A method comprising: providing an electric power transaction system comprising an electric power network, which is a network in which electric power is sold and bought between a plurality of homes forming a group, each having an electric power equipment, which is used by a user, including an electric power meter configured to measure an amount of electric power transmitted to or received from the electric power network; configuring the electric power transaction system to perform electric power transactions by utilizing a blockchain technique; providing at least three authentication servers (200a 200b 200c) in the electric power transaction system, each configured for: receiving (i) first transaction data from a first electric power equipment, the first transaction data including: electric power transmitting amount information indicating a first amount of electric power which the first electric power equipment transmitted to a second electric power equipment or (ii) second transaction data from the second electric power equipment, the second transaction data including: electric power receiving amount information indicating a second amount of electric power which the second electric power equipment received from the first electric power equipment; verifying validity of (i) the first transaction data whether the electric power transmitting amount information is confirmed as a third amount of electric power comprised in a matching result, of third transaction data, for electrical power to be transmitted by the first electric power equipment and used by the second electric power equipment, or (ii) the second transaction data whether the electric power receiving amount information is confirmed as said third amount of electric power; and recording the first transaction data or the second transaction data in a distributed ledger when the validity of the first transaction data or the second transaction data are verified successfully. providing an electric power transaction system comprising an electric power network, which is a network in which electric power is sold and bought between a plurality of homes forming a group, each having an electric power equipment, which is used by a user, including an electric power meter configured to measure an amount of electric power transmitted to or received from the electric power network; configuring the electric power transaction system to perform electric power transactions by utilizing a blockchain technique; providing at least three authentication servers (200a 200b 200c) in the electric power transaction system, each configured for: receiving (i) first transaction data from a first electric power equipment, the first transaction data including: electric power transmitting amount information indicating a first amount of electric power which the first electric power equipment transmitted to a second electric power equipment or (ii) second transaction data from the second electric power equipment, the second transaction data including: electric power receiving amount information indicating a second amount of electric power which the second electric power equipment received from the first electric power equipment; verifying validity of (i) the first transaction data whether the electric power transmitting amount information is confirmed as a third amount of electric power comprised in a matching result, of third transaction data, for electrical power to be transmitted by the first electric power equipment and used by the second electric power equipment, or (ii) the second transaction data whether the electric power receiving amount information is confirmed as said third amount of electric power; and recording the first transaction data or the second transaction data in a distributed ledger when the validity of the first transaction data or the second transaction data are verified successfully. receiving (i) first transaction data from a first electric power equipment, the first transaction data including: electric power transmitting amount information indicating a first amount of electric power which the first electric power equipment transmitted to a second electric power equipment or (ii) second transaction data from the second electric power equipment, the second transaction data including: electric power receiving amount information indicating a second amount of electric power which the second electric power equipment received from the first electric power equipment; verifying validity of (i) the first transaction data whether the electric power transmitting amount information is confirmed as a third amount of electric power comprised in a matching result, of third transaction data, for electrical power to be transmitted by the first electric power equipment and used by the second electric power equipment, or (ii) the second transaction data whether the electric power receiving amount information is confirmed as said third amount of electric power; and recording the first transaction data or the second transaction data in a distributed ledger when the validity of the first transaction data or the second transaction data are verified successfully.