Check the webhook signatures

Stripe can optionally sign the webhook events it sends to your endpoints by including a signature in each event’s Stripe-Signature header. This allows you to verify that the events were sent by Stripe, not by a third party. You can verify signatures either using our official libraries, or manually using your own solution.

Before you can verify signatures, you need to retrieve your endpoint’s secret from your Dashboard’s Webhooks settings. Select an endpoint that you want to obtain the secret for, then click the Click to reveal button.

Stripe generates a unique secret key for each endpoint. If you use the same endpoint for both test and live API keys, note that the secret is different for each one. Additionally, if you use multiple endpoints, you must obtain a secret for each one you want to verify signatures on. After this setup, Stripe starts to sign each webhook it sends to the endpoint.

Verifying signatures using our official libraries

Use one of our official libraries to verify signatures. You perform the verification by providing the event payload, the Stripe-Signature header, and the endpoint’s secret. If verification fails, Stripe returns an error.

# Set your secret key. Remember to switch to your live secret key in production.
# See your keys here: https://dashboard.stripe.com/apikeys
Stripe.api_key = 
'sk_test_rfaBmNUu1lWB7VZ0MMSIsYjH'

require 'stripe'
require 'sinatra'

# If you are testing your webhook locally with the Stripe CLI you
# can find the endpoint's secret by running `stripe listen`
# Otherwise, find your endpoint's secret in your webhook settings in
# the Developer Dashboard
endpoint_secret = 'whsec_...'

# Using the Sinatra framework
set :port, 4242

post '/my/webhook/url' do
  payload = request.body.read
  sig_header = request.env['HTTP_STRIPE_SIGNATURE']
  event = nil

  begin
    event = Stripe::Webhook.construct_event(
      payload, sig_header, endpoint_secret
    )
  rescue JSON::ParserError => e
    # Invalid payload
    status 400
    return
  rescue Stripe::SignatureVerificationError => e
    # Invalid signature
    status 400
    return
  end

  # Handle the event
  case event.type
  when 'payment_intent.succeeded'
    payment_intent = event.data.object # contains a Stripe::PaymentIntent
    puts 'PaymentIntent was successful!'
  when 'payment_method.attached'
    payment_method = event.data.object # contains a Stripe::PaymentMethod
    puts 'PaymentMethod was attached to a Customer!'
  # ... handle other event types
  else
    puts "Unhandled event type: #{event.type}"
  end

  status 200
end

Preventing replay attacks

A replay attack is when an attacker intercepts a valid payload and its signature, then re-transmits them. To mitigate such attacks, Stripe includes a timestamp in the Stripe-Signature header. Because this timestamp is part of the signed payload, it is also verified by the signature, so an attacker can’t change the timestamp without invalidating the signature. If the signature is valid but the timestamp is too old, you can have your application reject the payload.

Our libraries have a default tolerance of five minutes between the timestamp and the current time. You can change this tolerance by providing an additional parameter when verifying signatures. Use Network Time Protocol (NTP) to ensure that your server’s clock is accurate and synchronizes with the time on Stripe’s servers.

Stripe generates the timestamp and signature each time we send an event to your endpoint. If Stripe retries an event (for example, your endpoint previously replied with a non-2xx status code), then we generate a new signature and timestamp for the new delivery attempt.

Verifying signatures manually

The Stripe-Signature header included in each signed event contains a timestamp and one or more signatures. The timestamp is prefixed by t=, and each signature is prefixed by a scheme. Schemes start with v, followed by an integer. Currently, the only valid live signature scheme is v1. To aid with testing, Stripe sends an additional signature with a fake v0 scheme, for test mode events.

Stripe-Signature:
t=1492774577,
v1=5257a869e7ecebeda32affa62cdca3fa51cad7e77a0e56ff536d0ce8e108d8bd,
v0=6ffbb59b2300aae63f272406069a9788598b792a944a07aba816edb039989a39

Stripe generates signatures using a hash-based message authentication code (HMAC) with SHA-256. To prevent downgrade attacks, you should ignore all schemes that are not v1.

It is possible to have multiple signatures with the same scheme-secret pair. This can happen when you roll an endpoint’s secret from the Dashboard, and choose to keep the previous secret active for up to 24 hours. During this time, your endpoint has multiple active secrets and Stripe generates one signature for each secret.

Although it’s recommended to use our official libraries to verify webhook event signatures, you can create a custom solution by following these steps.

Step 1: Extract the timestamp and signatures from the header

Split the header, using the , character as the separator, to get a list of elements. Then split each element, using the = character as the separator, to get a prefix and value pair.

The value for the prefix t corresponds to the timestamp, and v1 corresponds to the signature (or signatures). You can discard all other elements.

Step 2: Prepare the signed_payload string

The signed_payload string is created by concatenating:

• The timestamp (as a string)
• The character .
• The actual JSON payload (that is, the request body)

Step 3: Determine the expected signature

Compute an HMAC with the SHA256 hash function. Use the endpoint’s signing secret as the key, and use the signed_payload string as the message.

Step 4: Compare the signatures

Compare the signature (or signatures) in the header to the expected signature. For an equality match, compute the difference between the current timestamp and the received timestamp, then decide if the difference is within your tolerance.

To protect against timing attacks, use a constant-time string comparison to compare the expected signature to each of the received signatures.