A correlation method for establishing provenance of timestamps in digital evidence

Abstract

Establishing the time at which a particular event happened is a fundamental concern when relating cause and effect in any forensic investigation. Reliance on computer generated timestamps for correlating events is complicated by uncertainty as to clock skew and drift, environmental factors such as location and local time zone offsets, as well as human factors such as clock tampering. Establishing that a particular computer's temporal behaviour was consistent during its operation remains a challenge. The contributions of this paper are both a description of assumptions commonly made regarding the behaviour of clocks in computers, and empirical results demonstrating that real world behaviour diverges from the idealised or assumed behaviour. We present an approach for inferring the temporal behaviour of a particular computer over a range of time by correlating commonly available local machine timestamps with another source of timestamps. We show that a general characterisation of the passage of time may be inferred from an analysis of commonly available browser records.