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Validate Google Extended Access Article signature (Python)

Google Extended Access
Google Extended Access provides access to news article beyond the Publisher paywall if the user signs in via Google OAuth. The number of access is based on metering. More info.
The news article is redirected to the publisher where it's determined if it's a valid visit from Google Showcase panel. One of the steps of validation is the verification of the signature sent along in the URL parameters (gaa_sig).
The signature is generated from the base URL and the other three GAA parameters, which you can use to verify that this is a valid visit from a Showcase panel.
Verification Steps
Transform the gaa_sig value from its "web safe" format by replacing all '' characters with '+', and the '' characters with '/'.
Base64 decode the transformed value from step 1.
Remove the gaa_sig URL parameter from the URL to form the data to verify.
Loop through the latest JSON web keys (JWKs):
For development: https://play.google.com/newsstand/api/v3/articleaccess/publicsigningkey/dev
Verify the signature value from step2 with the data from step 3 and the keys from step 4.
Working Code in Node
const { subtle } = require('crypto').webcrypto;
const fetch = (...args) => import('node-fetch').then(({default: fetch}) => fetch(...args));
GOOGLE_JSON_WEB_KEYS = "https://play.google.com/newsstand/api/v3/articleaccess/publicsigningkey/dev"
async function getPlaySigningKeys() {
let response = await fetch(GOOGLE_JSON_WEB_KEYS);
let data = await response.json();
return data;
}
async function verifyGaaUrlSignature(url, keys){
let urlObj = new URL(url);
let params = new URLSearchParams(urlObj.search);
let sigB64Str = params.get('gaa_sig');
if (!sigB64Str) {
return false;
}
let sigBuffer = Buffer.from(sigB64Str.replace(/-/g,'+').replace(/_/g,'/'), 'base64');
params.delete('gaa_sig');
let data = new TextEncoder().encode(urlObj.origin + urlObj.pathname + '?' + params);
async function verifySig(key) {
let cryptoKey = await subtle.importKey(
'jwk', key, {name: 'ECDSA', namedCurve: key.crv}, true, key.key_ops);
return subtle.verify(
{name: 'ECDSA', hash: 'SHA-256'}, cryptoKey, sigBuffer, data);
}
const results = await Promise.all(keys.map(verifySig));
return results.includes(true);
}
async function run() {
const playSigningKeys = await getPlaySigningKeys();
url = "https://www.bbc.com/?gaa_at=la&gaa_n=ATKjfPG-7F6PGpCXtPZFAfqigovblSKOl3G6jduKn8zWcjHMSu-a3wQ1ub-mKBl47rjP&gaa_ts=630be8f6&gaa_sig=ZGvbOCFg5J_zGAtd6R39YbEEYjcoarQ7AaAjQPsAae5jikZTjX57_Ja3vVyp8bUIcUbftI5dQdTP7gtwtIC3eQ%3D%3D"
const isValidSig = await verifyGaaUrlSignature(url, playSigningKeys.keys);
console.log('Valid Signature: ' + isValidSig);
}
if (require.main === module) {
run();
}
Steps to produce the parameters and signature
Generate the GAA parameters for the required url by appending it to the below url. The updated url will be redirected to the with the GAA parameters.
https://play.google.com/newsstand/api/v3/articleaccess?testurl=
Example:
https://play.google.com/newsstand/api/v3/articleaccess?testurl=https://bbc.com
Redirected to
https://www.bbc.com/?gaa_at=la&gaa_n=ATKjfPG-7F6PGpCXtPZFAfqigovblSKOl3G6jduKn8zWcjHMSu-a3wQ1ub-mKBl47rjP&gaa_ts=630be8f6&gaa_sig=ZGvbOCFg5J_zGAtd6R39YbEEYjcoarQ7AaAjQPsAae5jikZTjX57_Ja3vVyp8bUIcUbftI5dQdTP7gtwtIC3eQ%3D%3D
What would be the working code in Python?
I tried looking into python-jose. I couldn't figure out the equivalent. The Web API for SubtleCrypto.verify().

