Abstract: A computer-implemented method of permitting authentication of data added to an initial plurality of unique data items stored on a computer, all of the data items being converted via a one-way function to respective equal length unique digests (or hashes); and the hashes being stored as a linked dataset in which the value of each successive hash is dependent on the value of the previous hash combined with a new hash resulting from the hashing of the most recently added data. The most recent hash in the linked dataset (hash chain) is the cumulative result of all previous hashes in their original sequence, each hash in the dataset being unique to the most recently added data. Each cumulative hash is constructed by incorporating one or more pre-existing cumulative hashes into the source data, before the new hash is calculated.

Abstract: A computer-implemented method of permitting authentication of data added to an initial plurality of unique data items stored on a computer, all of the data items being converted via a one-way function to respective equal length unique digests (or hashes); and the hashes being stored as a linked dataset in which the value of each successive hash is dependent on the value of the previous hash combined with a new hash resulting from the hashing of the most recently added data. The most recent hash in the linked dataset (hash chain) is the cumulative result of all previous hashes in their original sequence, each hash in the dataset being unique to the most recently added data. Each cumulative hash is constructed by incorporating one or more pre-existing cumulative hashes into the source data, before the new hash is calculated.

Abstract: Data is transmitted between a first user and a second user via an information technology communications network, in a method comprising the steps of: generating a first hash value for a selected one of the data items; digitally signing and encrypting the first hash value with a secret identifier associated with the first user; transmitting to a second user the encrypted first hash value; receiving and storing the transmitted encrypted first hash value for audit purposes and generating a second hash value for the received encrypted first hash value; encrypting the second hash value with a private identifier associated with a second user and a public identifier associated with the first user; and returning the encrypted second hash value to the first user.