Additional technical information is stored on our servers, including randomly generated authentication tokens, keys, push tokens, and other material that is necessary to establish calls and transmit messages. Signal limits this additional technical information to the minimum required to operate the Services.</p> <p> <strong>Contacts.</strong> Signal can optionally discover which contacts in your address book are Signal users, using a service designed to protect the privacy of your contacts. Information from the contacts on your device may be cryptographically hashed and transmitted to the server in order to determine which of your contacts are registered.</p> <p> <strong>User Support.</strong> If you contact Signal User Support, any personal data you may share with us is kept only for the purposes of researching the issue and contacting you about your case.</p>