JPH01175629A - Blocking system for remainder operation - Google Patents

Abstract

PURPOSE:To facilitate the processing of a byte unit by blocking an inputted bit string with the same number of bits as the number of integers N, and flagging with respect to a block larger than N as the result. CONSTITUTION:A text to be ciphered is read in the byte unit and 64 bytes are set to be one block. When the bytes do not reach 64 bytes, zeros are fulled up, for example. In the case of Mi>=N, if the value of (i)-numbered block is set to Mi, (i)-numbered flag Fi is flagged. For ciphering, MiEmodN or (Mi-N)EmodN is calculated, the cipher sentence Ci of 64 bytes is obtained, and then the cipher sentence Ci and the flag Fi are transmitted or stored in a file. Here, N shows the positive integer, and E a cipher key. Thus, the processing of the byte unit is attained by remainder operation without increasing the length of the text so much.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of blocking an input bit string to be encoded by remainder arithmetic processing and its decoding.

(Prior art) When an input bit string is divided into blocks and a remainder operation is performed on each block modulo a positive integer N, a method is known in which the blocks are divided into blocks using a smaller number of bits than the number of bits of N. ing. For example, a computer (Com
A proposed standard format for cryptosystems (A.P. puter) magazine, September 1986.
roposed 5standard Format
For R8A Cryptosystems) J, a method is proposed in which an input byte string is divided into blocks with the number of bytes one less than the number of bytes of N.

(Problems to be solved by the invention) In the conventional system, if one bit less is blocked, it becomes difficult to process byte by byte, and if one byte less is blocked, the output after the remainder operation will be the same number of bytes as N. This process has the disadvantage that the length increases by 1 byte per block.

(Means for solving the problem) The above problem can be removed by the following blocking method. In other words, the input bit string is blocked with the same number of bits as the positive integer N, and blocks that are larger than N as a result are flagged, or the blocking method is the same as the positive integer N. Blocking is performed by the number of bits, and blocks whose result is larger than N are flagged, and then the bit strings subjected to the remainder operation are blocked by the same number of bits as N, When the flag corresponding to each block is on, N is added to that block.

(Example) An example will be given in which the present invention is implemented in the R8A cipher.

The R8A encryption will be briefly explained. Message M to be encrypted (O≦MAN) using encryption key E, C=M
Calculate EmodN and let C be the ciphertext. This is an encryption method in which M can be decrypted by calculating CDmodN using a decryption key. Details can be found in the above-mentioned document.

Now, let N be a number of 64 bytes.

First, an example of the first invention will be shown. FIG. 1 is a flowchart showing an embodiment.

Read the text you want to encrypt in byte units, and define 64 bytes as one block. If it is less than 64 bytes, pad it with zeros, for example. Letting the value of the i-th block be Mi, when Mi2:N, the i-th flag Fi is set. Encryption is MH”modN or (MH-N)EmodN
is calculated to obtain a 64-byte ciphertext Ci. Ciphertext C1
(i==0.1, 2...) and flag Fi (i=o,
1, 2. ...) or store it in a file.

For example, the ciphertext and the flag may be separate data, or the flag may be added to the beginning or end of the ciphertext. FIG. 2 is a diagram showing the format of this example, in which a flag is attached to the end of the ciphertext. Eight flags are packed into one byte.

Next, an example of the second invention will be shown.

FIG. 3 is a flowchart showing the second embodiment.

Decryption is performed using the ciphertext Ci encrypted as described above and the corresponding flag Fi. For example, suppose you receive a file formatted as shown in Figure 2. At this time, if the size of the file is known, the allocation of flags and ciphertext can be uniquely determined since 1 bit is attached to a flag for every 64 bytes of ciphertext.

Using the decryption key, calculate Mi'=03DmodN.

If the flag Fi is on, N is added to it and set as Ml'. Then Mi' for all i;
Mi is established.

(Effects of the Invention) As explained in detail above, by using the block method of the present invention, byte-by-byte processing can be performed using remainder operations without significantly increasing the length of the text, so it is highly effective when applied to cryptography, etc. .

[Brief explanation of the drawing]

FIG. 1 is a flowchart of encryption in an embodiment of the present invention, FIG. 2 is a diagram showing an example of the format of a cipher text and a flag, and FIG. 3 is a flowchart of decryption in an embodiment of the second invention.

Claims (1)

[Scope of Claims] 1. A blocking method for remainder calculations in which an input bit string is blocked with the same number of bits as a positive integer N, and blocks that are larger than N as a result are flagged. 2. After blocking with the same number of bits as the positive integer N, flags are set for blocks that are larger than N as a result, N and A blocking method for remainder calculations in which blocking is performed using the same number of bits, and when the flag corresponding to each block is set, N is added to that block.