Patent Publication Number: US-8538017-B2

Title: Encryption device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2010-209617, filed on Sep. 17, 2010; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an encryption device which performs encryption processing including nonlinear transform processing. 
     BACKGROUND 
     Various side channel attacks have been contrived. Such attacks use physical information of an operating encryption module including processing time, power consumption, and electromagnetic waves. There are analysis methods that use the power consumption information such as simple power analysis (SPA), differential power analysis (DPA), and correlation power analysis (CPA). The DPA is an attack method which statistically analyzes power consumption during the encryption processing to extract internal information. As the countermeasure against the DPA or CPA, a mask method is known. 
     In the mask method, a random number or a fixed value called a mask is added to data under encryption processing and the encryption processing is continued, thereby eliminating the correlation between power consumption and data under encryption processing. However, if secondary DPA or higher-order DPA which is extended from the secondary DPA is used, the encryption key can also be analyzed from an encryption circuit to which the mask method is applied. The secondary DPA is an attack method which determines the presence/absence of the correlation between power consumption and data under encryption processing in consideration of the effect of the mask using power at two points on the power consumption waveform. With regard to the two points on the power consumption waveform, for example, use is made of power consumption at a point at which masked data for intermediate data of the encryption processing is processed and power consumption at a point at which masked data is processed, or use is made of power consumption at points at which two pieces of data with the same mask are processed. As the countermeasure against the DPA or CPA, a duplication method is known. The duplication method is a method which segments data under encryption processing into two pieces of data, thereby eliminating the correlation between power consumption and data under encryption processing. 
     The duplication method is vulnerable to the secondary DPA. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a configuration example of an encryption device; 
         FIG. 2  is a block diagram showing a configuration example of a decryption device; 
         FIG. 3  is a block diagram showing a configuration example of an encryption device of a first embodiment; 
         FIG. 4  is a block diagram showing a configuration example of a SubByte processing unit; 
         FIG. 5  is a block diagram showing a configuration example of an MES; 
         FIG. 6  is a block diagram showing a configuration example of a transform unit; 
         FIG. 7  is a diagram showing an example of a transform table which is stored in a transform table storage unit; 
         FIG. 8  is a flowchart showing an example of the overall flow of encryption processing of the first embodiment; 
         FIG. 9  is a flowchart showing an example of a processing procedure of an MES when a transform table is used; 
         FIG. 10  is a block diagram showing a configuration example of an MES of a modification; 
         FIG. 11  is a block diagram showing a configuration example of a transform unit; 
         FIG. 12  is a block diagram showing a configuration example of an MES of a second embodiment; 
         FIG. 13  is a block diagram showing a configuration example of a transform unit; 
         FIG. 14  is a block diagram showing a configuration example of a transform unit; 
         FIG. 15  is a block diagram showing a configuration example of an MES of a third embodiment; 
         FIG. 16  is a block diagram showing a configuration example of a transform unit; 
         FIG. 17  is a block diagram showing a configuration example of an MES of a fourth embodiment; 
         FIG. 18  is a block diagram showing a configuration example of an encryption device of a fifth embodiment; 
         FIG. 19  is a block diagram showing a configuration example of an encryption device of a sixth embodiment; and 
         FIG. 20  is an explanatory view showing the hardware configuration of an encryption device according to each of the first to sixth embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, in an encryption device, a mask processing unit generates masked plain data from the plain data. A segmentation unit segments masked plain data into pieces of first segmented data. A first processing unit generates pieces of input segmented data from the pieces of first segmented data. A receiving unit receives the pieces of input segmented data, a first mask, and a second mask. A nonlinear transform unit generates pieces of output segmented data transformed from the pieces of input segmented data. A data integration unit integrates second segmented data to generate masked encrypted data. An unmask processing unit generates encrypted data from the masked encrypted data. The exclusive OR of the pieces of input segmented data matches the exclusive OR of input data, subjected to nonlinear transform processing and calculated from the plain data, and the first mask. The exclusive OR of the pieces of output segmented data matches the exclusive OR of transform data, obtained when the nonlinear transform processing is performed on the input data, and the second mask. 
     Hereinafter, embodiments of an encryption device will be described in detail with reference to the accompanying drawings. 
     In the following, an example will be described in which an encryption device uses an Advanced Encryption Standard (AES) scheme with a key length of 128 bits. However, an embodiment may also be applied to an encryption device which uses an AES scheme with a key length of 196 bits or 256 bits. An embodiment may also be applied to a device which processes an encryption algorithm using another nonlinear transform, such as Data Encryption Standard (DES) or Hierocrypt. An embodiment may also be applied to a hash function using nonlinear transform. 
     Here, configuration examples of an encryption device and a decryption device using an AES scheme will be described.  FIG. 1  is a block diagram showing an example of the configuration of an encryption device  1000 . As shown in  FIG. 1 , the encryption device  1000  includes an input unit  1001   a , an output unit  1001   b , a key storage unit  1002 , a round key generation unit  1003 , AddRoundKey  1004   a  to  1004   k , SubByte  1005   b  to  1005   k , ShiftRow  1006   b  to  1006   k , and MixColumn  1007   b  to  1007   j.    
     The input unit  1001   a  receives an input of plain data from the outside. The output unit  1001   b  outputs encrypted data of a processing result to the outside. An input/output unit  1001  having the functions of the input unit  1001   a  and the output unit  1001   b  may be provided. 
     The key storage unit  1002  stores a 128-bit secret key. The key storage unit  1002  can be formed by a generally used storage medium, such as a Hard Disk Drive (HDD), an optical disk, a memory card, or a Random Access Memory (RAM). 
     The round key generation unit  1003  calculates eleven keys, which are 128-bit round keys d 1003   a  to d 1003   k , from the secret key stored in the key storage unit  1002 , and supplies the round keys d 1003   a  to d 1003   k  to the AddRoundKey  1004   a  to  1004   k . The round keys d 1003   a  to d 1003   k  may be calculated before the AddRoundKey  1004   a  is executed or may be calculated in parallel with the execution of the AddRoundKey  1004   a  to  1004   k.    
     Data d 1001   a  which is input to the AddRoundKey  1004   a  is the same as input plain data. The AddRoundKey  1004   a  to  1004   k  perform AddRoundKey transform processing, which is defined by AES encryption, on data d 1001   a , d 1007   b  to d 1007   j , and d 1006   k , and output data d 1004   a  to d 1004   k . Data d 1004   a  to d 1004   j  are input to the SubByte  1005   b  to  1005   j . Data d 1004   k  is the same as encrypted data. 
     The SubByte  1005   b  to  1005   k  nonlinearly transform data d 1004   a  to d 1004   j  for every eight bits, and output data d 1005   b  to d 1005   k . Data d 1005   b  to d 1005   k  are input to the ShiftRow  1006   b  to  1006   k.    
     The ShiftRow  1006   b  to  1006   k  rearrange data d 1005   b  to d 1005   k  in units of eight-bit blocks, and output data d 1006   b  to d 1006   k . Data d 1006   b  to d 1006   j  are input to the MixColumn  1007   b  to  1007   j . Data d 1006   k  is input to the AddRoundKey  1004   k.    
     The MixColumn  1007   b  to  1007   j  linearly transform data d 1007   b  to d 1007   j  for every 32 bits, and output data d 1007   b  to d 1007   j . Data d 1007   b  to d 1007   j  are input to the AddRoundKey  1004   b  to  1004   j.    
       FIG. 2  is a block diagram showing an example of the configuration of a decryption device  1100 . As shown in  FIG. 2 , the decryption device  1100  includes an input unit  1101   a , an output unit  1101   b , a key storage unit  1102 , a round key generation unit  1103 , InvAddRoundKey  1104   a  to  1104   k , InvShiftRow  1105   a  to  1105   j , InvSubByte  1106   a  to  1106   j , and InvMixColumn  1107   b  to  1107   j.    
     The input unit  1101   a  receives an input of encrypted data from the outside. The output unit  1101   b  outputs plain data of a processing result to the outside. An input/output unit  1101  having the functions of the input unit  1101   a  and the output unit  1101   b  may be provided. 
     The key storage unit  1102  stores a 128-bit secret key. The key storage unit  1102  can be formed by a generally used storage medium, such as a Hard Disk Drive (HDD), an optical disk, a memory card, or a Random Access Memory (RAM). 
     The round key generation unit  1103  calculates eleven round keys, which are 128-bit round keys d 1103   a  to d 1103   k , from the secret key stored in the key storage unit  1102 , and supplies the round keys d 1103   a  to d 1103   k  to the InvAddRoundKey  1104   a  to  1104   k . The round keys d 1103   a  to d 1103   k  may be calculated before the InvAddRoundKey  1104   a  is executed or may be calculated in parallel with the execution of the InvAddRoundKey  1104   a  to  1104   k.    
     Data d 1101   a  which is input to the InvAddRoundKey  1104   a  is the same as input encrypted data. 
     The InvAddRoundKey  1104   a  to  1104   k  perform InvAddRoundKey transform processing, which is defined by AES encryption, on data d 1101   a  and d 1106   a  to d 1106   j , and output data d 1104   a  to d 1104   k . Data d 1104   a  is input to the InvShiftRow  1105   a . Data d 1104   b  to d 1104   j  are input to the InvMixColumn  1107   b  to  1107   j . Data d 1104   k  is the same as plain data to be output. 
     The InvShiftRow  1105   a  to  1105   j  rearrange data d 1104   a  and d 1107   b  to d 1107   j  in units of eight-bit blocks, and output data d 1105   a  to d 1105   j . Data d 1105   a  to d 1105   j  are input to the InvSubByte  1106   a  to  1106   j.    
     The InvSubByte  1106   a  to  1106   j  nonlinearly transform data d 1105   a  to d 1105   j  for every eight bits, and output data d 1106   a  to d 1106   j . Data d 1106   a  to d 1106   j  are input to the InvAddRoundKey  1104   b  to  1104   k.    
     The InvMixColumn  1107   b  to  1107   j  linearly transform data d 1104   b  to d 1104   j  for every    32   bits, and output data d 1107   b  to d 1107   j . Data d 1107   b  to d 1107   j  are input to the InvShiftRow  1105   b  to  1105   j.    
