Add RSA validation to Criteo FastBid

modules/criteoBidAdapter.js

@@ -3,8 +3,10 @@ import { registerBidder } from 'src/adapters/bidderFactory';
 import { parse } from 'src/url';
 import * as utils from 'src/utils';
 import find from 'core-js/library/fn/array/find';
+import JSEncrypt from 'jsencrypt/bin/jsencrypt';
+import sha256 from 'crypto-js/sha256';
 
-const ADAPTER_VERSION = 11;
+const ADAPTER_VERSION = 14;
 const BIDDER_CODE = 'criteo';
 const CDB_ENDPOINT = '//bidder.criteo.com/cdb';
 const CRITEO_VENDOR_ID = 91;
@@ -17,6 +19,13 @@ const PROFILE_ID_PUBLISHERTAG = 185;
 // Unminified source code can be found in: https://github.com/Prebid-org/prebid-js-external-js-criteo/blob/master/dist/prod.js
 const PUBLISHER_TAG_URL = '//static.criteo.net/js/ld/publishertag.prebid.js';
 
+export const FAST_BID_PUBKEY = `-----BEGIN PUBLIC KEY-----
+MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDO1BjAITkFTtP0IMzmF7qsqhpu
+y1dGaTPHnjMU9mRZsrnfR3C0sEN5pYEzEcFRPnkJjJuhH8Rnh5+CE+LcKg0Z8ZZ7
+OmOSj0/qnYTAYCu0cR5LiyWG79KlIgUyMbp92ulGg24gAyGrVn4+v/4c53WlOEUp
+4YWvb82G0CD5NcDNpQIDAQAB
+-----END PUBLIC KEY-----`;
+
 /** @type {BidderSpec} */
 export const spec = {
   code: BIDDER_CODE,
@@ -251,20 +260,52 @@ function createNativeAd(id, payload, callback) {
   </script>`;
 }
 
+export function cryptoVerify(key, hash, code) {
+  var jse = new JSEncrypt();
+  jse.setPublicKey(key);
+  return jse.verify(code, hash, sha256);
+}
+
+function validateFastBid(fastBid) {
+  // The value stored must contain the file's encrypted hash as first line
+  const firstLineEnd = fastBid.indexOf('\n');
+  const firstLine = fastBid.substr(0, firstLineEnd).trim();
+  if (firstLine.substr(0, 9) !== '// Hash: ') {
+    utils.logWarn('No hash found in FastBid');
+    return false;
+  }
+
+  // Remove the hash part from the locally stored value
+  const fileEncryptedHash = firstLine.substr(9);
+  const publisherTag = fastBid.substr(firstLineEnd + 1);
+
+  // Verify the hash using cryptography
+  try {
+    return cryptoVerify(FAST_BID_PUBKEY, fileEncryptedHash, publisherTag);
+  } catch (e) {
+    utils.logWarn('Failed to verify Criteo FastBid');
+    return undefined;
+  }
+}
+
 /**
  * @return {boolean}
  */
 function tryGetCriteoFastBid() {
   try {
     const fastBid = localStorage.getItem('criteo_fast_bid');
     if (fastBid !== null) {
-      eval(fastBid); // eslint-disable-line no-eval
-      return true;
+      if (validateFastBid(fastBid) === false) {
+        utils.logWarn('Invalid Criteo FastBid found');
+        localStorage.removeItem('criteo_fast_bid');
+      } else {
+        utils.logInfo('Using Criteo FastBid');
+        eval(fastBid); // eslint-disable-line no-eval
+      }
     }
   } catch (e) {
     // Unable to get fast bid
   }
-  return false;
 }
 
 registerBidder(spec);

package.json

@@ -103,7 +103,9 @@
   "dependencies": {
     "babel-plugin-transform-object-assign": "^6.22.0",
     "core-js": "^2.4.1",
+    "crypto-js": "^3.1.9-1",
     "gulp-sourcemaps": "^2.6.0",
+    "jsencrypt": "^3.0.0-rc.1",
     "just-clone": "^1.0.2"
   }
 }

test/spec/modules/criteoBidAdapter_spec.js

@@ -1,5 +1,5 @@
 import { expect } from 'chai';
-import { spec } from 'modules/criteoBidAdapter';
+import { cryptoVerify, spec, FAST_BID_PUBKEY } from 'modules/criteoBidAdapter';
 import * as utils from 'src/utils';
 
 describe('The Criteo bidding adapter', function () {
@@ -294,4 +294,21 @@ describe('The Criteo bidding adapter', function () {
       expect(bids[0].height).to.equal(90);
     });
   });
+
+  describe('cryptoVerify', function () {
+    const TEST_HASH = 'vBeD8Q7GU6lypFbzB07W8hLGj7NL+p7dI9ro2tCxkrmyv0F6stNuoNd75Us33iNKfEoW+cFWypelr6OJPXxki2MXWatRhJuUJZMcK4VBFnxi3Ro+3a0xEfxE4jJm4eGe98iC898M+/YFHfp+fEPEnS6pEyw124ONIFZFrcejpHU=';
+
+    it('should verify right signature', function () {
+      expect(cryptoVerify(FAST_BID_PUBKEY, TEST_HASH, 'test')).to.equal(true);
+    });
+
+    it('should verify wrong signature', function () {
+      expect(cryptoVerify(FAST_BID_PUBKEY, TEST_HASH, 'test wrong')).to.equal(false);
+    });
+
+    it('should return undefined with incompatible browsers', function () {
+      // Here use a null hash to make the call to crypto library fail and simulate a browser failure
+      expect(cryptoVerify(FAST_BID_PUBKEY, null, 'test')).to.equal.undefined;
+    });
+  });
 });