JPH02300834A - Semiconductor device - Google Patents

Abstract

PURPOSE:To surely protect ROM data from outside observation by complicating a cryptographic rule by performing a logical operation setting both an address and data as input, and outputting a computed result as enciphered data. CONSTITUTION:The semiconductor device is comprised by providing a data conversion circuit 4 which receives the address to a memory device 3 and the data read out of the memory device 3 according to the address, and executes the logical operation setting those address and data as input, and outputs the computed result to the outside. And the cryptographic rule is set by a logical operation equation setting the address and the data as input. Therefore, the cryptographic rule complicated according to the number of bits of the address or that of the data can be realized. Thereby, the cryptographic rule can be complicated, and the ROM data can be surely detected from the outside observation.

Description

[Detailed Description of the Invention] [Summary] With regard to semiconductor devices equipped with storage devices such as ROM, data is written in advance in order to complicate encryption rules and reliably protect ROM data from external observation. In a semiconductor device equipped with a storage device, a semiconductor device receives an address to the storage device and data read from the storage device according to the address, and executes a logical operation using these addresses and data as input (outputs the -1 operation result to the outside). It is configured by providing a data conversion circuit to do this.

[Field of Industrial Application] The present invention relates to a semiconductor device, and in particular to a semiconductor device equipped with a storage device such as a ROM in which data such as firmware is written in advance, and which makes it difficult to decode the ROM data from the outside. Related to semiconductor devices.

-a, in data processing devices such as microprocessors,
Various programs and data (for example, by masking)
A written ROM is provided.

These programs are responsible for an important part of processing functions and often contain advanced know-how.
Therefore, there is a need for a lock built into a microprocessor or the like to be difficult to read from the outside.

[Conventional technology]

Examples of methods to make it difficult to externally observe ROM data include appropriately changing the combination of external terminals for ROM data (first conventional example), or inverting some bits of ROM data. A device (second conventional example) is known in which the output is performed using the same method.

In other words, according to the first conventional example, the bit order of ROM data is changed depending on the combination of external terminals, so if you do not know this combination, you cannot select the correct ROM.
Unable to know the data. Further, according to the second conventional example, since some bits are inverted and output, correct ROM data cannot be known unless the position of the inverted bits is known.

According to such first and second conventional examples, the ROM
The person conducting the data read test is naturally in a position to know the combination of external terminals and the position of the inverted bit.
The test can be conducted without any problems.

[Problems to be Solved by the Invention] However, in the first and second conventional examples, the pin I position of the ROM data is swapped, or some bits are inverted. Since relatively simple encryption rules such as the above were adopted, there was a risk that the encryption rules could be discovered, and the ROM data was not sufficiently protected from external observation.

The present invention was made in view of these problems, and
The purpose is to complicate the encryption rules and reliably protect ROM data from external observation.

[Means to solve the problem]

In order to achieve the second object, the semiconductor circuit device according to the present invention is a semiconductor device equipped with a memory device in which data is written in advance, an address to the memory device and an address from the memory device according to the address. It is configured by providing a data conversion circuit that receives read data, executes logical operations using these addresses and data as input, and outputs the operation results to the outside.

[Effect]

In the present invention, encryption rules are set using logical expressions that take addresses and data as inputs. Therefore, it is possible to have encryption rules that are more complex than the number of address bits and data bits.

〔Example〕

Hereinafter, the present invention will be explained based on the drawings.

1 to 3 are diagrams showing an embodiment of a semiconductor device according to the present invention.

In FIG. 1, 1 is an LSI chip (or package), 2 is a CP (), and 3 is a ROM (storage means).
, 4 is a data conversion circuit, 80 to A7 are address signals, D0 to D, 1 is data output from ROM3, ○
D0 to OD are encrypted data output from the data conversion circuit 4.

FIG. 2 is a functional block diagram of the data conversion circuit 4. In this figure, 80 to A1 are input to the OR circuit 4a and the AND circuit 4b, and the same <D.

~D, are input to the OR circuit 4a and the AND circuit 4b. The OR circuit 4a has A0 to An and D0 to
Each bit pair of Dfi (A O and Do, A1, etc.)
...A, , and Dn), and the OR logic output is OR, ~OR.