     First Embodiment 
     Although in the following description, a case will be described where an embodiment is applied to encryption processing (the encryption device  1000  or the like), the embodiment may be applied to decryption processing (the decryption device  1100  or the like). 
     Next, the terms are defined. Intermediate data of encryption processing refers to data which is calculated during processing defined by an encryption algorithm. In the case of AES encryption, data which is input/output to AddRoundKey, SubByte, ShiftRow, and MixColumn and data which is internally handled, correspond to intermediate data. 
     Mask is data which is applied through exclusive OR, arithmetic addition, or multiplication to intermediate data of the encryption processing so as to eliminate the correlation between intermediate data of the encryption processing and power consumption. The mask which is applied to input data to the SubByte is referred to as an input mask (first mask), and the mask which is applied to output data from the SubByte is referred to as an output mask (second mask). In the description of the embodiments, an example will be described where a mask is applied through exclusive OR. 
       FIG. 3  is a block diagram showing a configuration example of an encryption device  100  of the first embodiment, which processes encryption algorithm AES. The encryption device  100  includes an input unit  101   a , an output unit  101   b , a key storage unit  102 , a round key generation unit  103 , a segmentation data generation unit  104 , a mask generation unit  105 , a mask processing unit  107 , an unmask processing unit  108 , a data segmentation unit  109 , a data integration unit  110 , AddRoundKey  111   a  to  111   k , SubByte processing units  112   b  to  112   k , ShiftRow  113   bl  to  113   kl , ShiftRow  113   br  to  113   kr , MixColumn  114   bl  to  114   jl , MixColumn  114   br  to  114   jr , and mask replacement units  115   b  to  115   j.    
     AddRoundKey  111   a  to  111   k  correspond to a first processing unit. SubByte processing units  112   b  to  112   k  correspond to a nonlinear transform unit. The ShiftRow  113   bl  to  113   kl , the ShiftRow  113   br  to  113   kr , the MixColumn  114   bl  to  114   jl , the MixColumn  114   br  to  114   jr , which process two pieces of data output from the SubByte processing unit  112   b  to  112   k , and the mask replacement units  115   b  to  115   j  correspond to a second processing unit. 
     The input unit  101   a  receives 128-bit plain data d 101   a  from the outside, and supplies plain data d 101   a  to the mask processing unit  107 . The output unit  101   b  outputs encrypted data d 108  of a processing result to the outside. The key storage unit  102  stores a 128-bit secret key. 
     The round key generation unit  103  calculates eleven 128-bit round keys d 103   a  to d 103   k  from the secret key stored in the key storage unit  102 , and supplies the round keys d 103   a  to d 103   k  to the AddRoundKey  111   a  to  111   k . The round keys d 103   a  to d 103   k  may be calculated before the AddRoundKey  111   a  is executed or may be calculated in parallel with the execution of the AddRoundKey  111   a  to  111   k.    
     The segmentation data generation unit  104  generates 128-bit segmentation data d 104 , and supplies segmentation data d 104  to the data segmentation unit  109 . Segmentation data d 104  may be a value which is prepared in advance, or the segmentation data generation unit  104  may include a random number generation unit and a random number generated by the random number generation unit may be used. 
     The mask generation unit  105  generates input masks d 120   b  to d 120   k  and output masks d 121   b  to d 121   k . The mask generation unit  105  generates replacement masks d 122   b  to d 122   j  from the input masks d 120   c  to d 120   k  and the output masks d 121   b  to d 121   j . The mask generation unit  105  supplies the input mask d 120   b  to the mask processing unit  107 , and respectively supplies the input masks d 120   b  to d 120   k  and the output masks d 121   b  to d 121   k  to the SubByte processing units  112   b  to  112   k . The mask generation unit  105  supplies the output mask d 121   k  to the unmask processing unit  108 , and respectively supplies the replacement masks d 122   b  to d 122   j  to the mask replacement units  115   b  to  115   j.    
     Each mask may be a value which is prepared in advance, or the mask generation unit  105  may include a random number generation unit, and a random number generated by the random number generation unit may be used. The random number generation unit provided in the mask generation unit  105  may be the same as the random number generation unit provided in the segmentation data generation unit  104 . 
     The mask generation unit  105  calculates the replacement mask d 122   b , for example, by d 122   b =d 120   b ^d 121   b . “A^B” means the exclusive OR of A and B. 
     The mask processing unit  107  calculates the exclusive OR of the input mask d 120   b  and plain data d 101   a , and outputs the result to the data segmentation unit  109  as masked plain data d 107 . 
     The data segmentation unit  109  segments 128-bit masked plain data d 107  on the basis of segmentation data d 104  and outputs two pieces of 128-bit segmented data d 109   l  and d 109   r  such that the exclusive OR of d 109   l  and d 109   r  coincide with masked plain data d 107 . For example, segmentation data d 104  can be used as segmented data d 109   l , and the exclusive OR of segmentation data d 104  and masked plain data d 107  can be used as segmented data d 109   r.    
     As described above, in this embodiment, an operation of generating a plurality of pieces of data from data, with which the exclusive OR of the pieces of data matches, is called segmentation. Each piece of generated data is called segmented data. 
     The AddRoundKey  111   a  calculates data d 111   a  which is the exclusive OR of input data d 109   l  and the round key d 103   a , and outputs the result to the SubByte processing unit  112   b . Similarly, the AddRoundKey  111   b  to  111   k  also calculate and output the exclusive OR of input data and the round key. 
     The SubByte processing unit  112   b  receives two pieces of data d 111   a  and d 109   r , and outputs two pieces of data d 112   bl  and d 112   br . Data d 111   a  and d 109   r  have a relationship in which the exclusive OR thereof becomes the exclusive OR of data d 1004   a  input to the SubByte  1005   b  of  FIG. 1  and the input mask d 120   b . Data d 112   bl  and d 112   br  have a relationship in which the exclusive OR thereof becomes the exclusive OR of data d 1005   b  output from the SubByte  1005   b  of  FIG. 1  and the output mask d 121   b.    
     The ShiftRow  113   bl  to  113   kl , the ShiftRow  113   br  to  113   kr , and the MixColumn  114   bl  to  114   jl , and the MixColumn  114   br  to  114   jr  mix input data. 
     The mask replacement unit  115   b  calculates and outputs data d 115   b  which is the exclusive OR of input data d 114   br  and the replacement mask d 122   b . Similarly, the mask replacement units  115   c  to  115   j  output the exclusive OR of input data d 114   cr  to d 114   jr  and the replacement masks d 122   c  to d 122   j.    
     The data integration unit  110  calculates and outputs data d 110  which is the exclusive OR of data d 111   k  and data d 113   kr . The unmask processing unit  108  calculates and outputs encrypted data d 108  which is the exclusive OR of data d 110  and the output mask d 121   k . The output unit  101   b  receives encrypted data d 108  and outputs encrypted data d 108  to the outside. 
     Next, a configuration example of the SubByte processing unit  112   b  will be described.  FIG. 4  is a block diagram showing a configuration example of the SubByte processing unit  112   b . The configuration of each of the SubByte processing units  112   c  to  112   k  is the same as the SubByte processing unit  112   b , thus description thereof will be omitted. 
     The SubByte processing unit  112   b  includes 16 masked and extended S-boxes (hereinafter, referred to as MES)  2200  to  2215 . 
     The SubByte processing unit  112   b  segments 128-bit data d 21   l  into eight-bit data d 2100   l  to d 2115   l  satisfying d 21   l =d 2100   l ∥ . . . ∥d 2115   l  (∥ means connection), and inputs data d 2100   l  to d 2115   l  to the MESs  2200  to  2215 . Similarly, the SubByte processing unit  112   b  segments 128-bit data d 21   r  into eight-bit data d 2100   r  to d 2115   r  satisfying d 21   r =d 2100   r ∥ . . . ∥d 2115   r , and inputs data d 2100   r  to d 2115   r  to the MESs  2200  to  2215 . 
     The SubByte processing unit  112   b  connects eight-bit data d 2200   l  to d 2215   l  output from the MESs  2200  to  2215  into d 22   l  satisfying d 22   l =d 2200   l ∥ . . . ∥d 2215   l  and outputs the result. Similarly, the SubByte processing unit  112   b  connects eight-bit data d 2200   r  to d 2215   r  output from the MESs  2200  to  2215  into d 22   r  satisfying d 22   r =d 2200   r ∥ . . . ∥d 2215   r  and outputs the result. 
     The MES  2200  receives two pieces of data d 2100   l  and d 2100   r , and outputs two pieces of data d 2200   l  and d 2200   r . The MESs  2201  to  2215  are operated in the same manner. 
       FIG. 5  is a block diagram showing a configuration example of the MES  2200 . Hereinafter, an example will be described where data in units of eight bits is processed. 
     The MES  2200  includes a transform unit  301   l , a transform unit  301   r , a transform unit  303 , a transform unit  304 , and an exclusive OR operation unit  302 . The MES  2200  inputs data d 300   l  to the transform unit  301   l , inputs data d 300   r  to the transform unit  301   r , and calculates data d 302  which is the exclusive OR of data d 301   l  output from the transform unit  301   l  and data d 301   r  output from the transform unit  301   r . The MES  2200  inputs data d 302  to the transform unit  303  and the transform unit  304 , outputs data d 303  transformed by the transform unit  303 , and outputs data d 304  transformed by the transform unit  304 . 
     The transform unit  301   l  receives data d 300   l  as an input and outputs data d 301   l  transformed through transform processing including linear transform. For example, the transform unit  301   l  may be configured to transform to output data d 301   l  which is the result of exclusive OR of data linearly transformed from input data d 300   l  by a function φ described below and transforming data d 301   a . The transform unit  301   l  may be configured to output data d 301   l  linearly transformed from input data d 300   l.    
     The transform unit  301   r  receives data d 300   r  as an input and outputs data d 301   r  transformed through transform processing including linear transform. For example, the transform unit  301   r  may be configured to transform to output data d 301   r  which is the result of exclusive OR of data linearly transformed from input data d 300   r  by the function φ and transforming data d 301   b . The transform unit  301   r  may be configured to output data d 301   r  linearly transformed from input data d 300   r.    
     The function φ is a function having an eight-bit input/output, and the following expression (1) can be used. x i  and y i  (0≦i≦7) respectively represent one-bit data. The input of the function φ is x i  and the output of the function φ is y i . 
     
