KeePassXC (source, wiki) is a password manager forked from KeePassX which is a Linux/Unix port of the Windows KeePass Password Safe. KeePassXC was started because of concern about the relatively slow integration of community code into KeePassX -- ie it is a "Community" fork with more maintainers. KeePassXC seems to have been making regular releases in 2017, with the most recent (KeePassXC 2.2.0) adding Yubikey 2FA support for unlocking databases. KeePassXC also provides builds for Linux, macOS, and Windows, including package builds for several Linux distributions (eg an unofficial Debian/Ubuntu community package build, built from the deb package source with full build instructions).
For macOS / OS X there is a KeePassXC 2.2.0 for macOS binary bundle, and KeePassXC 2.2.0 for macOS sha256 digest. They are GitHub "release" downloads, which are served off Amazon S3. KeePassXC provide instructions on verifying the SHA256 Digest and GPG signature. To verify the SHA256 digest:
wget https://github.com/keepassxreboot/keepassxc/releases/download/2.2.0/KeePassXC-2.2.0.dmgwget https://github.com/keepassxreboot/keepassxc/releases/download/2.2.0/KeePassXC-2.2.0.dmg.digestCheck the SHA256 digest matches:
ewen@ashram:~/Desktop$ shasum -a 256 -c KeePassXC-2.2.0.dmg.digest KeePassXC-2.2.0.dmg: OK ewen@ashram:~/Desktop$
To verify the GPG signature of the release:
wget https://github.com/keepassxreboot/keepassxc/releases/download/2.2.0/KeePassXC-2.2.0.dmg.sigwget https://keepassxc.org/keepassxc_master_signing_key.asc(which is stored inside the website repository)gpg --import keepassxc_master_signing_key.ascgpg --recv-keys 0xBF5A669F2272CF4324C1FDA8CFB4C2166397D0D2(alternatively or in addition; in theory it should report it is unchanged)ewen@ashram:~/Desktop$ gpg --recv-keys 0xBF5A669F2272CF4324C1FDA8CFB4C2166397D0D2 gpg: requesting key 6397D0D2 from hkps server hkps.pool.sks-keyservers.net gpg: key 6397D0D2: "KeePassXC Release <release@keepassxc.org>" not changed gpg: Total number processed: 1 gpg: unchanged: 1 ewen@ashram:~/Desktop$Compare the fingerprint on the website with the output of "
gpg --fingerprint 0xBF5A669F2272CF4324C1FDA8CFB4C2166397D0D2":ewen@ashram:~/Desktop$ gpg --fingerprint 0xBF5A669F2272CF4324C1FDA8CFB4C2166397D0D2 pub 4096R/6397D0D2 2017-01-03 Key fingerprint = BF5A 669F 2272 CF43 24C1 FDA8 CFB4 C216 6397 D0D2 uid KeePassXC Release <release@keepassxc.org> sub 2048R/A26FD9C4 2017-01-03 [expires: 2019-01-03] sub 2048R/FB5A2517 2017-01-03 [expires: 2019-01-03] sub 2048R/B59076A8 2017-01-03 [expires: 2019-01-03] ewen@ashram:~/Desktop$to check that the GPG key retrieved is the expected one.
Compare the GPG signature of the release:
ewen@ashram:~/Desktop$ gpg --verify KeePassXC-2.2.0.dmg.sig gpg: assuming signed data in `KeePassXC-2.2.0.dmg' gpg: Signature made Mon 26 Jun 11:55:34 2017 NZST using RSA key ID B59076A8 gpg: Good signature from "KeePassXC Release <release@keepassxc.org>" gpg: WARNING: This key is not certified with a trusted signature! gpg: There is no indication that the signature belongs to the owner. Primary key fingerprint: BF5A 669F 2272 CF43 24C1 FDA8 CFB4 C216 6397 D0D2 Subkey fingerprint: C1E4 CBA3 AD78 D3AF D894 F9E0 B7A6 6F03 B590 76A8 ewen@ashram:~/Desktop$at which point if you trust the key you downloaded is supposed to be signing the code you intend to run, the verification is complete. (There are some signatures on the signing key, but I did not try to track down a GPG signed path from my key to the signing keys, as the fingerprint verification seemed sufficient.)
