🏢 2. OV – Organization Validation
Purpose: Encrypts and authenticates the organization behind the domain.

✅ Validation Level: Confirms domain ownership and verifies company details (via business registration, phone, etc.)

📄 Certificate Info: Includes organization name and location

👁 Browser Bar: Padlock only, but company name visible in cert details

💰 Cost: Moderate

🧰 Use Case: Business websites, login portals, B2B platforms

Example:
Issued to: example.com
Organization: Example Corp, US

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📚 OS Concepts — What Happens When the System Runs Out of RAM? 💥🧵
Let’s break down how the OS reacts when memory is almost full! 🔍

🧠 The Problem:
Your system is running low on RAM. New apps need memory, but there’s no space left! What does the OS do?

🔹 Option 1: Swapping / Paging Out
💽 Move memory pages from RAM → disk (swap area)
🧊 Frees up RAM for urgent tasks
⚠️ Disk is much slower → system may feel sluggish ("thrashing")

📌 Think: Push books to a shelf to make space on your desk

🔹 Option 2: Killing Processes (OOM Killer / LMK)
💀 OS starts terminating processes to free memory

🧠 OOM Killer (Linux): kills least important process

📱 LMK (Android): aggressively frees memory by killing background apps

⚠️ Risk: Important work may be lost if a process is killed



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📚 OS & Computer Architecture — Understanding Caches & TLB 🧵
Let’s break down how your system stores & accesses memory efficiently!

🔸 A. L1 Cache (Level 1 Cache)
⚡️ Ultra-fast, small-sized cache (typically 16KB–128KB)
📍 Located inside the CPU core
🧠 Stores frequently used instructions & data
⚙️ Split into L1-I (Instructions) and L1-D (Data)
⏱️ Fastest access (~1–2 CPU cycles)
🚀 Purpose: Minimize delay between CPU and memory

🔸 B. Page Cache
🗃 Part of the OS's memory management
💾 Caches data read from or written to disk
🎯 Works at the file system level (pages, not bytes)
📈 Improves I/O performance by reducing disk access
✅ Example:
When you cat file.txt, the data goes to page cache so next reads are instant (RAM-based)!

🔸 C. TLB (Translation Lookaside Buffer)
🧭 Special cache inside the CPU
🔁 Maps virtual addresses → physical addresses
📍 Speeds up memory address translation
🔄 Without TLB, each memory access requires a page table lookup
⏱️ Much faster than walking full page tables
🚨 TLB Miss = CPU has to do extra work (slow)

🔸 D. L3 Cache (Level 3 Cache)
📦 Shared cache across multiple CPU cores
🔁 Larger but slower than L1/L2 (e.g., 4MB–64MB)
📉 Latency: ~10–20 CPU cycles
🧠 Holds data that doesn't fit in L1/L2 but is still reused often
🧰 Acts as a "last chance" before going to main memory

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🐞CVE is a catalog of known software flaws, with each ID representing a specific vulnerability. CWE, on the other hand, is a category system for software and hardware weaknesses that can lead to vulnerabilities.
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📚 OS Concepts — Cooperative vs Preemptive Scheduling 🧵
Ever wondered how your computer decides who gets the CPU and when? Let’s break it down:

🔹 1. Cooperative Scheduling
🤝 The process gives up the CPU voluntarily
🛑 If it never gives up, no one else runs
⚠️ One buggy program = system freeze
🏗 Used in old Windows, embedded systems

🔹 2. Preemptive Scheduling (Non-Cooperative)
⏱️ OS uses a timer to interrupt running processes
🔁 CPU is forcefully switched between tasks
💪 More stable & fair
🏃 Used in Linux, Android, Windows, etc.

📌 Key Difference:

Cooperative: “I’ll tell you when I’m done”

Preemptive: “Time’s up! Next process please”

💡 Modern OS = Preemptive, for fairness + safety!

#OS #Scheduling #Preemptive #Cooperative #CSBasics #InfoSecTube

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🪡Internet Key Exchange (IKE) is a secure key management protocol that establishes secure, authenticated communication channels over IP networks. It's used to set up security associations (SAs) in Internet Protocol Security (IPsec) for VPN connections, ensuring both parties use common encryption and authentication methods for secure data exchange.

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🏛 3. EV – Extended Validation
Purpose: Maximum trust; strictest authentication.

