A method for providing evidential data is described includes obtaining data items, generating a respective first hash value for each data item, generating a second hash value for a data set comprising the first hash values but excluding the one or more data items, obtaining one or more transaction identifiers including one or more static identifiers, generating a respective third hash value for each of the one or more static identifiers, transmitting a first message comprising the one or more data items, the one or more first hash values, the second hash value, and the one or more third hash values to a server.