PPA description

FINGERPRINT AUTHENTICATION FOR UBUNTU BASED ON FPRINTD

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This PPA contains packages that add a comprehensive fingerprint-based authentication functionality to Ubuntu, including a seamless integration into GNOME 2.x, Unity and GNOME 3.x. Please note that since Ubuntu 12.10 these packages are present in the standard repositories. Still, this PPA contains more recent version of the software, supporting a wider range of fingerprint readers. The version shipped in Ubuntu 18.10 and newer is up-to-date, and this PPA does not contain the packages.

Quick installation guide

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Supported devices are: https:/ /fprint. freedesktop. org/supported- devices. html

To find out your reader's ID, run the lsusb command and look into the sixth column of the output.

1. Add this PPA to your sources:

sudo add-apt-repository ppa:fingerprint /fprint

sudo apt-get update

sudo apt-get upgrade

2. Install the software:

sudo apt-get install libfprint0 fprint-demo libpam-fprintd

(Note: If you have experimented with fingerprint authentication before and have changed your /etc/pam. d/common- auth, you may be presented with a screen asking whether you want to override those changes. Select Yes. Under very special circumstances, you may get an error saying

pam-auth-update: Local modifications to /etc/pam. d/common- *, not updating.

pam-auth-update: Run pam-auth-update --force to override.

In this case, run “sudo pam-auth-update --force”, exactly as suggested, and enable the fprintd profile manually. Leave the standard system profiles (Unix, Keyring and ConsoleKit) enabled as well.)

3. Launch “fprint project demo” and check that you can enroll and verify your fingerprints and that your reader is indeed supported.

4. Run “fprintd-enroll” in terminal to save your fingerprint.

That's all! Test it: Lock and unlock screen, log out and back in, try sudo in terminal.

Known (minor) issues

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1. No fingerprint and password at the same time

At the moment, you cannot type in your password right away when you are asked for fingerprint. You need to make the fingerprint authentication fail first (swipe wrong finger or let it time out) before you are asked for password. This is a limitation of PAM because its modules mustn't be threaded and hence cannot support multiple means of authentication at the same time. (The old ThinkFinger used to do this, but it was a gross hack which caused many troubles.) A possible solution to this limitation is to make gdm, screensaver and policykit-1 support multiple alternative PAM stacks. Fedora 12 has enhanced the GDM login screen with a button that switches between password and fingerprint authentication mode (screenshot: http:// bit.ly/ cEjYbo). Similar enhancements for screensaver and PolicyKit are being worked on by Red Hat (see https:/ /bugzilla. redhat. com/show_ bug.cgi? id=500338).

Note on keyrings and passwordless logins

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If you log in with your fingerprint, the default keyring manager will not have access to your password or any other secret data to decrypt your enciphered content with. The same applies to encrypted partitions and their automatic unlocking with libpam-mount or eCryptFS. Please note that it is not possible to unlock the keyring unless you have typed in your password (there's nothing to unlock it with, and having a key stored somewhere on disk is a very naïve and insecure solution). If you are wondering why fingerprint authentication cannot provide any secret data to replace the standard password mechanism, please read section “How fingerprint authentication works” below.

There are basically 2 possible solutions to the keyring issue:

1. Keep logging in with your password as before (you will need to make the fingerprint authentication fail first by scanning a wrong finger) and then use fingerprint only for sudo and locked screens. This way you will have your standard password available in your session, and keyring and encrypted partitions will work as before.

2. Remove the password from your default keyring. This way the passwords in it will be stored unencrypted, but this may be perfectly acceptable for you if you store only insensitive data in it (such as passwords to Wi-Fi networks). If you decide to take this route, here is a short how-to: Go to Applications > Accessories > Passwords and Encryption Keys, card Passwords, right click on Passwords: login, Change Password and set it to empty string.

Contact & Feedback

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Packaging by https:/ /launchpad. net/~jurenka

Packaging requests: bug #376540, bug #346083

Feedback (via Launchpad, by email to ubuntu.box AT-SIGN imx.jurenka D.O.T cz, or by posting to the bugs above) is most welcome.

Issues with the software itself (and not the packaging) are best to be submitted directly to the upstream bug tracker at https:/ /gitlab. freedesktop. org/libfprint/ libfprint/ issues or to the upstream mailing list at http:// lists.freedeskt op.org/ mailman/ listinfo/ fprint .

You can run fprintd in debugging mode by executing:

sudo killall fprintd

sudo /usr/lib/ fprintd/ fprintd -t

How fingerprint authentication works

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When you set up fprintd and enroll your fingerprint for the first time, the scan (basically just an image) gets saved on your hard drive (it goes into /var/lib/ fprint/ <username> ). Then when you try to authenticate yourself, the system gets another scan from reader, and it checks whether the picture received looks more or less the same as the picture stored on disk. If that is the case, the user is let in.

This implies that the fingerprint authentication cannot serve as a source of any secret data that could then be used as a password (to decrypt the content of the default keyring or to unlock encrypted partitions, for instance).

Theoretically, one could think of a mathematical reduction of the fingerprint to a number, a reduction that would be comprehensive as well as consistent so that different scans of the same finger always be reduced to the same number but scans of different fingers produce different numbers. Then only a hash of such a description of the fingerprint pattern could be saved on disk for the sake of authentication, and the number itself could be used as a secret, not a particularly strong secret since you keep it publicly at a well known place (your fingertip) and keep leaving copies of it on everything you touch, but at least it wouldn't be stored on your disk, and it could be used for decrypting the keyring, for instance.

However, such a technology is not available at the moment, and it doesn't seem to be feasible either. One hundred years of forensic dactyloscopy haven't brought any applicable algorithm. For the time being, one has to settle for fingerprints only as means of authentication, not as source of passwords for decrypting one's enciphered content.

Additional reading:

Overview of current technology: http:// sourceforge. net/apps/ mediawiki/ sourceafis/ (section Similar projects)

Launchpad discussion on a related matter: bug #276384

Handbook of Fingerprint Recognition: http:// bias.csr. unibo.it/ maltoni/ handbook/

Upstream links

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Official website: https:/ /fprint. freedesktop. org/

Code repository: https:/ /gitlab. freedesktop. org/libfprint/ libfprint/

Mailing list: http:// www.freedesktop .org/wiki/ Software/ fprint/ Mailing_ list/

Bug tracker: https:/ /gitlab. freedesktop. org/libfprint/ libfprint/ issues