Secure computation apparatus, secure computation method, and program

A secure computation apparatus for performing arithmetic operations while keeping a database including a key column k→ which is an attribute column and a data column v→ which is a value column concealed, wherein

• a group flag column g→ represents a vector in which a value becomes 1 at a position where a value of the key column changes, and a value becomes 0 at other positions,
• a share of a value x according to replicated secret sharing is represented as {x},
• a current row number is represented by i, a window frame start position is represented by s, and a window frame end position is represented by t,
• a number of rows of the key column and the data column is set to 1, and the current row number i is incremented by one each time all flag column generation processing ends in a range of 0 or more and less than 1, the secure computation apparatus comprising:
• processing circuitry configured to
• generate, with respect to a vector subVector ({g→}, s+1, i} obtained by extracting elements from an (s+1)-th element to an i-th element of {g→}, a bit column obtained by an OR operation performed on all bits from the i-th element of the vector subVector ({g→}, s+1, i) to each position as a former half window frame flag column {wf→};
• generate, with respect to a vector subVector ({g→}, i+1, t} obtained by extracting elements from an (i+1)-th element to a t-th element of {g→}, a bit column obtained by an OR operation performed on all bits from i+1th element of the vector subVector ({g→}, i+1, i) to each position as a latter half window frame flag column {wl→};
• and
• generate a window frame flag column {w→} by combining the former half window frame flag column {wf→} from a front side and the latter half window frame flag column {wl→} from a rear side having {0} interposed between the former half window frame flag column {wf→} and the latter half window frame flag column {wl→}.