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Encrypted Communication

Twilio supports encryption to protect communications between Twilio and your web application. Just specify an HTTPS URL. Note: Twilio cannot currently handle self signed certificates.

Twilio supports the TLS cryptographic protocol. Support for SSLv3 is officially deprecated.

HTTP Authentication

Twilio supports HTTP Basic and Digest Authentication. This allows you to password protect your TwiML URLs on your web server so that only you and Twilio can access them. You may provide a username and password via the following URL format.

Twilio will authenticate to your web server using the provided username and password and will remain logged in for the duration of the call. We highly recommend that you use HTTP Authentication in conjunction with encryption. For more information on Basic and Digest Authentication, refer to your web server documentation.

If you specify a password-protected URL, Twilio will first send a request with no Authorization header. After your server responds with a 401 Unauthorized status code, a WWW-Authenticate header and a realm in the response, Twilio will make the same request with an Authorization header.

Example response from your server:

WWW-Authenticate: Basic realm="My Realm"
Date: Wed, 21 Jun 2017 01:14:36 GMT
Content-Type: application/xml
Content-Length: 327

Validating Requests are coming from Twilio

If your application exposes sensitive data, or is possibly mutative to your data, then you may want to be sure that the HTTP requests to your web application are indeed coming from Twilio, and not a malicious third party. To allow you this level of security, Twilio cryptographically signs its requests. Here's how it works:

  1. Turn on TLS on your server and configure your Twilio account to use HTTPS urls.
  2. Twilio assembles its request to your application, including the final URL and any POST fields.
    • If your request is a POST, Twilio takes all the POST fields, sorts them alphabetically by their name, and concatenates the parameter name and value to the end of the URL (with no delimiter).
    • If the request is a GET, the final URL includes all of Twilio's request parameters appended in the query string of your original URL using the standard delimiter & between the name/value pairs.
  3. Twilio takes the resulting string (the full URL with scheme, port, query string and any POST parameters) and signs it using HMAC-SHA1 and your AuthToken as the key.
  4. Twilio sends this signature in an HTTP header called X-Twilio-Signature

Then, on your end, if you want to verify the authenticity of the request, you can re-assemble the data string by going through the exact same process. If our two hashes match, then the request was authentic. You can then be sure that all the data used to construct the hash, including the full URL, query string and POST parameters were all sent to you by Twilio. Here's how you would perform the validation on your end:

  1. Take the full URL of the request URL you specify for your phone number or app, from the protocol (https...) through the end of the query string (everything after the ?).
  2. If the request is a POST, sort all of the POST parameters alphabetically (using Unix-style case-sensitive sorting order).
  3. Iterate through the sorted list of POST parameters, and append the variable name and value (with no delimiters) to the end of the URL string.
  4. Sign the resulting string with HMAC-SHA1 using your AuthToken as the key (remember, your AuthToken's case matters!).
  5. Base64 encode the resulting hash value.
  6. Compare your hash to ours, submitted in the X-Twilio-Signature header. If they match, then you're good to go.

Let's walk through an example request. Let's say Twilio made a POST to your page:

And let's say Twilio posted some digits from a <Gather> to that url, in addition to all the usual POST fields

  • Digits: 1234
  • To: +18005551212
  • From: +14158675310
  • Caller: +14158675310
  • CallSid: CA1234567890ABCDE

  • Create a string that is your URL with the full query string:

  • Sort the list of POST variables by the parameter name (using Unix-style case-sensitive sorting order):

    • CallSid: CA1234567890ABCDE
    • Caller: +14158675310
    • Digits: 1234
    • From: +14158675310
    • To: +18005551212
  • Append each POST variable, name and value, to the string with no delimiters: >

  • Hash the resulting string using HMAC-SHA1, using your AuthToken (Primary) as the key. Let's suppose your AuthToken is 12345. Then take the hash value returned from the following function call (or its equivalent in your language of choice): > hmac_sha1(, 12345)

  • Now take the Base64 encoding of the hash value (so it's only ASCII characters): > GvWf1cFY/Q7PnoempGyD5oXAezc==

  • Compare that to the hash Twilio sent in the X-Twilio-Signature HTTP header. Match them up!

Here are examples from our helper libraries:


        We highly recommend you use the helper libraries to do signature validation. If you are curious what the libraries are doing under the hood, here is an example written in PHP that you can copy:

            // Your auth token from
            $authToken = '456bef';
            public function computeSignature($url, $data = array()) {
                // sort the array by keys
                // append the data array to the url string, with no delimiters
                foreach ($data as $key => $value) {
                    $url = $url . $key . $value;
                // This function calculates the HMAC hash of the data with the key
                // passed in
                // Note: hash_hmac requires PHP 5 >= 5.1.2 or PECL hash:1.1-1.5
                // Or
                $hmac = hash_hmac("sha1", $url, $authToken, true);
                return base64_encode($hmac);

        A Few Notes

        • When creating the hash make sure you are using your Primary AuthToken as the key. If you have recently created a secondary AuthToken, this means you still need to use your old AuthToken until the secondary one has been promoted to your primary AuthToken.
        • For SMS and voice callbacks over HTTP, Twilio will drop the username and password (if any) from the URL before computing the signature. For SMS and voice callbacks over HTTPS, Twilio will drop the username, password and port (if any) before computing the signature. This behavior will continue to be supported in the 2008-08-01 and 2010-04-01 versions of the API to ensure compatibility with existing code. We understand this behavior is inconsistent, and apologize for the inconvenience.
        • The HMAC-SHA1 secure hashing algorithm should be available in all major languages, either in the core or via an extension or package.
        • If your URL uses an "index" page, such as index.php or index.html to handle the request, such as: where the real page is served from, then Apache or PHP may rewrite that URL so it has a trailing slash, e.g., Using the code above, or similar code in another language, you could end up with an incorrect hash, because Twilio built the hash using and you may have built the hash using

        A note on HMAC-SHA1

        Concerned about SHA1 security issues? Twilio does not use SHA-1 alone.

        In short, the critical component of HMAC-SHA1 that distinguishes it from SHA-1 alone is the use of your Twilio AuthToken as a complex secret key. While there are possible collision-based attacks on SHA-1, HMACs are not affected by those same attacks - it's the combination of the underlying hashing algorithm (SHA-1) and the strength of the secret key (AuthToken) that protects you in this case.

        It's a great idea to test your webhooks and ensure that their signatures are secure. The following sample Python code can test your unique endpoint against both valid and invalid signatures.

        To make this test work for you, you'll need to:

        1. Set your Auth Token as an environment variable
        2. Set the URL to the endpoint you want to test
        3. If testing BasicAuth, change HTTPDigestAuth to HTTPBasicAuth
              This sample test will test the validity of your webhook signature with HTTP Basic or Digest authentication.

              Test the validity of your webhook signature

              This sample test will test the validity of your webhook signature with HTTP Basic or Digest authentication.

              Validation using the Twilio Helper Libraries

              All of the official Twilio Helper Libraries ship with a Utilities class which facilitates request validation. Head over to the libraries page to download the library for your language of choice.

              Your Auth Token

              Please keep your AuthToken secure. It not only enables access to the REST API, but also to request signatures. Learn how to secure this token using environment variables.

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