28.2 Core Principles

By Ravindra Bagale Last updated: 15 October 2026

Forensics che kahi niyam kadhihi modaayche nahit:

Principle	Meaning
Preserve the original	Never work on the original device; it must not change
Work on a copy (image)	Make a bit-for-bit copy and examine that
Prove integrity with hashing	Hash the original and the copy; equal hashes prove nothing changed
Chain of custody	Document who handled the evidence, when, and why – every step
Use a write blocker	Hardware/software that lets you read a disk without writing to it
Document everything	Notes, timestamps, tools and versions, screenshots

Hashing for integrity (you met hashing in Chapter 22): compute a hash of the evidence when you collect it; anyone can recompute it later and confirm the data is unchanged.

sha256sum evidence.dd                 # hash a disk image
sha256sum evidence.dd > evidence.dd.sha256   # record it
sha256sum -c evidence.dd.sha256       # later: verify it still matches

Ravindra Bagale's Tip

The biggest forensic mistake: working directly on the original device. Once you do anything on the live disk, the evidence changes and the court rejects it. Always: take an image, take a hash, and work on the copy. This one rule is the difference between a professional and an amateur.

Practice task

Create a small file, compute its SHA-256, then change one character and hash again. Note how completely the hash changes – explain in one line why this proves integrity.

Extended teaching notes

Why this lesson matters

Use this lesson to strengthen systems you own: understand the risk, practise safely in a lab, then write and apply the fix.

Apply the fix across stacks

Same class of bug, same idea in every language.

Java / Spring Boot

Parameterise queries, encode output, CSRF tokens, limited Actuator, dependency scanning.

ASP.NET Core

EF Core / parameterised SQL, Razor encoding, HTTPS, Data Protection.

Node.js / Express

helmet, parameterised SQL, npm audit, avoid eval and shell concat.

Python / Django / Flask / FastAPI

ORM, autoescape, pip-audit, Bandit; never shell=True with user input.

PHP / Laravel

PDO/Eloquent, Blade escaping, composer audit.

Go / Ruby

database/sql placeholders / ActiveRecord; html/template / ERB escaping; govulncheck / Brakeman.

nginx / Apache / Tomcat

Hide versions, TLS, security headers, least-open ports.

MySQL / PostgreSQL / MongoDB / Redis

Private networks, auth on, least-privilege users, no 0.0.0.0/0.

AWS / Azure / GCP

Roles not long-lived keys, private data stores, cloud audit logs on.

Mini case study

Suppose we are on a purple-team exercise for an Indian mid-size company (sample data). Red notes a technique from this lesson against a lab clone. Blue must show the control that stops it, the log that would have fired, and the ticket that hardens production. That is the standard this course trains you for.

Defender's worksheet (do this today)

Write the lesson title, date and the exact lab target you are allowed to use.
List three owned systems (VMs, apps, or cloud accounts) where this lesson applies.
Run one safe check from the lesson on a lab system only. Paste the command and output.
Write a two-sentence fix you would give a teammate.
Name one related public advisory (CERT-In, CISA, NVD, or a vendor bulletin) with its date.

Indian workplace (sample data)

Suppose we are a junior analyst at Infosys, TCS, Wipro or a fintech SOC in Bengaluru/Pune. Turn this lesson into one checklist item with an owner, a due date and a place to store evidence (ticket + screenshot).

Global practice

Compare your notes with OWASP, CIS Benchmarks, NIST CSF/IR guidance or a cloud Well-Architected security question. Write five lines on what overlaps.

Everyday analogy

Explain the risk and the fix to a family member without jargon. If they can repeat the warning, you understand it well enough to teach juniors.

Key terms

Control: a safeguard (patch, config, process, detection).
Finding: a weakness backed by evidence.
Remediation: the fix plus how you verified it.
Scope: systems you have written permission to touch.
Least privilege: only the access the task needs.
Defence in depth: several layers so one failure does not end the story.

Common mistakes

Skipping written permission "just for a quick scan".
Practising on hostel, office or public targets without authorisation.
Collecting tool output without writing the fix.
Copying attack steps onto production to "verify". Defenders verify with versions, configs and patches.
Publishing screenshots that contain secrets, cookies or internal hostnames.

Recap

Evidence, fix, owner, date.
Own lab only.
Fix > spectacle.