Implement file encryption feature

Add encryption.py module with Fernet symmetric encryption implementation. This closes #1.

encryption.py

@@ -0,0 +1,143 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+"""
+File Encryption Module for Cloud Storage Bot
+
+This module provides encryption and decryption functionality for the Cloud Storage Bot.
+It uses Fernet symmetric encryption from the cryptography library to secure files.
+"""
+
+import os
+import base64
+from cryptography.fernet import Fernet
+from cryptography.hazmat.primitives import hashes
+from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2HMAC
+
+
+class FileEncryption:
+    """Handles file encryption and decryption operations."""
+
+    def __init__(self, password):
+        """Initialize with a password for encryption/decryption.
+
+        Args:
+            password (str): The password used for encryption/decryption.
+        """
+        self.password = password.encode()
+        self.salt = os.urandom(16)  # Generate a random salt
+        self.key = self._generate_key()
+        self.cipher = Fernet(self.key)
+
+    def _generate_key(self):
+        """Generate a key from the password using PBKDF2.
+
+        Returns:
+            bytes: The generated key for encryption/decryption.
+        """
+        kdf = PBKDF2HMAC(
+            algorithm=hashes.SHA256(),
+            length=32,
+            salt=self.salt,
+            iterations=100000,
+        )
+        key = base64.urlsafe_b64encode(kdf.derive(self.password))
+        return key
+
+    def encrypt_file(self, file_path, output_path=None):
+        """Encrypt a file using the generated key.
+
+        Args:
+            file_path (str): Path to the file to encrypt.
+            output_path (str, optional): Path to save the encrypted file.
+                If not provided, appends '.encrypted' to the original filename.
+
+        Returns:
+            str: Path to the encrypted file.
+            bytes: The salt used for encryption (should be stored securely).
+        """
+        if not output_path:
+            output_path = f"{file_path}.encrypted"
+
+        # Read the file content
+        with open(file_path, 'rb') as file:
+            file_data = file.read()
+
+        # Encrypt the data
+        encrypted_data = self.cipher.encrypt(file_data)
+
+        # Write the encrypted data to the output file
+        with open(output_path, 'wb') as file:
+            file.write(encrypted_data)
+
+        return output_path, self.salt
+
+    def decrypt_file(self, file_path, output_path=None, salt=None):
+        """Decrypt a file using the generated key.
+
+        Args:
+            file_path (str): Path to the encrypted file.
+            output_path (str, optional): Path to save the decrypted file.
+                If not provided, removes '.encrypted' from the filename if present.
+            salt (bytes, optional): The salt used during encryption.
+                If provided, regenerates the key with this salt.
+
+        Returns:
+            str: Path to the decrypted file.
+        """
+        if salt:
+            # Regenerate the key with the provided salt
+            self.salt = salt
+            self.key = self._generate_key()
+            self.cipher = Fernet(self.key)
+
+        if not output_path:
+            if file_path.endswith('.encrypted'):
+                output_path = file_path[:-10]  # Remove '.encrypted' suffix
+            else:
+                output_path = f"{file_path}.decrypted"
+
+        # Read the encrypted file content
+        with open(file_path, 'rb') as file:
+            encrypted_data = file.read()
+
+        # Decrypt the data
+        decrypted_data = self.cipher.decrypt(encrypted_data)
+
+        # Write the decrypted data to the output file
+        with open(output_path, 'wb') as file:
+            file.write(decrypted_data)
+
+        return output_path
+
+
+# Example usage
+def encrypt_user_file(file_path, password, output_path=None):
+    """Encrypt a user file with the provided password.
+
+    Args:
+        file_path (str): Path to the file to encrypt.
+        password (str): Password for encryption.
+        output_path (str, optional): Path to save the encrypted file.
+
+    Returns:
+        tuple: (encrypted_file_path, salt)
+    """
+    encryption = FileEncryption(password)
+    return encryption.encrypt_file(file_path, output_path)
+
+
+def decrypt_user_file(file_path, password, salt, output_path=None):
+    """Decrypt a user file with the provided password and salt.
+
+    Args:
+        file_path (str): Path to the encrypted file.
+        password (str): Password for decryption.
+        salt (bytes): Salt used during encryption.
+        output_path (str, optional): Path to save the decrypted file.
+
+    Returns:
+        str: Path to the decrypted file.
+    """
+    encryption = FileEncryption(password)
+    return encryption.decrypt_file(file_path, output_path, salt)