Abstract: A method and system for secure storage of digital data offers enhanced resistance to threat actors (whether insiders or hackers) gaining unauthorised access to extract and manipulate data, and to brute force computational attacks. The method employs double randomised fragmentation of source data into a random number of fragments of random sizes, encryption of each fragment with a separate encryption key, storage of the encrypted fragments and keys and a catalogue of the mappings of locations and fragments to keys all in physically and logically separate locations in a secure storage estate (1). The method may be repeatedly applied to encrypted fragments, keys and catalogue in a cascade fragmentation process to add further levels of security.