WO2008084966A1

WO2008084966A1 - Complement method for many languages text characters encryption algorithm

Info

Publication number: WO2008084966A1
Application number: PCT/KR2008/000110
Authority: WO
Inventors: Insup Lee
Original assignee: Insup Lee
Priority date: 2007-01-10
Filing date: 2008-01-08
Publication date: 2008-07-17
Also published as: KR100876525B1; KR20070013344A

Abstract

It is done by a feature to include the method of the present invention, when it ciphers the multi-lingual text string like the Korean, Japanese handled in the computer with symmetric key encryption algorithm, it provides the method for preventing from not being able to display the ciphertext on computer terminal console as it deviates from character code domain, it also provides the method which the length of ciphertext is maintained identically with the original plaintext. As especially, it fixes several bits of the multi- lingual character code defined as double-byte, and it encrypts the rest of bits when it ciphers the character string which is handled in the computer with the procedure of the several steps based on the mathematical operator. Then, the character code domain of the ciphertext is curbed in the domain of the fixed bits.

Description

COMPLEMENT METHOD FOR MANY LANGUAGES TEXT CHARACTERS ENCRYPTION ALGORITHM

Technical Field

[1] The present invention relates to the method, when it ciphers the multi-lingual text string like the Korean, Japanese handled in the computer with symmetric key encryption algorithm, it provides the method for preventing from not being able to display the ciphertext on computer terminal console as it deviates from character code domain, it also provides the method which the length of ciphertext is maintained identically with the original plaintext. As especially, it fixes several bits of the multilingual character code defined as double-byte, and it encrypts the rest of bits when it ciphers the character string which is handled in the computer with the procedure of the several steps based on the mathematical operator. Then, the character code domain of the ciphertext is curbed in the domain of the fixed bits.

[2] Generally, there are two kinds of encryption algorithm used in the computer. One is the symmetric algorithm which is used as the data encryption about file, packet, the other one is the asymmetric algorithm which is used in the authentication system like banking public certificate.

[3] The difference between symmetric and asymmetric algorithm is whether the secret key in encryption and decryption is identical or not. Symmetric algorithm uses the same key in encryption and decryption, however in asymmetric algorithm, the key for an encryption and decryption exists in pairs. If it encrypts with any one of the pair, a decryption process is possible through the rest of the pair.

[4] The present invention relates to the method for complementing the encrypted result about the multi-lingual text string like the Korean, Japanese into the character code which can be displayed on the terminal console, it follows to the former skill of the symmetric algorithm which is the technical field in which the present invention belongs.

[5] DES (Data Encryption Standard) algorithm which IBM develops represents the symmetric algorithm.

[6] DES is the block cypher algorithm which IBM develops. It was adopted as a standard in National Bureau of Standards (NBS) in 1977.

[7] It is the the block cypher algorithm which ciphers 64 bit entry block by using 56 bit secret key. It starts to be used as the data protection in U.S. federal. Until it is used as the standard cipher algorism of the ANSI (American National Standards Institute), the usage is expanded and it is all over the world widely most used. [8] It is general opinion that the DES is not safe any more due to the short key, 56 bit length.

[9] Complementary to these points, 3DES (Triple DES) which repeats DES in 3 times was recommended. And AES which is the next generation American Standard is settled and used.

[10] Triple DES which repeat DES in 3 times with 3 keys was used in order to resolve the stability problem due to the short key of DES's 56 bits.

[11] 3DES was used in another standard due to the advantage of solving the safety problem of DES, of being implemented by using the existing DES in spite of the disadvantage that speed was slow than DES.

[12] The development of the AES (Advanced Encryption Standard) which is strong encryption algorithm standard, and can use in the goverment and commerce, was carried out according to the necessity of the block cipher replacing DES in which the standard period was expired 1998 in NIST.

[13] The Algorithm satisfying the function which is more efficient than 3DES and safe and which has no royalty was collected publicly by NIST. The candidate algorithm of 15 was publicly evaluated through 3 year. AES algorithm was adopted finally in 2 October 2000.

