Quick authentication using mobile devices and QR Codes

Isaac Potoczny-Jones

February 18, 2014: This project has recently been spun-out into a new startup company, Tozny – read more about this world-class, secure login technology at www.tozny.com.


In this blog post, we propose an authentication scheme using QR codes and Internet-connected smart phones to allow a user to quickly sign into a web site without having to memorize or type in a username and password. The user only has to prove that they are in possession of their mobile phone. We’ve developed a demonstration app and web site for this approach which you can try if you have an Android smartphone. Or you can watch the video demonstration. We have also started work on a draft REST protocol, and welcome feedback.

This work is preliminary, so we are very interested in feedback on the concept and prototype.

In general, authentication can be done using multiple “factors”. The more factors that are used, the more confidence a web site can have that they have truly identified the user:

  • something a user knows, such as a password
  • something the user has, such as a smart-card or cryptographic key
  • something the user is, such as the user’s fingerprint
  • the user’s location
  • and probably many more

Many web sites currently use a single factor: a password. Our scheme can use a mobile phone as a second factor, or as a single factor: something the user has. In fact using a mobile phone as a single factor may be more convenient for the user and in some cases more secure than a password. One distinguishing feature of this approach is that it is not only a second factor but also a second channel. Unlike systems like Google Auth, the user does not input their second credential through their computer, but rather directly through the phone’s network connection.

About QR Codes

QR codes are two dimensional bar codes that can contain a significant amount of information such as a shared key or session cookie. As in the following photograph, it is possible to disp lay a QR code on a computer screen and to scan that code with a mobile phone. This is an extremely common thing for Android users to do when they want to download apps that they have discovered on their computers. We utilize this capability to securely share secret information between the web site and the user.

User Experience

In this scheme, there is a single step for both account creation and for subsequent log-in: The user scans a QR code. Edit: We have revised this workflow significantly. Please see the draft of the REST-based protocol.

Account creation: When a user visits a web site for the first time, the site generates and displays a QR code for login, and the user scans it. An account is created for them. They have no need to generate and record a username or password or any other information.

Log in: When a user subsequently visits a web site and needs to log in, the site displays a QR code that the user scans with the same mobile phone. The user is logged in without having to remember a username or password, or even remember whether they have visited that web site before.

The user can choose to increase security by locking their phone and encrypting its data. Since the web site and the phone can exchange complex data, a strong password can be generated and stored without the user having to memorize it.

In the following sections, we expand on this exchange by detailing the workflow, what is stored by each party, what attacks are mitigated, and what attacks are not mitigated.

Account Creation Workflow

  1. The user visits a web site on their computer for the first time.
  2. The web site generates and displays an Authentication Code (AC), which is a QR code.
    • The web site must generate a new session cookie to prevent against session fixation attacks.
    • The AC encodes the web site URL and a random secret. This will be the shared secret. (EDIT: There are trade-offs for this to become the shared secret, and that increases the trust in the QR code and the user’s computer. In some circumstances, it may be better to have the app generate the shared secret.)
    • The random secret is tied to the session cookie stored in the computer’s browser.
  3. The user scans the Authentication Code with the Animate Login App” (ALApp).
  4. The ALApp decodes the AC and looks up the web site in the ALApp password table.
  5. Since the web site is not in the ALApp password table, the ALApp creates a new entry and stores the random secret.(EDIT: Instead the App should generate a new random secret. This will become the shared secret.)
  6. The ALApp also generates a random user identifier, or chooses a preferred username.
  7. The ALApp uses the mobile phone’s Internet connection to transmit the shared secret, the random secret, the session cookie, and the user identifier to the web site.
  8. The web site verifies that the session cookie corresponds to the random secret. This random secret can only be used to authenticate this session cookie.
  9. The web site creates an account for the user and adds the user identifier, along with the random secret to its user database.
  10. The web site marks the session cookie as authenticated and redirects the browser into the authenticated portion of the web site.

User Login Workflow

  1. The user visits a web site on their computer.

  2. The web site generates and displays an Authentication Code (AC), session cookie, and random secret as above. (EDIT: Using both the session cookie and random secret is unnecessary. We have clarified this in the protocol draft.)

  3. The user scans the Authorization Code with the Animate Login App (ALApp).

  4. The ALApp decodes the AC and looks up the web site in its password table.

  5. Since the web site already has an entry in ALApp password table, the ALApp looks up the shared secret and the user identifier.

  6. The ALApp uses the mobile phone’s Internet connection to transmit the random secret, the shared secret, and the user identifier to the web site.

  7. The web site looks up the user identifier and verifies the shared secret.

  8. The web site verifies that the session cookie corresponds to the random secret. This random secret can only be used to authenticate this session cookie.

  9. The web site marks the session cookie as authenticated and redirects the browser into the authenticated portion of the web site.

