Digital Signature Guide

Digitally sign your request with an API key

Depending on your usage, a digital signature - in addition to an API key - may be required to authenticate requests. See the following articles:

How digital signatures work

Digital signatures are generated using a URL signing secret, which is available on the Google Cloud console. This secret is essentially a private key, only shared between you and Google, and is unique to your project.

The signing process uses an encryption algorithm to combine the URL and your shared secret. The resulting unique signature allows our servers to verify that any site generating requests using your API key is authorized to do so.

Limit unsigned requests

To ensure that your API key only accepts signed requests:

  1. Go to the Google Maps Platform Quotas page in the Cloud console.
  2. Click the project drop-down and select the same project you used when you created the API key for your application or site.
  3. Select the Maps Static API or Street View Static API from the APIs drop-down.
  4. Expand the Unsigned requests section.
  5. In the Quota Name table, click the edit button next to the quota you want to edit. For example, Unsigned requests per day.
  6. Update Quota limit in the Edit Quota Limit pane.
  7. Select Save.

Signing your requests

Signing your requests comprises the following steps:

Step 1: Get your URL signing secret

To get your project URL signing secret:

  1. Go to the Google Maps Platform Credentials page in the Cloud console.
  2. Select the project drop-down and select the same project you used when you created the API key for the Maps Static API or Street View Static API.
  3. Scroll down to the Secret Generator card. The Current secret field contains your current URL signing secret.
  4. The page also features the Sign a URL now widget that allows you to automatically sign the Maps Static API or Street View Static API request using your current signing secret. Scroll down to the Sign a URL now card to access it.

To get a new URL signing secret, select Regenerate Secret. The previous secret will expire 24 hours after you've generated a new secret. After the 24 hours have passed, requests containing the old secret no longer work.

Step 2: Construct your unsigned request

Characters not listed in the table below must be URL-encoded:

Summary of Valid URL Characters
SetcharactersURL usage
Alphanumeric a b c d e f g h i j k l m n o p q r s t u v w x y z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 0 1 2 3 4 5 6 7 8 9 Text strings, scheme usage (http), port (8080), etc.
Unreserved - _ . ~ Text strings
Reserved ! * ' ( ) ; : @ & = + $ , / ? % # [ ] Control characters and/or Text Strings

The same applies to any characters in the Reserved set, if they are passed inside a text string. For more info, see Special characters.

Construct your unsigned request URL without the signature. For instructions, see the following developer documentation:

Make sure to also include the API key in the key parameter. For example:

https://maps.googleapis.com/maps/api/staticmap?center=Z%C3%BCrich&size=400x400&key=YOUR_API_KEY

Generate the signed request

For one-off use cases, such as hosting a simple Maps Static API or Street View Static API image on your web page, or troubleshooting purposes, you can generate a digital signature automatically using the available Sign a URL now widget.

For dynamically generated requests, you need server-side signing, which requires a few additional intermediate steps

Either way, you should end up with a request URL that has a signature parameter appended to the end. For example:

https://maps.googleapis.com/maps/api/staticmap?center=Z%C3%BCrich&size=400x400&key=YOUR_API_KEY
&signature=BASE64_SIGNATURE
Using the Sign a URL now widget

To generate a digital signature with an API key using the Sign a URL now widget in the Google Cloud console:

  1. Locate the Sign a URL now widget, as described in Step 1: Get your URL signing secret.
  2. In the URL field, paste your unsigned request URL from Step 2: Construct your unsigned request.
  3. The Your Signed URL field that appears will contain your digitally signed URL. Be sure to make a copy.
Generate digital signatures server-side

Compared to the Sign a URL now widget, you will need to take a few additional actions when generating digital signatures server-side:

  1. Strip off the protocol scheme and host portions of the URL, leaving only the path and the query:

    2. /maps/api/staticmap?center=Z%C3%BCrich&size=400x400&key=YOUR_API_KEY

  2. The displayed URL signing secret is encoded in a modified Base64 for URLs.

    As most cryptographic libraries require the key to be in raw byte format, you will likely need to decode your URL signing secret into its original raw format before signing.

  3. Sign the above stripped request using HMAC-SHA1.

  4. As most cryptographic libraries generate a signature in raw byte format, you will need to convert the resulting binary signature using the modified Base64 for URLs to convert it into something that can be passed within the URL.

  5. Append the Base64-encoded signature to the original unsigned request URL in the signature parameter. For example:

    https://maps.googleapis.com/maps/api/staticmap?center=Z%C3%BCrich&size=400x400&key=YOUR_API_KEY
&signature=BASE64_SIGNATURE

For samples showing ways to implement URL signing using server-side code, see Sample code for URL signing below.

Sample code for URL signing

The following sections show ways to implement URL signing using server-side code. URLs should always be signed server-side to avoid exposing your URL signing secret to users.

Python

The example below uses standard Python libraries to sign a URL. (Download the code.)

