🧊A firewall DMZ (Demilitarized Zone) is a separate, isolated network segment designed to protect an organization's internal network from external threats. It acts as a buffer zone between the internal network and the untrusted internet, allowing public access to specific services while keeping sensitive data and resources secure.

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📚 OS Concepts — Why Timer Interrupts Matter ⏰🧵
Let’s talk about one of the most powerful tools the OS has — timer interrupts!

🔹 What is a Timer Interrupt?
⏱️ A signal from hardware to the CPU at regular intervals
💥 It interrupts the running process to let the OS take over

🔹 Why is it Important?

✅ 1. Preemptive Scheduling
🔁 Timer says: “Time’s up!” → OS switches to the next process

✅ 2. Time Tracking
⏳ Helps with sleep(), delays, and CPU usage accounting

✅ 3. System Maintenance
🔄 OS runs background tasks like cleaning memory, updating clocks

✅ 4. Crash Protection
🧯 Stops buggy apps from hanging the entire system

📌 Without timer interrupts, multitasking would be impossible!

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#OS #TimerInterrupt #Scheduling #Multitasking #ComputerScience

یکسال اشتراک رایگان هوش مصنوعی Perplexity به ارزش 200 دلار

🔹 نیازمندی‌ها: گوشی سامسونگ گلکسی + VPN با آی‌پی آمریکا

مراحل انجام کار:

💀. سیم‌کارتتو از تنظیمات غیرفعال کن یا کامل درش بیار

💀. حالت هواپیما رو روشن کن (اختیاریه)

💀. کش و دیتای برنامه‌ی Galaxy Store رو پاک کن

💀. یه vpn با آی پی آمریکا نصب کن

💀. گوشی رو ریستارت کن

💀. وارد اپ VPN شو، به ی آی پی آمریکا متصل شو

💀. این لینک رو باز کن:

https://apps.samsung.com/appquery/appDetail.as?appId=ai.perplexity.app.android

💀. برنامه‌ی Perplexity رو نصب کن

💀. موقع ورود، بهتره با یه ایمیل جدید وارد بشی (جیمیل یا آوت‌لوک پیشنهاد می‌شه)

💀💀. بعد از ورود، باید نسخه‌ی Perplexity Pro برات فعال شده باشه

💀💀. اگه فعال نشد، برنامه رو پاک کن، دوباره کش و دیتای Galaxy Store رو پاک کن، آی‌پی رو تو VPN عوض کن و از اول تست کن

درضمن بعد از ثبت نام میتونید با همون اکانت برای پلتفرم های دیگه مثل آیفون یا ... استفاده کنید

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A trampoline in inline hooking is a small piece of code that helps preserve and continue the original function’s execution after the hook has intercepted it.
🪜 Trampoline = Restore and Continue

A trampoline does two things:

🔶Recreates the original bytes (that were overwritten by the hook)

🔶Jumps back to the rest of the original function (after the overwritten area)


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✅ Telegram-Style Educational Post
📚 OS Concepts — What is Pooling? 🔁🧵
Pooling is one of the best performance tricks used in OS & systems. Let’s break it down!

🔹 What is Pooling?
It’s the idea of reusing a fixed set of resources instead of creating new ones every time.

🔧 Common Examples:

Thread Pool → Reuse threads instead of making new ones

Connection Pool → Share open DB connections across users

Memory Pool → Pre-allocate memory blocks for reuse

Buffer Pool → Speed up disk & file I/O

🧠 Why Pool?

✅ Faster than creating/destroying resources
✅ Saves memory and CPU
✅ Prevents system overload during high traffic

📌 Think of it like a shared bike station: You grab a bike, use it, and return it — instead of buying a new one each time.

#OS #ThreadPool #ConnectionPool #MemoryManagement #Performance #InfoSecTube

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💉A code property graph of a program is a graph representation of the program obtained by merging its abstract syntax trees (AST), control-flow graphs (CFG) and program dependence graphs (PDG) at statement and predicate nodes.

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🎯Top-K pooling is a technique used in various deep learning applications, particularly in Graph Neural Networks (GNNs) and image processing, to select and retain the top 'k' most important elements from a set, while discarding the rest. It's a way to condense information and focus on the most relevant features.


