Techniques fondamentales de criminalistique numérique

Welcome to Basic Digital Forensic Techniques! In this lesson, we'll learn how to properly collect and preserve digital evidence during a security incident.

Digital forensics is the process of identifying, preserving, recovering, analyzing, and presenting facts about digital evidence. It's crucial for understanding breaches and for potential legal action.

A typical digital forensic investigation follows several key stages:

• Identification: Recognizing a potential incident.
• Preservation: Protecting potential evidence from alteration.
• Collection: Acquiring the evidence.
• Analysis: Examining the collected data.
• Reporting: Documenting findings.

This lesson focuses on the crucial steps of Preservation and Collection.

The golden rule in digital forensics is immutability: never alter the original evidence. Any change, no matter how small, can compromise the integrity and admissibility of the evidence.

Always work on copies of the data. This means creating bit-for-bit duplicates of storage devices and capturing volatile data without modifying the live system more than absolutely necessary.

Volatile data is information that exists only while a system is running and is lost when the system is powered off or rebooted. Examples include:

• System memory (RAM)
• Running processes
• Network connections and open ports
• Logged-on users

This data must be collected first, as it's highly perishable. Tools are used to extract this information from the live system.

While we won't run code directly, understanding common commands helps identify volatile data:

• netstat -an: Shows active network connections.
• ps aux: Lists running processes.
• who: Displays logged-in users.
• ipconfig (Windows) / ifconfig (Linux): Shows network interface configuration.

These commands provide a snapshot of the system's current state.

Non-volatile data persists even after a system is powered off. This primarily refers to data stored on hard drives, SSDs, USB drives, etc.

To preserve this evidence, a forensic image (a bit-for-bit copy) of the entire storage device is created. This image includes not just active files, but also deleted files, unallocated space, and file system metadata.

After collecting any digital evidence (volatile or non-volatile), its integrity must be verified. This is done using cryptographic hashing.

A hash function generates a unique, fixed-size string (a 'fingerprint') from a block of data. If even a single bit changes in the original data, the hash value will be completely different.

You calculate the hash of the original evidence and its copy. If they match, you've proven the copy is identical to the original and hasn't been tampered with.

Maintaining a chain of custody is vital for ensuring evidence is admissible in legal proceedings. It's a detailed, chronological record of who has had access to the evidence, when, and for what purpose.

Every transfer, examination, or storage event related to the evidence must be documented precisely. This proves the evidence has been protected from unauthorized access or alteration.

When collecting digital evidence:

• Isolate the system: Disconnect from networks to prevent further compromise or data loss.
• Document everything: Take photos, notes, and log all actions.
• Use write-blockers: Hardware or software tools that prevent any writes to the original evidence drive.
• Prioritize: Collect volatile data before non-volatile.
• Verify: Always use hashing to ensure integrity of copies.

You've just learned about critical steps in digital evidence collection. Let's test your understanding.

Great job! In this lesson, we covered the fundamental techniques for collecting and preserving digital evidence. You learned about:

• The importance of immutability and working on copies.
• Prioritizing volatile data collection.
• Creating forensic images of non-volatile data.
• Using hashing to verify evidence integrity.
• Maintaining a strict chain of custody.

These techniques are essential for any effective incident response and investigation.