[14] The block cipher adopted in AES was the algorithm which was developed by

Daemem and Rijmen and named RIJNDAEL. The algorithm used as a new industry standard instead of DES and Triple DES in December 2001.

[15] An algorithm to be used as a standard was developed in Korea. SEED is the 128 bit block cypher algorithm of the symmetric key method under the KISA and ETRI in Korea in order to protect the information and personal privacy at the civil sector. It was adopted as a standard of TTA in September 1999, and it was settled as a international standard at the 31 ISO/IEC nternational Standards Organization, November 2005.

[16] But the former skill was common for a data enciphering. When it ciphers the multilingual text string like the Korean, Japanese, the result can deviate from the code area of the original plaintext. It has no problem when the code is saved as binary mode. But it has some problem when it displays the code as text mode on computer terminal c onsole, the character code can be invisible because the code is out of area, or be a control code.

[17] Complementary to these points, it usually uses the method for ciphering the hexa code after separating the double-byte multi-lingual code like the Korean, Japanese into the each lbyte hexa code, but there is a disadvantage that the length string extends to 2 times.

[18] If it use the compression algorithm with that, the length can be reduced. But the problem that the compacted length is not fixed occurs. [19] Besides, the method which manage the double-byte multi-lingual code like the

Korean, Japanese as the separate code table, or the method for ciphering as the substitution etc. are also introduced. However, it has the disadvantage also of increasing than the length of the original, or it is not desirable method like substitution which is not based on the bit operation. The substitution method is going against era.

[20] Therefore, when the multi-lingual text string like the Korean, Japanese were ciphered, the result maintains the code area of the original. The skill which the length is maintained identically with the original copy is required.

[21]

Disclosure of Invention Technical Problem

[22] Two problems as follows occurs in case of ciphering the multi-lingual text string like the Korean, Japanese by the former existing symmetric encryption algorithm. The first, there is a case being able to display the ciphertext on computer terminal console as it deviates from character code domain. The second, there are many transformed algorithm for preventing the problem of the first, but it has the disadvantage that the length of the cipher text is lengthened than that of the original. The ideal algorithm complementing the above problem is that the ciphertext does not deviate from the original code domain, and the length of the cipher is the same as that of the original.

[23] The present invention was started with the purpose of implementing the ideal algorithm described in the above. And The present invention itself is not symmetric encryption algorithm. It is in-between procedure to complement the former existing symmetric encryption algorithm.

[24] The object of the present invention is the complementing the encrypted result about the multi-lingual text string like the Korean, Japanese handled in computer into the character code which can be displayed on the terminal console. So the encrypted result is managed with the text format which is not binary, so it can store as the encrypted format itself in the e-mail, internet board, messenger, the word processor etc. And it provides a printing with the paper document.

[25] Moreover, the object of the present invention is the complement. The length of encrypted result is maintained identically with the original. Therefore the computing system software transferring, storing data does not have to be modified. It can handle the encrypted data itself.

[26] For example, in data transmission, the system is transmitting a communication packet between the sending and receiving with the predefined packet. There might be a fixed- length packet, and there can be variable-length. In the case of a fixed- length, let's suppose that a 20-length field which is Korean character is on the arbitrary location of a packet. If it encrypts the field using the former existing algorithm, the field is lengthened. So the system has to be modified in order to handle the increased length.

[27] In data storing, the field which composes the table of database might be a fixed- length packet, and can be variable-length. In case of the fixed length handling Korean character, if the length of the encrypted result is changed, the expense problem which amends a system occurs in order to store the changed length. When it applies the skill of the present invention, it will be able to reduce like this expense.

[28]

Technical Solution

[29] It is done by a feature to include the method of the present invention to achieve above object, and the procedure when it ciphers the multi-lingual text string like the Korean, Japanese handled in the computer with symmetric key encryption algorithm, it provides the method for preventing from not being able to display the ciphertext on computer terminal console as it deviates from character code domain, it also provides the method which the length of ciphertext is maintained identically with the original plaintext. As especially, it fixes several bits of the multi-lingual character code defined as double-byte, and it encrypts the rest of bits when it ciphers the character string which is handled in the computer with the procedure of the several steps based on the mathematical operator. Then, the character code domain of the ciphertext is curbed in the domain of the fixed bits.

