Core Principles of Forensic Science
These principles form the philosophical foundation of all forensic disciplines—physical, biological, and digital. They explain why evidence is meaningful and identifiable, complementing the procedural principles of digital forensics which govern how investigations are conducted.
1. Probability
Forensic conclusions are rarely absolute. They are expressed as probabilities or likelihoods. A fingerprint "match" represents an extremely high probability, not 100% certainty. In digital forensics, this applies to hash matches, statistical analysis of log patterns, and evidentiary weight.
2. Comparison
Evidence has meaning only when compared against a known standard. A crime scene fingerprint is compared to a suspect's print; malware is compared to known threat databases; unknown file artifacts are compared to baseline system images. No evidence exists in a vacuum.
3. Progressive Change
Everything changes over time. Crime scenes degrade, logs rotate, and volatile memory is lost on reboot. The longer the delay between an incident and investigation, the more evidence is lost. This principle underlines the urgency of preserving evidence and maintaining chain of custody.
4. Individuality
Every object or person is unique. Identical twins have different fingerprints; every device has unique artifacts (MAC addresses, file system quirks, hardware configurations). This principle is what makes identification and attribution possible in both physical and digital domains.
5. Exchange Principle (Locard's Principle)
"Every contact leaves a trace."
When two objects interact, material is exchanged between them. In digital forensics, this means an attacker interacting with a system inevitably leaves traces—registry modifications, log entries, file timestamps, deleted artifacts, or network packets. Even cleanup attempts often leave their own traces.
Connection to Digital Forensics
These principles justify why digital evidence is reliable. The procedural principles in your The 5 Principles of Digital Forensics note (especially Integrity and Objectivity) ensure that the traces identified through these core principles are collected and presented in a legally sound way.