Cryptography – Particular algorithmic function encoding
Reexamination Certificate
2000-03-14
2002-06-18
Barron, Jr., Gilberto (Department: 2132)
Cryptography
Particular algorithmic function encoding
C380S044000, C380S268000, C713S174000, C708S491000
Reexamination Certificate
active
06408075
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an information processing equipment, and more particularly to a tamper resistance device such as an IC card (smart cart) having high security.
An IC card is mainly used for storing information in a manner so as not to be altered by a third party or for enciphering data or deciphering a cipher text by using a cipher key which is kept in secret. Since the IC card is not provided with a power source, it becomes operable when it is inserted into a reader-writer. The IC card receives a command from the reader-writer to execute data transfer. A general explanation of IC cards is given, for example, in “IC Card” by Jyunichi Mizusawa, by Ohm Publication Co., compiled by the Institute of Electronics, Information and Communication Engineers.
As shown in
FIG. 1
, an IC card has the structure that an IC card chip
102
is fabricated on a card
101
. A general IC card has contacts via which a power is supplied from a reader-writer and data is transferred.
The structure of an IC card chip is basically the same as that of a microcomputer. As shown in
FIG. 2
, the IC card chip includes a central processor
201
, a storage memory
204
, an input/output port
207
, and a co-processor
202
. The central processor
201
executes logical and arithmetic calculations, and the storage memory
204
stores programs and data. The input/output port
207
communicates with a reader-writer. The co-processor is a special calculation device for executing modular calculations, and is used for calculations in anti-symmetric RSA or the like. Many of IC card processors have no co-processor. A data bus
203
interconnects components of the IC card.
The storage memory
204
includes a ROM (Read Only Memory), a RAM (Random Access Memory), an EEPROM (Electrically Erasable Programmable Read Only Memory) and the like. ROM is a memory whose contents cannot be rewritten freely and stores mainly programs. RAM is a memory whose contents can be rewritten freely and are erased if a power supply is intercepted. When the IC card is disconnected from the reader-writer, a supply of the power is intercepted so that the contents of RAM cannot be retained. EEPROM is a memory whose contents can be retained even if a supply of the power is intercepted. Therefore, EEPROM is used for storing data which may be rewritten and can be retained even if the IC card is disconnected from the reader-writer. For example, the number of prepaid times of a prepaid card is stored in EEPROM because it is updated each time the card is used and the contents thereof are required to be retained even if the card is disconnected from the reader-writer.
An IC card is used for storing programs and important information in the IC card chip to execute a cipher process. It has been long considered that the difficulty in decryption of a cipher process executed in the IC card is the same as decryption of a ciphering algorithm. However, it has been suggested recently that there is a possibility of presuming the contents of a cipher process and a cipher key by measuring and analyzing a consumption current while the cipher process is executed, easier than decryption of a cipher algorithm. The consumption current can be monitored by measuring the current supplied from the reader-writer. This possible danger is described in “Smart Card Handbook”, by W. Rankl & W. Effing, John Wiley & Sons, paragraph 8.5.1.1 “Passive protective mechanisms”, at p. 263.
CMOSs constituting an IC card chip consume current when an output state changes from “1” to “0” or vice versa. The data bus
203
in particular flows a large current when its state changes from “1” to “0” or vice versa, because it has a large electrical capacitance. This suggests a possibility of presuming the operation state in the IC card chip by monitoring the consumption current.
FIG. 5
shows wave shapes of consumption current during one cycle of an IC card chip. Depending upon processed data, the current wave shape becomes different as indicated at
501
and
502
. This difference is generated depending upon data on the bus
203
and data processed by the central processor
201
.
The co-processor
202
can execute a modular calculation of a long train of bits, e.g., 512 bits, in parallel with the central processor
201
. Therefore, it is possible to monitor the wave shape of a consumption current different from that of the central processing unit
201
during a long period of time. By monitoring its distinctive wave shape, the number of operations of the co-processor can be easily measured. If there is any correlation between the number of operations of the co-processor and a cipher key, it is possible to presume the cipher key from the number of operations of the co-processor.
If the calculation contents of the co-processor have any shift specific to the cipher key, there is also a possibility of presuming a cipher key by identifying the shift from the consumption current. Such possibilities are also applicable to the central processor. Since the value of bits of a cipher key is fixed, an influence of the value of bits of the cipher key may possibly be monitored by monitoring the consumption current by changing data to be processed.
SUMMARY OF THE INVENTION
The main issue to be solved by the invention is to reduce the correlation or dependency between data processing and its consumption current of an IC card chip. If the correlation between data processing and its consumption current is reduced, it becomes difficult to presume the operation of the IC card chip and a cipher key from the monitored wave shape of a consumption current. The invention pays attention to that a presumption of the operation and cipher key from the wave shape of a consumption current can be made difficult by randomizing the process sequence in an IC card chip and inserting a dummy process.
A tamper resistance device, typically an IC card, can be considered as an information processing equipment having a program storage unit for storing a program and a data storage unit for storing data and a central processing unit for executing a predetermined process in accordance with the program to process the data, the program including one or more data process units each having a process instruction for giving an execution instruction to the central processing unit. In this invention, as one method of reducing the dependency of consumption current of an IC chip upon data process, normal input data and its bit inverted data are processed. By using the normal input data and its bit inverted data by the same instruction, the number of transitions of the data on a data bus, from “0” to “1” or vice versa, can be made constant. The data transition on the data bus consumes large current. By making the number of transitions on the data bus constant, the number of current consumptions is made constant so that the dependency of consumption current upon data process can be reduced.
As an alternative method of processing normal data and bit inverted data in the same manner, a routine of processing the bit inverted data by an instruction same as the normal instruction, if the same routine cannot process both the normal data and bit inverted data. Normal input data and bit inverted data are always generated for the data once processed in order to process the normal data and bit inverted data in the same manner.
As an alternative method of reducing the dependency of consumption current upon data process, if there are repetitive processes as many as the number of data sets to be processed, the data is not processed in the predetermined order but the process order is changed randomly. Another method is to add a dummy process which does not influence the corresponding process of a program, so that what operation of the equipment is executed at which place cannot be known. A combination of dummy processes and random execution of repetitive processes is effective for reducing the dependency of consumption current upon data process.
Use of both the normal data and bit inverted data and a combination of dummy p
Fukuzawa Yasuko
Kaminaga Masahiro
Ohki Masaru
Okuhara Susumu
Barron Jr. Gilberto
Callahan Paul E.
Mattingly Stanger & Malur, P.C.
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