# Patent

## Title
Image data recording device, method for controlling image data recording device, and a program for controlling an image data recording system, each using a common key

## Abstract

A computer generates a print ID based on input image data on which a forgery preventing process is performed, and transfers the print ID to a printer. The printer generates a common key corresponding to the print ID, and transfers it to the computer. The computer encrypts the image data using a common key, represents it as a print control command, and transfers the data with the print ID to the printer. The printer analyzes the command of the print control data, extracts the encrypted print image data, decrypts the data using the common key, and stores the decrypted print image data in a storage medium, thereby preventing the data from being printed on a number of unspecified printers.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image processing apparatus for preventing the forgery of bills, etc. in a recording system for processing an image in a host computer and printing the image on a recording device.
2. Related Background Art
Many systems for preventing the forgery of bills, valuable securities, etc. are designed as input/output device built-in systems such as copying units, etc. However, with an increasing number of personal computers, high-performance peripheral devices such as a scanner, a digital camera, a printer, etc. have been developed. As a result, with these high-performance peripheral devices, the personal computers can output an image at a quality level higher than an image output by the input/output device built-in copying units. Thus, in a personal computer environment, a forgery preventing system is required.
As a characteristic of a forgery preventing system in the personal computer environment, a host computer controls input and output devices. Therefore, it is necessary to allow an image process program of the host computer to recognize specified patterns of bills, valuable securities, etc. A personal computer can output data without a specific image process program only if it is informed of the control code of the output device.
Accordingly, a method of encrypting the control code of the output device is effective to prevent the use of a program other than the specific image process program for a forgery preventing process. The above mentioned method is disclosed by, for example, by Japanese Patent Application Laid-Open No. 6-105141 although not in the personal computer environment. FIG. 2 shows an example when this method is applied to the personal computer environment.
In FIG. 2, the processes in steps S2001 to S2005 are performed by the host computer, and the processes in steps S2006 to S2009 are performed by the recording device.
In the first step S2001, image data is input from an OS (basic software) or an application. Then, in step S2002, an image process including a forgery preventing process is performed. The image process in step S2002 includes color matching, gamma correction, and quantizing processes to convert an input image into print image data. In the forgery preventing process in step S2002, determination is normally made on a specified image by performing a pattern recognizing process. If the input image matches the specified image, then an error process is performed on the image data.
Then, the print data on which an image process has been performed is encrypted in step S2003. The encrypted print data is converted into print control data as a command for control of a printer in step S2004.
The print control data as a command is transferred to the printer by controlling (control can be practically performed by the OS) the data transfer circuit (not shown in the attached drawings) in step S2005.
Next, in step S2006, the printer receives the print control data. A command analyzing process is performed on the received print control data in step S2007, and encrypted print image data is generated.
Then, the encrypted print image data is converted into print data in a decryption process in step S2008, and the decrypted print data is printed on a storage medium in step S2009.
However, since in the above mentioned system which performs the encryption process between the host computer and the printer, there is an one to one correspondence between the input image and the data transferred to the printer, the encrypted data can be easily decrypted.
That is, it is the same as the case where the control code of the printer used in the conventional system is not open, and there is a problem that the image forgery preventing process cannot be effectively performed.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above mentioned problems, and provide an improved image processing apparatus and method.
Another object of the present invention is to provide an image processing apparatus and method capable of effectively performing a forgery preventing process on an input image.
A further object of the present invention is to provide an image processing apparatus and method by hardening the decryption of a forgery preventing process.
A further object of the present invention is to provide an image processing apparatus and method capable of effectively preventing a print process performed by a number of unspecified image recording devices by encrypting print control data for controlling an image recording device using a common key issued by an image recording device when the image recording device is allowed to print an image, and by disabling any other image recording devices than the image recording device by which the common key has been generated to record the image.
Further objects of the present invention will be clearly described by the following explanation based on the attached drawings and the claims.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flowchart of the procedure of the operations of the recording system according to the first embodiment of the present invention;
FIG. 2 is a flowchart of the procedure of the encryption process according to the recording system of the conventional technology;
FIG. 3 is a flowchart of the procedure of an encryption process according to the first embodiment of the present invention;
FIG. 4 is a flowchart of the procedure of a decryption process according to the first embodiment of the present invention;
FIG. 5 is a flowchart of the procedure of an encryption table generating process according to the first embodiment of the present invention;
FIG. 6 is a flowchart of the procedure of a decryption table generating process according to the first embodiment of the present invention; and
FIG. 7 is a block diagram of an example of the configuration of the image data recording system realizing the present invention.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
The embodiments of the present invention are described below in detail by referring to the attached drawings.
FIG. 1 is a flowchart of the procedure of processing data in the recording system according to the present invention.
In FIG. 1, the processes in steps S1001 to S1004 and steps S1009 to S1012 are performed by a host computer. The processes in steps S1005 to S1008 and steps S1013 to S1017 are performed by s recording device.
In the first step S1001, image data is input. Then, in step S1002, an image process including a forgery preventing process is performed.
Next, in step S1003, a print ID is generated, and then the print ID is transferred to a recording device in step S1004.
Next, in step S1005, the recording device receives a print ID, and stores the received print ID in step S1006.
Next, in step S1007, a common key is generated. At this time, the recording device is managed such that a print ID is paired with a common key.
If a common key is generated in step S1007, it is irregularly generated such that the common key cannot be associated with the value of the print ID.
Then, in step S1008, the generated common key is transmitted to the host computer.
The common key transmitted from the recording device is received by the host computer in step S1009. Thus, since the recording device issues the common key in response to the transfer of the print ID of the host computer, the transfer of the print ID in step S1004 indicates a request to issue a common key.
In step S1010, the print image data generated in the process performed in step S1002 is encrypted by the common key received in step S1009.
Then, in step S1011, the encrypted print image data is converted into a print control command. Then, in step S1012, the print ID and the print control data command are transferred to the recording device side.
In step S1013, the recording device receives a print ID and print control data. Then, in step S1014, the common key corresponding to the received print ID is retrieved and obtained from a managed pair of the print ID and the common key. Then, in step S1015, the command of the print control data is analyzed, and the encrypted print image data is extracted.
Then, in step S1016, the print image data is decrypted using the common key obtained in step S1014. In step S1017, the print image data is stored on the storage medium in the print process.
The print data transferring process in steps S1012 and S1013 and the process in steps S1015 to S1017 can be sequentially repeated in parallel. Although not shown in FIG. 1, the used print ID and the common key paired therewith may be discarded after performing the print process in step S1017.
FIG. 3 is a flowchart of the contents of the encryption process performed in step S1010.
The random number table according to this embodiment comprises series of irregularly arranged integers (1-byte length each) of “0” to “255”. That is, the table size is 256 bytes. The common key is formed by integers from 0 to 255.
First, in step S3001, a random number table is stored on the memory (RAM) of the host computer. Then, in step S3002, the random number table on the memory (RAM) is converted into an encryption table using a common key.
In step S3003, the print image data is encrypted using the generated encryption table. In this case, the print image data is sequentially read in a byte unit, the data value of one read byte is set as an offset from the leading address of the encryption table, and the value of the corresponding address is set as the encryption print image data.
FIG. 5 is a flowchart of the process performed in step S3002.
First, in step S5000, the process is started. then, in step S5001, a variable n is set to “0”. The variable n is a management counter for 100 times repetition of the processes in steps S5003 to S5005 described later.
Then, in step S5002, the value of the common key is assigned to a variable B. Then, in step S5003, a variable A is computed using the variable B by the following Equation (1). ‘mod’ is a well-known function for use in obtaining a residue in a division.

