Webhook signature verification in Rest API - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the module needed for HMAC.

Rest API

import [1]

Drag options to blanks, or click blank then click option'

Ahmac

Brequests

Cjson

Dhashlib

Attempts:

3 left

💡 Hint

Common Mistakes

Importing hashlib instead of hmac

Forgetting to import any module

The hmac module is used to create and verify message signatures.

2fill in blank

medium

Complete the code to create an HMAC object using the secret key and message.

Rest API

signature = hmac.new([1], message, hashlib.sha256).hexdigest()

Drag options to blanks, or click blank then click option'

Asecret_key

Bmessage

Chashlib

Dsignature

Attempts:

3 left

💡 Hint

Common Mistakes

Using the message as the key

Using hashlib instead of the key

The secret key is used as the key argument in hmac.new to create the signature.

3fill in blank

hard

Fix the error in the code to correctly compare the computed signature with the received signature.

Rest API

if hmac.compare_digest(signature, [1]):
    print('Valid signature')

Drag options to blanks, or click blank then click option'

Amessage

Bsignature

Csecret_key

Dreceived_signature

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing the signature to itself

Comparing signature to message or secret key

We compare the computed signature with the received_signature from the webhook.

4fill in blank

hard

Fill both blanks to decode the received signature from hex and compare it safely.

Rest API

received_sig_bytes = bytes.fromhex([1])
if hmac.compare_digest(signature_bytes, [2]):
    print('Signature verified')

Drag options to blanks, or click blank then click option'

Areceived_signature

Bsignature_bytes

Creceived_sig_bytes

Dsecret_key

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing hex string directly without decoding

Mixing up variable names

The received signature string is converted to bytes using bytes.fromhex. Then we compare the computed signature_bytes with received_sig_bytes.

5fill in blank

hard

Fill all three blanks to create a function that verifies a webhook signature.

Rest API

def verify_signature(secret, message, [1]):
    computed_sig = hmac.new(secret, message, [2]).hexdigest()
    return hmac.compare_digest(computed_sig, [3])

Drag options to blanks, or click blank then click option'

Areceived_signature

Bhashlib.sha256

Dmessage

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong parameter names

Not using the correct hashing algorithm

Comparing wrong variables

The function takes the received signature as an argument. It uses hashlib.sha256 to create the HMAC digest. Finally, it compares the computed signature with the received one.

Practice

1. What is the main purpose of webhook signature verification?

easy

A. To confirm the webhook is from a trusted source

B. To speed up the webhook delivery

C. To encrypt the webhook payload

D. To log the webhook request time

Solution

1. Step 1: Understand webhook security

   Webhook signature verification is used to check if the webhook request is really from the expected sender.

2. Step 2: Identify the purpose of verification

   This process confirms the webhook is trusted by comparing the signature with a secret key.

3. Final Answer:

   To confirm the webhook is from a trusted source -> Option A

4. Quick Check:

   Verification = Trusted source confirmation [OK]

Hint: Verification means checking trust, not speed or encryption [OK]

Common Mistakes:

• Confusing verification with encryption
• Thinking it speeds up webhook delivery
• Assuming it logs request time

2. Which of the following is the correct Python code snippet to compute an HMAC SHA256 signature for webhook verification?

easy

A. hmac.new(secret.encode(), payload.encode(), hashlib.sha256).hexdigest()

B. hmac.new(payload.encode(), secret.encode(), hashlib.md5).hexdigest()

C. hashlib.sha256(secret + payload).hexdigest()

D. hmac.sha256(secret, payload).hexdigest()

Solution

1. Step 1: Understand HMAC function parameters

   The correct order is secret key first, then message (payload), and the hashing algorithm.

2. Step 2: Identify correct syntax and algorithm

   hmac.new(secret.encode(), payload.encode(), hashlib.sha256).hexdigest() uses hmac.new with secret encoded, payload encoded, and hashlib.sha256, which is correct.