[30] The above double-byte multi-lingual code, which is defined as double-byte in order to handle the language of all the countries of the world like the Korean, Japanese in the computer. There are the character codes which are standard of each country like KSC5601, the character codes which are provided by software company like microsoft, and the Unicode which standardizes alphabet and all multi-linguals to double-byte etc. (in especially the alphabet expressed as double-byte is regarded as Unicode).

[31] Moreover, in the character code consisting of one or two bytes, the above bit masking means the blocking the bit value of the specific location. That is, the n ecessary bits pass through, and the unnecessary bits block. Such bit operation can implement by the AND operation mathematically. Referring to the below (table 1), if the original bit is computed by AND with 0, it is outputted to 0 irrespectively of the value of the original. If the original bit is computed by AND with 1, the same value as the original bit is outputted. This concept can be used in case as follows. In lbyte, if the high 4 bits remove, and the only low 4 bits want to use, the high 4 bits perform the AND operation with 0, and the low 4 bits perform the AND operation with 1. That is, the bit mask like "00001111" is added to the original through the AND operation. [32] Table 1

[33] In the meantime, the above encryption is the symmetric cipher algorithm, the technical field in which the present invention belongs. The mathematical theory of the symmetric cipher algorithm implemented in the computer is based on the XOR operation of showing in (table 2). Simply, even if the XOR operation performs each bit of the original with each bit of the secret key, the successful cipher text can be produced. If it computes reversely with the secret key used in the former encoding process like (the equation 1), the ciphertext can acquire the original again. The name called symmetric is caused that it uses the same secret key in an encoding and decoding. The symmetric algorithm having the characteristic of this XOR operation, and adding a procedure including the confusion (diffusion), substitution etc. for security enhancement are announced enough. DES and SEED represent the algorithm. The one is used globally, the other is developed in Korea.

[34] Table 2

[35] MathFigure 1

A(+}K=B

[36] B(+)K=A

[37] [38] According to the preferred embodiment of the present invention, it is illustrated below with reference to attached drawings. In case the concrete description to the notification function which relates in illustrating the present invention or the configuration is gist of the present invention determined because of being gratuitously cloudy, detailed description will be omitted. [39] In embodiment of the present invention, in order to provide the function complementing the encrypted result about the multi-lingual text string like the Korean, Japanese handled in computer into the character code which can be displayed on the terminal console, the character code is classified according to several bit masking groups. Encryption process is implemented after the secret key is complemented by bit mask corresponding to each group.

[40] Generally, there are two kinds of encryption algorithm used in the computer. One is the symmetric algorithm which is used as the data encryption about file, packet, the other one is the asymmetric algorithm which is used in the authentication system like banking public certificate. However the symmetric algorithm which is used presently is the algorithm which just ciphers binary data. Therefore when the text string is ciphered, it can be out of the character code domain, so it cannot be outputted to the terminal console. In addition, it cannot be saved as the text file format. New algorithm complementing this problem developed, but another problem that the coding result was lengthened than the original occured again.

[41] Therefore, the present invention suggests the method, complementing lest the encoding result should deviate from the character code domain, which it can display the ciphertext on computer terminal console, which it can save as the text file format, which the length of ciphertext is maintained identically with the original plaintext.

[42] First, it explains the method of the present invention which tries to refer to Figure 1.

[43] Figure 1 is a drawing in which when the double-byte multi-lingual code like the

Korean, Japanese were ciphered with a secret key, the result can be out of the corresponding code area according to the embodiment in the present invention.

[44] Referring to the above Figure 1, when the double-byte multi-lingual code area which is the original domain (101) is ciphered with a secret key domain (102), it shows that the cipher text domain (103) which is the result can deviate from the original domain (101).

[45] The above original domain (101) is the double-byte multi-lingual code area like the

Korean, Japanese. Here is Korean area in the KSC5601 code.

[46] Generally, in the notation of text string in computer, English, number, basic symbol use the ASCII code which use the lower 7 bits in 1 byte. However, the multi-lingual notation like the Korean, Japanese, Chinese, Arabic use the double-byte code.