       
         
           
             
               
                 
                   
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     The function φ is not limited to the expression (1), and for example, may be identical transform. In the case of identical transform, the transform processing by the function φ may not be performed. Transforming data d 301   a  may be 0, and in this case, exclusive OR may not be performed. Transforming data d 301   b  may be 0, and in this case, exclusive OR may not be performed. When transforming data d 301   a= 0 and transforming data d 301   b= 0, the transform unit  301   l  is the same as the transform unit  301   r.    
     The transform unit  304  transforms input data d 302  to data d 304  using predetermined transform and outputs data d 304 . The transform unit  304  may be nonlinear transform, such as the SubByte (S-box) of AES, linear transform, such as the function φ, or arbitrary transform. The transform unit  304  may be identical transform, and in this case, transform processing may not be performed. 
     The transform unit  301   l , the transform unit  301   r , and the transform unit  304  may be configured such that a transform table is prepared in advance and transform processing is performed with reference to the prepared transform table. 
       FIG. 6  is a block diagram showing a configuration example of the transform unit  303 . The transform unit  303  includes a transform unit  401 , an exclusive OR operation unit  402 , an S-box  403 , a transform unit  404 , an exclusive OR operation unit  405 , and an exclusive OR operation unit  406 . The transform unit  303  receives data d 302 , d 400   a , and d 400   b . Data d 302  is input to the transform unit  401 . The transform unit  401  transforms data d 302  to data d 401 . The exclusive OR operation unit  402  calculates data d 402  which is the exclusive OR of data d 401  and data d 400   a , and inputs the result to the S-box  403 . The transform unit  404  transforms data d 302  to data d 404 . The exclusive OR operation unit  405  calculates data d 405  which is the exclusive OR of data d 403  output from the S-box  403  and d 404 . The exclusive OR operation unit  406  calculates and outputs data d 303  which is the exclusive OR of data d 405  and d 400   b.    
     Data d 400   a  is one of sixteen pieces of data obtained by segmenting the 128-bit input mask d 120   b  output from the mask generation unit  105  in units of eight bits. Data d 400   b  is one of sixteen pieces of data obtained by segmenting the 128-bit output mask d 121   b  output from the mask generation unit  105  in units of eight bits. 
     The transform unit  401  is configured to transform data, which is the result of exclusive OR of transforming data d 301   a  and transforming data d 301   b  to input data d 302 , using an inverse function φ −1  of the function φ and configured to output data d 401 . The inverse function φ −1  of the function φ is expressed by, for example, the following expression (2). 
     
       
         
           
             
               
                 
                   
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     The S-box  403  is the same nonlinear transform as the SubByte (S-box) of AES, and transforms input data d 402  to data d 403 . 
     The transform unit  404  is the same transform as the transform unit  304  of  FIG. 5 , and transforms input data d 302  to data d 404 . 
     If S-box transform is denoted by S, the transform unit  404  is denoted by h, and the transform unit  401  is denoted by g −1 , the transform unit  303  satisfies the relationship of the following expression (3).
 
 d 303 =S ( g   −1 ( d 302)^ d 400 a )^ h ( d 302)^ d 400 b   (3)
 