A=(5×B+13) mod 256  (1)

Next, in step S5004, the variable B is computed using the variable A by the following Equation (2).

B=(5×A+13) mod 256  (2)

In the computation by the Equations (1) and (2), pseudo random numbers are generated in a linear congruential method. That is, the common key is used for the initial value in the linear congruential method.
Then, in step S5005, the table value whose offset from the leading address of the random number table stored in the memory in step S3001 is A and the table value whose offset is B are interchanged. Then, in step S5006, n is incremented by 1.
It is determined in step S5007 whether or not n is “100”. If it is “100”, then control is passed to step S5008, and the converting operation terminates. If it is determined in step S5007 that n is not 100, control is passed to step S5003.
FIG. 4 is a flowchart explaining the procedure of the decryption process performed in step S1016. The random number table used in this embodiment is the same table as that used in the process in step S3001.
First, in step S4001, the random number table is developed on the memory (RAM) of the recording device.
Then, in step S4002, the random number table on the memory (RAM) is converted into a decryption table using a common key. In the obtained decryption table, the offset value from the leading address of the series and the integer stored at the address can be obtained by interchanging the values on the above mentioned encryption table.
For example, when the 25th value from the start of the encryption table is “12”, the 12th value from the start of the decryption table is “25” (assume that the start of the table is set to 0).
That is, the encryption table is an inverse conversion table of the decryption table. Assuming that a function A( ) indicates the conversion using the encryption table and a function B( ) indicates the conversion using the decryption table, the following Equations exist.

