🔐 RSA Encryption & Decryption with Python (playmode ON)

This repository provides basic tools to demonstrate RSA public-key cryptography using Python and the cryptography library.

You can:

• Generate public/private key pairs.
• Encrypt a plaintext file using a public key.
• Decrypt it back using the private key.

📦 Requirements

Install the required Python package:

pip install cryptography

How to play this game?

This section explains, step-by-step, how to use the RSA encryption and decryption scripts in this project — designed for beginner-level computer science students learning cryptography.

---

🔹 Step 1: What Is Plain Text?

Plain text is a normal, readable message. For example:

Meet me at 5 PM near the library.

We call this "plain text" because it's not hidden or protected in any way.

🔹 Step 2: Why Do We Encrypt?

We encrypt messages to protect them from being read by anyone except the intended recipient.

Encryption turns plain text into cipher text — a scrambled, unreadable format that looks like random letters and numbers.

🔹 Step 3: What Is a Public Key?

Great question! 🔑

In public-key cryptography (like RSA), we use two keys:

• A public key: This can be shared with everyone — even strangers.
• A private key: This is kept secret and never shared.

To send a secure message:

• You encrypt the message using the recipient's public key.
• Only the person with the matching private key can decrypt and read the message.

💡 Think of the public key like a locked mailbox:
Anyone can drop a message inside, but only the owner with the private key can open it.

This script creates a 2048-bit RSA key pair and saves them to a keys/ directory.

python3 RSA_key_generated.py

🔧 Output:

• keys/public_key.pem – Public key
• keys/private_key.pem – Private key

💡 Remember, this key is pairing.

🔹 Step 4: How to Encrypt a File

1. First, create a text file with a message:

echo "This is a secret mission." > message.txt

2. Then, encrypt the file using the recipient's public key:

python3 do_encrypt.py -i message.txt -o encrypted.txt -pubkey keys/public_key.pem

• -i = input (plain text file)
• -o = output (cipher text file)
• -pubkey = path to the recipient’s public key (for the sake of example, we can use public key that we've create before)

🔹 Step 5: How to Decrypt It

Only the person with the matching private key can unlock the message.

python3 do_decrypt.py -i encrypted.txt -o decrypted.txt -privkey keys/private_key.pem

• -i = input (cipher text file)
• -o = output (decrypted plain text)
• -privkey = path to your private key

Now, decrypted.txt will contain the original message.

🧠 Summary

• ✍️ Plain text = your original message
• 🔒 Cipher text = encrypted message
• 🔑 Public key = used to encrypt (can be shared)
• 🔐 Private key = used to decrypt (must be secret)

This is the foundation of secure communication on the internet — used in messaging apps, banking, websites (HTTPS), and more.

Happy encrypting! 🔐✨