Transmitting terminal, receiving terminal, id numbering device, and key transmission method

A transmitting terminal transmitting an encryption key, comprising:

• a random block generating section that generates a random block by randomly selecting and concatenating mask value blocks;
• an inquiry ID generating section that generate a bit sequence as an inquiry ID, the bit sequence being obtained by embedding the encryption key in a result obtained by XORing an ID of a receiving terminal with which the encryption key is to be shared and the random block in accordance with a predetermined key embedding rule;
• and
• a transmitting section that transmits the inquiry ID to multiple apparatuses including the receiving terminal,
• wherein the predetermined key embedding rule is a rule for inverting bit values at bit positions corresponding to values of the bits in the encryption key, the inversion being based on a block position correspondence relationship between the bit positions in the encryption key and positions of blocks into which the result of the logical XOR operation is divided, and a bit position correspondence relationship between the values of bits in the encryption key and the positions of bits in the block.