     As long as the expression (3) is satisfied, the above-described calculation procedure may not be used. For this reason, the transform unit  303  may calculate output data d 303  in advance when input data d 302  is in a rage of 0 to 255, and may store data d 303  as a transform table T 2200 , in which data d 302  and data d 303  are associated, in a transform table storage unit  410 . In this case, the transform unit  303  receives data d 302  and outputs data d 303  corresponding to received data d 302  with reference to the transform table T 2200 .  FIG. 7  is a diagram showing an example of the transform table T 2200  which is stored in the transform table storage unit  410 . 
     Although a configuration example has been described where the SubByte processing unit  112   b  processes 128-bit data by eight bits, the units of processing is not limited to eight bits, and may be 16 bits or 128 bits. A different number of bits may be used as the units of processing. When the unit of processing is 128 bits, for example, the SubByte processing unit  112   b  may include a single MES  2200 . 
     The MES  2200  to the MES  2215  provided in the SubByte processing unit  112   b  may have the same configuration. Similarly, the SubByte processing unit  112   c  to  112   k  may have the MES of the same configuration. The SubByte processing unit  112   b  to  112   k  may have the same configuration. 
     Although in  FIG. 3 , the AddRoundKey  111   b  to  111   k  are arranged in the left sequence of segmented data, the AddRoundKey  111   b  to  111   k  may be arranged on the right sequence of segmented data. In this case, the AddRoundKey  111   b  receives data d 115   b  output from the mask replacement unit  115   b , calculates data d 111   b  which is the exclusive OR of the round key d 103   b  and data d 115   b , and outputs data d 111   b  to the SubByte processing unit  112   c . At this time, the MixColumn  114   bl  outputs data d 114   bl  to the SubByte processing unit  112   c . Devices represented by the same numeral may be the same device. 
     Next, a processing procedure of the encryption device  100  will be described with reference to a flowchart of  FIG. 8 .  FIG. 8  is a flowchart showing an example of the overall flow of encryption processing in the encryption device  100  of the first embodiment when the same device is used for devices represented by the same numeral. 
     The input unit  101   a  of the encryption device  100  receives 128-bit plain data d 101   a  (ST 101 ). The round key generation unit  103  generates the round keys d 103   a  to d 103   k  on the basis of an encryption key d 102  supplied from the key storage unit  102 , and respectively supplies the round keys d 103   a  to d 103   k  to the AddRoundKey  111   a  to  111   k  (ST 102 ). 
     The mask generation unit  105  generates the input masks d 120   b  to d 120   k , the output masks d 121   b  to d 121   k , and the replacement masks d 122   b  to d 122   j  (ST 103 ). The mask processing unit  107  processes input mask d 120   b  on plain data d 101   a  and outputs masked plain data d 107  (ST 104 ). Masked plain data d 107  is the exclusive OR of plain data d 101   a  and the input mask d 120   b.    
     The data segmentation unit  109  segments masked plain data d 107  into two pieces of data d 109   l  and data d 109   r  on the basis of segmentation data d 104  supplied from the segmentation data generation unit  104  (ST 105 ). The exclusive OR of data d 109   l  and data d 109   r  is d 107 . For example, calculated are d 109   l =d 104 , and d 109   r =d 107 ^d 104 . 
     The AddRoundKey  111   a  calculates and outputs data d 111   a  which is the exclusive OR of round key d 103   a  supplied from the round key generation unit  103  and data d 109   l  (ST 106 ). 
     The SubByte processing unit  112   b  receives data d 111   a  output from the AddRoundKey  111   a , data d 109   r  output from the data segmentation unit  109 , the input mask d 120   b , and the output mask d 121   b , performs nonlinear transform processing in a state of being masked, and outputs two pieces of data d 112 b l  and data d 112   br  (ST 107 ). 
     The ShiftRow  113   bl  rearranges data d 112   bl  output from the SubByte processing unit  112   b  in units of eight-bit blocks (ST 108 ). 
     The encryption device  100  determines whether or not the round number is tenth (ST 109 ). When the round number is first to ninth (No in ST 109 ), the MixColumn  114   bl  linearly transforms data d 113   bl  output from the ShiftRow  113   bl  for every 32 bits, and outputs data d 114   bl  after transform to the AddRoundKey  111   b  (ST 110 ). 
     The ShiftRow  113   br  rearranges data d 112   br  output from the SubByte processing unit  112   b  in units of eight-bit blocks (ST 111 ). 
     The encryption device  100  determines whether or not the round number is tenth (ST 112 ). 
     When the round number is first to ninth (No in ST 112 ), the MixColumn  114   br  linearly transforms data d 113   br  output from the ShiftRow  113   br  for every 32 bits, and outputs data d 114   br  after transform to the mask replacement unit  115   b  (ST 113 ). 
     The mask replacement unit  115   b  calculates data d 115   b  which is the exclusive OR of data d 114   br  output from the MixColumn  114   br  and the replacement mask d 122   b  supplied from the mask generation unit  105 , and outputs data d 115   b  to the SubByte processing unit  112   c  (ST 114 ). 
     The SubByte processing unit  112   c  receives data d 111   b  output from the AddRoundKey  111   b  and data d 115   b  output from the mask replacement unit  115   b , performs nonlinear transform processing in a state of being masked, and outputs two pieces of data d 112   cl  and data d 112   cr  (ST 107 ). 
     The AddRoundKey  111   b  to  111   j  in the first to tenth rounds perform the same processing as the AddRoundKey  111   a , the SubByte processing units  112   c  to  112   k  in the second to tenth rounds perform the same processing as the SubByte processing unit  112   b , the ShiftRow  113   cl  to  113   kl  and the ShiftRow  113   cr  to  113   kr  in the second to tenth rounds perform the same processing as the ShiftRow  113   bl  and the ShiftRow  113   br , the MixColumn  114   cl  to  114   jl  and the MixColumn  114   cr  to  114   jr  in the second to ninth rounds perform the same processing as the MixColumn  114   bl  and the MixColumn  114   br , and the mask replacement units  115   c  to  115   j  in the second to ninth rounds perform the same processing as the mask replacement unit  115   b . Thus, description thereof will be omitted. 
     When the round number is tenth (Yes in ST 109 , Yes in ST 112 ), the AddRoundKey  111   k  outputs data clink, which is the exclusive OR of the round key d 103   k  supplied from the round key generation unit  103  and data d 113   kl  output from the ShiftRow  113   kl , to the data integration unit  110  (ST 115 ). 
     The data integration unit  110  calculates data d 110  which is the exclusive OR of data d 113   kr  as masked encrypted data output from the ShiftRow  113   kr  and data d 111   k  output from the AddRoundKey  111   k , and outputs data d 110  to the unmask processing unit  108  (ST 116 ). 
     The unmask processing unit  108  removes output mask d 121   k  from masked encrypted data d 110 , and calculates encrypted data d 108  (ST 117 ). Encrypted data d 108  is the exclusive OR of masked encrypted data d 110  and the output mask d 121   k . The output unit  101   b  outputs encrypted data d 108  (ST 118 ). 
     A processing procedure of the MES  2200  when the MES  2200  generates the transform table T 2200  in advance will be described with reference to  FIG. 9 .  FIG. 9  is a flowchart showing an example of a processing procedure of the MES  2200  when a transform table is used. 
     The MES  2200  receives two pieces of data d 300   l  and data d 300   r  (ST 201 ). The transform unit  301   l  transforms data d 300   l  and outputs d 301   l , and the transform unit  301   r  transforms data d 300   r  and outputs d 301   r  (ST 202 ). 
     The MES  2200  calculates the exclusive OR of data d 301   l  and data d 301   r , and supplies the result to the transform unit  303  and the transform unit  304  (ST 203 ). The transform unit  303  references the transform table T 2200 , and obtains data d 303  corresponding to data d 302  (ST 204 ). The transform unit  304  transforms data d 302  to d 304  using predetermined transform (ST 205 ). The MES  2200  outputs data d 303  and data d 304  (ST 206 ). 
     According to this embodiment, the input/output of the MES  2200  satisfies the relationship of the following expression (4).
 