[47] For example, English 'A' notation is needed for the 1 byte, the corresponding code is '01000001', as defined in the ASCII code table. '01000001' is the expression as the bi nary number. '41' is that of hexadecimal number.

[48] While Korean 'Ga'(whose KSC-5601 code is OxBOAl and Unicode is OxACOO) notation needs for 2 bytes, the corresponding code is '1011000010100001' in KSC5601 Korean code table. 'BOAT is the hexadecimal number. In this way, all multi-linguals is defined in the double -byte code table.

[49] The above secret key domain (102) is defined as the arbitrary domain. Therefore it can be the whole range of '0000' ~ 'FFFF' as the hexadecimal notation. It can directly input the secret key with the keyboard which is the computer terminal, and it can read it from a file stored in CD, USB memory etc. which is the external storage device. Therefore the secret key domain (102) can be defined in the whole area even if the code is out of the character code area.

[50] The above cipher text domain (103) is the region which the encrypted result can occupy. The result is what ciphers the above original domain (101) with the secret key domain (102) by the symmetric key encipherment algorithm (104). The original domain (101) is restrictive to the character string code area of the specific multilingual. However, the secret key domain is not limited. Therefore the cipher text domain (103) which is the result which ciphers can deviate from the original domain (101). It shows in fig. 1. The symmetric key encipherment algorithm like DES which it use generally, includes the XOR operation internally. And the operation does not guarantee lest the result ciphering the original domain (101) should deviate from the original domain. Moreover, the algorithm including DES etc. is added some procedure including the confusion (diffusion), substitution etc. besides the XOR operation. So it is harder to guarantee the original domain (101). Therefore, in order that the cipher text domain (103) does not deviate from the original domain (101), the necessity which has to fixes several bits of the original domain occurs.

[51] Referring to the case 1 of (Table 3), the character code of the encrypted result is not defined in the computer. Therefore it is just outputted as '?' on the computer terminal console. Of course, it may be valid internally if the code itself is stored in binary file, not being outputted on the computer terminal console. However, it is impossible to be outputted in a viewer program, aneditor, or a word processor etc. which reads the text file.

[52] If it looks at the case 2, the result ciphering Korean character deviates from the

Korean character domain, and it is outputted to the Chinese character. It is not a problem to be outputted to the Chinese character. However, the Chinese character is also used a Chinese windows, a Japanese windows, and each code area is respectively different. Therefore the problem of bringing the disruption of compatability contains that the coding result about Korean character invades the Chinese character code area.

[53] If it looks at the case 3, and 4, the result ciphering Korean is outputted to two bytes of ASCII character. It is not serious problem. However, it seems to be so desirable that the result ciphering the double-byte multi-lingual code is changed to two of lbyte code.

[54] In the result of looking around from case 1 to 4. the ciphering of the character string had to be encrypted in the character code domain which can be displayed on the terminal console. And it is desirable to be transformed in the same language code domain.

[55] Table 3

[56] In below (table 4), it shows the KSC5601 Korean code table referring to the concrete embodiment of the present invention. [57] Table 4

[58] The above symmetric key encipherment algorithm (104) use the secret key which is identical as to encoding and decoding, and the mathematical basis of the symmetric key encipherment algorithm (104) is based on the XOR operation in the computer. The standardized algorithm including DES, SEED etc. is internally based on the XOR operation. Procedure including the confusion (diffusion), substitution etc. is added for the security enhancement. In embodiment of the present invention, in order that object of the present invention is specifically illustrated, performing the only XOR operation represent the symmetric key encipherment algorithm. Even if the XOR operation just performs, the successful cipher text can be produced.

[59] Figure 2 is a drawing according to the embodiment in the present invention, which classifies the original into several bit masking groups lest the code area of the cipher text should deviate from the code area of the original ,which schematizes the method for complementing the secret key with the bit mask corresponding to each group.

