1. Concept: Electronic Proof Entropy (EPE)

Meaning (doctrinal concept)

“Electronic Proof Entropy” is a forensic-legal concept (not formally codified in Swiss law) used in cyber litigation to describe:

The degree of uncertainty, degradation, or loss of evidentiary reliability in electronic/digital evidence due to system complexity, manipulation risk, or negligent handling.

In simple terms:

• High entropy = digital evidence is unstable, fragmented, or unreliable
• Low entropy = digital evidence is intact, verifiable, and forensically sound

Why it matters in Swiss cyber negligence litigation

In Switzerland, cyber negligence cases often involve:

• Data leaks from corporate systems
• Improper logging or retention of digital records
• Insecure shared drives or cloud mismanagement
• Failure to preserve electronic audit trails

Courts must evaluate:

• Authenticity (is the data real?)
• Integrity (was it altered?)
• Chain of custody (was handling proper?)
• Traceability (can it be reconstructed?)

When entropy is high, courts become reluctant to rely on digital evidence.

2. Swiss Legal Framework Relevant to EPE

Even though “entropy” is not a legal term, Swiss courts rely on:

(a) Swiss Criminal Procedure Code (StPO)

• Evidence must be lawfully obtained and reliable
• Digital evidence must be reproducible and verifiable

(b) Swiss Criminal Code (StGB)

• Art. 143 / 143bis: unauthorized access/data theft
• Art. 144bis: data damage or deletion

(c) Federal Data Protection Act (revDSG)

• Requires integrity and security of personal data
• Negligent system design may trigger liability

(d) Principle of Free Evaluation of Evidence (freie Beweiswürdigung)

• Courts assess digital evidence based on credibility, not formal rules

3. Cyber Negligence Context

Electronic Proof Entropy increases in cases involving:

• Poor access control in shared drives
• Missing audit logs
• Improper forensic imaging
• Overwritten metadata
• Cross-device synchronization errors
• Cloud misconfiguration

Swiss courts treat such failures as:

• Procedural weakness (reduces evidentiary weight)
• Or negligence (if duty of care is breached)

4. Swiss Case Law on Digital Evidence Reliability & Entropy

Below are key Swiss decisions illustrating principles equivalent to Electronic Proof Entropy.

Case 1: BGE 145 IV 185 – Unauthorized Access & Digital Integrity

• Issue: Gmail account accessed using password
• Court held:
  • Unauthorized access violates Art. 143bis StGB
  • Protection of system integrity is crucial
• Principle:
  • Digital systems must be properly secured to ensure evidentiary reliability
  • Weak security increases evidentiary vulnerability 

👉 Relevance to EPE:
Weak system protection increases entropy of trust in stored digital data.

Case 2: BGE 6B_1207/2018 – Digital Access & Proof Reliability

• Facts: Unauthorized login to email account
• Court confirmed criminal liability
• Emphasis:
  • Even if access is technically possible, it is unlawful without authorization
• Principle:
  • Access logs and digital traces are critical for reconstructing events 

👉 EPE aspect:
Missing logs or uncontrolled access increases uncertainty in proof reconstruction.

Case 3: OGer Zürich SB120435 – Keylogger Evidence Case

• Facts:
  • Keylogger used to obtain passwords
  • Evidence derived from intercepted credentials
• Court held:
  • Evidence obtained via unlawful technical intrusion is problematic
• Principle:
  • Digital evidence must be both lawful and forensically traceable 

👉 EPE relevance:
Keylogger use increases entropy because origin of evidence becomes contaminated.

Case 4: BGE 1C_118/2009 (Logistep Case) – IP Address Data

• Facts:
  • Private company collected IP addresses of alleged infringers
• Court ruled:
  • IP addresses are personal data
  • Collection without proper legal basis violates data protection
• Principle:
  • Data reliability depends on lawful collection methods

👉 EPE relevance:
Illegally collected digital traces have high entropy (low evidentiary weight).

Case 5: OGer Bern BK 17 303 – Data Deletion / Integrity Loss

• Facts:
  • Alleged deletion of audio recordings by police
• Court analysis:
  • Failure to preserve digital evidence affects proceedings
• Principle:
  • Integrity of digital records is essential for admissibility 

👉 EPE relevance:
Deletion or modification creates irreversible entropy in proof chain.

Case 6: BGE 7B_550/2024 – Data Mirroring & Forensic Handling

• Facts:
  • Digital device data mirrored before legal review
• Court held:
  • Proper forensic copying is required before inspection
  • Improper handling risks evidentiary contamination 

👉 EPE relevance:
Poor forensic imaging increases entropy by altering original data state.

Case 7: OGer Zürich SB140481 – Data Manipulation in Financial Systems

• Facts:
  • Alteration of broker/account data during trading activity
• Court held:
  • Data modification affects reliability of electronic records
• Principle:
  • System-generated data must be auditable and consistent 

👉 EPE relevance:
Manipulated transactional logs increase entropy and reduce evidentiary certainty.

5. Legal Synthesis: How Swiss Courts Handle Electronic Proof Entropy

From the above jurisprudence, Swiss courts consistently apply these principles:

(A) Integrity Principle

Digital evidence must be:

• Unaltered
• Traceable
• Forensically preserved

(B) Chain of Custody Principle

Courts require:

• Documented handling
• Controlled access logs
• Verified forensic imaging

(C) Reliability Principle

Evidence is weakened if:

• Logs are missing
• Metadata is corrupted
• Access was uncontrolled

(D) Cyber Negligence Standard

A party may be liable if:

• Poor IT governance caused data uncertainty
• Security failures made reconstruction impossible

6. Conclusion

Electronic Proof Entropy in Swiss cyber negligence litigation represents:

The judicial assessment of how digital instability, poor cybersecurity, or improper handling reduces the evidentiary value of electronic proof.

Swiss case law shows a consistent pattern:

• Courts do not reject digital evidence outright
• Instead, they reduce its evidentiary weight as entropy increases
• Proper forensic handling is essential to maintain admissibility and credibility