Message Format Notes

  • Since no one has to memorize the shared secret, it can be long and complex, protecting against brute-force attacks and simple guessing.
  • The shared secret can be generated by the web site, and so follow that site’s password complexity policy. However, if it’s included in the QR code, then the code is much more sensitive.
  • If the user’s phone does not have a signal for an Internet connection, the user has a backup option of having the ALApp display the shared secret so the user can type it in.
  • All messages must use HTTPS to authenticate the web site to the user and the smart phone.
  • User identifiers can be random numbers and can be generated by the user or by the web site. Alternately, the user might set a preference on the ALApp for their favorite usernames, and the ALApp can negotiate with the web site to choose a username.
  • User identifiers can be an email address.
  • During account creation, the ALApp can be instructed to share or not share information with the web site depending on user preferences. For instance, the ALApp can share the user’s email address, real name, photo, etc. On the other hand, the ALApp could only share a randomly generated username that can’t be tied to user names on other web sites. Of course, some sites might require more information, and if so the user might decline to create an account on that web site.

Improving Security with Another Factor

This scheme is most interesting (to us) as a single factor authentication for web sites which currently only use username and password combinations. This scheme makes logging into such sites quick and easy. However, this scheme can be used as a single factor or as a part of a multi-factor login. There are a variety of ways to add the second factor:

  • The web site can maintain a username and password as before. The web site can enforce multi-factor authentication this way.
  • The user can keep their phone locked, requiring a login password, unlock pattern (as on Android), or other method to unlock the phone. In this case, the user is accountable for deciding whether to use a second factor.
  • Similarly, the user can store all of the shared secrets encrypted on their phone. They will need a master password to encrypt and decrypt these secrets, so the login process will be slightly slower, but they will still only have to memorize a single password. (EDIT: The newest version of the code in the git repository implements this.)
  • Alternately, the user can choose which shared secrets they value most highly, and only encrypt those passwords, allowing them to log in to low-value web sites quickly, and higher-value web sites only by decrypting those passwords.

Attacks Mitigated & Other Benefits

  • Since the shared secret (the password) does not have to be memorized, or even typed in by a human, it can be long and complex. This mitigates against brute-force password crackers like John the Ripper (Peslyak, 2010) and Cain and Abel (Montoro, n.d.) both on the user’s side and on the web site’s side. This would prevent against attacks such as those used to crack so many users’ passwords in the Gawker password database spill described in (Kennedy, 2010).
  • Since the user does not type their password into the computer, a virus-installed keylogger or shoulder-surfer cannot capture their password.
  • Similarly, the user can use an untrusted computer (such as one in an Internet cafe or hotel) without revealing their password.
  • A phishing web site cannot capture the user password by tricking them into typing it in. The phone sends the shared secret, and will only send it to the web site in its database.
  • Since the password is randomly generated, the user will not re-use passwords on different web sites, so a password crack on one web site will not lead to escalation of privileges on another, again as happened in the Gawker password database spill (Pompeo, 2010).
  • If the user chooses to use a randomly generated username, the user’s account on one web site cannot be associated with the user’s account on another web site, again as happened in the Gawker password database spill.
  • Users have more privacy options since it is easier to generate and recall random passwords.
  • The user will not lose access to a web site because they cannot remember a password.
  • Since the authentication code is sent encrypted, and the web site authenticates itself to the user via HTTPS, the random secret can’t be intercepted to authenticate another user’s session.
  • In several respects, this approach is similar to a browser storing passwords on behalf of a user. The major advantage this approach has is that one can easily move identities between machines.
  • Finally, the login process is quicker and easier than typing a username and password.


  • This scheme does not prevent man-in-the-middle attacks; these need to be mitigated by HTTPS.
  • Edit: A vulnerability pointed out by Michael Tschannen is a variant of session fixation that requires a phishing attack. An attacker generates an AC for a target site and therefore knows the session cookie. The attacker tricks a user into visiting a less-trusted site and trying to log into that site. The attacker puts the AC for the target site into the (fake) less-trusted site. The user scans the AC, authenticating the attacker to the target site. This can be mitigated in two ways: 1) require that the user select the site they are logging into on the ALApp, or 2) confirm with the user the site they are logging into before sending the shared secret.
  • If the phone is lost or damaged, the user cannot access their web sites. This can be mitigated by storing the user’s email address for password reset or authorizing a new phone. Another option is to encrypt the phone’s password database and store it in the cloud or otherwise backing it up.
  • If the phone is stolen, the attacker can impersonate the user; therefore it is most likely desirable to encrypt the shared secrets on the phone and to authenticate the user to the phone with a single password, as above. This may not be necessary for web sites that are of low value to the user.
  • If the phone is stolen, it may be desirable to issue a revocation of all related passwords at once, rather than individually logging into different web sites.
  • When using an untrusted computer (one with a virus or in a hotel lobby), the user’s account is still vulnerable as long as the session is active.
  • Many of these vulnerabilities are equivalent to any system which stores a user’s passwords on their phone.