a=A(d), d=B(a)

Then, the encryption print image data is decrypted using the generated decryption table in step S4003. In step S4003, the encryption print image data is sequentially read in a byte unit. The read 1-byte data value is an offset from the leading address of the encryption table, and the value of the corresponding address is the print image data.
FIG. 6 is a flowchart of the process in step S4002.
In FIG. 6, the processes in steps S6000 to S6007 are the same as the converting operation in steps S5000 to S6007 on the encryption table. After generating the encryption table, the address value and the table value are interchanged in step S6008 for conversion into the decryption table.
The following Tables 1, 2, and 3 are the tables used or generated in this embodiment.










Random Number Table










x
R(x)














0
88



1
197



2
230



3
139



4
196



5
225



6
114



7
71



8
112



9
61



10
62



11
67



12
92



13
217



14
74



15
127



16
136



17
181



18
150



19
251



20
244



21
209



22
34



23
183



24
160



25
45



26
238



27
179



28
140



29
201



30
250



31
239



32
184



33
165



34
70



35
107



36
36



37
193



38
210



39
39



40
208



41
29



42
158



43
35



44
188



45
185



46
170



47
95



48
232



49
149



50
246



51
219



52
84



53
177



54
130



55
151



56
0



57
13



58
78



59
147



60
236



61
169



62
90



63
207



64
24



65
133



66
166



67
75



68
132



69
161



70
50



71
7



72
48



73
253



74
254



75
3



76
28



77
153



78
10



79
63



80
72



81
117



82
86



83
187



84
180



85
145



86
226



87
119



88
96



89
237



90
174



91
115



92
76



93
137



94
186



95
175



96
120



97
101



98
6



99
43



100
228



101
129



102
146



103
231



104
144



105
221



106
94



107
227



108
124



109
121



110
106



111
31



112
168



113
85



114
182



115
155



116
20



117
113



118
66



119
87



120
192



121
205



122
14



123
83



124
172



125
105



126
26



127
143



128
216



129
69



130
102



131
11



132
68



133
97



134
242



135
199



136
240



137
189



138
190



139
195



140
220



141
89



142
202



143
255



144
8



145
53



146
22



147
123



148
116



149
81



150
162



151
55



152
32



153
173



154
110



155
51



156
12



157
73



158
122



159
111



160
56



161
37



162
198



163
235



164
164



165
65



166
82



167
167



168
80



169
157



170
30



171
163



172
60



173
57



174
42



175
223



176
104



177
21



178
118



179
91



180
212



181
49



182
2



183
23



184
128



185
141



186
206



187
19



188
108



189
41



190
218



191
79



192
152



193
5



194
38



195
203



196
4



197
33



198
178



199
135



200
176



201
125



202
126



203
131



204
156



205
25



206
138



207
191



208
200



209
245



210
214



211
59



212
52



213
17



214
98



215
247



216
224



217
109



218
46



219
243



220
204



221
9



222
58



223
47



224
248



225
229



226
134



227
171



228
100



229
1



230
18



231
103



232
16



233
93



234
222



235
99



236
252



237
249



238
234



239
159



240
40



241
213



242
54



243
27



244
148



245
241



246
194



247
215



248
64



249
77



250
142



251
211



252
44



253
233



254
154



255
15

















TABLE 2







Encryption Table










x
A(x)














