BACKGROUND

1. Field

The disclosure relates to an apparatus for performing a rebooting method for an approximately encrypted encryption effectively, and a method thereof.

2. Description of Related Art

As communication technologies are being developed, and distribution of electronic apparatuses are becoming active, continuous efforts for maintaining communication security among electronic apparatuses are being made. Accordingly, in most communication environments, encryption/decryption technologies are being used.

When a message encrypted by an encryption technology is transmitted to a counterpart, the counterpart has to perform decryption to use the message. In this case, waste of resources and time occurs in the process that the counterpart decrypts the encrypted data. Also, there is a problem that, in case hacking by a third party occurs while the counterpart temporarily decrypted the message for an operation, the message can be easily leaked to the third party.

For overcoming such a problem, a homomorphic encryption method is being researched. According to homomorphic encryption, even if an operation is performed in an encryption itself without decrypting encrypted information, the same result as a value which is a result of performing an operation for a plain text and encrypting the text can be achieved. Accordingly, various types of operations can be performed while an encryption is not decrypted.

However, as an operation proceeds, q in a homomorphic encryption is reduced, and thus it becomes impossible to proceed with the operation anymore. For preventing this, a rebooting method is being applied.

However, a conventional rebooting method requires a large amount of calculation or the accuracy of calculation is low. Accordingly, there is a demand for a rebooting method which can reduce the amount of calculation, and at the same time, of which accuracy of calculation is high.

SUMMARY

Accordingly, the disclosure was devised for overcoming the aforementioned problem, and the purpose of the disclosure is in providing an apparatus for performing a rebooting operation for an approximately encrypted encryption effectively, and a method thereof.

The disclosure is for achieving the aforementioned purpose, and a method for processing a homomorphic encryption according to an embodiment of the disclosure includes the steps of linearly transforming a homomorphic encryption for an approximate message including an error, performing an approximate modulus operation for the linearly transformed homomorphic encryption by using a multi-degree polynomial set such that input values within a predetermined range are approximate to an integer point, and linearly transforming the homomorphic encryption which was approximately modulus operated into a form of encryption.

In this case, the multi-degree polynomial may be a polynomial having a degree among any one of a 7th degree to an 80th degree, and the predetermined range may be from −12 to 12.

Meanwhile, in the step of performing an approximate modulus operation, a double-angle number of times and a multi-degree polynomial corresponding to the double-angle number of times may be set, and an approximate modulus operation may be performed by operating the linearly transformed homomorphic encryption as many times as the set double-angle number of times by using the set multi-degree polynomial.

Meanwhile, the step of linearly transforming a homomorphic encryption may include the steps of converting the homomorphic encryption into a form of polynomial, and applying the converted homomorphic encryption to a predefined matrix.

In this case, in the applying step, the predefined matrix may be decomposed into a plurality of block diagonal matrices wherein there is a value in a diagonal component and the other values are 0, and the homomorphic encryption may be applied sequentially to the plurality of block diagonal matrices.

In this case, in the applying step, the homomorphic encryption may be applied to the plurality of block diagonal matrices in units of two continuous matrices.

Meanwhile, an operation apparatus according to an embodiment of the disclosure may include a memory storing a homomorphic encryption for an approximate message including an error, and a processor performing an operation for the homomorphic encryption. The processor may linearly transform the homomorphic encryption for an approximate message including an error, perform an approximate modulus operation for the linearly transformed homomorphic encryption by using a multi-degree polynomial set such that input values within a predetermined range are approximate to an integer point, and linearly transform the homomorphic encryption which was approximately modulus operated into a form of encryption.

In this case, the multi-degree polynomial may be a polynomial having a degree among any one of a 7th degree to an 80th degree, and the predetermined range may be from −12 to 12.

Meanwhile, the processor may set a double-angle number of times and a multi-degree polynomial corresponding to the double-angle number of times, and perform an approximate modulus operation by operating the linearly transformed homomorphic encryption as many times as the set double-angle number of times by using the set multi-degree polynomial.

Meanwhile, the processor may convert the homomorphic encryption into a form of polynomial, and linearly transform the homomorphic encryption by applying the converted homomorphic encryption to a predefined matrix.

In this case, the processor may decompose the predefined matrix into a plurality of block diagonal matrices wherein there is a value in a diagonal component and the other values are 0, and linearly transform the homomorphic encryption by applying the homomorphic encryption sequentially to the plurality of block diagonal matrices.

Meanwhile, the processor may linearly transform the homomorphic encryption by applying the homomorphic encryption to the plurality of block diagonal matrices in units of two continuous matrices.

According to the aforementioned various embodiments of the disclosure, as an approximate polynomial optimized for homomorphic encryptions is used, it is possible to perform a modulus operation faster and with high accuracy. Also, as linear transformation is performed by using a plurality of block diagonal matrices, it is possible to operate with low operation complexity, and accordingly, a faster operation becomes possible.