In addition for Windows and OS X, KeePassXC raised funds for an
AuthentiCode code signing
certificate
earlier this
year.
When signed, this results in a "known publisher" which avoids the
Windows and OS X warnings about running "untrusted" code, and acts
as a second verification of the intended code running. It is not
clear that the .dmg or KeePassXC.app on OS X is signed at
present, as "codesign -dv ..." reports both the .dmg file and
the .app as not signed (note that it is possible to use Authenticode
Code Signing Certificate with OS X's Signing
Tools). My guess is maybe the KeePassXC developers
focused on Windows executable signing first (and Apple executables
normally need to be signed by a key signed by Apple anyway).
Having verified the downloaded binary package, on OS X it can be installed
in the usual manner by mounting the .dmg file, and dragging the .app
to somewhere in /Applications. There is a link to /Applications in
the .dmg file, but without the clever folder background art that some
.dmg files it is less obvious that you are intended to drag it into
/Applications to install. (However there is no included installer, so
the obvious alternative is "drag'n'drop" to install.)
Once installed, run KeePassXC.app to start. Create a new password
database and give it at least a long master password, then save the
database (with the updated master password). After the database is
created it is possible to re-open KeePassXC.app with the relevant
database with the usual:
open PATH/TO/DATABASE.kdbx
thanks to the application association with the .kdbx file extension.
This makes it easier to manage multiple databases. When opened in
this way the application will propmpt for the master password of
the specific database immediately (with the other known databases
available as tabs).
KeePassXC YubiKey Support
KeePassXC YubiKey support is via the YubiKey HMAC-SHA1 Challenge-Response authentication, where the YubiKey mixes a shared secret with a challenge token to create a response token. This method was chosen for the KeePassXC YubiKey support because it provides a determinstic response without, eg, needing to reliably track counters or deal with gaps in monotonically increasing values, such as is needed with U2F -- Universal 2nd Factor. This trades a reduction in security (due to just relying on a shared secret) for robustness (eg, not getting permanently locked out of password database due to the YubiKeys counter having moved on to a newer value than the password database), and ease of use (eg, not having to activate the YubiKey at both open and close of a database; the KeePassXC ticket ticket #127 contains some useful discussion of the tradeoffs with authentiction modes needing counters; pwsafe also uses YubiKey Challenge-Response mode, presumably for similar reasons).
The design chosen seems similar to KeeChallenge, a plugin for KeePass2 (source) to support YubiKey authentiction for the Windows KeePass. There is a good setup guide to Securing KeePass with a Second Factor descriting how to set up the YubiKey and KeeChallenge, which seems broadly transferrable to using the similar KeePassXC YubiKey Challenge-Response feature. (A third party YubiKey Handbook contains an example of configuring the Challenge-Response mode from the command line for a slightly different purpose.)
By contrast, the Windows KeePass built in support is OATH-HOTP authentication (see also KeePass and YubiKey), which does not seem to be supported on KeePassXC -- some people also note OTP 2nd Factor provides authentication not encryption which may limit the extra protection in the case of a local database. HOTP also uses a shared key and a counter so suffers from similar shared secret risks as the Challenge Response mechanism, as well as robustness risks in needing to track the counter value -- one guide to the OATH-HOTP mode warns about keeping OTP recovery codes to get back in again after being locked out due to the counter getting out of sync. See also HOTP and TOTP details; HOTP hashes a secret key and a counter, whereas TOTP hashes a secret key and the time, which means it is easier to accidentally get out of sync with HOTP. TOTP seems to be more widely deployed in client-server situations, presumably because it is self-recovering given a reasonably accurate time source.
Configuring a YubiKey to support Challenge-Response HMAC-SHA1
To configure one or more YubiKeys to support Challenge-Response you need to:
Install the YubiKey Personalisation Tool from the Apple App Store; it is a zero cost App, but obviously will not be very useful without a YubiKey or two. (The YubiKey Personalisation Tool is also available for other platforms, and in a command line version.)