Related Authentication Systems

  • The ALApp can be integrated with an InfoCard/CardSpace client on the phone.
  • As with any authentication mechanism, this can be used to authenticate to an OpenID provider.
  • The workflow can be modified to use a Public Key Infrastructure instead of shared secrets. This might allow smoother revocation by issuing a revocation certificate if the phone is stolen.

Demonstration System Notes

We have implemented a demonstration system which you can try out to experiment with this method of logging in. It has a number of limitations, the most obvious of which is that it can only be used to log into the demonstration web site; it will only remember one username and password. We implemented the web site login by creating a Drupal module in the hopes that it will eventually be possible to allow this type of login by installing the module. Not all of the features discussed in this paper are in the current module version. Our plan is to release the module and the app open source.

One attractive feature of this scheme is that web sites don’t have to move away from using cookies, usernames, and passwords so their back-end functionality does not have to change, only the login process.

Zebra Crossing (ZXing) is a QR-code reader on Android that can easily be integrated with other apps such as ALApp.

OI Safe is an encrypted password store on Android that has an API allowing other authorized apps, such as the ALApp, to store and retrieve passwords (Potoczny-Jones, 2009).

Related Work

There is a lot of work in using mobile phones as a factor in authentication. Google web applications can be configured to use a second factor, either an app installed on a phone, or a text message sent to a phone (Feigenbaum, 2010). In each case, the user is presented with a code that they type into the web site. Our proposed scheme does not require the user to type anything into the web site. It also uses a separate channel, and so mitigates “man in the browser” attacks to some extent.

Liao & Lee (2010) propose a QR-code authentication system for generating one-time passwords. Their system is more complex since it provides for mutual authentication (we use HTTPS) and yet still requires some secure channel between the web site and the mobile app.

Safelayer describes a similar authentication system using asymmetric encryption (Safelayer, n.d.). However, this is described as a multi-factor system, and requires web sites to modify their back-end systems to use public/private keypairs. Our proposed system still uses simple username / password combinations.

A system for authenticating transactions on untrusted terminals using QR codes is described in (Starnberger, Froihofer, and Goeschka, 2009) but also uses PKI and requires the user to enter a code into the computer after the smart phone performs a computation.


We are seeking feedback on this approach. If you see any security issues, please inform us. EDIT: We have received a lot of good feedback. There was a good discussion on Reddit’s netsec that was mostly positive.

We have outlined a scheme whereby a mobile phone can be used as an authentication mechanism using QR codes. This scheme could allow users to log into a web site using a single step: scanning a QR code from their mobile phones. Alternately, this scheme can be used as one factor in multi-factor authentication.

QR codes, mutli-factor authentication, and Internet-connected smart-phones are “in the air” and others have likely come up with similar schemes. We have written this paper because we haven’t found any other description of such a system, nor seen one in the wild. Mostly, we would like to use such a system since it would improve security and convenience on the Internet, so please implement this and release it open source, or help us to do so 🙂


Feigenbaum, E. (2010). A more secure cloud for millions of Google Apps users. Official Google enterprise blog. Retrieved from http://googleenterprise.blogspot.com/2010/09/more-secure-cloud-for-millions-of.html

Kennedy, D. (2010). The real lessons of Gawker’s security mess, The Firewall. Forbes. Retrieved from http://blogs.forbes.com/firewall/2010/12/13/the-lessons-of-gawkers-security-mess/

Liao, K., & Lee, W. (2010). A Novel User Authentication Scheme Based on QR-Code . Journal of networks, vol. 5, no. 8. Retrieved from http://www.academypublisher.com/ojs/index.php/jnw/article/viewFile/0508937941/2055

Montoro, M. (n.d.). Cain & Abel user manual. Retrieved from http://www.oxid.it/ca_um/

Peslyak, A. (2010). John the Ripper user manual. Retrieved from http://www.openwall.com/john/doc/CREDITS.shtml

Pompeo, J. (2010). Leaked Gawker passwords cause trouble on GMail, Twitter [web log post]. Retrieved from http://news.yahoo.com/s/yblog_thecutline/20101213/bs_yblog_thecutline/leaked-gawker-passwords-cause-problems-on-twitter-gmail

Potoczny-Jones, I. (2009). CryptoIntents, A discussion of the cryptography and keystore intents in OI Safe. Retrieved from https://code.google.com/p/openintents/wiki/CryptoIntents

Safelayer. (n.d.) QR-Scan OTP: ergonomic authentication. Retrieved from http://sandbox.safelayer.com/index.php?option=com_content&view=article&id=466%3Aqr-scan-otp-ergonomic-authentication&catid=1%3Asemantic-web-trust-portal&Itemid=2&lang=en

Starnberger G., Froihofer L., and Goeschka, K. M. (2009) . QR-TAN: Secure Mobile Transaction Authentication . IEEE Computer Society. Retrieved from http://citeseerx.ist.psu.edu/viewdoc/download?doi=