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🔶SSL stripping, also known as TLS stripping, is a type of man-in-the-middle (MitM) attack that forces a secure HTTPS connection to downgrade to an insecure HTTP connection. This allows attackers to intercept and potentially manipulate data sent between a user and a website, even though the user believes they are on a secure connection.

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🧾 1. What Is PEM (Privacy-Enhanced Mail)?
Originally, PEM was a set of IETF standards (from the 1990s) designed to provide:

📧 Confidentiality (encryption of emails)

✅ Authentication (sender verification)

🔐 Integrity (tamper protection)

📜 Key management (using public-key infrastructure)

However, as a secure email standard, PEM was never widely adopted, and modern secure email uses standards like PGP and S/MIME instead.

📂 2. What Is PEM Today? (File Format)
In practice, PEM is now best known for its file format used to store:

SSL/TLS certificates (X.509)

Private keys

Certificate signing requests (CSRs)

Public keys

These files are Base64-encoded with headers and footers like:

-----BEGIN CERTIFICATE-----
[Base64 encoded data]
-----END CERTIFICATE-----

PEM file extensions: .pem, .crt, .cer, .key, .csr (often interchangeable, depending on content)
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📚 OS & Hardware — What is DMA (Direct Memory Access)? ⚙️🧵
Let’s explore how computers move data super efficiently without burdening the CPU!

🔹 DMA = Direct Memory Access

🧠 It lets devices talk directly to RAM, skipping the CPU
💥 Makes data transfer much faster & more efficient

🔧 Without DMA:
CPU handles every byte of data → slow + distracting

🔧 With DMA:
CPU gives the job to the DMA controller, then goes back to work.
Once done → DMA sends an interrupt

📦 Used In:

File transfers 📂

Network packets 🌐

GPU / sound systems 🎮

Embedded devices 📷

🍔 Analogy:
DMA = Assistant who moves stuff so the chef (CPU) can focus on cooking!

#OS #DMA #Memory #Interrupts #HardwareAcceleration #InfoSecTube

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🔐 What Does Forward Secrecy Do?
1)When you establish a secure connection (like HTTPS), the session uses a temporary session key to encrypt data.

2)Forward secrecy ensures that each session key is unique and ephemeral — it’s generated for that session only and not derived solely from the server’s long-term key.

3)If an attacker obtains the server’s private key later on, they cannot decrypt past communications recorded from earlier sessions.

🧠 How Is Forward Secrecy Achieved?
Typically, through ephemeral key exchange algorithms such as:

Ephemeral Diffie-Hellman (DHE)

Elliptic Curve Ephemeral Diffie-Hellman (ECDHE)

These generate a fresh temporary key pair per session.

PGP stands for Pretty Good Privacy, and it is a widely used encryption and digital signing system that provides confidentiality, integrity, and authentication for digital communication—especially emails and files.

🔐 What Does PGP Do?
PGP allows you to:

Encrypt messages/files so only the intended recipient can read them

Digitally sign messages/files to prove they came from you and weren't altered

🧠 How PGP Works (High-Level):
PGP uses a hybrid cryptographic approach:

Asymmetric encryption (public/private keys) for key exchange and digital signatures

Symmetric encryption (e.g., AES) for actual message encryption (faster)


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🐞Feature learning, also known as representation learning, is a machine learning technique where a model automatically learns the most relevant features from raw data without manual intervention. Instead of a human "feature engineer" explicitly defining features, the model learns them through training. This process allows the model to discover complex patterns and structures in the data, leading to improved performance in tasks like classification, anomaly detection, and clustering.


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📚 Linux Tip — What is fsck? 💻🧵
Your file system got corrupted after a crash? Time to meet your new best friend: fsck 🔧

🔹 What is it?
fsck = File System Consistency Check
🩺 It scans & fixes file system errors

🧠 Why use it?

Crash recovery 💥

Power failure ⚡️

Dirty shutdowns 🔌

Fix broken file links, bad inodes, orphan blocks

🔧 Basic Usage:

sudo fsck /dev/sda1

✅ Fix all: fsck -y
🔍 Check only: fsck -n

📌 Unmount first!

umount /dev/sda1

🧠 fsck = Disk Doctor for Linux
One command that can save your whole system! 🔥

#Linux #FSCK #FileSystem #DiskRecovery #InfoSecTube

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🧬 Process Data Structures
OS keeps a process list (or task list)

Each entry is a Process Control Block (PCB) or struct proc

Contains:

Memory info

Register context (for context switch)

Process ID

State

Parent pointer

Open files

Other runtime data

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🧠 Core Idea
How can an OS create, control, and manage processes?

