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To ensure that the webhook notifications you receive are sent by CHIP and have not been tampered with, you should validate the signature included in each request.

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Signature Header

Each webhook delivery request includes an X-Signature header field. This field contains a base64-encoded RSA PKCS#1 v1.5 signature of the SHA512 digest of the request body buffer.

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Obtaining the Public Key

Unlike CHIP Collect, CHIP Send provides a dedicated public key for each webhook. You can obtain the public key by retrieving the webhook details via the Retrieve a Webhook API. The public_key field in the response contains the PEM-encoded RSA public key.

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Verification Steps

  1. Retrieve the Payload: Get the raw request body (buffer) of the webhook notification.
  2. Get the Signature: Extract the value of the X-Signature header and base64-decode it.
  3. Verify: Use the RSA public key to verify the signature against the SHA512 digest of the raw request body.

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Code Examples

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Ruby

require 'openssl'
require 'base64'

# webhook_public_key: The PEM-encoded public key from the Webhook object
# x_signature_header: The value of the X-Signature header
# request_body: The raw JSON body of the request

public_key = OpenSSL::PKey::RSA.new(webhook_public_key)
signature = Base64.decode64(x_signature_header)
digest = OpenSSL::Digest::SHA512.new

is_valid = public_key.verify(digest, signature, request_body)

if is_valid
  puts "Signature is valid"
else
  puts "Signature is invalid"
end

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PHP

<?php

// $webhook_public_key: The PEM-encoded public key from the Webhook object
// $x_signature_header: The value of the X-Signature header
// $request_body: The raw JSON body of the request

$public_key = openssl_pkey_get_public($webhook_public_key);
$signature = base64_decode($x_signature_header);

$is_valid = openssl_verify($request_body, $signature, $public_key, OPENSSL_ALGO_SHA512);

if ($is_valid === 1) {
    echo "Signature is valid";
} elseif ($is_valid === 0) {
    echo "Signature is invalid";
} else {
    echo "Error checking signature";
}
The provider is not responsible for any financial losses incurred due to not implementing payload signature verification.