SECURE COMPUTATION DEVICE, SECURE COMPUTATION METHOD, AND PROGRAM
A secure computation device includes a dummy record separating/sorting unit that sorts a table, a boundary flag generation unit that generates a boundary flag, an addition value generation unit that generates an addition value, a boundary sorting unit that stably sorts a table, a difference value generation unit that generates a difference value, and an operation result output unit that outputs a table.
1 . A secure computation device that performs a Groupby-sum operation on an encrypted first table including a key column, a value column, and a dummy flag column indicating whether or not a corresponding record is a dummy record, in a state where the first table is concealed based on the key column, the secure computation device comprising:
processing circuitry configured to
sort the first table by giving a first priority to a case where, in a case where the corresponding record is not a dummy record, the record is set to have a higher rank, and giving a second priority to the key column;
when a case where a certain record is not the dummy record and a key of the certain record is different from a key of a record immediately below the certain record is set as a first case, a case where a certain record is not the dummy record and a record immediately below the certain record is the dummy record is set as a second case, and a case where a certain record is not the dummy record and is a record located at a bottom is set as a third case, generate a boundary flag having a flag value indicating that a record is a boundary in a case where the record corresponds to any of the first to third cases, and that a record is not the boundary in a case where the record does not correspond to any of the first to third cases;
add all values located at positions higher than a certain record to a value of the certain record and generate an addition value of the corresponding record;
stably sort a second table including a key column, an addition value column, and a boundary flag column by giving a priority to a case where a boundary record is set to have a higher rank;
generate a difference value by setting an addition value of a highest record in the second table as the difference value as it is and setting, as the difference value, a difference of an addition value of a second record and a subsequent record in the second table from an addition value of a record immediately above the second record or subsequent record; and
output a third table including a key column, a difference value column, and a boundary flag column.
2 . The secure computation device according to claim 1 ,
processing circuitry configured to
in a case where the boundary flag of a certain record in the second table indicates that the certain record is not the boundary, replace a key of the corresponding record with a key obtained by concealing a predetermined character string, replace a difference value of the corresponding record with a value obtained by concealing 0, and output a fourth table including a key column, a difference value column, and a boundary flag column.
3 . A secure computation method performed by a secure computation device that performs a Groupby-sum operation on an encrypted first table including a key column, a value column, and a dummy flag column indicating whether or not a corresponding record is a dummy record, in a state where the first table is concealed based on the key column, the secure computation method comprising:
a step of sorting the first table by giving a first priority to a case where, in a case where the corresponding record is not a dummy record, the record is set to have a higher rank, and giving a second priority to the key column;
a step of, when a case where a certain record is not the dummy record and a key of the certain record is different from a key of a record immediately below the certain record is set as a first case, a case where a certain record is not the dummy record and a record immediately below the certain record is the dummy record is set as a second case, and a case where a certain record is not the dummy record and is a record located at a bottom is set as a third case, generating a boundary flag having a flag value indicating that a record is a boundary in a case where the record corresponds to any of the first to third cases, and that a record is not the boundary in a case where the record does not correspond to any of the first to third cases;
a step of adding all values located at positions higher than a certain record to a value of the certain record and generating an addition value of the corresponding record;
a step of stably sorting a second table including a key column, an addition value column, and a boundary flag column by giving a priority to a case where a boundary record is set to have a higher rank;
a step of generating a difference value by setting an addition value of a highest record in the second table as the difference value as it is and setting, as the difference value, a difference of an addition value of a second record and a subsequent record in the second table from an addition value of a record immediately above the second record or subsequent record; and
a step of outputting a third table including a key column, a difference value column, and a boundary flag column.
4 . The secure computation method according to claim 3 , further comprising:
a step of, in a case where the boundary flag of a certain record in the second table indicates that the certain record is not the boundary, replacing a key of the corresponding record with a key obtained by concealing a predetermined character string, replacing a difference value of the corresponding record with a value obtained by concealing 0, and outputting a fourth table including a key column, a difference value column, and a boundary flag column.
5 . A non-transitory computer readable medium storing a computer program for causing a computer to function as the secure computation device according to claim 1 .