3. Final Answer:

   hmac.new(secret.encode(), payload.encode(), hashlib.sha256).hexdigest() -> Option A

4. Quick Check:

   Secret first, payload second, SHA256 used [OK]

Hint: Secret key is first argument in hmac.new() [OK]

Common Mistakes:

• Swapping secret and payload order
• Using wrong hash function like md5
• Incorrect function call syntax

3. Given the following Python code snippet, what will be the output if the signature matches the computed HMAC?

import hmac
import hashlib

secret = "mysecret"
payload = "testdata"
signature = hmac.new(secret.encode(), payload.encode(), hashlib.sha256).hexdigest()
computed = hmac.new(secret.encode(), payload.encode(), hashlib.sha256).hexdigest()
if computed == signature:
    print("Signature verified")
else:
    print("Signature mismatch")

medium

A. None

B. "Signature verified"

C. RuntimeError

D. "Signature mismatch"

Solution

1. Step 1: Analyze the signature comparison

   The code compares the computed signature with the received signature and prints "Signature verified" if they match.

2. Step 2: Determine output when signatures match

   Since the signatures match, the output will be the success message "Signature verified".

3. Final Answer:

   "Signature verified" -> Option B

4. Quick Check:

   Matching signatures print verification message [OK]

Hint: Match means print verified message [OK]

Common Mistakes:

• Confusing mismatch message as output
• Expecting an error instead of message
• Assuming no output (None)

4. Identify the error in this Python webhook verification snippet:

import hmac
import hashlib

secret = "mysecret"
payload = "data"
signature = "abc123"

computed = hmac.new(secret, payload.encode(), hashlib.sha256).hexdigest()
if computed == signature:
    print("Verified")
else:
    print("Not verified")

medium

A. payload should not be encoded

B. hashlib.md5 should be used instead of sha256

C. secret should be encoded before use in hmac.new

D. signature comparison should use != instead of ==

Solution

1. Step 1: Check data types for hmac.new

   hmac.new requires the secret key as bytes, but secret is a string and not encoded.

2. Step 2: Identify correct fix

   Encoding secret with secret.encode() fixes the error; payload encoding is correct.

3. Final Answer:

   secret should be encoded before use in hmac.new -> Option C

4. Quick Check:

   Secret must be bytes, so encode it [OK]

Hint: Encode secret string before hmac.new call [OK]

Common Mistakes:

• Not encoding secret key
• Changing payload encoding incorrectly
• Using wrong hash function
• Wrong comparison operator

5. You receive webhook requests with a signature header. To securely verify the webhook, which steps should you perform in order? Select the correct sequence.

hard

A. 1. Retrieve secret key
2. Compare signatures
3. Compute HMAC of payload
4. Accept webhook if signatures do not match

B. 1. Accept webhook
2. Compute HMAC of payload
3. Compare signatures
4. Log the webhook

C. 1. Compute HMAC of payload
2. Retrieve secret key
3. Compare signatures
4. Reject webhook if signatures match

D. 1. Retrieve the secret key
2. Compute HMAC of the payload using the secret
3. Compare computed signature with header signature
4. Accept webhook if signatures match

Solution

1. Step 1: Retrieve the secret key

   You need the secret key first to compute the HMAC signature.

2. Step 2: Compute HMAC of the payload using the secret

   Use the secret key and payload to compute the signature.

3. Step 3: Compare computed signature with header signature

   Check if the computed signature matches the one sent in the webhook header.

4. Step 4: Accept webhook if signatures match

   Only accept the webhook if the signatures are the same to ensure trust.

5. Final Answer:

   1. Retrieve the secret key 2. Compute HMAC of the payload using the secret 3. Compare computed signature with header signature 4. Accept webhook if signatures match -> Option D

6. Quick Check:

   Secret -> Compute -> Compare -> Accept [OK]

Hint: Always compute signature before comparing and accepting [OK]

Common Mistakes:

• Accepting webhook before verification
• Comparing before computing signature
• Rejecting on matching signatures