Run the
YubiKey Personalization Tool.appPlug in a suitable YubiKey, eg, YubiKey 4; the cheaper YubiKey U2F security key does not have sufficient functionality. (Curiously the first time that I plugged a new YubiKey 4 in, the Keyboard Assistant in OS X 10.11 (El Capitan) wanted to identify it as a keyboard, which seems to be a known problem -- apparently one can just kill the dialog, but I ended up touching the YubiKey, then manually selecting a ANSI keyboard, which also seems to a valid approach. See also the YubiKey User Guide examples for mac OS X.)
Having done that, the YubiKey Personalisation Tool should show "YubiKey is inserted", details of the programming status, serial number, and firwmware version, and a list of the features supported.
Change to the "Challenge Response" tab, and click on the "HMAC-SHA1" button.
Select "Confguration Slot 2" (if you overwrite Configuration Slot 1 then YubiKey Cloud will not work, and that apparently is not recoverable, so using Slot 2 is best unless you are certain you will never need YubiKey Cloud; out of the factory only Configuration Slot 1 is programmed).
Assuming you have multiple YubiKeys (and you should, to allow recovery if you lose one or it stops functioning) tick "Program Multiple YubiKeys" at the top, and choose "Same Secret for all Keys" from the dropdown, so that all the keys share the same secret (ie, they are interchangable for this Challenge-Response HMAC-SHA1 mode).
You probably want to tick "Require user input (button press)", to make it harder for a remote attacker to activate the Challenge-Response functionality.
Select "Fixed 64-byte input" for the HMAC-SHA1 mode (required by KeeChallenge for KeePass; unclear if it is required for KeePassXC but selecting it did work).
Click on the "Generate" button to generate a random 20-byte value in hex.
Record a copy of the 20-byte value somewhere safe, as it will be needed to program an additional/replacement YubiKey with the same secret later (unlike KeeChallenge it is not needed to set up KeePassXC; instead KeePassXC will simply ask the YubiKey to run through the Challenge-Response algorithm as part of the configuration process, not caring about the secret key used, only caring about getting repeatable results).
Beware the dialog box seems to be only wide enough to display 19 of the bytes (not 20), and not resizeable, so you have to scroll in the input box to see all the bytes :-( Make sure you get all 20 bytes, or you will be left trying to guess the first or last byte later on. (And make sure you keep the copy of the shared secret secure, as anyone with that shared secret can program a working YubiKey that will be functionally identical to your own. Printing it out and storing it somewhere safe would be better than storing it in plain text on the computers you are using KeePassXC on... and storing it inside KeePassXC creates a catch-22 situation!)
Double check your settings, then click on "Write Configuration" to store the secret key out to the attached YubiKey.
The YubiKey Personalisation Tool will want to write a "log" file (actually a
.csvfile), which will also *contain the secret key, so make sure you keep that log safe, or securely delete it.Pull out the first YubiKey, and insert the next one. You should see a "YubiKey is removed" message then a "YubiKey is inserted" message. Click on "Write Configuration" for the next one. Repeat until you have programmed all the YubiKeys you want to be interchangeable for the Challenge-Response HMAC-SHA1 algorithm. (Two, kept separately, seems like the useful minimum, and three may well make sense.)
Configuring a KeePassXC to use password and YubiKey authentication
Insert one of the programmed YubiKeys
Open KeePassXC on an existing password database (or create a new one), and authenticate to it.
Go to Database -> Change Master Key.
Enter your Password twice (ie, so that the Password will be set back to the same password)
Tick "Challenge Response" as well (so that the Password and "Challenge Respone" are both ticked)
An option like "YubiKey (nnnnnnn) Challenge Response - Slot 2 - Press" should appear in the drop down list
Click the "OK" button
Save the password database
When prompted press the button on your YubiKey (which will allow it to use the YubiKey Challenge Response secret to update the database).
Accessing the KeePassXC database with password and YubiKey authentication
To test that this has worked, close KeePassXC (or at least lock the database), then open KeePassXC again. You will get a prompt for access credentials as usual, without any options ticked.
Verify that you can open the database using both the password and the YubiKey Challenge-Response, by typing in the password and ticking "Challenge Response" (after checking it detected the YubiKey) and then clicking on "OK". When prompted, click the button on your YubiKey, and the database should open. (KeePassXC seems to recognise that the Challenge-Response is needed if you have opened the database with the YubiKey and the YubiKey is present; but you will need to remember to also enter the password each time you authenticate. At least it will auto-select the Password as soon as you type one in. The first time around opening a specific database is just one additional box to tick, which is fairly easy to remember particularly if you use the same combination -- password and YubiKey Challenge-Response -- on all your databases.)
