InfoSecTube
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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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🌈 Rainbow Table Attack Explained 🔓

A Rainbow Table Attack is a fast and sneaky way to crack passwords by using precomputed tables of hash values and their matching plain-text passwords.

💡 Unlike brute-force attacks (which try every combo one by one), rainbow tables match the hash directly using a huge database of known values.

🔁 Why It Works:
Hash functions are one-way by design — but if you don’t add extra protection (like salting), attackers can reverse them using these tables.
Basically:
👉 You hash a password → attacker finds that hash in their rainbow table → password cracked instantly! ⚠️

🧂 How to Stay Safe:
Always salt your passwords — add random data before hashing.
Use strong hashing algorithms like bcrypt, scrypt, or Argon2.
Never store plain hashes without extra protection.

#CyberSecurity #RainbowTable #PasswordCracking #Hashing #Salting #InfoSec #CyberAttack #StaySecure

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📚 OS Concepts — What is a Context Switch? 🧵
Ever wonder how your system runs multiple apps at once on one CPU core? The magic is in context switching!

🔁 Context Switch = Save + Swap Process State

🧠 The CPU saves the current process state
📦 Loads another process's state
🚀 Starts running the new process like nothing changed!

🕒 Happens when:

Time slice ends (preemptive multitasking)

Process blocks (waiting for I/O)

OS handles system call

Switching between threads or users

📌 What’s saved?

CPU registers

Stack pointer

Program counter

Memory mapping info
🔐 Stored in the Process Control Block (PCB)

⚠️ Costly Operation
💸 Takes time & resources
📉 Too many = performance drop

Tip: Efficient schedulers reduce unnecessary switches!

#OS #ContextSwitch #Multitasking #Scheduling #ComputerScience

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📚 OS Concepts — How Are System Calls Secure? 🧵
Apps talk to the kernel using system calls — but how does the OS stop them from breaking things? Let’s see 🔒

🔹 1. Trap = Safe Doorbell
🔔 User apps can’t run kernel code directly — they trigger a trap (e.g., int 0x80) to switch modes.

🔹 2. Syscall Table Lookup
📋 Each syscall has a number (like read = 0, write = 1)
🔍 The kernel uses this to safely run a registered handler — no custom functions allowed.

🔹 3. Secure Input Handling
🛡 Kernel checks:

Are pointers valid?

Are arguments safe?


Can this memory be read/written?


No check = no execution.

🔹 4. Safe Copy Functions
🚫 Kernel never touches user memory directly!
Uses:

copy_from_user()

get_user() / put_user()

🔹 5. Return to User Mode

Once done, the OS switches the CPU back to user mode — kernel stays protected.

📌 TL;DR: System calls are like guarded gates. The kernel:

Controls entry

Validates everything

Exits cleanly


#OS #Syscall #Security #KernelMode #Trap #SystemCalls

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📚 OS Concepts — Producer-Consumer Problem 🧵
Let’s break down this classic synchronization problem with a tasty example 🍔👇

🔸 Scenario:
A chef (producer) makes burgers 🍔
A customer (consumer) eats them
They share a tray (buffer) with limited space (e.g., 5 slots)

🔸 The Problem:

Chef shouldn't add burgers if the tray is full

Customer shouldn't take burgers if the tray is empty

They shouldn't touch the tray at the same time


🔸 The Solution:
Use semaphores + mutex

empty: Blocks producer if tray is full

full: Blocks consumer if tray is empty

mutex: Stops race conditions on the tray

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🔔The Matthews Correlation Coefficient (MCC) is a metric used in machine learning to evaluate the quality of binary classification. It's considered a robust measure, particularly for imbalanced datasets, as it takes into account true and false positives and negatives. MCC values range from -1 to +1, where +1 indicates a perfect prediction, 0 indicates no better than random guessing, and -1 indicates total disagreement.

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🎤The Softmax activation function is a mathematical function that transforms a vector of raw model outputs, known as logits, into a probability distribution. In simpler terms, it takes a set of numbers and converts them into probabilities that sum up to 1.

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📌 Understanding the Sticky Bit in Linux/Unix 🧠💻

The Sticky Bit is a special permission used on directories to control file deletion. When set, only the file owner, directory owner, or root can delete or rename files inside that directory — even if others have write access.

🔐 Why It Matters:
In shared directories (like /tmp), users need to create files — but you don’t want anyone deleting someone else’s stuff. That’s where the Sticky Bit comes in!

🧪 Example:

Let's say you have a shared folder /shared:

sudo mkdir /shared
sudo chmod 777 /shared


# Everyone can read/write/execute
Without sticky bit:
➡️ Any user can delete anyone else's files 😬

Now set the sticky bit:

sudo chmod +t /shared

Check permissions:


ls -ld /shared

You’ll see something like:

drwxrwxrwt 2 root root 4096 Jun 6 10:00 /shared

🔸 The t at the end means sticky bit is active.

Key Takeaway:
Use the sticky bit to protect files in public directories where multiple users need access, but file ownership should be respected.

#LinuxTips #StickyBit #Permissions #Unix #SysAdmin #CyberSecurity #InfoSec #FileSecurity #LinuxBasics

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🧊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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📚 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.
🍩Living of the file sharing systems
https://www.lolfs.app/

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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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