✅ Validation Level: Very thorough business verification (legal, physical, operational existence)

📄 Certificate Info: Full organization details

👁 Browser Bar: Padlock + organization name in address bar (some browsers now hide this, but cert details still contain it)

💰 Cost: Most expensive

🧰 Use Case: Banks, e-commerce, government portals, high-trust sites

Example:
Address bar: 🔒 [Example Corp] https://example.com


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A one-time pad is a cryptographic technique that ensures perfect secrecy, meaning it's mathematically impossible to decrypt a message without knowing the key. It works by using a random key of the same length as the message, encrypting each character or bit of the plaintext with the corresponding character or bit from the key using operations like XOR or modular addition. Crucially, the key is only used once and then discarded.

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📚 OS Concepts — Dining Philosophers Problem 🧵
Let’s solve a dinner table mystery that teaches us all about deadlock and resource sharing 👇

👨‍🎓 The Setup:

5 philosophers sit around a table 🍽

5 forks placed between them 🍴

To eat, each needs 2 forks (left + right)

After eating → Think → Get hungry again

😱 The Problem:
If each picks up their left fork first, they all wait forever for the right fork
→ This causes a deadlock 💥

🔑 Solutions:

✅ Lock Ordering: Always pick lower-numbered fork first
✅ Asymmetric Strategy: Odd picks left-first, even picks right-first
✅ At Most 4 at Table: Prevents total deadlock
✅ Use a Waiter: Central manager checks availability

📌 Core Concepts:

Philosophers = Threads

Forks = Shared Resources

Eat = Critical Section

Think = Non-Critical Work

Deadlock, starvation, and concurrency — all on one dinner table!

#OS #Deadlock #DiningPhilosophers #Semaphores #Concurrency #InfoSecTube



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🚨 Replay Attack Explained 🔁
A replay attack is a sneaky cyber trick where attackers intercept legit data and resend it to fool systems into thinking it’s real — leading to unauthorized access or action manipulation.

🔍 How It Works:
1️⃣ Interception:
Attacker sniffs data between two parties (e.g. login or transaction).
2️⃣ Re-transmission:
They replay that data to the receiver, pretending to be the legit sender.
3️⃣ Deception:
The receiver gets tricked, thinking it’s valid — and boom 💥, the attacker is in!

📌 Examples:
🔓 Login Replay:
Stealing & reusing login credentials to access accounts.
💸 Transaction Replay:
Duplicating a payment to drain funds or cause confusion.
🛡 Session Replay:
Using stolen session tokens to impersonate users.

🧠 Stay safe! Use encryption, session expiration, and anti-replay mechanisms.
#CyberSecurity #ReplayAttack #InfoSec #HackingExplained #CyberAwareness #StaySecure


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🔐 What is HOTP? (HMAC-based One-Time Password) 🔁

HOTP is a powerful algorithm used in multi-factor authentication (MFA) to boost your security beyond just passwords.

🧠 It works by generating one-time, unique passwords using:
🔑 A shared secret key
📈 A counter value (increases with each use)

Every time the counter updates, a new password is created — and it’s valid only once. Even if someone sees it, they can't reuse it! 🙅‍♂️

✅ Why Use HOTP?
🔸 Adds an extra layer of security
🔸 Prevents password reuse
🔸 Great for offline devices (no need for real-time clock)

💡 Used in hardware tokens, MFA apps, and enterprise systems.

#CyberSecurity #HOTP #MFA #OneTimePassword #Authentication #SecureAccess #InfoSec #IdentityVerification #2FA

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⛑Port mirroring, also known as SPAN (Switched Port Analyzer), is a networking technique where a network switch or router duplicates network packets from one port (the source port) and forwards them to another port (the destination or mirrored port). This allows network administrators to monitor and analyze traffic on a specific port without interrupting normal network operations.

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💻 4. IV – Individual Validation (for Code Signing)
Purpose: Authenticates individual developers for signing software/code.

✅ Validation Level: Verifies personal identity (via government ID, utility bills, etc.)

📄 Certificate Info: Includes individual's legal name

👁 Prompt: Shows developer’s name when users run signed software

💰 Cost: Varies

🧰 Use Case: Independent developers releasing apps or tools

Example (in a code-signing dialog):
"Publisher: John Doe"

📚 OS Concepts — When Do Kernel Modules Run? 🧵
Let’s break down how and when kernel module or device driver code executes!

🔧 A kernel module (like a device driver) is a piece of code that can be loaded/unloaded into the kernel at runtime. But when does it actually run?


✅ It runs when…

🔹 A device or syscall triggers a registered event
🔹 You load the module → insmod → runs init_module()
🔹 You unload the module → rmmod → runs cleanup_module()
🔹 A special file (like /dev/zero) is accessed → the corresponding driver’s function runs

🧠 Example:
Reading from /dev/zero calls the read handler of its device driver.

