exceeds 1500 bytes, the packet is discarded or divided into two packets and transmitted. In order to prevent the converted data from exceeding the maximum datagram, it is conceivable to set the data per packet before conversion to be sufficiently smaller than 1500 bytes, but the data per packet is limited. By doing so, the number of packets may increase. In either case, an increase in the amount of data increases the load on the network. SUMMARY OF THE INVENTION The present invention has been made to solve the problem of a network load caused by an increase in the amount of data in the padding method of the block cipher processing described above, and has as its object to reduce the network load. SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method for dividing / converting target data into blocks of unit length and performing a conversion / reverse conversion process based on a block cipher. To compensate for the shortage of blocks less than the unit length,
In a padding method in which data of a predetermined length is interpolated (padding) and shaped into a block of a unit length, a part of another block which has already been subjected to the conversion / inverse conversion processing is cut out as interpolation data of a block having a unit length less than the unit length. It was used. Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. FIG. 1 is a diagram showing an example of a padding method in a block cipher process according to the present invention, in which a data length is N bytes, a unit length is L bytes, and N ≠ mL (N, L, and m are integers) according to the drawing. The conversion procedure will be described. FIG. 1A shows encryption target data having a data length of N bytes. FIG. 1B shows that the data to be encrypted is divided into blocks B1, B2, B3, and B4 for each unit length L bytes from the beginning of the data, and the final block is a block B5 having a unit length less than L bytes. ing. FIG. 1C shows a block B having a unit length of L bytes.
1, B2, B3, and B4 are all converted (encrypted), the respective blocks are referred to as blocks b1, b2, b3, and b4, and the block B5 is not converted.
FIG. 1D shows the converted block b4, which is one block before the last block B5, divided into a block c and a block d. Here, the block d is divided so that the length (α bytes) becomes the interpolation data length of the last block B5 (α = L−the data length of the block B5). FIG. 1E shows a block B obtained by extracting a block d from the converted block b4.
5 shows that these are concatenated and shaped into a unit length of L bytes. FIG. 1F shows that a block having a unit length of L bytes obtained by connecting the block d and the block B5 is converted to obtain a block e. FIG. 1G shows data obtained by combining the converted blocks b1, b2, b3, c, and e. Here, the block c is shorter than the unit length L bytes by α bytes. As shown in FIG. 1 (g), the data length of the data obtained by combining all the converted blocks is N bytes,
The data length before conversion is the same as N bytes. The case where the converted data shown in FIG. 1 (g) is inversely transformed (decoded) will be described by following FIG. 1 from bottom to top in the reverse direction. First, the data to be decoded shown in FIG. 1 (g) is divided into blocks e having a unit length of L bytes from the end, and the remaining data to be decoded is divided into units of L bytes from the beginning of the data to form blocks b1, b2 and b3, and a block less than the unit length L bytes is a block c. Then, the last block e is inversely transformed (decoded). (FIG. 1 (f)) The inversely transformed block e is separated into a block d of the upper α byte for interpolating the block c and the remaining block B5. (FIG. 1E) The block d is joined to the lower part of the block c to obtain a block b4 having a unit length of L bytes. (FIGS. 1 (d) and (c)) Blocks b1, 2b, b3 and b4 are inversely transformed, respectively.
Obtain the decoded blocks B1, B2, B3, B4.
Blocks B1, B2, B3, B4 and block B5 are combined. The data length of the combined data is N bytes.
(FIGS. 1 (b) and 1 (a)) Next, the conversion / inverse conversion processing when the data length is 14 bits and the unit length is 4 bits will be described with reference to FIGS. Here, bits are used instead of bytes to facilitate understanding. FIG. 2 is a table showing a 4-bit conversion / inversion rule. FIG. 3 shows a procedure for converting data having a data length of 14 bits into a unit length of 4 bits.
FIG. 4 shows a procedure for inversely converting the data converted in FIG.
The data to be encrypted “11100100000101” is divided into four unit bits in order from the top. 3 from the beginning
Until the block, “1110”, “0100”, “00”
01 ", and the last block is" 01 "smaller than the unit length. 3 blocks “1110”, “0100”, “00”
01 in accordance with the conversion rule of FIG.
11 "," 1101 ", and" 1010 ". here,
Lower 2 of the third block (one before the last block)
The bit “10” is padded to the upper position of the last block “01” to obtain “1001” having a unit length of 4 bits. This "1
"001" according to the conversion rule of FIG.
It becomes. The converted first block “0011”, the second block “1101”, and the top two of the third block
The bit “10” and the last block “0100” are combined. The combined converted data becomes “00111101100100” having the same data length as the original data. Next, the inverse transformation will be described. The converted data “00111101100100” is divided into unit lengths of 4 bits in order from the top. The first block is “0011”, “1101”, and “1001”, and the last block is “00”, which is less than the unit length. The third (one before the last block) block “1001” is divided into upper two bits “10” and lower two bits “01”, and the lower two bits “01” are connected to the upper part of the final block “00” Then, "0100" having a unit length of 4 bits is obtained. When this “0100” is inversely transformed according to the inverse transformation rule of FIG.
001 ”. Next, this “1001” is divided into upper two bits “10” and lower two bits “01”,
The bit “10” is combined with the lower 2 bits of the upper 2 bits “10” of the third block to form a 4-bit unit length “101”.
0 "and the lower two bits" 01 "are taken as the inversely transformed final block. Excluding the last block, three blocks of unit length 4 bits “0011”, “1101”,
"1010" is inversely transformed according to the inverse transformation rule of FIG.
0 "," 0100 ", and" 0001 "are obtained. The three blocks “1110”, “0100”, and “0”
The reverse conversion data obtained by combining “001” and the last block “01” is the same as the original data “11100100000101”. According to the present invention, the data length does not change due to the padding processing of the block cipher processing, and the load on the network can be reduced.

[Brief description of the drawings] FIG. 1 shows an example of a data conversion procedure according to the present invention. FIG. 2 shows an example of conversion / inverse conversion according to the present invention. FIG. 3 shows an embodiment of data conversion according to the present invention. FIG. 4 shows an embodiment of the data reverse conversion according to the present invention. FIG. 5 shows an example of a conventional data conversion procedure. [Explanation of symbols]

Claims (1)

Claims: 1. When a target data is divided into blocks of a unit length and a conversion / reverse conversion process based on a block cipher is performed, a deficiency of blocks less than a unit length is compensated. In a padding method in which data of a predetermined length is interpolated (padding) and shaped into a block of a unit length, a part of another block which has already been subjected to the conversion / inversion process is cut out as interpolation data of a block having a unit length less than the unit length Padding method characterized by using