[60] Referring to Figure 2, the original domain (210) is classified into the three bit masking group. As to the first bit masking group (211), the result ciphered with the secret key (221) masked by the bit mask corresponding to the group does not deviate from the first area (231). In this way, as to the second bit masking group (212), and the third bit masking group (213), it is guaranteed that the ciphered result does not deviate from the original domain.

[61] Here, the criterion classifying into several groups is the common high bits.

Referring to below (table 5), the Korean characters from 'Ga'(whose KSC-5601 code is OxBOAl and Unicode is OxACOO) to 'We'(whose KSC-5601 code is OxBFFE and Unicode is 0xC6E8) have the common high 4 bits of the upper byte, and common high 3 bits of the lower byte. That is, the criterion distinguishing the characters from 'Ga' to 'We' is the low 4 bits of the upper byte, and low 5 bits of the lower byte. Here, even if the second bit among the high 3 bits of the lower byte is not common, the high 3 bits is bound with one, and it ciphers the only low 5 bits. If it masks several bits between the bits, it can be confused.

[62] Therefore, in order that the result ciphering the original in this range does not also deviate from this range, it maintains the common high bits, and it ciphers the low bits.

[63] In this way, it can complement lest the other range of Korean character should deviate from the corresponding domain, and the other multi-lingual code including Japanese, Chinese etc. can maintain the domain of the original with the method for ciphering the only different low bits after grouping the common bits.

[64] Table 5

[65] Figure 3 is a drawing showing the embodiment on the present invention, it fixes several bits, and it just ciphers the rest of bits.

[66] Referring to Figure 3, it is the method of the concrete embodiment for fixing several bits, and just ciphering the rest of bits. It shows that the fixed bits (311) of the upper lbyte and that (312) of the lower lbyte in a plaintext is identical to the bits (351) of the same position of the upper lbyte and that (352) of the lower lbyte in a ciphertext.

[67] In order to produce this result, referring to fig. 3 which is embodiment of the present invention, it shows the procedure ciphering the specific group (310) of the original domain with the new secret key domain (340) operating the secret key domain (320) by the bit mask (330). The symmetric key encipherment algorithm in this example performs the only XOR operation. Therefore if it has the bit which it wants to fix, it has only to operate the bit with '0'. As to the characteristic of the XOR operation, it maintains the original value after computing with '0'. For your reference, the bit computed with T has the opposite value. Therefore, if it makes the position of the bits which it wants to fix into the mask, and it filters the secret key with the corresponding mask, and it performs the ciphering operation, then it fixes the masked bits, and it ciphers the only bits which are not masked.

[68] Here, the specific group (310) of the original domain is one of bit masking group classified in fig. 2, as a concrete example, the domain 1 in (table 5) is shown. It can be various method to fix several bits, and to cipher the only rest of bits. Here, it shows a simple example, the method for bit-masking the secret key. This example just helps the understanding of this patent claims. It clarifies that the example itself is not the claims.

[69] The specific group of the original domain (310) is comprised of total 2 bytes with upper lbyte and lower lbyte. And the upper lbyte is comprised of the common high 4 bits (311) and the low 4 bits which can distinguish each character code. Moreover, the lower lbyte is comprised of the common high 3 bits (312) and the low 5 bits which can distinguish each character code.

[70] Here, even if the second bit among the high 3 bits of the lower lbyte is not common, the high 3 bits is bound with one, and it ciphers the only low 5 bits. If it masks several bits between the bits, it can be confused.

[71] In below (table 6), the concrete embodiment corresponding to fig. 3 is shown. It looks in the case 1, if it performs the Korean 'Go'(whose KSC-5601 code is OxBOED and Unicode is OxACEO) with the secret key 'ab' by the XOR operation, the result deviates from the character code domain. Therefore it displays '?' on the computer terminal console. In order to solve this problem, in the case 2, it shows the result complementing with the bit masking. In the case 2, if it complements the hexadecimal code '61 62' of the secret key 'ab' with the bit mask 'OF IF', it can see that the result of the Korean 'Go'(whose KSC-5601 code is OxBOED and Unicode is OxACEO) becomes the Korean 'Goolh'(whose KSC-5601 code is OxBlBF and Unicode is 0xAD7B).