( d 303 ^d 304)^ d 400 b=S (( d 300 l^d 300 r )^ d 400 a )  (4)
 
     The MES  2200  receives two pieces of data segmented from masked intermediate data of encryption processing as an input, and performs nonlinear transform in a state of being masked, thereby outputting segmented data of the correction calculation result. 
     The secondary DPA identifies a secret key by using power consumption at two points of processing the mask and masked intermediate data, or power consumption of two pieces of intermediate data with the same mask of the encryption processing. In this embodiment, the encryption processing is performed in a state where masked intermediate data of the encryption processing is segmented. Thus, power consumption at the time when masked intermediate data of the encryption processing is processed cannot be measured. For this reason, there is resistance against the secondary DPA. Also, power consumption at the time when the intermediate data of the encryption processing is processed cannot be measured. The correlation between intermediate data of the encryption processing and power consumption is eliminated, and there is resistance against power analysis. 
     When all the SubByte processing units  112   b  to  112   k  have the same configuration, the input masks d 120   b  to d 120   k  can be set as identical data, the output masks d 121   b  to d 121   k  can be set as identical data, and the replacement mask d 122   b  to d 122   k  can be set as identical data. 
     When all the MESs  2200  to  2215  provided in the SubByte processing unit  112   b  have the same configuration, the same input mask and output mask can be used for all the MESs. Thus, the 128-bit input mask d 120   b  can be set to eight-bit data, and the 128-bit output mask d 121   b  can be set to eight-bit data. With regard to the SubByte processing units  112   c  to  112   k , when the input mask and the output mask have eight bits, the 128-bit replacement masks d 122   b  to d 122   j  can be set to eight-bit data. 
     When all the SubByte processing units  112   b  to  112   k  have the same configuration, and all the MESs provided in the SubByte processing units  112   b  to  112   k  have the same configuration, the encryption device  100  can perform the encryption processing by using a single MES. In implementing with use of a transform table, the encryption device  100  can calculate SubByte by generating and storing a single transform table, and can reduce the circuit size, storage capacity, processing time, and power consumption while having resistance against the secondary DPA. 
     Modification of First Embodiment 
       FIG. 10  is a block diagram showing a configuration example of an MES  2200 - 2  which is a modification of the MES  2200 . Hereinafter, an example will be described where eight-bit data is processed. 
     The MES  2200 - 2  includes a transform unit  1201   l , a transform unit  1201   c , a transform unit  1201   r , a transform unit  1203 , a transform unit  1204 , a transform unit  1205 , and an exclusive OR operation unit  1202 . 
     The MES  2200 - 2  inputs data d 1200   l  to the transform unit  1201   l , inputs data d 1200   c  to the transform unit  1201   c , and inputs data d 1200   r  to the transform unit  1201   r . The MES  2200 - 2  calculates data d 1202  which is the exclusive OR of data d 1201   l  output from the transform unit  1201   l , data d 1201   c  output from the transform unit  1201   c , and data d 1201   r  output from the transform unit  1201   r . The MES  2200 - 2  inputs data d 1202  to the transform unit  1203 , the transform unit  1204 , and the transform unit  1205 . The MES  2200 - 2  outputs data d 1203  transformed by the transform unit  1203 , outputs data d 1204  transformed by the transform unit  1204 , and data d 1205  transformed by the transform unit  1205 . 
     The transform unit  1201   l  receives data d 1200   l  as an input and outputs data d 1201   l . For example, the transform unit  1201   l  is configured to transform to output data d 1201   l  which is the result of exclusive OR of data transformed from input data d 1200   l  by the function φ and transforming data d 301   a . Transforming data may be 0, and in this case, exclusive OR may not be performed. 
     The transform unit  1201   c  receives data d 1200   c  as an input and outputs data d 1201   c . For example, the transform unit  1201   c  is configured to transform to output data d 1201   c  which is the result of exclusive OR of data transformed from input data d 1200   c  by the function φ and transforming data d 301   b . Transforming data may be 0, and in this case, exclusive OR may not be performed. 
     The transform unit  1201   r  receives data d 1200   r  as an input and outputs data d 1201   r . For example, the transform unit  1201   r  is configured to transform to output data d 1201   r  which is the result of exclusive OR of data transformed from input data d 1200   r  by the function φ and transforming data d 301   c . Transforming data may be 0, and in this case, exclusive OR may not be performed. 
     The transform unit  1204  transform input data d 1202  to data d 1204  by using predetermined transform and outputs data d 1204 . The transform unit  1204  may be nonlinear transform, such as the SubByte (S-box) of AES, linear transform, such as the function φ, or arbitrary transform. The transform unit  1204  may be identical transform, and in this case, transform processing may not be performed. 
     The transform unit  1205  transforms input data d 1202  to data d 1205  by using predetermined transform and outputs data d 1205 . The transform unit  1205  may be nonlinear transform, such as the SubByte (S-box) of AES, linear transform, such as the function φ, or arbitrary transform. The transform unit  1205  may be identical transform, and in this case, transform processing may not be performed. 
     The transform unit  1201   l , the transform unit  1201   c , the transform unit  1201   r , the transform unit  1203 , the transform unit  1204 , and the transform unit  1205  may prepare a transform table in advance, and may calculate the MES  2200 - 2  with reference to the prepared transform table. 
       FIG. 11  is a block diagram showing a configuration example of the transform unit  1203 . The transform unit  1203  includes a transform unit  1301 , an exclusive OR operation unit  1302 , an S-box  1303 , a transform unit  1304 , an exclusive OR operation unit  1305 , an exclusive OR operation unit  1306 , a transform unit  1307 , and an exclusive OR operation unit  1308 . 
     The transform unit  1203  receives data d 1202 , d 400   a , and d 400   b . The transform unit  1203  inputs data d 1202  to the transform unit  1301 , calculates data d 1302  which is the exclusive OR of output data d 1301  of the transform unit  1301  and data d 400   a , and inputs data d 1302  to the S-box  1303 . The transform unit  1203  transforms data d 1202  to data d 1304  in the transform unit  1304 . The transform unit  1203  calculates data d 1305  which is the exclusive OR of data d 1303  output from the S-box  1303  and data d 1304  output from the transform unit  1304 . The transform unit  1203  calculates data d 1306  which is the exclusive OR of data d 1305  and data d 400   b . The transform unit  1203  transforms data d 1202  to data d 1307  in the transform unit  1307 . The transform unit  1203  calculates and outputs data d 1203  which is the exclusive OR of data d 1306  and data d 1307  output from the transform unit  1307 . 
     Data d 400   a  is one of sixteen pieces of data which are obtained by segmenting the 128-bit input mask d 120   b  output from the mask generation unit  105  in units of eight bits. Data d 400   b  is one of sixteen pieces of data which are obtained by segmenting the 128-bit output mask d 121   b  output from the mask generation unit  105  in units of eight bits. For example, the transform unit  1301  is configured to transform and output the result of exclusive OR of input data d 1202 , transforming data d 301   a , and transforming data d 301   b  to data d 1301  by the inverse function φ −1  of the function φ. 
     The S-box  1303  is the same nonlinear transform as the SubByte (S-box) of AES, and transforms input data d 1302  to d 1303 . 
     The transform unit  1304  is the same transform as the transform unit  1204 , and transforms input data d 1202  to d 1304 . The transform unit  1307  is the same transform as the transform unit  1205 , and transforms input data d 1202  to d 1307 . 
     If S-box transform is denoted by S, the transform unit  1301  is denoted by g −1 , the transform unit  1304  is denoted by h 1 , and the transform unit  1307  is denoted by h 2 , the transform unit  1203  satisfies the relationship of the following expression (5).
 
 d 1203 =S ( g   −1 ( d 1202)^ d 400 a )^ h   1 ( d 1202)^ d 400 b^h   2 ( d 1307)  (5)
 