UNIX uses three key system calls to do this:

fork() — Create a new process

exec() — Replace the process’s memory with a new program

wait() — Wait for a child process to finish

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🍩A "hub-and-spoke" CA model in Public Key Infrastructure (PKI) is a hierarchical structure where a central authority, the "hub," acts as the root CA, and multiple subordinate authorities, the "spokes," act as issuing CAs. This model distributes the workload and responsibility for issuing certificates, improving scalability and security.

Here's a more detailed breakdown:
🔥Root CA (Hub):
The top-level CA, trusted by all entities in the PKI. It's responsible for issuing certificates to the issuing CAs (spokes).
🔰Issuing CAs (Spokes):
These CAs are subordinate to the Root CA and are responsible for issuing certificates to end entities (users, devices, servers).
🧊End Entities:
The entities that use the certificates issued by the issuing CAs (spokes).

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🕸 DNS Rebinding: When the Browser Turns Against You
Imagine inviting someone into your house, and they quietly unlock a door to your private network.
That’s DNS rebinding — where the attacker tricks your browser into attacking your own LAN. 🧠🏠

🧠 What Is DNS Rebinding?
DNS rebinding is a technique that allows attackers to bypass browser security and interact with internal resources (like 192.168.x.x) by abusing how DNS works.

It turns the browser into a proxy, rebinding a domain name to a different IP — often a private one.

📘 “DNS rebinding attacks subvert the browser’s same-origin policy by making a trusted domain resolve to a local IP after initial connection.”

🔍 How It Works:

Victim visits attacker.com

The DNS server returns a public IP (so the browser allows connection)

After the page loads, the DNS record is updated (rebinding) to a private IP, like 127.0.0.1 or 192.168.1.1

Browser still trusts it — because it's from the “same origin”

Scripts from attacker.com now access your router, printer, or internal APIs 😱

🧪 Real-World Impact:

Steal sensitive data from internal dashboards

Change router DNS settings

Exploit vulnerable IoT devices on your LAN

Attack services not exposed to the internet

🛡 Defenses:

🔒 Block private IP responses on DNS resolvers (e.g., dnsmasq or cloud firewalls)

🛑 Use browser protections (modern browsers limit DNS rebinding by default)

⚙️ Disable Web access to local admin interfaces when possible

🔍 Monitor DNS behavior and HTTP requests for anomalies

📌 Fun Fact:
Even Google Home and routers have been attacked using DNS rebinding in real-world exploits.

🧩 TL;DR
DNS rebinding is like social engineering for browsers — it tricks your machine into attacking itself or your local network.
Same domain, different IP, total compromise.

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📁 What Is a Directory, Really?
In the OS world, a directory isn’t magic — it’s just a special file that holds tuples:

🧾 (name, i-number) — a mapping from a human-readable name to a file or directory’s low-level ID.

🔍 What’s Inside a Directory?
Each entry can point to:

A file (e.g., report.pdf → inode 1024)

Another directory (e.g., projects/ → inode 2048)

Even the directory itself has its own i-number!

📘 The OS doesn’t care about file names — only i-numbers (inode numbers).
The directory just maps human names → actual files via these numbers.

🔗 Special Entries You’ll Always Find:

. → refers to itself

.. → refers to its parent directory

These are essential for navigating the file system (e.g., cd .. to go up a level).

🧪 Example — Inside a folder called /home/user:

.      → i-number 4567 (this directory)  
..     → i-number 2345 (its parent)  
notes  → i-number 6789 (a file)  
docs   → i-number 8910 (a sub-directory)

🧩 TL;DR
A directory is just a list of (name, i-number) pairs that map names to files or subdirectories — including itself (.) and its parent (..).

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💞A Program Dependence Graph (PDG) is a representation of a program's control and data dependencies, using a directed graph. Nodes in the PDG represent program statements, and edges represent the relationships between those statements, showing how one statement might affect the execution of another. These dependencies are crucial for compiler optimization and analysis.

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