#!/usr/bin/python
# -*- coding: utf-8 -*-
""" Signs a URL using a URL signing secret """

import hashlib
import hmac
import base64
import urllib.parse as urlparse


def sign_url(input_url=None, secret=None):
    """ Sign a request URL with a URL signing secret.
      Usage:
      from urlsigner import sign_url
      signed_url = sign_url(input_url=my_url, secret=SECRET)
      Args:
      input_url - The URL to sign
      secret    - Your URL signing secret
      Returns:
      The signed request URL
  """

    if not input_url or not secret:
        raise Exception("Both input_url and secret are required")

    url = urlparse.urlparse(input_url)

    # We only need to sign the path+query part of the string
    url_to_sign = url.path + "?" + url.query

    # Decode the private key into its binary format
    # We need to decode the URL-encoded private key
    decoded_key = base64.urlsafe_b64decode(secret)

    # Create a signature using the private key and the URL-encoded
    # string using HMAC SHA1. This signature will be binary.
    signature = hmac.new(decoded_key, str.encode(url_to_sign), hashlib.sha1)

    # Encode the binary signature into base64 for use within a URL
    encoded_signature = base64.urlsafe_b64encode(signature.digest())

    original_url = url.scheme + "://" + url.netloc + url.path + "?" + url.query

    # Return signed URL
    return original_url + "&signature=" + encoded_signature.decode()


if __name__ == "__main__":
    input_url = input("URL to Sign: ")
    secret = input("URL signing secret: ")
    print("Signed URL: " + sign_url(input_url, secret))

Java

The example below uses the java.util.Base64 class available since JDK 1.8 - older versions may need to use Apache Commons or similar. (Download the code.)

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.net.URI;
import java.net.URISyntaxException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.util.Base64;  // JDK 1.8 only - older versions may need to use Apache Commons or similar.
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import java.net.URL;
import java.io.BufferedReader;
import java.io.InputStreamReader;

public class UrlSigner {

  // Note: Generally, you should store your private key someplace safe
  // and read them into your code

  private static String keyString = "YOUR_PRIVATE_KEY";
  
  // The URL shown in these examples is a static URL which should already
  // be URL-encoded. In practice, you will likely have code
  // which assembles your URL from user or web service input
  // and plugs those values into its parameters.
  private static String urlString = "YOUR_URL_TO_SIGN";

  // This variable stores the binary key, which is computed from the string (Base64) key
  private static byte[] key;
  
  public static void main(String[] args) throws IOException,
    InvalidKeyException, NoSuchAlgorithmException, URISyntaxException {
    
    BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
    
    String inputUrl, inputKey = null;

    // For testing purposes, allow user input for the URL.
    // If no input is entered, use the static URL defined above.    
    System.out.println("Enter the URL (must be URL-encoded) to sign: ");
    inputUrl = input.readLine();
    if (inputUrl.equals("")) {
      inputUrl = urlString;
    }
    
    // Convert the string to a URL so we can parse it
    URL url = new URL(inputUrl);
 
    // For testing purposes, allow user input for the private key.
    // If no input is entered, use the static key defined above.   
    System.out.println("Enter the Private key to sign the URL: ");
    inputKey = input.readLine();
    if (inputKey.equals("")) {
      inputKey = keyString;
    }
    
    UrlSigner signer = new UrlSigner(inputKey);
    String request = signer.signRequest(url.getPath(),url.getQuery());
    
    System.out.println("Signed URL :" + url.getProtocol() + "://" + url.getHost() + request);
  }
  
  public UrlSigner(String keyString) throws IOException {
    // Convert the key from 'web safe' base 64 to binary
    keyString = keyString.replace('-', '+');
    keyString = keyString.replace('_', '/');
    System.out.println("Key: " + keyString);
    // Base64 is JDK 1.8 only - older versions may need to use Apache Commons or similar.
    this.key = Base64.getDecoder().decode(keyString);
  }

  public String signRequest(String path, String query) throws NoSuchAlgorithmException,
    InvalidKeyException, UnsupportedEncodingException, URISyntaxException {
    
    // Retrieve the proper URL components to sign
    String resource = path + '?' + query;
    
    // Get an HMAC-SHA1 signing key from the raw key bytes
    SecretKeySpec sha1Key = new SecretKeySpec(key, "HmacSHA1");

    // Get an HMAC-SHA1 Mac instance and initialize it with the HMAC-SHA1 key
    Mac mac = Mac.getInstance("HmacSHA1");
    mac.init(sha1Key);

    // compute the binary signature for the request
    byte[] sigBytes = mac.doFinal(resource.getBytes());

    // base 64 encode the binary signature
    // Base64 is JDK 1.8 only - older versions may need to use Apache Commons or similar.
    String signature = Base64.getEncoder().encodeToString(sigBytes);
    
    // convert the signature to 'web safe' base 64
    signature = signature.replace('+', '-');
    signature = signature.replace('/', '_');
    
    return resource + "&signature=" + signature;
  }
}

Node JS

The example below uses native Node modules to sign a URL. (Download the code.)