     As long as the expression (5) is satisfied, the above-described calculation procedure may not be provided. For example, when input data d 1202  is in a range of 0 to 255, the transform unit  1203  may calculate output data d 1203  in advance and may hold data d 1203  as the transform table T 2200  shown in  FIG. 7 . In this case, the transform unit  1203  receives data d 1202 , and outputs data d 1203  corresponding to received data d 1202  with reference to the transform table T 2200 . 
     As described above, in the encryption device of the first embodiment, the encryption processing is performed while masked intermediate data of the encryption processing is segmented. For this reason, power consumption at the time when masked intermediate data of the encryption processing is processed cannot be measured, and there is resistance against the second DPA. 
     Second Embodiment 
     A second embodiment is different from the first embodiment in that, in place of the MESs  2200  to  2215 , MESs  600  are provided.  FIG. 12  is a block diagram showing a configuration example of the MES  600 . The MESs  601  to  615  have the same configuration as the MES  600 , thus description thereof will be omitted. 
     The MES  600  includes a transform unit  601 , a transform unit  602 , a transform unit  603 , a transform unit  604 , a transform unit  605 , and a transform unit  606 . 
     The MES  600  receives two pieces of eight-bit data d 600   l  and d 600   r , inputs data d 600   l  to the transform unit  601  and the transform unit  603 , and inputs data d 600   r  to the transform unit  602  and the transform unit  604 . The MES  600  inputs data d 601  output from the transform unit  601  and data d 602  output from the transform unit  602  to the transform unit  605 . The MES  600  inputs data d 603  output from the transform unit  603  and data d 604  output from the transform unit  604  to the transform unit  606 . The MES  600  outputs data d 605  output from the transform unit  605  and data d 606  output from the transform unit  606 . 
     The transform unit  601  transforms data d 600   l  to d 601  by transform having inverse transform. The transform unit  602  transforms data d 600   r  to d 602  by transform having inverse transform. The transform unit  603  transforms data d 600   l  to d 603  by transform having inverse transform. The transform unit  604  transforms data d 600   r  to d 604  by transform having inverse transform. 
     The transform unit  601 , the transform unit  602 , the transform unit  603 , and the transform unit  604  may be formed by using, for example, the function φ described in the first embodiment, the S-box of AES, or identical transform. When identical transform is used, transform processing may not be performed. 
       FIG. 13  is a block diagram showing a configuration example of the transform unit  605 .  FIG. 14  is a block diagram showing a configuration example of the transform unit  606 . 
     The transform unit  605  includes an exclusive OR operation unit  701 , an exclusive OR operation unit  702 , an S-box  703 , a transform unit  707 , a transform unit  708 , a transform unit  704 , an exclusive OR operation unit  705 , and an exclusive OR operation unit  706 . 
     The transform unit  605  receives data d 601 , d 602 , d 700   a , and d 700   b , inputs data d 601  to the transform unit  707 , and input data d 602  to the transform unit  708 . The transform unit  605  calculates data d 701  which is the exclusive OR of data d 707  output from the transform unit  707  and data d 708  output from the transform unit  708 . The transform unit  605  calculates data d 702  which is the exclusive OR of data d 701  and data d 700   a  and inputs data d 702  to the S-box  703 . The transform unit  605  inputs data d 707  output from the transform unit  707  and data d 708  output from the transform unit  708  to the transform unit  704 . The transform unit  605  calculates data d 705  which is the exclusive OR of data d 703  output from the S-box  703  and data d 704  output from the transform unit  704 . The transform unit  605  calculates and outputs data d 605  which is the exclusive OR of data d 705  and data d 700   b.    
     Data d 700   a  is one of sixteen pieces of data obtained by segmenting the 128-bit input mask d 120   b  output from the mask generation unit  105  in units of eight bits. Data d 700   b  is one of sixteen pieces of data obtained by segmenting the 128-bit output mask d 121   b  output from the mask generation unit  105  in units of eight bits. 
     The S-box  703  is the same nonlinear transform as the S-box of AES, and transforms input data d 702  to d 703 . 
     The transform unit  707  outputs the result d 707  of inverse transform of the transform unit  601  on input data d 601 . The transform unit  708  outputs the result d 708  of inverse transform of the transform unit  602  on input data d 602 . The transform unit  704  transforms input eight-bit data d 707  and data d 708  to eight-bit data d 704  by predetermined transform and outputs data d 704 . The transform unit  704  may use arbitrary transform which has 16-bit input and eight-bit output. 
     When the transform unit  601  is identical transform, the transform unit  707  is also identical transform, and in this case, the transform processing of the transform unit  707  may not be performed. The same is applied to the transform unit  708 . Even when the transform unit  704  is identical transform, the transform processing may not be performed. 
     The transform unit  606  includes a transform unit  710 , a transform unit  711 , and a transform unit  712 . The transform unit  606  receives two pieces of eight-bit data d 603  and data d 604 , input data d 603  to the transform unit  710 , and inputs data d 604  to the transform unit  711 . The transform unit  606  inputs data d 710  output from the transform unit  710  and data d 711  output from the transform unit  711  to the transform unit  712 , and outputs data d 606  output from the transform unit  712 . The transform unit  712  outputs the result d 606  of the same transform as the transform unit  704  on input data d 710 . 
     If S-box transform is denoted by S, Input/output data of the MES  600  satisfies the relationship of the following expression (6).
 
 d 605 ^d 606 ^d 700 b=S ( d 600 l^d 600 r^d 700 a )  (6)
 
     The transform unit  605  may calculate output data d 605  for input data d 601  and data d 602  in advance, and may hold data d 605  as a transform table. In this case, the transform unit  605  receives input data d 601  and data d 602 , and outputs corresponding data d 605  with reference to the transform table. 
     The transform unit  606  may calculate output data d 606  for input data d 603  and data d 604  in advance, and may hold data d 606  as a transform table. In this case, the transform unit  606  receives input data d 603  and data d 604 , and outputs corresponding data d 606  with reference to the transform table. 
     The MES  600  may calculate output data d 605  and data d 606  for input data d 600   l  and data d 600   r  in advance, and may hold data d 605  and data d 606  as a transform table. In this case, the MES  600  receives input data d 600   l  and data d 600   r , and outputs corresponding data d 605  and data d 606  with reference to the transform table. 
     Third Embodiment 
     A third embodiment is different from the first embodiment in that, in place of the MESs  2200  to  2215 , MESs  1600  are provided.  FIG. 15  is a block diagram showing a configuration example of the MES  1600 . The MES  1601  to the MES  1615  have the same configuration as the MES  1600 , thus description thereof will be omitted. 
     The MES  1600  includes a transform unit  1601 , a transform unit  1602 , and a transform unit  1603 . The MES  1600  receives data d 1600   l  and data d 1600   r  which are segmented data of masked data under the encryption processing, and inputs data d 1600   l  and data d 1600   r  to the transform unit  1601 . The MES  1600  inputs data d 1601  output from the transform unit  1601  to the transform unit  1602  and the transform unit  1603 . The MES  1600  outputs data d 1602  output from the transform unit  1602  and data d 1603  output from the transform unit  1603 . 
     The transform unit  1601  receives eight-bit data d 1600   l  and data d 1600   r , transforms the result of exclusive OR of data d 1600   l  and d 1600   r  and transforming data d 1601   a  to eight-bit data by using the function φ, and outputs the result d 1601  of exclusive OR of the transform result and transforming data d 1601   b . The function φ has an inverse function φ −1 . The function φ may be identical transform, and in this case, the transform processing may not be performed. 
     Transforming data d 1601   a  and transforming data d 1601   b  may be 0, and in this case, exclusive OR may not be performed. 
     The transform unit  1601  may be calculated by referencing a transform table calculated in advance. The transform table represents the correspondence relationship between input data d 1600   l  and d 1600   r  and output data d 1601 , and is generated in accordance with the function φ and transforming data d 1601   a.    
     The transform unit  1603  transforms data d 1601  output from the transform unit  1601  to data d 1603  by using predetermined transform and outputs data d 1603 . The transform unit  1603  may be nonlinear transform, such as S-box, linear function, such as the function φ described in the first embodiment, or arbitrary transform. The transform unit  1603  may be identical transform, and in this case, the transform processing may not be performed. 
       FIG. 16  is a block diagram showing a configuration example of the transform unit  1602 . The transform unit  1602  includes a transform unit  1701 , an exclusive OR operation unit  1702 , a transform unit  1704 , an S-box  1703 , an exclusive OR operation unit  1705 , and an exclusive OR operation unit  1706 . 
     The transform unit  1602  receives data d 1601 , d 1700   a , and d 1700   b , and inputs data d 1601  to the transform unit  1701 . The transform unit  1602  calculates data d 1702  which is the exclusive OR of data d 1701  output from the transform unit  1701  and data d 1700   a  and inputs data d 1702  to the S-box  1703 . The transform unit  1602  transforms data d 1601  to data d 1704  in the transform unit  1704 . The transform unit  1602  calculates data d 1705  which is the exclusive OR of data d 1703  output from the S-box  1703  and data d 1704  output from the transform unit  1704 . The transform unit  1602  calculates and outputs data d 1602  which is the exclusive OR of data d 1705  and d 1700   b.    
     Data d 1700   a  is one of sixteen pieces of data which are obtained by segmenting the 128-bit input mask d 120   b  output from the mask generation unit  105  in terms of eight bits. Data d 1700   b  is one of sixteen pieces of data which are obtained by segmenting the 128-bit output mask d 121   b  output from the mask generation unit  105  in terms of eight bits. 
     The transform unit  1701  outputs the result d 1701  of exclusive OR of the result, which is obtained by transforming the result of the exclusive OR of input data d 1601  and transforming data d 1601   b  by the inverse function φ −1  of the function φ, and transforming data d 1601   a.    
     The S-box  1703  is the same nonlinear transform as the S-box of AES, and transforms input data d 1702  to d 1703 . The transform unit  1704  is the same transform as the transform unit  1603 , and transforms input data d 1601  to d 1704 . When input data d 1601  is in a range of 0 to 255, the transform unit  1602  may calculate output data d 1602  in advance and may hold data d 1602  as a transform table. In this case, the transform unit  1602  receives data d 1601  and outputs data d 1602  corresponding to received data d 1601  with reference to the transform table. 
     If S-box transform is denoted by S, input/output data of the MES  1600  satisfies the relationship of the following expression (7).
 
