A computer system comprising a plurality of processing nodes constituting a blockchain network for providing service using a blockchain, and a connection apparatus that connects to the blockchain network, wherein the plurality of processing nodes hold ledger information that is information including a history of transaction information in the service and for managing transactions, and is information in which blocks including a plurality of the transactions are connected in a chronological order; the connection apparatus includes a connection processing unit that generates a transaction and transmits the transaction to at least one of the processing nodes; the connection processing unit includes an encryption processing unit that generates searchable ciphertext from a keyword based on a probabilistic encryption method, wherein in the probabilistic encryption method plaintext and ciphertext have a one-to-many correspondence; the encryption processing unit generates, from the keyword, the searchable ciphertext to be used as an address indicating a transmission source or a transmission destination of the transaction; and the connection processing unit generates the transaction including the searchable ciphertext, wherein the encryption processing unit generates an encryption key to be used for encryption and decryption of data related to the transaction, by using the searchable ciphertext, wherein each of the processing nodes has a service processing unit that manages the ledger information; the service processing unit of the at least one of the processing nodes includes a search processing unit that executes search processing of the transaction; the connection processing unit generates a search query for searching for a transaction including searchable ciphertext generated from a first keyword, and transmits the search query to the at least one of the processing nodes; and the search processing unit performs a search for a transaction including searchable ciphertext generated from the first keyword by executing search processing based on the search query, and returns a result of the search to the connection apparatus. the plurality of processing nodes hold ledger information that is information including a history of transaction information in the service and for managing transactions, and is information in which blocks including a plurality of the transactions are connected in a chronological order; the connection apparatus includes a connection processing unit that generates a transaction and transmits the transaction to at least one of the processing nodes; the connection processing unit includes an encryption processing unit that generates searchable ciphertext from a keyword based on a probabilistic encryption method, wherein in the probabilistic encryption method plaintext and ciphertext have a one-to-many correspondence; the encryption processing unit generates, from the keyword, the searchable ciphertext to be used as an address indicating a transmission source or a transmission destination of the transaction; and the connection processing unit generates the transaction including the searchable ciphertext, wherein the encryption processing unit generates an encryption key to be used for encryption and decryption of data related to the transaction, by using the searchable ciphertext, wherein each of the processing nodes has a service processing unit that manages the ledger information; the service processing unit of the at least one of the processing nodes includes a search processing unit that executes search processing of the transaction; the connection processing unit generates a search query for searching for a transaction including searchable ciphertext generated from a first keyword, and transmits the search query to the at least one of the processing nodes; and the search processing unit performs a search for a transaction including searchable ciphertext generated from the first keyword by executing search processing based on the search query, and returns a result of the search to the connection apparatus.