[72] Table 6

[73] [74] Figure 4 is a flowchart showing the embodiment on the present invention, it inputs the plaintext and secret key, and it performs the ciphering procedure.

[75] Fig. 4 shows the example, how it can apply the present invention to the former existing symmetric key encipherment algorithm. This flowchart itself is not included in the range of the patent claim.

[76] Referring to Figure 4, if it requests the encryption about the plaintext through the computer, it inputs (401 step) the plaintext and secret key as the character array. [77] It successively reads the original plain text per lbyte (402 step) until it becomes a

NULL terminated character (410 step), it repeats and ciphers. It successively reads the secret key per lbyte (402 step) just like the plain text. [78] If the original code which it successively reads corresponds to the ASCII code domain, it calls the ASCII encrypting function (404 step), and if the domain does not correspond to the ASCII code domain, it reads one more byte (406 step), and it calls

(403 step) the double-byte multi-lingual encrypting function (407 step). [79] It illustrates the ASCII encrypting function (404 step) in fig. 5.

[80] It illustrates the double-byte multi-lingual encrypting function (407 step) in fig. 6.

[81] If it completes the ASCII encrypting function (404 step), it increases the index by one (405 step) in order to read the next byte of the original character string. [82] If it completes the double-byte multi-lingual encrypting function (407 step), it increases the index by two (408 step) in order to read the next byte of the original character string. [83] The length of secret key is different from that of plain text. Therefore the index has to be respectively managed for reading the next byte of string. Generally, if it reads the secret key character string to the final byte, it returns the index to the first (409 step). [84] If it finishes to the final byte of the original character string, it outputs the cipher text (411 step). [85] Figure 5 is the subsequent procedure of fig. 4 according to the embodiment in the present invention, it is the flowchart performing the procedure encrypting the ASCII code, reading the character string of the original by lbyte. [86] Referring to Figure 5, it reads the lbyte of plain text, and the lbyte of secret key

(510 step). If the original lbyte corresponds to the domain which it does not have to cipher, or should not (520 step), it replaces the lbyte of cipher text with the lbyte of plain text itself (570 step). [87] If the lbyte of plain text comes under domain between C3 and C4, it performs the bit- masking (550 step) the lbyte of secret key with the bit mask (551) corresponding to the domain. [88] It ciphers (580 step) the lbyte of plain text with the bit-masked secret key (581) by the symmetric key encipherment algorithm. Here, the performing simply XOR operation represents the symmetric key encipherment algorithm in order to clarify the concrete example. [89] In this way, it performs the procedure of encipherment after masking with the bit mask defined respectively regarding that the original lbyte comes under the domain between C5 and C6, and the generalized domain between Cn and Cn+1 (n=l, 3, 5, .). [90] Figure 6 is subsequent procedure of fig. 4 according to the embodiment in the present invention. While it reads the character string of the original by lbyte, if the original character is the multi-lingual code, it reads one more byte, and performs the encryption process. [91] Referring to Figure 6, it reads the original 2 bytes, and secret key lbyte (6010 step).

If the original upper lbyte corresponds to the domain which it does not have to cipher, or should not (6020 step), it replaces the 2 bytes of cipher text with the 2 bytes of plain text. (6070 step, 6110 step). [92] If the upper lbyte of plain text comes under domain between C3 and C4, it performs the bit- masking (6050 step) the lbyte of secret key with the bit mask (6051) corresponding to the domain. [93] It ciphers (6080 step) the upper lbyte of plain text with the bit-masked secret key

(6081) by the symmetric key encipherment algorithm.

