reCAPTCHA Enterprise password leak verification

Detect password leaks and breached credentials to prevent account takeovers (ATOs) and credential stuffing attacks.

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For detailed documentation that includes this code sample, see the following:

Code sample


import java.util.List;
import java.util.concurrent.ExecutionException;

public class CreatePasswordLeakAssessment {

  public static void main(String[] args)
      throws IOException, ExecutionException, InterruptedException {
    // TODO(developer): Replace these variables before running the sample.
    // GCloud Project ID.
    String projectID = "project-id";

    // Site key obtained by registering a domain/app to use recaptcha Enterprise.
    String recaptchaSiteKey = "recaptcha-site-key";

    // The token obtained from the client on passing the recaptchaSiteKey.
    // To get the token, integrate the recaptchaSiteKey with frontend. See,
    String token = "recaptcha-token";

    // Action name corresponding to the token.
    String recaptchaAction = "recaptcha-action";

    checkPasswordLeak(projectID, recaptchaSiteKey, token, recaptchaAction);

  * Detect password leaks and breached credentials to prevent account takeovers (ATOs)
  * and credential stuffing attacks.
  * For more information, see:
  * and

  * Steps:
  * 1. Use the 'createVerification' method to hash and Encrypt the hashed username and password.
  * 2. Send the hash prefix (2-byte) and the encrypted credentials to create the assessment.
  * (Hash prefix is used to partition the database.)
  * 3. Password leak assessment returns a database whose prefix matches the sent hash prefix.
  * Create Assessment also sends back re-encrypted credentials.
  * 4. The re-encrypted credential is then locally verified to see if there is a
  * match in the database.
  * To perform hashing, encryption and verification (steps 1, 2 and 4),
  * reCAPTCHA Enterprise provides a helper library in Java.
  * See,

  * If you want to extend this behavior to your own implementation/ languages,
  * make sure to perform the following steps:
  * 1. Hash the credentials (First 2 bytes of the result is the 'lookupHashPrefix')
  * 2. Encrypt the hash (result = 'encryptedUserCredentialsHash')
  * 3. Get back the PasswordLeak information from reCAPTCHA Enterprise Create Assessment.
  * 4. Decrypt the obtained 'credentials.getReencryptedUserCredentialsHash()'
  * with the same key you used for encryption.
  * 5. Check if the decrypted credentials are present in 'credentials.getEncryptedLeakMatchPrefixesList()'.
  * 6. If there is a match, that indicates a credential breach.
  public static void checkPasswordLeak(
      String projectID, String recaptchaSiteKey, String token, String recaptchaAction)
      throws ExecutionException, InterruptedException, IOException {
    // Set the username and password to be checked.
    String username = "username";
    String password = "password123";

    // Instantiate the java-password-leak-helper library to perform the cryptographic functions.
    PasswordCheckVerifier passwordLeak = new PasswordCheckVerifier();

    // Create the request to obtain the hash prefix and encrypted credentials.
    PasswordCheckVerification verification =
        passwordLeak.createVerification(username, password).get();

    byte[] lookupHashPrefix = verification.getLookupHashPrefix();
    byte[] encryptedUserCredentialsHash = verification.getEncryptedLookupHash();

    // Pass the credentials to the createPasswordLeakAssessment() to get back
    // the matching database entry for the hash prefix.
    PrivatePasswordLeakVerification credentials =

    // Convert to appropriate input format.
    List<byte[]> leakMatchPrefixes =

    // Verify if the encrypted credentials are present in the obtained match list.
    PasswordCheckResult result =

    // Check if the credential is leaked.
    boolean isLeaked = result.areCredentialsLeaked();
    System.out.printf("Is Credential leaked: %s", isLeaked);

  // Create a reCAPTCHA Enterprise assessment.
  // Returns:  PrivatePasswordLeakVerification which contains
  // reencryptedUserCredentialsHash and credential breach database
  // whose prefix matches the lookupHashPrefix.
  private static PrivatePasswordLeakVerification createPasswordLeakAssessment(
      String projectID,
      String recaptchaSiteKey,
      String token,
      String recaptchaAction,
      byte[] lookupHashPrefix,
      byte[] encryptedUserCredentialsHash)
      throws IOException {
    try (RecaptchaEnterpriseServiceClient client = RecaptchaEnterpriseServiceClient.create()) {

      // Set the properties of the event to be tracked.
      Event event = Event.newBuilder().setSiteKey(recaptchaSiteKey).setToken(token).build();

      // Set the hashprefix and credentials hash.
      // Setting this will trigger the Password leak protection.
      PrivatePasswordLeakVerification passwordLeakVerification =

      // Build the assessment request.
      CreateAssessmentRequest createAssessmentRequest =
              .setParent(String.format("projects/%s", projectID))
                      // Set request for Password leak verification.

      // Send the create assessment request.
      Assessment response = client.createAssessment(createAssessmentRequest);

      // Check validity and integrity of the response.
      if (!checkTokenIntegrity(response.getTokenProperties(), recaptchaAction)) {
        return passwordLeakVerification;

      // Get the reCAPTCHA Enterprise score.
      float recaptchaScore = response.getRiskAnalysis().getScore();
      System.out.println("The reCAPTCHA score is: " + recaptchaScore);

      // Get the assessment name (id). Use this to annotate the assessment.
      String assessmentName = response.getName();
          "Assessment name: " + assessmentName.substring(assessmentName.lastIndexOf("/") + 1));

      return response.getPrivatePasswordLeakVerification();

  // Check for token validity and action integrity.
  private static boolean checkTokenIntegrity(
      TokenProperties tokenProperties, String recaptchaAction) {
    // Check if the token is valid.
    if (!tokenProperties.getValid()) {
          "The Password check call failed because the token was: "
              + tokenProperties.getInvalidReason().name());
      return false;

    // Check if the expected action was executed.
    if (!tokenProperties.getAction().equals(recaptchaAction)) {
          "The action attribute in the reCAPTCHA tag '%s' does not match "
              + "the action '%s' you are expecting to score",
          tokenProperties.getAction(), recaptchaAction);
      return false;
    return true;

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