📌 Takeaway:
Drivers respond to events, they don’t idle or run endlessly!

#Kernel #DeviceDriver #OS

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🔄 Reflection Attack in Symmetric Protocols 🛡

A Reflection Attack is a clever trick used by attackers to exploit symmetric authentication protocols, especially when both parties use the same secret key. The attacker "reflects" a challenge back to the sender to bypass authentication without knowing the secret key.

⚙️ How It Works:
1️⃣ The attacker initiates a connection to the victim and receives a challenge (e.g. a nonce).
2️⃣ Instead of solving it, the attacker opens a second connection to the victim and sends the same challenge back.
3️⃣ The victim unknowingly solves their own challenge, thinking it's coming from a legit source.
4️⃣ The attacker grabs the valid response and uses it to authenticate in the original session. 😈

💥 Why It’s Dangerous:
Because the same protocol and key are used for both sides, there's no way to tell that the challenge came from the same party. It allows attackers to bypass authentication without breaking encryption.

🛑 Mitigation Tips:
✅ Use different keys or roles for client/server
✅ Add origin identifiers in challenges
✅ Employ asymmetric authentication if possible

#CyberSecurity #ReflectionAttack #SymmetricEncryption #NetworkSecurity #InfoSecTube #Hacking101 #StaySecure

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⛱A value flow graph (VFG) is a representation of a program's data flow, showing how values are defined and used throughout the code. It's a directed graph where nodes represent definitions and uses of values, and edges represent the flow of data between them. VFGs are used in static analysis to understand how data changes during program execution and are crucial for analyzing things like vulnerabilities, optimizations, and code transformations.
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Defense in depth is a security strategy that uses multiple layers of protection to safeguard assets. It's a proactive approach that aims to deter threats before they happen and mitigate damage if an attack is successful. By layering security controls, defense in depth provides redundancy and helps contain breaches, even if one layer fails.

Examples of Security Controls in a DiD Strategy:
Perimeter Security: Firewalls, intrusion prevention systems.
Network Security: Network segmentation, VPNs.
Endpoint Security: Antivirus, endpoint detection and response (EDR).
Application Security: Security testing, vulnerability management.
Data Security: Encryption, access control lists.
Identity and Access Management: Multi-factor authentication, least privilege principle.
Security Awareness Training: Educating users about potential threats.

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⏱️ What is TOTP? (Time-based One-Time Password) 🔐

TOTP stands for Time-based One-Time Password, a widely used algorithm in multi-factor authentication (MFA) that generates a new, temporary password every 30 seconds based on time and a shared secret.

🛠 How It Works:
🔑 A shared secret key
🕒 The current timestamp
Together, these generate a short, unique code — valid for a limited time (usually 30 seconds). After that, it's gone! 🚫

📲 Commonly used in apps like Google Authenticator, Authy, and Microsoft Authenticator.

✅ Why TOTP is Great:
🔒 Codes constantly refresh
💥 Resistant to replay attacks
📶 No need for constant internet — works offline
🚀 Easy to implement and user-friendly

⚠️ Just remember: if your device's time is off, TOTP might not work correctly!

#CyberSecurity #TOTP #2FA #OneTimePassword #MFA #Authentication #InfoSec #StaySecure #AuthApps #TimeBasedSecurity

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⛑Intermediate code (also known as intermediate representation, or IR) is a machine-independent representation of a program, generated by a compiler as a step between the source code and machine code. It allows for better optimization and portability, making it easier to target different hardware architectures with a single compiler.

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📚 OS Concepts — Deadlocks Made Simple! 🧵
Let’s break down how deadlocks happen, how to avoid them, and how to fix them if things go wrong 💥

🔒 Deadlock Needs 4 Conditions:

Mutual Exclusion → Only one thread uses a resource

Hold & Wait → Hold one lock, wait for another

No Preemption → Can’t force release of resources

Circular Wait → A waits for B, B for C, C for A

🛡 How to Avoid Deadlocks:

🔁 Lock Ordering → Always lock in the same order

✋ Hold & Wait Prevention → Grab all locks at once

🔄 Try-Lock + Retry → Release & retry after random delay

⚙️ Lock-Free (Atomic ops) → Avoid locks entirely

🚨 If Deadlock Happens:

☠️ Kill one thread → Free its resources

⏪ Rollback & Restart → Safer but needs saved state

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