[94] Moreover, in order that it ciphers the lower lbyte of plain text, it performs the bit- masking (6090 step) the lbyte of secret key with the bit mask (6091) corresponding to the domain. [95] It ciphers (6120 step) the lower lbyte of plain text with the bit-masked secret key

(6121) by the symmetric key encipherment algorithm. Here, the performing simply

XOR operation represents the symmetric key encipherment algorithm in order to clarify the concrete example. [96] In this way, it performs the procedure of encipherment after masking with the bit mask defined respectively regarding that the original upper lbyte comes under the domain between C5 and C6, and the generalized domain between Cn and Cn+ 1 (n=l,

3, 5, .). [97] First, the problem of just performing XOR operation is shown, next, the problem of ciphering by DES algorithm is shown. Finally, the successful result of complementing with the method of this research is shown. [98] Table 7

[99] [100] In the meantime, in embodiment of the present invention, it illustrated about a concrete embodiment. Many transformation is possible in the limit which it does not deviate from scope of the present invention. Therefore, while being limited to the explained embodiment and not being determined, the scope of the present invention determines with the range of not only the range of the patent claim which will be described later but also the equal things to this patent claim.

[101]

Advantageous Effects

[102] According to the present invention, it provides the method complementing the encrypted result about the multi-lingual text string like the Korean, Japanese handled in computer into the character code which can be displayed on the terminal console. So the encrypted result can be stored in a text format which is not binary. It can store to the form encrypted in the E-mail, internet board, messenger, the word processor etc. It provides so that it be possible to a printing in a need with the paper document. Moreover, the present invention, the coding result of the double-byte multi-lingual text string code like the same code area. Therefore it makes the length of the plain and cipher text identical.

[103] If it utilize the feature having the coding result which can be displayed on the terminal console and the same length as the original, it can operate the security management of the computing system more efficiently.

[104] For example, the present invention can be effectively used as the way how to prevent the leakage of customer information. The customer information can flow out by approaching to a database, hacking the communication packet. Therefore, the customer information has to be ciphered. If it use the present invention, the expense modifying the field length of the database or the communication packet can be reduced. Moreover, the encrypted result is maintained in the same code area of the plain text. Therefore the encrypted result itself can be stored in a database. A log file has to be left through the text format so that the system operator monitor the communication packet. The log is left in the text string code area, so it can monitor the log file cleanly. If it use the former existing encryption algorithm, it has the case of deviating from the code domain. Therefore the unnecessary character remains in a log file like control character.

[105] Moreover, the SMS message of the cellular phone, the length is limited to 80.

Therefore the length of result ciphering the plain text should not be over 80. However, if it use the present invention, it can convert the 80 characters of plain text into the same length of cipher text. The possibility of tapping in the cellular phone became true. However, if it use the present invention, it can communicate safely.

[106]

Brief Description of the Drawings

[107] Figure 1 is a drawing in which when the double-byte multi- lingual code like the

[108] Figure 2 is a drawing according to the embodiment in the present invention, which classifies the original into several bit masking groups lest the code area of the cipher text should deviate from the code area of the original ,which schematizes the method for complementing the secret key with the bit mask corresponding to each group.

[109] Figure 3 is a drawing showing the embodiment on the present invention, it fixes several bits, and it just ciphers the rest of bits.

[110] Figure 4 is a flowchart showing the embodiment on the present invention, it inputs the plaintext and secret key, and it performs the ciphering procedure.

[I l l] Figure 5 is the subsequent procedure of fig. 4 according to the embodiment in the present invention, it is the flowchart performing the procedure encrypting the ASCII code, reading the character string of the original by lbyte.

[112] Figure 6 is subsequent procedure of fig. 4 according to the embodiment in the present invention. While it reads the character string of the original by lbyte, if the original character is the multi-lingual code, it reads one more byte, and performs the encryption process.

[113] <The description of reference numerals about the main part>

[114] 104 : symmetric key encipherment algorithm (It simplely performs the only XOR operation in embodiment of the present invention) [115] 221 : the secret key bit- masked in the specific area 1.

[116] 320 : secret key domain

[117] 330 : bit mask

[118] 340 : the secret key domain bit-masked

[119] 403 : Determination whether it is the ASCII code or not, reading the character string of the plaintext by lbyte.

[120] 404 : When it is the ASCII code, it calls the ASCII encrypting function.

