Registers – Records – Conductive
Reexamination Certificate
2001-03-16
2003-12-23
Lee, Michael G. (Department: 2876)
Registers
Records
Conductive
Reexamination Certificate
active
06666381
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a tamper-resistant information processing device. It is particularly very effective when applied to cards such as the IC card.
An IC card is a device used for such purposes as to hold personal information which should not be altered without permission, to encrypt data by use of a cryptographic key (which is secret information), or to decrypt ciphertext. The IC card does not have any power source therein, but when it is inserted in a,reader/writer for IC cards, the IC card is supplied with power and becomes operable. When the IC card is in the operable state, it receives a command transmitted from the reader/writer, and carries out a process such as transfer of data according to the command.
FIG. 1
shows a basic conceptual configuration of an IC card in which an IC card chip
102
is mounted on a card
101
. As shown in the figure, an IC card generally has disposed thereon a supply voltage terminal Vcc, a ground terminal GND, a reset terminal RST, an input/output terminal I/O, and a clock terminal CLK. The positions of these terminals are specified in ISO International Standard 7816. The IC card receives power from the reader/writer and exchanges data with the reader/writer. Such communication between the IC card and the reader/writer is described, for example, on page 41 of a book entitled “SMARTCARD HANDBOOK” authored by W. Rankl and W. Effing and published by John Wiley & Sons in 1997.
The configuration of the semiconductor chip mounted on an IC card is basically the same as that of the ordinary microcomputer.
FIG. 2
is a block diagram showing the basic configuration of the semiconductor chip mounted on an IC card. As shown in
FIG. 2
, the semiconductor chip for cards has a central processing unit (CPU)
201
, a memory device
204
, an input/output (I/O) port
207
, and coprocessor
202
. Some systems do not employ the coprocessor. The CPU
201
is a device for performing logic and arithmetic operations, while the memory device
204
stores programs and data. The input/output port is a device for communicating with the reader/writer. The coprocessor performs cryptographic processing itself or operations necessary for cryptographic processing at high speed. For example, types of coprocessors employed include a particular operation device for performing a residue operation for RSA and a cryptographic device for performing a rounding process for DES. There are many IC card processors which do not have any coprocessors. A data bus
203
is a bus connecting one device to another.
The memory device
204
includes such memories as a ROM (Read Only Memory), a RAM (Random Access Memory), and an EEPROM (Electric Erasable Programmable Read Only Memory). Information stored in a ROM cannot be altered, and therefore ROMs are used to store mainly programs. Information stored in a RAM, on the other hand, can be freely rewritten, but the stored information disappears once the power supply is interrupted. That is, since the power supply to an IC card is interrupted when the IC card is removed from the reader/writer, the RAM can no longer hold its contents after that. The EEPROM, in contrast, can continue holding its contents even if its power supply is interrupted. Therefore, the EEPROM is used for storing data which it is necessary to rewrite, and hold even when the IC card is removed from the reader/writer. For example, the number of the remaining call units of a prepaid telephone card is rewritten each time the card is used, and the call unit data must continue to be held even after the card is removed from the reader/writer. This is why the call unit data of the prepaid card is held in an EEPROM.
SUMMARY OF THE INVENTION
The present invention provides a tamper-resistant information device for use with cards having high security.
Specifically, an object of an embodiment according to the present invention is to reduce the correlation between the contents of data processing operations and consumed currents in a card component such as the IC card chip. Reducing the correlation between the contents of the data processing operations and the consumed currents in the chip makes it difficult to estimate what is being processed in the IC card chip and how, and to derive the cryptographic key from the observed waveforms of the consumed currents. Thus, the present invention provides cards with high security.
Since IC cards have an IC card chip mounted thereon which is capable of holding programs and important information, they are used to store important information or internally perform cryptographic processing. It has been conventionally considered that the difficulty of breaking a code stored in an IC card is the same as the difficulty of deriving its encryption algorithm. However, it is pointed out that the details of the encryption processing operation and the cryptographic key may be derived by observing and analyzing the current consumed during the encryption process in the IC card, which may be easier than deriving of the encryption algorithm. The consumed current is obtained by measuring the current supplied from the reader/writer to the IC card. The details of this attack and its danger are described, for example, on page 263 (8.5.1.1 Passive Protective Mechanisms) of the book “SMARTCARD HANDBOOK” authored by W. Rankl & W. Effing and published by John Wiley & Sons. The following specifically describes the attack. Each CMOS constituting an IC card chip consumes a current when its output state switches from “1” to “0” or vice versa. Particularly, a large current flows through the data bus
203
when the bus value changes from 1 to 0 or vice versa. The current of the bus driver, the wiring employed, and the capacitance associated with transistors connected to the wiring cause such a current to flow. Therefore, it is possible to identify what is operating in the IC card chip by observing the consumed current.
FIG. 3
shows single-cycle waveforms of currents consumed in an IC card chip. The current waveforms are different from one another as indicated by reference numerals
301
and
302
, depending on the processed data. More specifically, such a difference occurs depending on data flowing through the bus
203
and data processed in the central processing unit
201
.
The coprocessor
202
can perform, for example, 512-bit modular multiplication in parallel with the CPU processing. This means that it is possible to observe the waveform of a current different from that in the CPU for a long time. Therefore, the number of operations performed by the coprocessor can be measured by observing its particular current waveform. If the number of operations performed by the coprocessor has some relationship to the cryptographic key, it might be possible to derive the key from the number of the operations.
Further, if which operation is performed or what is operated by the coprocessor changes depending on the cryptographic key, the dependency might be found by observing the corresponding change in the consumed current, and the cryptographic key might be derived.
Similarly, in the CPU, the influence of each bit value of the cryptographic key on processed data might be obtained by changing the data a plurality of times and observing the corresponding change in each consumed current. It might be possible to derive the cryptographic key by statistically processing the waveforms of these consumed currents.
The ideas on which embodiments of the present invention are based include: dividing a process performed in an IC card so that attackers cannot specify the process as a whole; and inserting a dummy process. These methods make it difficult to identify the original process and derive the cryptographic key from the waveforms of the consumed currents.
A tamper-resistant device as represented by the IC card chip is regarded as an information processing device having one or more data processing means which each comprise: a program storage unit for storing a program; a memory unit having a data storage unit for storing data; and a central processing un
Endo Takashi
Kaminaga Masahiro
Ohki Masaru
Watanabe Takashi
Antonelli, Terry, Stout & Krause, LLP
Franklin Jamara A.
Lee Michael G.
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