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33. Cryptography Basics

33.1 Goals and the Big Three: Encoding, Hashing, Encryption

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Quick answer: the short, self-contained version of this lesson is the guide Cryptography, TLS, Certificates and PKI in Practice.

Cryptography protects four things, often remembered as CIA + non-repudiation:

Goal Meaning Tool
Confidentiality Only the right people can read it Encryption
Integrity Nobody changed it Hashing, MAC
Authentication It really came from who it claims Signatures, certificates, MAC
Non-repudiation The sender cannot deny sending it Digital signatures

Now the trio students mix up:

Encoding Hashing Encryption
Purpose Change format for transport Fingerprint / integrity check Keep data secret
Key needed? No No Yes
Reversible? Yes, by anyone No (one-way) Yes, only with the key
Example Base64, URL encoding SHA-256, bcrypt AES, RSA 
echo -n "Pune123" | base64                 # UHVuZTEyMw==  (encoding – NOT security)
echo "UHVuZTEyMw==" | base64 -d            # anyone can decode it
echo -n "Pune123" | sha256sum              # one-way fingerprint

Ravindra Bagale's Tip

"I saved the password in base64, so it's encrypted" – say this in an interview and you are rejected on the spot! Base64 is only encoding; anyone can decode it with one command. Encoding = format, hashing = fingerprint, encryption = a lock with a key. Remember firmly that these three are different.

Practice task

Encode your name in Base64 and decode it. Hash the same text with md5sum, sha1sum and sha256sum and note the output length of each. Change one letter and hash again – how much of the hash changed?

Extended teaching notes

Why this lesson matters

Part 11 turns tool skills into professional defensive practice: web risks, cloud, SOC work, hardening, cryptography, Indian law and careers. Every example below stays inside systems you own or public teaching material.

Indian company (sample data)

Suppose we are a junior security engineer at an Infosys or TCS client project. You take this lesson's checklist, map it to three production services (for example a Spring Boot API, a Node.js portal and a Python job), and open tickets with evidence and owners.

Global practice

Follow public guidance from OWASP, CERT-In, CISA and cloud provider Well-Architected / security pillars. Cite them in reports.

Everyday analogy

A cricket team that only practises hitting but never fielding loses matches. Offence skills in a lab exist to improve fielding in real systems.

Apply across stacks

Wherever code appears, ask the same questions.

Java / Spring Boot

Parameterise queries, encode output, limit Actuator, patch dependencies.

.NET

EF Core parameters, HTTPS, Data Protection API, patch NuGet.

Node.js

helmet, parameterized SQL, npm audit, lockfiles.

Python

ORM, autoescape, pip-audit, Bandit.

Go / PHP / Ruby

Safe templates, prepared statements, govulncheck / composer audit / Brakeman.

nginx / Apache / Tomcat

Hide versions, TLS, least-open ports.

MySQL / PostgreSQL / MongoDB / Redis

No public ports, auth on, least-privilege users.

AWS / Azure / GCP

Roles not keys, private data stores, cloud logs on.

Defender worksheet

  1. Write a 5-line summary.
  2. Name one related public breach or advisory.
  3. Practise one safe command on a lab you own.
  4. Write the fix for a teammate.

Recap

  • Permission first.
  • Fix over spectacle.
  • Evidence in notes.

Defender's worksheet (do this today)

  1. Write the lesson title and date.
  2. List three owned systems where it applies.
  3. Run one safe lab check and paste evidence.
  4. Write a two-sentence fix for a teammate.
  5. Note one CERT-In or CISA advisory that relates (title + date).

Indian workplace (sample)

At a Wipro or LTIMindtree client SOC, turn this lesson into one playbook step with an owner and a due date.

Global practice

Compare your notes with OWASP, CIS Benchmarks or a cloud Well-Architected security question. Write the overlap in five lines.

Family test

Explain the risk and the fix without jargon. If a parent or sibling can repeat the warning, you are ready to teach juniors.

Common mistakes

  • Skipping permission.
  • Tool collecting without fixing.
  • Publishing lab screenshots that contain secrets.
  • Treating encoding as encryption.

Recap

  • Evidence, fix, owner, date.
  • Own lab only.

Key terms for this page

  • Control: a safeguard (patch, config, process).
  • Finding: a weakness with evidence.
  • Remediation: the fix and how you verified it.
  • Scope: systems you are allowed to touch.
  • Least privilege: only the access required for the task.
  • Defence in depth: several controls in layers.

Mini case study

Suppose we are a junior engineer at Zoho or Freshworks (sample data). A weekly review asks each person to present one control from their area. You pick a control from this lesson, show a before/after screenshot from a lab, and list the production ticket you would open. That habit builds both skill and credibility.