 d 1602 ^d 1603 ^d 1700 b=S ( d 1600 l^d 1600 r^d 1700 a )  (7)
 
     Although a configuration example has heretofore been described where 128-bit data is processed by eight bits, the processing unit is not limited to eight bits, and may be 16 bits or 128 bits. A different number of bits may be used as the units of processing. The MESs  1600  to  1615  provided in the SubByte processing unit  112   b  may have the same configuration. 
     Fourth Embodiment 
     A fourth embodiment is different from the first embodiment in that, in place of the MESs  2200  to  2215 , MESs  1800  are provided.  FIG. 17  is a block diagram showing a configuration example of the MES  1800 . The MES  1801  to the MES  1815  have the same configuration as the MES  1800 , thus description thereof will be omitted. 
     The MES  1800  includes an exclusive OR operation unit  1801 , an exclusive OR operation unit  1802 , an exclusive OR operation unit  1804 , an exclusive OR operation unit  1806 , an S-box  1803  which is defined by an encryption algorithm, and a transform unit  1805 . 
     The MES  1800  receives data d 1800   l  and data d 1800   r , which are segmented data of masked data under the encryption processing, and data d 1806   a  and data d 1806   b . The MES  1800  calculates data d 1801  which is the exclusive OR of data d 1800   l  and data d 1800   r . The MES  1800  calculates data d 1802  which is the exclusive OR of data d 1801  and data d 1806   a  and inputs data d 1802  to the S-box  1803 . The MES  1800  calculates data d 1804  which is the exclusive OR of data d 1803  output from the S-box  1803  and data d 1806   b . The MES  1800  inputs data d 1800   r  to the transform unit  1805 . The MES  1800  outputs data d 1805   l  which is the exclusive OR of data d 1805   r  output from the transform unit  1805  and data d 1804 . 
     The transform unit  1805  transforms data d 1800   r  to data d 1805   r  by using predetermined transform and outputs data d 1805   r . The transform unit  1805  may be nonlinear transform, such as S-box, linear function, such as the function φ described in the first embodiment, or arbitrary transform. 
     The MES  1800  may calculate output data for input data in advance and hold output data as a transform table. In this case, the MES  1800  receives input data d 1800   l  and data d 1800   r , and outputs data d 1805   l  and data d 1805   r  with reference to the transform table. 
     If S-box transform is denoted by S, input/output data of the MES  1800  satisfies the relationship of the following expression (8).
 
 d 1805 l^d 1805 r^d 1806 b=S ( d 1800 l^d 1800 r^d 1806 a )  (8)
 
     Although a configuration example has heretofore been described where 128-bit data is processed by eight bits, the unit of processing is not limited to eight bits, and may be 16 bits or 128 bits. A different number of bits may be used as the units of processing. The MESs  1800  to  1815  provided in the SubByte processing unit  112   b  may have the same configuration. 
     Fifth Embodiment 
       FIG. 18  is a block diagram showing a configuration example of an encryption device  500  according to a fifth embodiment. The same processing units and data as those in  FIG. 3  which is a block diagram of the encryption device  100  of the first embodiment are represented by the same reference numerals as in  FIG. 3 , and description thereof will be omitted. 
     The encryption device  500  further includes exclusive OR operation units  1901   l  to  1910   l  and  1901   r  to  1910   r.    
     The exclusive OR operation unit  1901   l  inputs data d 1901   l , which is the result of exclusive OR of data d 109   r  output from the data segmentation unit  109  and data d 112   bl  output from the SubByte processing unit  112   b , to the ShiftRow  113   bl.    
     The exclusive OR operation unit  1901   r  inputs data d 1901   r , which is the result of exclusive OR of data d 109   r  output from the data segmentation unit  109  and data d 112   br  output from the SubByte processing unit  112   b , to the ShiftRow  113   br.    
     The exclusive OR operation unit  1901   l  may input data d 1901   l , which is the result of exclusive OR of data d 109   l  output from the data segmentation unit  109  and data d 112   bl  output from the SubByte processing unit  112   b , to the ShiftRow  113   bl.    
     At this time, the exclusive OR operation unit  1901   r  inputs data d 1901   r , which is the result of exclusive OR of data d 109   l  output from the data segmentation unit  109  and data d 112   br  output from the SubByte processing unit  112   b , to the ShiftRow  113   br.    
     The exclusive OR operation unit  1901   l  may input data d 1901   l , which is the result of exclusive OR of data d 109   l  or data d 109   r  output from the data segmentation unit  109  and data d 113   bl  output from the ShiftRow  113   bl , to the MixColumn  114   bl.    
     The exclusive OR operation unit  1901   r  may input data d 1901   r , which is the result of exclusive OR of data d 109   l  or d 109   r  output from the data segmentation unit  109  and data d 113   br  output from the ShiftRow  113   br , to the MixColumn  114   br.    
     The exclusive OR operation units  1902   l  to  1910   l  respectively input data d 1902   l  to d 1910   l , which are the results of exclusive OR of data d 114   bl  to d 114   jl  output from the MixColumn  114   bl  to  114   jl  or data d 114   br  to d 114   jr  output from the MixColumn  114   br  to  114   jr  and data d 112   cl  to d 112   kl  output from the SubByte processing unit  112   c  to  112   k , to the ShiftRow  113   cl  to  113   kl.    
     The exclusive OR operation units  1902   r  to  1910   r  respectively input data d 1902   r  to d 1910   r , which are the results of exclusive OR of data d 114   bl  to d 114   jl  output from the MixColumn  114   bl  to  114   jl  or data d 114   br  to d 114   jr  output from the MixColumn  114   br  to  114   jr  and the data d 112   cr  to d 112   kr  output from the SubByte processing unit  112   c  to  112   k , to the ShiftRow  113   cr  to  113   kr.    
     The exclusive OR operation units  1902   l  to  1910   l  may respectively input data d 1902   l  to d 1910   l , which are the results of exclusive ORs of data d 114   bl  to d 114   jl  output from the MixColumn  114   bl  to  114   jl  or data d 114   br  to d 114   jr  output from the MixColumn  114   br  to  114   jr  and data d 113   cl  to d 113   kl  output from the ShiftRow  113   cl  to  113   kl , to the MixColumn  114   cl  to  114   jl  and the AddRoundKey  111   k.    
     The exclusive OR operation unit  1902   r  to  1910   r  may respectively input data d 1902   r  to d 1910   r , which are the results of exclusive OR of data d 114   bl  to d 114   jl  output from the MixColumn  114   bl  to  114   jl  or data d 114   br  to d 114   jr  output from the MixColumn  114   br  to  114   jr  and data d 113   cr  to d 113   kr  output from the ShiftRow  113   cr  to  113   kr , to the MixColumn  114   cr  to  114   jr  and the data integration unit  110 . 
     Sixth Embodiment 
       FIG. 19  is a block diagram showing a configuration example of an encryption device  6000  according to a sixth embodiment. The same processing units and data as those in  FIG. 3  which is a block diagram of the encryption device  100  of the first embodiment are represented by the same reference numerals as in  FIG. 3 , and description thereof will be omitted. 
     The encryption device  6000  includes a mask generation unit  2001 , and further includes a mask processing unit  2002  and an unmask processing unit  2003 . 
     The mask generation unit  2001  generates input masks d 2012   b  to d 2012   k , segmented data d 2010   b  to d 2010   k  of the input masks, and segmented data d 2011   b  to d 2011   k  of the input masks. The input masks d 2012   b  to d 2012   k  are the exclusive OR result of segmented data d 2010   b  to d 2010   k  and d 2011   b  to d 2011   k  of the input masks. 
     The mask generation unit  2001  generates output masks d 2015   b  to d 2015   k , segmented data d 2013   b  to d 2013   k  of the output masks, and segmented data d 2014   b  to d 2014   k  of the output masks. The output masks d 2015   b  to d 2015   k  are the exclusive OR result of segmented data d 2013   b  to d 2013   k  and d 2014   b  to d 2014   k  of the output masks. 
     The mask generation unit  2001  generates replacement masks d 2016   b  to d 2016   j . The replacement masks d 2016   b  to d 2016   j  are the result of exclusive OR of the input masks d 2012   c  to d 2012   k  and the output masks d 2015   b  to d 2015   j.    
     The mask generation unit  2001  supplies segmented data d 2010   b  of the input mask to the mask processing unit  107 , supplies segmented data d 2011   b  of the input mask to the mask processing unit  2002 , and supplies the input masks d 2012   b  to d 2012   k  to the SubByte processing units  112   b  to  112   k.    
     The mask generation unit  2001  may supply data having connected segmented data d 2010   b  to d 2010   k  and d 2011   b  to d 2011   k  of the input masks to the SubByte processing units  112   b  to  112   k  as the input masks d 2012   b  to d 2012   k.    
     The mask generation unit  2001  supplies segmented data d 2013   k  of the output mask to the unmask processing unit  2003 , supplies segmented data d 2014   k  of the output mask to the unmask processing unit  108 , and supplies the output masks d 2015   b  to d 2015   k  to the SubByte processing unit  112   b  to  112   k.    
     The mask generation unit  2001  may supply data having connected segmented data d 2013   b  to d 2013   k  and d 2014   b  to d 2014   k  of the output masks to the SubByte processing unit  112   b  to  112   k  as the output masks d 2015   b  to d 2015   k.    
     The mask generation unit  2001  respectively supplies the replacement masks d 2016   b  to d 2016   j  to the mask replacement units  115   b  to  115   j . The mask generation unit  2001  may supply data having connected segmented data d 2010   c  to d 2010   k  and d 2011   c  to d 2011   k  of the input masks and segmented data d 2013   b  to d 2013   j  and d 2014   b  to d 2014   j  of the output masks as the replacement masks d 2016   b  to d 2016   j.    
     The mask processing unit  2002  inputs the result d 2002  of exclusive OR of data d 109   r  output from the data segmentation unit  109  and segmented data d 2011   b  of the input mask to the SubByte processing unit  112   b.    
     The mask processing unit  2002  may input result d 2002  of exclusive OR of data d 109   l  output from the data segmentation unit  109  and segmented data d 2011   b  of the input mask to the AddRoundKey  111   a.    
     The mask processing unit  2002  may input the result d 2002  of exclusive OR of data d 107  output from the mask processing unit  107  and segmented data d 2011  of the input mask to the data segmentation unit  109 . 
     The unmask processing unit  2003  inputs the result d 2003  of exclusive OR of data d 113   kr  output from the ShiftRow  113   kr  and segmented data d 2013   k  of the output mask to the data integration unit  110 . 
     The unmask processing unit  2003  may input the result d 2003  of exclusive OR of data d 111   k  output from the AddRoundKey  111   k  and segmented data d 2013   k  of the output mask to the data integration unit  110 . 
     The unmask processing unit  2003  may input the result d 2003  of exclusive OR of data d 110  output from the data integration unit  110  and segmented data d 2013   k  of the output mask to the unmask processing unit  108 . 
     In the SubByte processing unit  112   b , if S-box transform is denoted by S, and the result of exclusive OR of two pieces of input data of the SubByte processing unit  112   b  is denoted by d 2020   b , input/output data of the SubByte processing unit  112   b  satisfies the relationship of the following expression (9) .
 
