A method comprising: a) receiving, by a computer, first interaction data for a first interaction between a user and an interacting entity, or a first hash of the interaction data and determining, by the computer a first hash of the first interaction data, or identifying the first hash of the first interaction data; b) determining, by the computer, an interaction identifier associated with the first interaction data or the first hash of the first interaction data; c) storing, by the computer, the first hash of the first interaction data in a database along with the interaction identifier; d) determining, by the computer, a root hash of a hash tree, the hash tree including the hash of the first interaction data and hashes (301B-301D) of other interaction data of other interactions by other users; e) providing, by the computer, the root hash of the hash tree to a public blockchain; f) receiving, by the computer, a request to verify the interaction between the user and the interacting entity from an inquiring entity device; and g) providing, by the computer, a verification result indicating that the interaction between the user and the interacting entity occurred, wherein the method further comprises: determining the first hash based on the request to verify the interaction; determining the hash tree using the first hash and the hashes (301B-301D) of other interaction data for other interactions by other users; determining the root hash; comparing, by the computer, the root hash to a corresponding root hash on the public blockchain; and providing the verification result in step g) based on the comparison, characterized in that determining the hash tree using the first hash and the hashes (301B-301D) of other interaction data for other interactions by other users comprises referencing a mapping table to determine the interaction identifiers of the hashes (301B-301D) of other interaction data of other users. a) receiving, by a computer, first interaction data for a first interaction between a user and an interacting entity, or a first hash of the interaction data and determining, by the computer a first hash of the first interaction data, or identifying the first hash of the first interaction data; b) determining, by the computer, an interaction identifier associated with the first interaction data or the first hash of the first interaction data; c) storing, by the computer, the first hash of the first interaction data in a database along with the interaction identifier; d) determining, by the computer, a root hash of a hash tree, the hash tree including the hash of the first interaction data and hashes (301B-301D) of other interaction data of other interactions by other users; e) providing, by the computer, the root hash of the hash tree to a public blockchain; f) receiving, by the computer, a request to verify the interaction between the user and the interacting entity from an inquiring entity device; and g) providing, by the computer, a verification result indicating that the interaction between the user and the interacting entity occurred, determining the first hash based on the request to verify the interaction; determining the hash tree using the first hash and the hashes (301B-301D) of other interaction data for other interactions by other users; determining the root hash; comparing, by the computer, the root hash to a corresponding root hash on the public blockchain; and providing the verification result in step g) based on the comparison, characterized in that determining the hash tree using the first hash and the hashes (301B-301D) of other interaction data for other interactions by other users comprises referencing a mapping table to determine the interaction identifiers of the hashes (301B-301D) of other interaction data of other users.