'use strict'

const crypto = require('crypto');
const url = require('url');

/**
 * Convert from 'web safe' base64 to true base64.
 *
 * @param  {string} safeEncodedString The code you want to translate
 *                                    from a web safe form.
 * @return {string}
 */
function removeWebSafe(safeEncodedString) {
  return safeEncodedString.replace(/-/g, '+').replace(/_/g, '/');
}

/**
 * Convert from true base64 to 'web safe' base64
 *
 * @param  {string} encodedString The code you want to translate to a
 *                                web safe form.
 * @return {string}
 */
function makeWebSafe(encodedString) {
  return encodedString.replace(/\+/g, '-').replace(/\//g, '_');
}

/**
 * Takes a base64 code and decodes it.
 *
 * @param  {string} code The encoded data.
 * @return {string}
 */
function decodeBase64Hash(code) {
  // "new Buffer(...)" is deprecated. Use Buffer.from if it exists.
  return Buffer.from ? Buffer.from(code, 'base64') : new Buffer(code, 'base64');
}

/**
 * Takes a key and signs the data with it.
 *
 * @param  {string} key  Your unique secret key.
 * @param  {string} data The url to sign.
 * @return {string}
 */
function encodeBase64Hash(key, data) {
  return crypto.createHmac('sha1', key).update(data).digest('base64');
}

/**
 * Sign a URL using a secret key.
 *
 * @param  {string} path   The url you want to sign.
 * @param  {string} secret Your unique secret key.
 * @return {string}
 */
function sign(path, secret) {
  const uri = url.parse(path);
  const safeSecret = decodeBase64Hash(removeWebSafe(secret));
  const hashedSignature = makeWebSafe(encodeBase64Hash(safeSecret, uri.path));
  return url.format(uri) + '&signature=' + hashedSignature;
}

C#

The example below uses the default System.Security.Cryptography library to sign a URL request. Note that we need to convert the default Base64 encoding to implement a URL-safe version. (Download the code.)

using System;
using System.Collections.Generic;
using System.Security.Cryptography;
using System.Text;
using System.Text.RegularExpressions;
using System.Web;

namespace SignUrl {

  public struct GoogleSignedUrl {

    public static string Sign(string url, string keyString) {
      ASCIIEncoding encoding = new ASCIIEncoding();

      // converting key to bytes will throw an exception, need to replace '-' and '_' characters first.
      string usablePrivateKey = keyString.Replace("-", "+").Replace("_", "/");
      byte[] privateKeyBytes = Convert.FromBase64String(usablePrivateKey);

      Uri uri = new Uri(url);
      byte[] encodedPathAndQueryBytes = encoding.GetBytes(uri.LocalPath + uri.Query);

      // compute the hash
      HMACSHA1 algorithm = new HMACSHA1(privateKeyBytes);
      byte[] hash = algorithm.ComputeHash(encodedPathAndQueryBytes);

      // convert the bytes to string and make url-safe by replacing '+' and '/' characters
      string signature = Convert.ToBase64String(hash).Replace("+", "-").Replace("/", "_");
            
      // Add the signature to the existing URI.
      return uri.Scheme+"://"+uri.Host+uri.LocalPath + uri.Query +"&signature=" + signature;
    }
  }

  class Program {

    static void Main() {
    
      // Note: Generally, you should store your private key someplace safe
      // and read them into your code

      const string keyString = "YOUR_PRIVATE_KEY";
  
      // The URL shown in these examples is a static URL which should already
      // be URL-encoded. In practice, you will likely have code
      // which assembles your URL from user or web service input
      // and plugs those values into its parameters.
      const  string urlString = "YOUR_URL_TO_SIGN";
      
      string inputUrl = null;
      string inputKey = null;
    
      Console.WriteLine("Enter the URL (must be URL-encoded) to sign: ");
      inputUrl = Console.ReadLine();
      if (inputUrl.Length == 0) {
        inputUrl = urlString;
      }     
    
      Console.WriteLine("Enter the Private key to sign the URL: ");
      inputKey = Console.ReadLine();
      if (inputKey.Length == 0) {
        inputKey = keyString;
      }
      
      Console.WriteLine(GoogleSignedUrl.Sign(inputUrl,inputKey));
    }
  }
}

Examples in additional languages

Examples that cover more languages are available in the url-signing project.

Troubleshooting

If the request includes an invalid signature, the API returns an HTTP 403 (Forbidden) error. This error most likely occurs if the used signing secret isn't linked to the passed API key, or if non-ASCII input isn't URL-encoded before signing.

To troubleshoot the issue, copy the request URL, strip the signature query parameter, and regenerate a valid signature following the instructions below:

To generate a digital signature with an API key using the Sign a URL now widget in the Google Cloud console:

  1. Locate the Sign a URL now widget, as described in Step 1: Get your URL signing secret.
  2. In the URL field, paste your unsigned request URL from Step 2: Construct your unsigned request.
  3. The Your Signed URL field that appears will contain your digitally signed URL. Be sure to make a copy.