Sign a message with EdDSA algorithm in Javascript to get JWT

I need to get JWT with EdDSA algorithm to be able to use an API. I have the private key to sign the message and I could do that with PHP with the next library: https://github.com/firebase/php-jwt (you can see the example with EdDSA at README). Now I need to do the same in JS but I didn't find the way to get JWT with a given secret key (encoded base 64) like that (only an example is not the real secretKey):
const secretKey = Dm2xriMD6riJagld4WCA6zWqtuWh40UzT/ZKO0pZgtHATOt0pGw90jG8BQHCE3EOjiCkFR2/gaW6JWi+3nZp8A==
I tried a lot of libraries like jose, js-nacl, crypto, libsodium, etc. And I am really close to get the JWT with libsodium library, now I attach the code:
const base64url = require("base64url");
const _sodium = require("libsodium-wrappers");
const moment = require("moment");
const getJWT = async () => {
await _sodium.ready;
const sodium = _sodium;
const privateKey =
"Dm2xriMD6riJagld4WCA6zWqtuWh40UzT/ZKO0pZgtHATOt0pGw90jG8BQHCE3EOjiCkFR2/gaW6JWi+3nZp8A==";
const payload = {
iss: "test",
aud: "test.com",
iat: 1650101178,
exp: 1650101278,
sub: "12345678-1234-1234-1234-123456789123"
};
const { msg, keyAscii} = encode(payload, privateKey, "EdDSA");
const signature = sodium.crypto_sign_detached(msg, keyDecoded); //returns Uint8Array(64)
//Here is the problem.
};
const encode = (payload, key, alg) => {
const header = {
typ: "JWT",
alg //'EdDSA'
};
const headerBase64URL = base64url(JSON.stringify(header));
const payloadBase64URL = base64url(JSON.stringify(payload));
const headerAndPayloadBase64URL = `${headerBase64URL}.${payloadBase64URL}`;
const keyAscii= Buffer.from(key, "base64").toString("ascii");
return {headerAndPayloadBase64URL , keyAscii}
};
The problem is in the sodium.crypto_sign_detached function because it returns an Uint8Array(64) signature and and I need the JWT like that:
eyJ0eXAiOiJKV1QiLCJhbGciOiJFZERTQSJ9.eyJpc3MiOiJ0ZXN0IiwiYXVkIjoidGVzdC5jb20iLCJpYXQiOjE2NTAxMDExNzgsImV4cCI6MTY1MDEwMTI3OCwic3ViIjoiMTIzNDU2NzgtMTIzNC0xMjM0LTEyMzQtMTIzNDU2Nzg5MTIzIn0.f7WG_02UKljrMeVVOTNNBAGxtLXJUT_8QAnujNhomV18Pn5cU-0lHRgVlmRttOlqI7Iol_fHut3C4AOXxDGnAQ
How can I change the Uint8Array(64) to get the signature in a right format to get the JWT? I tried with base64, base64url, hex, text, ascii, etc and the final JWT is not valid (because the signature is wrong).
If you compare my code with the code that I mentioned with PHP is very similar but the function sodium.crypto_sign_detached returns Uint8Array(64) at JS library and the same function in PHP returns an string and I can get the token.
Or maybe there a way to adapt my given private key for use in other library (like crypto or jose where I received an error for the private key format)
Thank you!

