US 8,479,018 B2 · System for making program difficult to read, device for making program difficult to read, and method for making program difficult to read

Abstract

An obfuscating apparatus creates a table for inputting the same number of arguments for multiplying and squaring operations, and sets the output values of the table so that the outputs may depend on the arguments. With regard to the squaring operations, there are added and tabulated adding operations using the arguments necessary only for the multiplications, so that the number of arguments is equal to that of the multiplication operations. The outputs depend on all the arguments, so that the presence or absence of the added arguments is unknown unlike the case in which dummy arguments that are not processed are added.

A program obfuscating apparatus which obfuscates an information security program instructing execution of a security operation that processes target information securely and reliably with use of key information, the program obfuscating apparatus comprising:

a non-transitory memory device that stores a program;
and
a processing device that executes the program and causes the program obfuscating apparatus to operate as:
an acquisition unit that acquires the information security program in which a plurality of basic operations are placed in an order determined by the key information such that an operation result of the plurality of basic operations is equivalent to an operation result of the security operation, the plurality of basic operations being one or more first basic operations and one or more second basic operations, each of the first basic operations requiring a plurality of inputs, and each of the second basic operations requiring only part of the plurality of inputs;
a transformation unit that places an input dependent conversion operation and an input dependent inverse conversion operation before and after each of the second basic operations, respectively, the input dependent conversion operation depending on, among the plurality of inputs, one or more inputs unrequired for the second basic operation, and the input dependent inverse conversion operation being an inverse conversion of the input dependent conversion operation;
a table generating unit that, for each of the second basic operations, (i) generates a table which yields an operation result equivalent to an operation result of a set of operations including the input dependent conversion operation placed immediately before the second basic operation, the second basic operation, and the input dependent inverse conversion operation placed immediately after the second basic operation, and (ii) generates a reference instruction to refer to the table;
and
an output unit that outputs an obfuscated program including the generated tables and the generated reference instructions, wherein
each of the second basic operations is a squaring operation,
for each squaring operation included in the information security program, the transformation unit places an input value conversion operation and an inverse thereof, each depending on one or more inputs unrequired for the squaring operation, before and after each of the squaring operations, and
the table generating unit generates, for each of the squaring operations, a table which yields an operation result equivalent to an operation result of a set of operations including the input dependent conversion operation, the squaring operation, and the input dependent inverse conversion operation, wherein
the transformation unit further, with respect to each of the first basic operations, (a) places an input dependent conversion operation before the first basic operation, (b) places an input dependent inverse conversion operation after the first basic operation, or (c) places an input dependent conversion operation and an input dependent inverse conversion operation before and after the first basic operations, respectively, the input dependent conversion operation depending on the inputs required for the first basic operation, and the input dependent inverse conversion operation being an inverse conversion of the input dependent conversion operation which depends on the inputs required for the first basic operation, and
each input dependent conversion operation is a subtraction operation, and each input dependent inverse conversion operation is an addition operation, wherein
the transformation unit further places a first conversion operation and a second conversion operation immediately before each of the plurality of basic operations except for before a basic operation placed first in the information security program, the first conversion operation applying a first conversion to an operation result of a basic operation immediately preceding the basic operation, and the second conversion operation applying a second conversion to an operation result of the first conversion operation, the second conversion being an inverse conversion of the first conversion,
the table generating unit further (i) generates a first table which yields an operation result equivalent to an operation result of a set of operations including the basic operation placed first in the information security program and the first conversion operation placed immediately thereafter, and (ii) generates a reference instruction to refer to the first table,
for each of the plurality of basic operations except for the basic operation placed first and a basic operation placed last in the information security program, (iii) generates a second table which yields an operation result equivalent to a set of operations including the second conversion operation and the first conversion operation in addition to the subtraction operation placed immediately before the basic operation, the basic operation, and the addition operation placed immediately thereafter, and (iv) generates a reference instruction to refer to the second table, and
(v) generates a third table which yields an operation result equivalent to a set of operations including the basic operation placed last in the information security program and a second conversion operation placed immediately before the basic operation, and (vi) generates a reference instruction to refer to the third table, and
the output unit outputs the obfuscated program including the generated first, second, and third tables and all generated reference instructions, and
wherein the transformation unit (i) decomposes the basic operations, the subtraction operations, the addition operations, the first conversion operations, and the second conversion operations placed in the information security program into a plurality of digit operations, and (ii) places the generated digit operations within the security information program,
the table generating unit
(i) generates a first digit operation table which yields an operation result equivalent to an operation result of digit operations among the generated digit operations such that the operation result of the first digit operation table is equivalent to the operation result of the set of operations including the basic operation placed first in the information security program and the first conversion operation placed immediately thereafter, and (ii) generates a digit operation reference instruction to refer to the first digit operation table,
for each of the plurality of basic operations except for the basic operation placed first and the basic operation placed last in the information security program, (iii) generates a second digit operation table which yields an operation result equivalent to an operation result of digit operations among the generated digit operations such that the operation result of the second digit operation table is equivalent to the operation result of the set of operations including the subtraction operation placed immediately before the basic operation, the basic operation, the addition operation placed immediately thereafter, the second conversion operation, and the first conversion operation, and (iv) generates a digit operation reference instruction to refer to the second digit operation table,
(v) generates a third digit operation table which yields an operation result equivalent to an operation result of digit operations among the generated digit operations such that the operation result of the third digit operation table is equivalent to the operation result of the set of operations including the basic operation placed last in the information security program and the second conversion operation placed immediately therebefore, and (vi) generates a digit operation reference instruction to refer to the third digit operation table, and
the output unit outputs the obfuscated program including the generated first, second, and third digit operation tables and all generated digit operation table reference instructions.

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System for making program difficult to read, device for making program difficult to read, and method for making program difficult to read

Life of this patent

System for making program difficult to read, device for making program difficult to read, and method for making program difficult to read

Life of this patent

Abstract

Claims11