A method of securely synchronizing cache contents of a mobile browser with a server includes initiating a session between the browser and server, including transmission of browser state information regarding the cache contents and an authentication key to the server; maintaining a record of data sent from the server to the browser for storage in the cache; maintaining a record of the state information regarding the cache contents transmitted from the browser to the server; and transmitting data requests from the browser to the server, in response to which the server uses the key as a seed generation function and accesses each the record of data and returns only data that does not already form part of the cache contents, and wherein the data includes a result of a hash of data generated by the generation function for authentication by the browser before updating the cache contents with the data.