Using Digital Chains of Custody on Constrained Devices to Verify Evidence

A digital chain of custody is an account documenting digital data at a particular place and time. This paper gives a method of validating and authenticating a digital chain of custody using an algorithm by Jakobsson and by providing a new algorithm that compliments Jakobsson´s algorithm. Our method assumes specialized hardware. The physical hardware is assumed to be memory and processor constrained. Our new algorithm is an online algorithm that generates a hash chain of n hash elements without knowledge of n before it starts. At the same time, as n grows our new algorithm stores only the [log n] pebbles which are inputs for Jakobsson´s amortized hash chain traversal algorithm. Jakobsson´s algorithm is then used to validate hash elements and thus the digital chain of custody. The complimentary algorithm presented here is used to generate and store the hash chain. The compact representation used by these algorithms is useful to store a large digital chain of custody on a small and constrained device. Our proposed method allows the use of constrained devices to validate complex and ephemeral data such as shipping manifests and handling logs.