[121] 407 : When it is not the ASCII code, it reads one more byte, and it calls the double- byte multi-lingual encrypting function. [122] 550 : In ASCII encrypting function, the procedure complementing the secret key with the bit mask corresponding to domain 1 if the character code reading in the plain text comes under the arbitrary domain 1. [123] 560 : In ASCII encrypting function, the procedure complementing the secret key with the bit mask corresponding to domain 2 if the character code reading in the plain text comes under the arbitrary domain 2. [124] 6050 : the procedure complementing the secret key for ciphering upper lbyte with the bit mask of the corresponding domain when the upper byte character code of original plain text which reads on the double-byte multi-lingual encrypting function comes under the arbitrary domain 1. [125] 6060 : the procedure complementing the secret key for ciphering upper lbyte with the bit mask of the corresponding domain when the upper byte character code of original plain text which reads on the double-byte multi-lingual encrypting function comes under the arbitrary domain 2. [126] 6090 : the procedure complementing the secret key for ciphering lower lbyte with the bit mask of the corresponding domain when the upper byte character code of original plain text which reads on the double-byte multi-lingual encrypting function comes under the arbitrary domain 1. [127] 6100 : the procedure complementing the secret key for ciphering lower lbyte with the bit mask of the corresponding domain when the upper byte character code of original plain text which reads on the double-byte multi-lingual encrypting function comes under the arbitrary domain 2. [128] Industrial Applicability

[129] According to the present invention, it can display ciphertext itself on the terminal console and maintain the same length as the plaintext. If it utilize the above feature, it can operate the security management of the computing system more efficiently.

[130] For example, the present invention is to provide the new paradigm as the core technology of database security. A database is the most representative media storing data as the structuralized text format. The factor of structuralized text refer to the two folio wings.

[131] The first, supporting the language code corresponding to each country.

[132] The second, data classification like table, field.

[133] It has to select the language corresponding to the nation when it installs database as if it installed the operating system like Windows, Unix. For example, if it use Japanese, it has to select Japanese code. However, if the supporting language is Japanese, but the encrypted result become the Korean code or binary code, then it can not save the result in the database. The former solution of database security performs the text encoding in addition to data encrypting in order to solve the above problem. This cause the low performance, and the ciphertext which is lengthened than plaintext. It goes with the fatal problem of extending the former field length, or managing another table for storing the ciphertext. But if it use the present invention, the problem can be solved.

[134] The field in which the present invention can be applied with industrial is infinite.

The above database security is the most effective as the alternative method to solve the problem of the former solution.

[135] Besides, in the field of data communication security, log management, document security, cellular phone SMS security, E-mail security, the internet board security etc, the present invention can be efficiently used. Particularly, in the secret document production and electronic approval system of the national defense field, the present invention can be effectively used.

[136]

[137]

Claims

[1] The method for complementing the symmetric key encryption about the text string, wherein it fixes several bits of the multi-lingual character code defined as double -byte, and it encrypts the rest of bits when it ciphers the character string which is handled in the computer with the procedure of the several steps based on the mathematical operator. Then, the character code domain of the ciphertext is curbed in the domain of the fixed bits.

[2] The method for complementing the symmetric key encryption about the text string of claim 1, wherein the text string is character code group whose display is possible with reference to the defined character code table on the computer terminal console, whose input, output, delete, save is possible in the text editor like notepad etc. The present invention is applied to the multi-lingual text string like the Korean, Japanese in which one character is comprised of double-byte.

[3] The method for complementing the symmetric key encryption about the text string of claim 1, wherein the symmetric key encryption is the algorithm using the secret key which is identical as to an encoding and decoding; The present invention can be applied to the symmetric key encryption. It includes a simple method like the XOR operating each bit of the original with each bit of the secret key, an applicable algorithm adding a procedure like confusion or substitution, and an standardized algorithm like DES, 3DES, SEED. The present invention can be inserted in the symmetric key encryption procedure step in-between.

[4] The method for complementing the symmetric key encryption about the text string of claim 1, wherein the multi- lingual character code is defined as double- byte in order to handle the language of all the countries of the world like the Korean, Japanese in the computer. There are the character codes which are standard of each country like KSC5601, the character codes which are provided by software company like microsoft, and the Unicode which standardizes alphabet and all multi-linguals to double-byte etc. Especially the alphabet expressed as double-byte is regarded as Unicode.