Detect password leaks and breached credentials

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reCAPTCHA Enterprise can detect password leaks and breached credentials to prevent account takeovers (ATOs) and credential stuffing attacks. With reCAPTCHA Enterprise, you can conduct regular audits of user credentials (passwords) as part of any assessment to ensure that they have not been leaked or breached. To perform these assessments, Google uses the Password Checkup feature.

Before you begin

  1. Choose the best method for setting up reCAPTCHA Enterprise in your environment and complete the setup.

  2. Make sure that billing is enabled for your Cloud project. Learn how to check if billing is enabled on a project.

    reCAPTCHA Enterprise requires billing to be linked and enabled on the project to use the password leak detection feature. You can enable billing by using either a credit card or an existing Google Cloud project billing ID. If you require assistance with billing, contact the Cloud Billing Support.

Check for breached and/or leaked credentials

To check if a set of credentials has been compromised, query the Password Checkup database during assessments for actions, such as logins and password changes or resets.

To use the password leak detection service and to determine whether there was a leak or not from the response, you must calculate the parameters by using the cryptographic functions required by the high-privacy protocol. To do this, reCAPTCHA Enterprise provides a Java library: java-recaptcha-password-check-helpers.

Generate the request parameters

  1. To create password check verifications, create a PasswordCheckVerifier object.

    PasswordCheckVerifier verifier = new PasswordCheckVerifier();
  2. To initiate a verification, call PasswordCheckVerifier#createVerification. This method uses the username and password to calculate the parameters to perform the password check.

    PasswordCheckVerification verification = verifier.createVerification("username", "password").get();
  3. Create an assessment by using the verification parameters.

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

The byte arrays lookupHashPrefix and encryptedUserCredentialsHash contain the parameters that are required to initiate a password check Assessment.

API request

Use the projects.assessments.create method.

Before using any of the request data, make the following replacements:

  • PROJECT_ID: your Google Cloud project ID
  • LOOKUP_HASH_PREFIX: prefix of the username Scrypt hash hash prefix
  • ENCRYPTED_USER_CREDENTIALS_HASH: encrypted user credentials SHA-256 hash

HTTP method and URL:


Request JSON body:

  "private_password_leak_verification": {
    "lookup_hash_prefix": "LOOKUP_HASH_PREFIX"
    "encrypted_user_credentials_hash": "ENCRYPTED_USER_CREDENTIALS_HASH"

To send your request, choose one of these options:


Save the request body in a file called request.json, and execute the following command:

curl -X POST \
-H "Authorization: Bearer $(gcloud auth application-default print-access-token)" \
-H "Content-Type: application/json; charset=utf-8" \
-d @request.json \


Save the request body in a file called request.json, and execute the following command:

$cred = gcloud auth application-default print-access-token
$headers = @{ "Authorization" = "Bearer $cred" }

Invoke-WebRequest `
-Method POST `
-Headers $headers `
-ContentType: "application/json; charset=utf-8" `
-InFile request.json `
-Uri "" | Select-Object -Expand Content

You should receive a JSON response similar to the following:

  "name": "projects/698047609967/assessments/fb22000000000000",
  "score": 0,
  "reasons": [],
  "privatePasswordLeakVerification": {
    "lookupHashPrefix": "zoxZwA==",
    "encryptedUserCredentialsHash": "AyRihRcKaGLj/FA/r2uqQY/fzfTaDb/nEcIUMeD3Tygp",
    "reencryptedUserCredentialsHash": "Aw65yEbLM39ww1ridDEfx5VhkWo11tzn/R1B88Qqwr/+"
    "encryptedLeakMatchPrefixes": [
      "n/n5fvPD6rmQPFyb4xk=", "IVQqzXsbZenaibID6OI=", ..., "INeMMndrfnlf6osCVvs=",
      "MkIpxt2x4mtyBnRODu0=", "AqUyAUWzi+v7Kx03e6o="]

Verify a password leak

From the CreateAssessment response extract the fields reEncryptedUserCredentials and encryptedLeakMatchPrefixes, and pass them to the verifier object to determine if the credentials are leaked or not.

PasswordCheckResult result = verifier.verify(verification,

System.out.println("Credentials leaked: " + result.areCredentialsLeaked());

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;