0
217



1
197



2
183



3
154



4
165



5
32



6
35



7
246



8
177



9
156



10
207



11
146



12
253



13
88



14
187



15
127



16
136



17
84



18
150



19
138



20
85



21
144



22
83



23
230



24
97



25
12



26
255



27
179



28
173



29
200



30
235



31
94



32
57



33
196



34
70



35
122



36
5



37
0



38
131



39
214



40
208



41
124



42
47



43
114



44
188



45
185



46
27



47
78



48
233



49
52



50
71



51
106



52
181



53
112



54
130



55
198



56
193



57
236



58
95



59
98



60
13



61
169



62
90



63
62



64
24



65
164



66
119



67
75



68
101



69
224



70
227



71
7



72
113



73
92



74
254



75
82



76
189



77
153



78
123



79
46



80
73



81
20



82
167



83
74



84
21



85
80



86
19



87
166



88
96



89
204



90
191



91
66



92
76



93
137



94
171



95
30



96
249



97
132



98
215



99
43



100
228



101
192



102
67



103
231



104
209



105
60



106
239



107
50



108
29



109
248



110
219



111
14



112
168



113
244



114
182



115
42



116
117



117
48



118
115



119
134



120
129



121
172



122
31



123
34



124
205



125
104



126
11



127
143



128
89



129
100



130
55



131
26



132
37



133
160



134
242



135
118



136
240



137
28



138
79



139
195



140
125



141
216



142
202



143
238



144
9



145
212



146
103



147
10



148
116



149
16



150
162



151
102



152
225



153
140



154
110



155
2



156
45



157
72



158
107



159
111



160
56



161
68



162
151



163
250



164
133



165
128



166
3



167
86



168
145



169
252



170
175



171
163



172
221



173
184



174
155



175
206



176
105



177
180



178
199



179
234



180
53



181
49



182
51



183
23



184
65



185
108



186
223



187
226



188
141



189
40



190
203



191
190



192
25



193
36



194
38



195
218



196
4



197
33



198
99



199
54



200
241



201
220



202
15



203
210



204
61



205
152



206
251



207
174



208
201



209
245



210
39



211
59



212
149



213
17



214
147



215
247



216
161



217
109



218
63



219
194



220
237



221
8



222
58



223
158



224
121



225
229



226
87



227
186



228
69



229
64



230
18



231
22



232
81



233
93



234
222



235
178



236
157



237
120



238
91



239
142



240
41



241
213



242
135



243
170



244
148



245
176



246
243



247
6



248
1



249
77



250
159



251
211



252
44



253
232



254
139



255
126

















TABLE 3







Decryption Table










x
B(x)