You can confirm that both the password and the YubiKey Challenge Response and required, by trying to authenticate just using the Password (enter Password, untick "Challenge Response", press OK), and by trying to authenticate just using the YubiKey (tick "Challenge Response", untick Password, press OK). In both cases it should tell you "Unable to open database" (the "Wrong key or database file is corrupt" really means "insufficient authentication" to recover the database encryption key in this case; they could perhaps more accurately say "could not decrypt master key" here, perhaps with a suggestion to check the authentication details provided).
If you have programmed multiple YubiKeys with the same Challenge-Response shared secret (and hopefully you have programmed at least two), be sure to check opening the database with each YubiKey to verify that they are programmed identically and thus are interchangable for opening the password database. It should open identically with each key (because they all share the same secret when you programmed the keys, and thus the Challenge Response values are identical).
If you have multiple databases that you want to protect with the YubiKey Challenge-Response method, you will need to go through the Database -> Change Master Key steps and verification steps for each one. It probably makes sense to change them all at the same time, to avoid having to try to remember which ones need the YubiKey and which ones do not.
Usability of KeePassXC with Password and YubiKey authentiction
Once you have configured KeePassXC for Password and YubiKey authentication, and opened the database at least once using the YubiKey, the usability is fairly good. Use:
open PATH/TO/DATABASE.kdbx
to open a specific KeePassXC password database directly, and KeePassXC will launch with a window to authenticate to that password database. So long as one of the appropriate YubiKeys is plugged in, after a short delay (less time than it takes to type in your password) the YubiKey will be detected, and Challenge-Response selected. The you just type in your password as usual (which auto selects "Password" as well), hit enter (which auto-OKs the dialog), and touch your YubiKey when prompted.
One side effect of configuring your KeePassXC databases like this is that they are not able to be opened in other KeePass related tools, except maybe the Windows KeePass with the KeeChallenge plugin (which uses a similar method; I have not tested that). For desktop use, KeePassXC should work pretty much everywhere that is likely to be useful (modern Windows, modern macOS / OS X, modern Linux), as should the YubiKey, so desktop portability is fairly good. But, for instance, MiniKeePass (source, on the iOS App Store) will not be able to open the password database. Amongst other reasons, while the "camera connection kit" can be used to link a YubiKey to an iOS device, the YubiKey iOS HowTo points out that U2F, OATH-TOTP and Challenge-Response functionality will not work (and I found suggestions on the Internet this only worked with older iOS versions).
If access from a mobile device is important, then you may want to divide your passwords amongst multiple KeePass databases: a "more secure" one including the YubiKey Challenge-Response and a "less secure" one that only requires a password for compatibility. For instance it might make sense to store "low risk" website passwords in their own database protected only by a relatively short master password, and synchronise that database for use by MiniKeePass (using the DropBox app). But keep higher security/higher risk passwords protected by password and YubiKey Challenge-Response and only accessible from a desktop application (and not synchronised via DropBox to reduce exposure of the database itself).
It also looks like, in the UI, it should be possible to configure KeePassXC to require only the YubiKey Challenge-Response (no password), simply by changing the master key and only specifying YubiKey Challenge-Response. Since the Challenge-Response shared secret is fairly short (20 bytes, so 160 bits), secured only by that shared key, and the algorithm is known, that too would be a relatively low security form of authentication. Possibly again for "low value" passwords like random website logins with no real risk it might offer a more secure way to store per-website random passwords, ratehr than reusing the same password on the each website. But the combination of password and YubiKey Challenge-Response would be preferable for most password databases over the YubiKey Challenge-Response alone, even if the password itself was fairly short (eg under 16 characters).
ETA, 2018-01-11: KeePassXC has an official Ubuntu PPA which includes packages for all currently supported Ubuntu versions, including Ubuntu 16.04 LTS. To install:
sudo add-apt-repository ppa:phoerious/keepassxc
sudo apt-get update
sudo apt-get install keepassxc