In the posted NodeJS code there are the following issues:
crypto_sign_detached() returns the signature as a Uint8Array, which can be imported with Buffer.from() and converted to a Base64 string with base64url().
Concatenating headerAndPayloadBase64URL and the Base64url encoded signature with a . as separator gives the JWT you are looking for.
The raw private key must not be decoded with 'ascii', as this generally corrupts the data. Instead, it should simply be handled as buffer. Note: If for some reason a conversion to a string is required, use 'binary' as encoding, which produces a byte string (however, this is not an option with crypto_sign_detached() as this function expects a buffer).
With these changes, the following NodeJS code results:
const _sodium = require('libsodium-wrappers');
const base64url = require("base64url");
const getJWT = async () => {
await _sodium.ready;
const sodium = _sodium;
const privateKey = "Dm2xriMD6riJagld4WCA6zWqtuWh40UzT/ZKO0pZgtHATOt0pGw90jG8BQHCE3EOjiCkFR2/gaW6JWi+3nZp8A==";
const payload = {
iss: "test",
aud: "test.com",
iat: 1650101178,
exp: 1650101278,
sub: "12345678-1234-1234-1234-123456789123"
};
const {headerAndPayloadBase64URL, keyBuf} = encode(payload, privateKey, "EdDSA");
const signature = sodium.crypto_sign_detached(headerAndPayloadBase64URL, keyBuf);
const signatureBase64url = base64url(Buffer.from(signature));
console.log(`${headerAndPayloadBase64URL}.${signatureBase64url}`) // eyJ0eXAiOiJKV1QiLCJhbGciOiJFZERTQSJ9.eyJpc3MiOiJ0ZXN0IiwiYXVkIjoidGVzdC5jb20iLCJpYXQiOjE2NTAxMDExNzgsImV4cCI6MTY1MDEwMTI3OCwic3ViIjoiMTIzNDU2NzgtMTIzNC0xMjM0LTEyMzQtMTIzNDU2Nzg5MTIzIn0.f7WG_02UKljrMeVVOTNNBAGxtLXJUT_8QAnujNhomV18Pn5cU-0lHRgVlmRttOlqI7Iol_fHut3C4AOXxDGnAQ
};
const encode = (payload, key, alg) => {
const header = {
typ: "JWT",
alg //'EdDSA'
};
const headerBase64URL = base64url(JSON.stringify(header));
const payloadBase64URL = base64url(JSON.stringify(payload));
const headerAndPayloadBase64URL = `${headerBase64URL}.${payloadBase64URL}`;
const keyBuf = Buffer.from(key, "base64");
return {headerAndPayloadBase64URL, keyBuf};
};
getJWT();
Test:
Since Ed25519 is deterministic, the NodeJS code can be checked by comparing both JWTs: If, as in the above NodeJS code, the same header and payload are used as in the PHP code, the same signature and thus the same JWT is generated as by the PHP code, namely:
eyJ0eXAiOiJKV1QiLCJhbGciOiJFZERTQSJ9.eyJpc3MiOiJ0ZXN0IiwiYXVkIjoidGVzdC5jb20iLCJpYXQiOjE2NTAxMDExNzgsImV4cCI6MTY1MDEwMTI3OCwic3ViIjoiMTIzNDU2NzgtMTIzNC0xMjM0LTEyMzQtMTIzNDU2Nzg5MTIzIn0.f7WG_02UKljrMeVVOTNNBAGxtLXJUT_8QAnujNhomV18Pn5cU-0lHRgVlmRttOlqI7Iol_fHut3C4AOXxDGnAQ
which shows that the NodeJS code works.
Note that instead of the moment package, Date.now() could be used. This will return the time in milliseconds, so the value has to be divided by 1000, e.g. Math.round(Date.now()/1000), but saves a dependency.

AWS Signature V2: generate a signature for a Query request in Javascript

i am trying to re-create AWS signature version 2 authentication on javascript, what i have right now is
String.prototype.getBytes = () => {
return this.toString()
.split('')
.map((i) => i.charCodeAt(0));
};
let key = 'redacted_access_key_id';
const bytes = key.getBytes();
let signingKey = crypto.HmacSHA256(bytes, key);
let data = JSON.stringify({ lang: 'en', pageNumber: 0, pageSize: 20 });
const contentMd5 = crypto.MD5(data).toString();
data = data.getBytes();
signingKey = crypto.HmacSHA256(data, key);
const result = Buffer.from(signingKey.toString()).toString('base64');
Which outputs something like
ZGY0MmI3MDVjNmJlNzY5ZWYwZjU1ZTc5MDhhOGNkYzI3ZWVjYzQ5ODBmY2M1NGI5NTc2MmVmNTY1NzEwNjhhMA== 
which is incorrect, because the hash should be exactly 28 characters in length. Now the AWS signature version 2 auth docs show how it is being made, but only in java
import java.security.SignatureException;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import com.amazonaws.util.*;
/**
* This class defines common routines for generating
* authentication signatures for AWS Platform requests.
*/
public class Signature {
private static final String HMAC_SHA256_ALGORITHM = "HmacSHA256";
public static String calculateRFC2104HMAC(String data, String key)
throws java.security.SignatureException
{
String result;
try {
// Get an hmac_sha256 key from the raw key bytes.
SecretKeySpec signingKey = new SecretKeySpec(key.getBytes("UTF-8"), HMAC_SHA256_ALGORITHM);
// Get an hmac_sha256 Mac instance and initialize with the signing key.
Mac mac = Mac.getInstance(HMAC_SHA256_ALGORITHM);
mac.init(signingKey);
// Compute the hmac on input data bytes.
byte[] rawHmac = mac.doFinal(data.getBytes("UTF-8"));
// Base64-encode the hmac by using the utility in the SDK
result = BinaryUtils.toBase64(rawHmac);
} catch (Exception e) {
throw new SignatureException("Failed to generate HMAC : " + e.getMessage());
}
return result;
}
}
I am trying to recreate this exact same code in javascript but something is wrong. Can someone please help me with this, i cant find any examples in javascript.
Thank you.