0
37



1
248



2
155



3
166



4
196



5
36



6
247



7
71



8
221



9
144



10
147



11
126



12
25



13
60



14
111



15
202



16
149



17
213



18
230



19
86



20
81



21
84



22
231



23
183



24
64



25
192



26
131



27
46



28
137



29
108



30
95



31
122



32
5



33
197



34
123



35
6



36
193



37
132



38
194



39
210



40
189



41
240



42
115



43
99



44
252



45
156



46
79



47
42



48
117



49
181



50
107



51
182



52
49



53
180



54
199



55
130



56
160



57
32



58
222



59
211



60
105



61
204



62
63



63
218



64
229



65
184



66
91



67
102



68
161



69
228



70
34



71
50



72
157



73
80



74
83



75
67



76
92



77
249



78
47



79
138



80
85



81
232



82
75



83
22



84
17



85
20



86
167



87
226



88
13



89
128



90
62



91
238



92
73



93
233



94
31



95
58



96
88



97
24



98
59



99
198



100
129



101
68



102
151



103
146



104
125



105
176



106
51



107
158



108
185



109
217



110
154



111
159



112
53



113
72



114
43



115
118



116
148



117
116



118
135



119
66



120
237



121
224



122
35



123
78



124
41



125
140



126
255



127
15



128
165



129
120



130
54



131
38



132
97



133
164



134
119



135
242



136
16



137
93



138
19



139
254



140
153



141
188



142
239



143
127



144
21



145
168



146
11



147
214



148
244



149
212



150
18



151
162



152
205



153
77



154
3



155
174



156
9



157
236



158
223



159
250



160
133



161
216



162
150



163
171



164
65



165
4



166
87



167
82



168
112



169
61



170
243



171
94



172
121



173
28



174
207



175
170



176
245



177
8



178
235



179
27



180
177



181
52



182
114



183
2



184
173



185
45



186
227



187
14



188
44



189
76



190
191



191
90



192
101



193
56



194
219



195
139



196
33



197
1



198
55



199
178



200
29



201
208



202
142



203
190



204
89



205
124



206
175



207
10



208
40



209
104



210
203



211
251



212
145



213
241



214
39



215
98



216
141



217
0



218
195



219
110



220
201



221
172



222
234



223
186



224
69



225
152



226
187



227
70



228
100



229
225



230
23



231
103



232
253



233
48



234
179



235
30



236
57



237
220



238
143



239
106



240
136



241
200



242
134



243
246



244
113



245
209



246
7



247
215



248
109



249
96



250
163



251
206



252
169



253
12



254
74



255
26










The above mentioned Table 1 is an example of the random number table according to this embodiment. The Table 2 is an encryption table when the common key is “15” in this embodiment. The Table 3 is a decryption table when the common key is “15” in this embodiment.
In the above mentioned embodiment, the encryption process and the decryption process are performed by the conversion system using the tables. This system requires a smaller load in performing an operation, thereby preventing the printing speed from being reduced.
Furthermore, according to this embodiment, the recording device manages both print ID and common key. Therefore, when the recording device is connected to a plurality of host computers, the print process can be performed in the transfer order of print control data regardless of the common key issue order.
Other Embodiments
In the above mentioned embodiments, an encryption table is generated by converting a random number table using a common key, but the encryption table can be the common key. Furthermore, the common key can be used as a parameter in the congruential method, and an encryption table can be generated by generating pseudo random numbers.
The encryption table may be generated by conversion using the common key according to not only the congruential method but also an average method. Since a common key of a specified value can be issued in the above mentioned embodiments, the value of an internal timer of the recording device can be used.
An example of the configuration of the image data recording system embodying the present invention is described below by referring to the block diagram shown in FIG. 7.
In FIG. 7, reference numeral 70 denotes an image data processing device; reference numeral 71 denotes an interface; reference numeral 72 denotes an image processing unit; reference numeral 73 denotes a print ID generating unit; reference numeral 74 denotes a print ID storage unit; reference numeral 75 denotes a first transfer unit; reference numeral 76 denotes an encryption unit; reference numeral 77 denotes a print control data generating unit; and reference numeral 78 denotes a second transfer unit.
Furthermore, reference numeral 80 denotes an image data recording device; reference numeral 81 denotes an interface; reference numeral 82 denotes a common key generating unit; reference numeral 83 denotes a management unit; reference numeral 84 denotes a common key issue unit; reference numeral 85 denotes a common key obtaining unit; reference numeral 86 denotes an analyzing unit; reference numeral 87 denotes a decryption unit; and reference numeral 88 denotes a print unit.
As shown in FIG. 7, the image data recording system comprises the image data processing device 70 and the image data recording device 80. Through the interface 71 and the interface 81 respectively provided in the image data processing device 70 and the image data recording device 80, various data and commands are transmitted and received to print the image data input to the image data processing device 70 on the image data recording device 80, and then output.
In FIG. 7, the image processing unit 72 performs the image process including the forgery preventing process on the input image data. The print ID generating unit 73 generates a print ID corresponding to the image data processed by the image processing unit 72 in the forgery preventing process. The generated print ID is stored in the print ID storage unit 74, and transferred by the first transfer unit 75 to the image data recording device 80.
The encryption unit 76 encrypts the image data processed by the image processing unit 72 in the predetermined processes using the common key transmitted from the image data recording device 80. The print control data generating unit 77 generates print control data by converting the print image data encrypted by the encryption unit 76 into a print control command. Then, the generated print control data and the print ID generated by the print ID generating unit 73 and stored in the print ID storage unit 74 are transferred by the second transfer unit 78 to the image data recording device 80.
The common key generating unit 82 generates a common key based on the print ID transferred from the image data processing device 70. Then, the generated common key and the transferred print ID are stored and managed in the memory of the management unit 83.
The common key issue unit 84 transmits the common key generated by the common key generating unit 82 to the image data processing device 70. When the print ID and the print control data are transmitted from the image data processing device 70, the common key obtaining unit 85 obtains a common key corresponding to the print ID from the management unit 83.
The analyzing unit 86 analyzes the command of the above mentioned print data using the common key obtained by the common key obtaining unit 85, and extracts the encrypted print image data. The decryption unit 87 decrypts the print image data extracted by the analyzing unit 86 using the common key obtained by the common key obtaining unit 85. Then, the decrypted print image data is stored in a storage medium (not shown in the attached drawings) by the print unit 88.
Other Embodiments according to the Present Invention
The present invention can be applied to either a system comprising a plurality of appliances (for example, a host computer, an interface appliance, a leader, a printer, etc.) or a device comprising one appliance.
In addition, the present invention further includes an embodiment in which a program code of software for realizing the functions of the above mentioned embodiments are provided for the computer in the device or the system connected to each of the above mentioned devices so that various devices can be operated to realize the functions of the above mentioned embodiments, and the above mentioned devices are operated according to the program stored in the computer (CPU or MPU) of the system or the device.
In this case, the program code of the software realizes the functions of the above mentioned embodiment, and the program code itself and the unit for providing the program code for the computer, for example, a storage medium storing the program code constitute the present invention. The storage medium storing the program code can be, for example, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, CD-ROM, a magnetic tape, a non-volatile memory card, ROM, etc.
In addition, it is needless to say that the program code is included in the embodiment of the present invention not only in the case where the function described in the above description of the embodiment is realized by a computer executing the program code provided thereto, but also in the case the function is realized by the program code cooperating with the OS (operating system) or other application software operating in the computer.
Furthermore, after the provided program code is stored in the memory in a function extension board of a computer or a function extension unit connected to the computer, the CPU, etc. provided in the function extension board or the function extension unit can perform all or part of an actual process at an instruction of the program code to realize the function of the above mentioned embodiment in the process. The present invention can also include the above mentioned case.
As described above, the print control data is encrypted using a common key issued by an image data recording device. Therefore, when the image data processing device generates a recording image by controlling the image data recording device, the image data recording device which has issued the common key is required, thereby effectively preventing a number of unspecified image data recording devices from printing image data, and ensuring that the forgery preventing process is performed by the image data processing device. Thus, the forgery of bills, valuable securities, etc. can be prevented without fail.

