🔐 CLI Password Authentication System

# Double Hashing Implementation
import hashlib
import os

def hash_password(password):
    # Step 1: Generate random salt (16 bytes)
    salt = os.urandom(16)
    
    # Step 2: First hash - SHA-256(password + salt)
    first_hash = hashlib.sha256(
        password.encode() + salt
    ).hexdigest()
    
    # Step 3: Second hash - PBKDF2 with 100,000 iterations
    final_hash = hashlib.pbkdf2_hmac(
        'sha256',
        first_hash.encode(),
        salt,
        100000
    )
    
    # Store: salt + final_hash in database
    return salt.hex() + ":" + final_hash.hex()

# Login Verification Process
def verify_password(username, password):
    # 1. Retrieve salt and stored hash from database
    stored_data = db.get_user(username)
    salt = bytes.fromhex(stored_data['salt'])
    stored_hash = stored_data['password_hash']
    
    # 2. Apply same double hashing with stored salt
    first_hash = hashlib.sha256(
        password.encode() + salt
    ).hexdigest()
    
    computed_hash = hashlib.pbkdf2_hmac(
        'sha256', first_hash.encode(),
        salt, 100000
    ).hex()
    
    # 3. Compare hashes (constant-time comparison)
    return hmac.compare_digest(computed_hash, stored_hash)