The following code is the equivalent of the Java version of calculateRFC2104HMAC in JS.
const CryptoJS = require('crypto-js');
const calculateRFC2104HMAC = (data, key) => {
const rawHmac = CryptoJS.HmacSHA256(CryptoJS.enc.Utf8.parse(data), CryptoJS.enc.Utf8.parse(key));
return CryptoJS.enc.Base64.stringify(rawHmac);
}
Sample usage based on the example on AWS Signature V2 page
const urlSafeSignature = (data, key) => encodeURIComponent(calculateRFC2104HMAC(data, key));
const data =
`GET
elasticmapreduce.amazonaws.com
/
AWSAccessKeyId=AKIAIOSFODNN7EXAMPLE&Action=DescribeJobFlows&SignatureMethod=HmacSHA256&SignatureVersion=2&Timestamp=2011-10-03T15%3A19%3A30&Version=2009-03-31`
const key = `wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY`
console.log(urlSafeSignature(data, key));
The documentation advises to use AWS Signature V4 which has a AWS published library on NPM here. The AWS signed requests are for AWS Services and the signature in the request helps validating the request, prevents replay attacks. I'm not sure what you are trying to send in the following code and for which AWS service.
let data = JSON.stringify({ lang: 'en', pageNumber: 0, pageSize: 20 });
You must provide all details required to sign a request as per the AWS documentation.

InvalidKey at Kraken API with JS, not with Python

My code to get my Balance from the Kraken API does work in Python (based on the krakenex library), but not in the JS version (based loosely off the kraken-api library, but with the crypto library substituted for crypto-js). The error is always: Invalid Key.
Even when I copy the headers and the nonce sent by the Python client into Postman, I get Invalid Key.
I believe the signature and nonce to be valid, because when they are not, Kraken retorts that either the signature or nonce are invalid.
Is there anything else that Javascript's fetch does differently than Python3 requests? Because the body and headers are otherwise identical.
JS code that generates auth data:
const getMessageSignature = (path, request, secret, nonce) => {
// API-Sign = Message signature using HMAC-SHA512 of (URI path + SHA256(nonce + POST data)) and base64 decoded secret API key
const message = qs.stringify(request);
console.log(message);
const secret_buffer = btoa(secret);
const hash = CryptoJS.algo.SHA256.create();
const hmac = CryptoJS.algo.HMAC.create(CryptoJS.algo.SHA512, secret_buffer);
const hash_digest = hash.update(nonce + message).finalize().toString(CryptoJS.enc.Hex);
const hmac_digest = hmac.update(path + hash_digest).finalize().toString(CryptoJS.enc.Base64);
// CANNOT USE ORIGINAL LIB CODE (Buffer, got and crypto not supported)
// const secret_buffer = new Buffer(secret, 'base64');
// const hash = new crypto.createHash('sha256');
// const hmac = new crypto.createHmac('sha512', secret_buffer);
// const hash_digest = hash.update(nonce + message).digest('binary');
// const hmac_digest = hmac.update(path + hash_digest, 'binary').digest('base64');
return hmac_digest;
};
Update:
In fact, the following observations are weird:
correct key + correct signature = "incorrect key"
incorrect key + correct signature = "incorrect key"
incorrect key + incorrect signature = "incorrect key"
correct key + incorrect signature = "invalid signature"
what gives?
Update2
Seems the requests are identical (other than the signature and nonce of course, which will and should change with every request).

Turns out it was the signature after all and Kraken simply doesn't give very accurate responses (which makes some sense, but is a pain if you're trying to figure something out). Finally I was able to rewrite the code using CryptoJS only:
const getMessageSignature = (path, request, secret, nonce) => {
// API-Sign = Message signature using HMAC-SHA512 of (URI path + SHA256(nonce + POST data)) and base64 decoded secret API key
const message = JSON.stringify(request);
const hash = CryptoJS.SHA256(nonce + message);
const secret_buffer = CryptoJS.enc.Base64.parse(secret);
const hmac = CryptoJS.algo.HMAC.create(CryptoJS.algo.SHA512, secret_buffer);
hmac.update(path, secret_buffer);
hmac.update(hash, secret_buffer);
return hmac.finalize().toString(CryptoJS.enc.Base64);
};
This yields a correct signature and Kraken no longer complains. Zzah.