(Incidentally, OR is the OR logical result of Ao and Do). Further, the AND circuit 4b has 80 to A.

Andri. -D, , takes AND logic for each bit bear, and the AND logic output is AN 00 to AND
It is expressed as fi (by the way, the AND logic result of AND, iiA, and Tori).

These OR, ~OR, and ANDo~AND7 are input to the selection circuit 4c, and the selection circuit 4c receives the selection signal SEL.
0RO-ORrl or ANDo -AND according to
, select one of the logical outputs, and encrypt data OD.
Output as o~OD. In addition, the above A0 to A, 1 and SEL can be controlled from outside Sentsubu 1.
Alternatively, the status can be monitored from the outside.

In such a configuration, OD6 to OD are SE I-
According to ORo ~ ORn-A N Do”-A
N D 11-〇R0~ORn→ANDO~AND, →
Manipulate... Here, OR, ~OR, and A N D .

~AND is expressed by the following logical operation formulas (1) and (2).

OR, = A, +p, ...... ■ AND, -A, xD, ...... ■ However, i: bit number 0 to n, that is, Di at any time (read data of ROM3 ) is observed outside the chip, the OD corresponding to D is OR or AND.

This means that the data has been converted according to the above formula 〇 or the encryption rule of the above formula 〇.

On the other hand, when testing the data in ROM3, the person executing the test is in a position to know the selection order of the above equations O.D.

It is easy to decipher and there is no problem in running the test.

Here, an example embodying the data conversion circuit 4 in FIG. 2 is as follows.
This will be explained based on FIG. Note that for the sake of simplicity, a 3-bit configuration is used.

In FIG. 3, three or gates G, -G.

constitutes the logical sum circuit 4a, and the three ant games)
04 to G constitute an AND circuit 4b, which further includes an inverter gate G1 and an AND gate G.

~0. and ORGATE G14-G1. is the selection circuit 4c
It consists of

Table 1 below shows the truth value of one bit.

(This page, blank space below) Table 1 However, ×: Undefined value This truth table is a cipher deciphering table (however, 1 pit 1 minute)
Can be used as That is, now when A is set to 0, OD is 5EL-L" and 01SEL-"TI
” becomes 1, then the deciphered value of D is 1
It can be seen from this truth table that The truth table shown in Table 2 below (however, in the case of the 3-bit configuration shown in FIG. 3) is used as the actual decoding table.

(This page, blank space below) In Table 2, now A, ,A, ,A, is (001)
When , ODZ , OD, , OD. But 5EL
='“L’” (001L 5EL-“’IN”
If it becomes (111), then 1]2,D at this time
It can be seen that the deciphered values of t and Do are (111]. Or, if 00..00..00. does not become as above, it is known that there is a failure. Therefore, knowing such a truth table Since only a person in a position can decode the contents of the ROM 3 from the outside, the data in the ROM 3 can be reliably protected. Also, the test can be executed without any problems.

It should be noted that the present invention is not limited to the above-mentioned embodiments.In short, the present invention is a circuit configuration that can perform logical operations on A, ~A, and D0~D and output the result, and that the logical operation It is sufficient if it has a truth table (used as a decoding table) representing .

〔Effect of the invention〕

According to the present invention, since a logical operation is performed using both an address and data as input, and the result of the operation is output as encrypted data, it is possible to complicate the encryption rule, and it is possible to Data can be reliably protected.

[Brief explanation of drawings]

1 to 3 are diagrams showing one embodiment of a semiconductor device according to the present invention, in which FIG. 1 is a configuration diagram thereof, FIG. 2 is a functional block diagram of its data conversion circuit, and FIG. 3 is its data conversion circuit. FIG. 2 is a specific circuit diagram of an example of a circuit. 3...ROM (storage device), 4...Data conversion circuit. Figure 1: Configuration diagram of the embodiment

Claims (1)

[Scope of Claims] In a semiconductor device equipped with a memory device in which data is written in advance, a logic device that receives an address to the memory device and data read from the memory device according to the address, and receives these addresses and data as input. A semiconductor device characterized by being provided with a data conversion circuit that executes arithmetic operations and outputs the arithmetic results to the outside.