 d 112 bl^d 112 br^d 2015 b=S ( d 2020 b^d 2012 b )  (9)
 
     If the expression (9) is satisfied, the above-described calculation procedure may not be provided. 
     As described above, when the mask generation unit  2001  supplies segmented data d 2010   b  and d 2011   b  of the input mask to the SubByte processing unit  112   b , input/output data of the SubByte processing unit  112   b  satisfies the relationship of the following expression (10).
 
 d 112 bl^d 112 br^d 2015 b=S ( d 2020 b^d 2012 b )= S ( d 2020 b^d 2010 b^d 2011 b )  (10)
 
     If the expression (10) is satisfied, the above-described calculation procedure may not be provided. 
     Similarly, when the mask generation unit  2001  supplies segmented data d 2013   b  and d 2014   b  of the output mask to the SubByte processing unit  112   b , input/output data of the SubByte processing unit  112   b  satisfies the relationship of the following expression (11).
 
 d 112 bl^d 112 br^d 2015 b=d 112 bl^d 112 br^d 2013 b ^d 2014 b=S ( d 2020 b^d 2012 b )  (11)
 
     If the expression (11) is satisfied, the above-described calculation procedure may not be provided. The same relationship is established for the SubByte processing units  112   c  to  112   k.    
     When the mask generation unit  2001  supplies segmented data d 2010   c  and d 2011   c  of the input mask and segmented data d 2013   b  and d 2014   b  of the output mask to the mask replacement unit  115   b , input/output data of the mask replacement unit  115   b  satisfies the relationship of the following expression (12).
 
 d 115 b=d 114 br^d 2010 c^d 2011 c^d 2013 b^d 2014 b   (12)
 
     If the expression (12) is satisfied, the above-described calculation procedure may not be provided. The same relationship is established for the mask replacement units  115   c  to  115   j.    
     As described above, according to the first to sixth embodiments, it is possible to provide an encryption device having resistance against power analysis including high-order DPA with an encryption module using nonlinear transform. That is, according to the above-described embodiments, the MES receives a plurality of pieces of data obtained by segmenting masked intermediate data of the encryption processing and performs nonlinear transform in a state of being masked, thereby outputting a plurality of data obtained by segmenting the correct nonlinear transform result. Thus, the correlation between intermediate data of the encryption processing and power consumption is eliminated, and there is resistance against power analysis. When one type of MES is used in single encryption processing, there is resistance for a countermeasure against secondary DPA, and it becomes possible to reduce the circuit size, storage capacity, processing time, and power consumption, compared to a random mask method as a related-art technique against secondary DPA. 
     Next, the hardware configuration of the encryption device according to each of the first to sixth embodiments will be described with reference to  FIG. 20 .  FIG. 20  is an explanatory view showing the hardware configuration of the encryption device according to each of the first to sixth embodiments. 
     The encryption device according to each of the first to sixth embodiments includes a control device, such as a Central Processing Unit (CPU)  51 , a storage device, such as a Read Only Memory (ROM)  52  or a Random Access Memory (RAM)  53 , a communication I/F  54  which is connected to a network and performs communication, an external storage device, such as a Hard Disk Drive (HDD) or a Compact Disc (CD) drive device, a display device, such as a display device, an input device, such as a keyboard or a mouse, and a bus  61  which connects the respective units. The encryption device has the hardware configuration using a typical computer. 
     A program which is executed in the encryption device according to each of the first to sixth embodiments is recorded in a computer-readable recording medium, such as a Compact Disk Read Only Memory (CD-ROM), a flexible disk (FD), a Compact Disk Recordable (CD-R), or a Digital Versatile Disk (DVD), in an installable or executable format and is provided as a computer program product. 
     The program which is executed in the encryption device according to each of the first to sixth embodiments may be stored in a computer which is connected to a network, such as the Internet, and may be downloaded through the network. The program which is executed in the encryption device according to each of the first to sixth embodiments may be provided or distributed through a network, such as the Internet. 
     The program of each of the first to sixth embodiments may be incorporated into a ROM or the like and provided. 
     The image processing program which is executed in the image processing apparatus according to each of the first to fourth embodiments may be configured as a module including the above-described units. As actual hardware, the CPU  51  (processor) reads the image processing program from the storage device and executes the image processing program, such that the above-described units are loaded and generated on a main storage device. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.