Token-based authentication (JWT) in IOT Protocols - Mini Project: Build & Apply

Token-based authentication (JWT)

📖 Scenario: You are working on a simple IoT device management system. Each device needs to authenticate itself using a token before it can send data. The system uses JSON Web Tokens (JWT) to verify device identity securely.

🎯 Goal: Build a small program that creates a JWT token for a device, sets a secret key for signing, encodes the token with device info, and finally prints the token string.

📋 What You'll Learn

Create a dictionary called device_info with keys device_id and device_type and exact values 'device123' and 'sensor'

Create a variable called secret_key and set it to the string 'mysecretkey'

Use the jwt.encode() function to create a token from device_info signed with secret_key and assign it to token

Print the token variable to display the JWT token string

💡 Why This Matters

🌍 Real World

IoT devices often use JWT tokens to prove their identity securely to servers before sending data.

💼 Career

Understanding JWT token creation and usage is essential for roles in IoT security, backend development, and DevOps automation.

1

Create device information dictionary

Create a dictionary called device_info with these exact entries: 'device_id': 'device123' and 'device_type': 'sensor'.

IOT Protocols

# Your code here

Hint

Think of device_info as a small card with device details.

2

Set the secret key for signing

Create a variable called secret_key and set it to the string 'mysecretkey'.

IOT Protocols

device_info = {'device_id': 'device123', 'device_type': 'sensor'}
# Your code here

Hint

The secret key is like a password only your system knows.

3

Create the JWT token

Use the jwt.encode() function to create a token from device_info signed with secret_key and assign it to token. Assume jwt is already imported.

IOT Protocols

device_info = {'device_id': 'device123', 'device_type': 'sensor'}
secret_key = 'mysecretkey'
# Your code here

Hint

Use algorithm='HS256' for signing the token.

4

Print the JWT token

Write print(token) to display the JWT token string.

IOT Protocols

token = jwt.encode(device_info, secret_key, algorithm='HS256')
# Your code here

Hint

The printed token should start with eyJ, which is common for JWT tokens.

Practice

1. What is the main purpose of a JWT (JSON Web Token) in IoT device communication?

easy

A. To store large files securely on the device

B. To encrypt all data sent between devices

C. To prove the device's identity without sending passwords repeatedly

D. To replace the device's IP address

Solution

1. Step 1: Understand JWT role in authentication

   JWT tokens are used to prove identity securely without resending passwords each time.

2. Step 2: Compare options with JWT purpose

   Only To prove the device's identity without sending passwords repeatedly matches this purpose; others describe unrelated functions.

3. Final Answer:

   To prove the device's identity without sending passwords repeatedly -> Option C

4. Quick Check:

   JWT = Identity proof without password [OK]

Hint: JWTs prove identity without passwords [OK]

Common Mistakes:

• Thinking JWT encrypts all data
• Confusing JWT with file storage
• Assuming JWT replaces IP addresses

2. Which of the following is the correct structure of a JWT token?

easy

A. header.payload.signature

B. payload.header.signature

C. signature.payload.header

D. header.signature.payload

Solution

1. Step 1: Recall JWT token parts order

   A JWT consists of three parts separated by dots: header, payload, and signature in that order.

2. Step 2: Match options with correct order

   Only header.payload.signature shows header.payload.signature correctly.

3. Final Answer:

   header.payload.signature -> Option A

4. Quick Check:

   JWT format = header.payload.signature [OK]

Hint: JWT parts order: header, payload, signature [OK]

Common Mistakes:

• Mixing the order of parts
• Placing signature before payload
• Confusing payload and header positions

3. Given this JWT payload JSON: {"sub":"device123","exp":1700000000}, what does the "exp" field represent?

medium

A. The token's signature

B. The device's unique ID

C. The encryption algorithm used

D. The token's expiration time as a Unix timestamp

Solution

1. Step 1: Identify the meaning of 'exp' in JWT payload

   The 'exp' field stands for expiration time, given as a Unix timestamp.

2. Step 2: Match 'exp' meaning with options

   The token's expiration time as a Unix timestamp correctly states it is the token's expiration time; others are unrelated.

3. Final Answer:

   The token's expiration time as a Unix timestamp -> Option D

4. Quick Check:

   exp = expiration time [OK]

Hint: "exp" means token expiration time [OK]

Common Mistakes:

• Confusing 'exp' with device ID
• Thinking 'exp' is encryption info
• Mixing 'exp' with signature data

4. You receive this JWT token string: eyJhbGciOiJIUzI1NiJ9.eyJzdWIiOiJkZXZpY2UxMjMiLCJleHAiOjE3MDAwMDAwMDB9. When verifying, you get an error about the signature. What is the most likely cause?

medium

A. The token is missing the expiration field

B. The token's signature does not match because the secret key used is incorrect

C. The header is not base64 encoded

D. The payload is missing the device ID

Solution

1. Step 1: Understand signature verification in JWT

   Signature errors usually happen when the secret key used to verify does not match the one used to sign.

2. Step 2: Check other options for signature error cause

   Missing payload fields or encoding issues cause different errors, not signature mismatch.

3. Final Answer:

   The token's signature does not match because the secret key used is incorrect -> Option B

4. Quick Check:

   Signature error = wrong secret key [OK]

Hint: Signature errors usually mean wrong secret key [OK]

Common Mistakes:

• Assuming missing fields cause signature errors
• Ignoring base64 encoding correctness
• Thinking expiration absence causes signature failure

5. You want to limit IoT device access by making JWT tokens expire after 10 minutes. Which approach correctly sets this expiration in the token payload?

hard

A. Set the "exp" field to the current Unix timestamp plus 600 seconds

B. Set the "iat" field to 600

C. Set the "exp" field to the current date string

D. Omit the "exp" field to allow unlimited token life

Solution

1. Step 1: Understand JWT expiration setting

   The 'exp' field must be a Unix timestamp indicating when the token expires, so add 600 seconds (10 minutes) to current time.

2. Step 2: Evaluate other options

   'iat' is issued-at time, not expiration; date string is invalid format; omitting 'exp' disables expiration.

3. Final Answer:

   Set the "exp" field to the current Unix timestamp plus 600 seconds -> Option A

4. Quick Check:

   Use 'exp' with timestamp + 600 seconds [OK]

Hint: Use 'exp' = now + 600 seconds for 10-minute expiry [OK]

Common Mistakes:

• Using 'iat' instead of 'exp' for expiration
• Setting 'exp' as a date string
• Leaving out 'exp' to limit token life