Scenario-based encryption device and operating method thereof

1. An encryption device, comprising:

a parameter generating circuit configured to generate an encryption parameter including a number of initial valid bits based on an operation scenario;

an encryption circuit configured to generate a cipher text by encrypting a plain text received from the outside, based on the encryption parameter;

an operation circuit configured to generate a final cipher text by performing a plurality of operations on the cipher text according to the operation scenario and to tag, to the final cipher text, history information of the operations performed on the final cipher text; and

a decryption circuit configured to generate a decrypted plain text by decrypting the final cipher text and to output a number of reliable bits of the decrypted plain text based on the history information.

2. The encryption device of claim 1 , wherein the parameter generating circuit is further configured to determine the number of initial valid bits based on a number of multiplication operations included in the operation scenario and to generate the encryption parameter including the number of initial valid bits.

3. The encryption device of claim 2 , wherein the encryption parameter includes a total length of the cipher text and a number of error bits included in the cipher text, and

the parameter generating circuit is further configured to determine the total length of the cipher text and the number of error bits based on a security level received from the outside.

4. The encryption device of claim 3 , wherein the encryption parameter includes a number of removal bits to be removed from the cipher text after the plurality of operations are performed, and

the parameter generating circuit is further configured to determine, as the number of removal bits, a value obtained by dividing the total length of the cipher text by the number of multiplication operations.

5. The encryption device of claim 4 , wherein the parameter generating circuit is further configured to determine, as the number of initial valid bits, a difference between the number of removal bits and the number of error bits.

6. The encryption device of claim 5 , wherein the operation circuit is further configured to perform, on the cipher text, an approximation operation included in the operation scenario, and

the parameter generating circuit is further configured to compare a number of approximate accuracy bits of the cipher text according to the approximation operation to a number of final valid bits of the cipher text, which is expected when a multiplication operation is performed, and to determine the number of initial valid bits of the cipher text according to a result of comparing the number of approximate accuracy bits of the cipher text to the number of final valid bits of the cipher text.

7. The encryption device of claim 6 , wherein the parameter generating circuit is further configured to determine the number of initial valid bits so that the number of approximate accuracy bits is identical to the number of final valid bits, when the number of approximate accuracy bits is different from the number of final valid bits.

8. The encryption device of claim 6 , wherein the operation circuit is further configured to change the approximate accuracy bits by determining a highest order of an approximating polynomial to be used for the approximation operation so that the number of approximate accuracy bits is identical to the number of final valid bits, when the number of approximate accuracy bits is different from the number of final valid bits.

9. The encryption device of claim 7 , wherein the operation circuit is further configured to tag, to the cipher text, history information of operations performed on the cipher text while the plurality of operations included in the operation scenario are performed on the cipher text.

10. An operating method of an encryption device, the method comprising:

generating an encryption parameter including a number of initial valid bits based on an operation scenario of a homomorphic operation;

generating a cipher text by encrypting a plain text received from the outside, based on the encryption parameter;

generating a final cipher text by performing a plurality of homomorphic operations on initial cipher text according to the operation scenario; and

outputting a decrypted plain text by decrypting the final cipher text,

wherein the initial valid bits are valid bits included in the cipher text before the plurality of homomorphic operations are performed, and

wherein the operation scenario includes the plurality of homomorphic operations to be performed on the cipher text.

11. The method of claim 10 , wherein the generating of the encryption parameter comprises:

counting a number of multiplication operations included in the operation scenario; and

determining the number of initial valid bits based on the number of multiplication operations counted in the operation scenario.

12. The method of claim 10 , wherein the generating of the encryption parameter comprises:

obtaining a number of approximate accuracy bits by an approximation operation included in the operation scenario;

comparing the number of approximate accuracy bits of the cipher text to a number of final valid bits of the cipher text, which is expected when a multiplication operation included in the operation scenario is performed; and

determining the number of initial valid bits according to a result of comparing the number of approximate accuracy bits of the cipher text to the number of final valid bits of the cipher text.

13. The method of claim 12 , wherein the determining of the number of initial valid bits comprises

determining the number of initial valid bits so that the number of approximate accuracy bits is identical to the number of final valid bits, based on a result of comparing the number of approximate accuracy bits to the number of final valid bits which indicates that the number of approximate accuracy bits is different from the number of final valid bits.

14. The method of claim 12 , wherein the generating of the final cipher text comprises determining a highest order of an approximating polynomial to be used for the approximation operation so that the number of approximate accuracy bits is identical to the number of final valid bits, based on a result of comparing the number of approximate accuracy bits to the number of final valid bits which indicates that the number of approximate accuracy bits is different from the number of final valid bits.

15. The method of claim 10 , further comprising tagging, to the cipher text, history information of operations performed on the cipher text while the plurality of homomorphic operations included in the operation scenario are performed on the cipher text.

16. The method of claim 15 , further comprising:

identifying a number of reliable bits in the decrypted plain text based on the history information of operations; and

and outputting the number of reliable bits identified in the identifying,

wherein the history information of operations includes a number of multiplication operations performed on the cipher text or approximate accuracy bits of an approximation operation performed on the cipher text.

17. A storage controller, comprising:

a parameter generating circuit configured to generate an encryption parameter including a number of initial valid bits based on an operation scenario of a homomorphic operation and output the encryption parameter to a host; and

an operation circuit configured to receive, from the host, a cipher text encrypted according to the encryption parameter, generate a final cipher text by performing at least one homomorphic operation on the cipher text according to the operation scenario, and output the final cipher text to the host,

wherein the initial valid bits are valid bits included in the cipher text before the at least one homomorphic operation is or are performed, and

wherein the operation scenario includes the at least one homomorphic operation to be performed on the cipher text.

18. The storage controller of claim 17 , wherein the parameter generating circuit is further configured to determine the number of initial valid bits based on a number of multiplication operations included in the operation scenario.

19. The storage controller of claim 17 , wherein the parameter generating circuit is further configured to compare a number of approximate accuracy bits of the cipher text according to an approximation operation included in the operation scenario and a number of final valid bits of the cipher text, which is expected when a multiplication operation included in the operation scenario is performed, and determine the number of initial valid bits of the cipher text according to a result of comparing the number of approximate accuracy bits of the cipher text to the number of final valid bits of the cipher text.

20. The storage controller of claim 17 , wherein the operation circuit is further configured to tag, to the cipher text, history information of operations performed on the cipher text while the at least one homomorphic operation included in the operation scenario is or are performed on the cipher text.