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Date: Wed, 8 May 2019 11:29:39 +0200
From: Noel Kuntze <>
To:, Roman Drahtmueller
 <>, Seong-Joong Kim <>
Subject: Re: Re: fprintd: found storing user fingerprints
 without encryption

Hello List,

Am 08.05.19 um 11:19 schrieb Roman Drahtmueller:
>>> Dear all,
>>> I would like to report a vulnerability of 'fprintd'.
>>> 'fprintd' does not encrypt sensitive information before storage.
>>> *CWE-311: Missing Encryption of Sensitive Data*
> [...]
> This misses the point.
> * Encryption shifts the problem to protecting the symmetric key, which
>   is the very same problem. => Encryption solves other problems, but not
>   this one.
> * If you have sufficient privileges to access the fingerprint data,
>   then you no longer need the data.
> * You can't "safeguard" the fingerprint data by applying additional O/S
>   controls such as SELinux, AppArmor, etc, you can only add more useful
>   privilege transitions and protect against attacks that exploit
>   implementation errors. Google "store fingerprint data ios android",
>   there are suitable solutions.
> Mostly: Your fingerprint is not a secret like a password, it is a username.
> Since you can't change the fingerprint (biometrics problem), it is not very useful as a single authentication factor. Either you live with this, or you combine the fingerprint with a different authentication factor type.
> Roman.

Another argument: You leave your fingerprint on everything you touch. The glass you drank from at the bar on Saturday evening? That has your fingerprints. Your front door? It has those, too.
Fingerprints aren't sensitive information. The only entities attributing any sensitivity to them are the following: Court systems where fingerprints are allowed as evidence (although it's stupid because you can easily duplicate fingerprints) and companies/persons using fingerprints for authentication (which for the same reason as previously mentioned is not a good idea).
And as Roman mentioned already, you can't change your fingerprints easily (Sand paper and acids are your friends, but that's not comfortable at all and compromises your ability to hold things in your hands. So don't to that.).

If, for some reason, you still want to "securely" (at least with a higher level of security than plain text) store your fingerprint, you need to use a hardware backed kernel keyring that stores the encryption keys or use a hardware based security solution for storing the fingerprints in the first case. You likely won't find any such solution though that isn't broken already in some regard.

Kind regards


Noel Kuntze
IT security consultant

GPG Key ID: 0x0739AD6C
Fingerprint: 3524 93BE B5F7 8E63 1372 AF2D F54E E40B 0739 AD6C

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