## Claims

1. An image data recording device, comprising:
common key generating means for generating a common key based on a print ID transferred from an image data processing device;
management means for managing the common key generated by said common key generating means and the print ID transferred from said image data processing device in pairs;
common key issue means for transmitting the common key generated by said common key generating means to said image data processing device;
common key obtaining means for obtaining the common key corresponding to the print ID from said management means when the print ID and print control data are transmitted from said image data processing device;
analyzing means for analyzing the print control data to extract print image data from the print control data wherein said print image data that has been forgery-preventing-image-processed, encrypted, and converted into a command in the image data processing device;
decryption means for decrypting the encrypted print image data extracted by said analyzing means using a key corresponding to the print ID; and
print means for recording the print image data decrypted by said decryption means on a recording medium,
wherein the print image data has been forgery-preventing-image-processed and encrypted in the image data processing device using the common key received from said image data recording device.

2. The apparatus according to claim 1, wherein said common key generating means generates the common key without regularity independent of a value of the print ID.

3. The apparatus according to claim 1, wherein said decryption means performs a decryption process using a conversion table generated using said key corresponding to the print ID.

4. A method for controlling an image data recording device, comprising the steps of:
generating a common key based on a print ID transferred from an image data processing device;
managing the generated common key and the print ID transferred from the image data processing device in pairs;
transmitting the generated common key to the image data processing device;
obtaining the common key corresponding to the print ID when the print ID and print control data are transmitted from the image data processing device;
analyzing the print control data to extract print image data from the print control data wherein said print image data that has been forgery-preventing-processed, encrypted, and converted into a command in the image data processing device;
decrypting the extracted, encrypted print image data using a key obtained from the print ID; and
recording the decrypted print image data in a storage medium,
wherein the print image data has been forgery-preventing-image-processed and encrypted in the image data processing device using the common key received from the image data recording device.

5. The method according to claim 4, wherein
said common key generating step generates the common key without regularity independent of a value of the print ID.

6. The method according to claim 4, wherein
said decrypting step performs a decryption process using a conversion table generated using the key obtained from the print ID.

7. A program, embodied in a computer-readable medium, for controlling an image data recording system including an image data processing device, said program comprising a plurality of program codes instructing the image data processing system to perform the steps of:
generating a common key based on a print ID transferred from the image data processing device;
managing the generated common key and the print ID transferred from the image data processing device in pairs;
transmitting the generated common key to the image data processing device;
obtaining the common key corresponding to the print ID when the print ID and print control data are transmitted from the image data processing device;
analyzing the print control data to extract print image data from the print control data wherein said print image data that has been forgery-preventing-image-processed, encrypted, and converted into a command in the image data processing device;
decrypting the extracted, encrypted print image data using a key obtained from the print ID; and
recording the decrypted print image data in a storage medium,
wherein the print image data has been forgery-preventing-image-processed and encrypted in the image data processing device using the common key received from the image data recording device.