Validate Facebook signed_request signature in Javascript

I'm building a Facebook Page app in Classic ASP. I've been unable to match the signature that Facebook passes into the app as the first part of the POSTed signed_request.
Because there are few libraries for cryptography in VBScript, I'm using server side Javascript and the crypto-js library from https://code.google.com/archive/p/crypto-js/
I've tried to translate the PHP code example from Facebook's docs at https://developers.facebook.com/docs/games/gamesonfacebook/login#parsingsr into Javascript. I can generate an HMAC SHA256 hash of the signed_request payload but that doesn't match the signed_request signature.
I think the problem is that Facebook's signature is in a different format. It looks to be binary (~1抚Ö.....) while the HMAC SHA256 hash I'm generating is a hexadecimal string (7f7e8f5f.....). In Facebook's PHP example the hash_hmac function uses the raw binary parameter. So I think I need to either convert Facebook's signature to hexadecimal or my signature to binary in order to do an "apples-to-apples" comparison and get a match.
Here's my code:
/* Use the libraries from https://code.google.com/archive/p/crypto-js/
crypto-js/crypto-js.min.js
crypto-js/hmac-sha256.min.js
crypto-js/enc-base64.min.js
*/
var signedRequest = Request.queryString("signed_request")
var FB_APP_SECRET = "459f038.....";
var arSR = signedRequest.split(".");
var encodedSig = arSR[0];
var encodedPayload = arSR[1];
var payload = base64UrlDecode(encodedPayload);
var sig = base64UrlDecode(encodedSig);
var expectedSig;
expectedSig = CryptoJS.HmacSHA256(encodedPayload, FB_APP_SECRET); // Unaltered payload string; no match
expectedSig = CryptoJS.HmacSHA256(payload, FB_APP_SECRET); // base64-decoded payload string; no match
if (sig == expectedSig) {
Response.write(payload);
} else {
Response.write("Bad signature");
}
function base64UrlDecode(input) {
// Replace characters and convert from base64.
return Base64.decode(input.replace("-", "+").replace("_", "/"));
}

After looking into the crypto-js documentation about encoding I found the solution. The de-/encoding methods provided by crypto-js are listed under 'Encoders' at the bottom of https://code.google.com/archive/p/crypto-js/ (Thanks for the nudge, CBroe.)
The solution was to use .toString() on the signatures. It seems like crypto-js uses a word format that was preventing a comparison match. I did also switch to using the base64 decoding provided by crypto-js in order to stick with one library.
Here's my updated code:
/* Use the libraries from https://code.google.com/archive/p/crypto-js/
crypto-js/crypto-js.min.js
crypto-js/hmac-sha256.min.js
crypto-js/enc-base64.min.js
*/
var signedRequest = Request.queryString("signed_request")
var FB_APP_SECRET = "459f038.....";
var arSR = signedRequest.split(".");
var encodedSig = arSR[0];
var encodedPayload = arSR[1];
var payload = base64UrlDecode(encodedPayload);
var sig = base64UrlDecode(encodedSig);
var expectedSig = CryptoJS.HmacSHA256(encodedPayload, FB_APP_SECRET); /******** Correct payload */
if (sig.toString() != expectedSig.toString()) { /******* Use .toString() to convert to normal strings */
Response.write(payload);
} else {
Response.write("Bad signature");
}
function base64UrlDecode(input) {
return CryptoJS.enc.Base64.parse( /******** Decode */
input.replace("-", "+").replace("_", "/") // Replace characters
);
}

I recently implemented this for their required user data deletion webhook. No external dependencies needed anymore:
const crypto = require('crypto');
function parseSignedRequest(signedRequest, secret) {
const [signatureReceived, encodedPayload] = signedRequest.split('.', 2);
const payload = b64decode(encodedPayload)
const data = JSON.parse(payload);
const hmac = crypto.createHmac('sha256', secret).update(payload);
const expectedSignature = hmac.digest('base64');
if (signatureReceived === expectedSignature) {
return data;
} else {
throw new Error("Signature mismatch");
}
}
function b64decode(data) {
const buff = Buffer.from(data, 'base64');
return buff.toString('ascii');
}
It's a translation of their example PHP code. I also have a repo setup with tests.

I found this worked for me.
const crypto = require('crypto')
const _atob = (str) => Buffer.from(str, 'base64').toString('binary')
const parseSignedRequest = (signed_request, app_secret) => {
const [encoded_sig, payload] = signed_request.split('.')
const json = _atob(payload)
const data = JSON.parse(json)
if (!data.algorithm || data.algorithm.toUpperCase() !== 'HMAC-SHA256') {
return {error: true, type: 'Unknown algorithm. Expected HMAC-SHA256'}
}
// check sig
const expected_sig = crypto.createHmac('sha256', config.facebook.app_secret)
.update(payload).digest('base64')
.replace(/\+/g, '-').replace(/\//g, '_')
.replace(/=/g, '')
if (encoded_sig !== expected_sig) {
return ({error: true, type: 'invalid_signature'})
}
return {error: false, parsedRequest: data}
}
const {error, type, parsedRequest} = parseSignedRequest(signed_request)