sphinx: a password Store that Perfectly Hides from Itself (No Xaggeration)

pwdsphinx is python wrapper around libsphinx - a cryptographic password storage as described in https://eprint.iacr.org/2015/1099

Dependencies

You need libsphinx and libequihash for the python reference frontend.

You need also to install pysodium using either your OS package manager or pip.

If you want to use also the websphinx browser extension you need to install also an X11 variant of pinentry from the gnupg project:

• either apt-get install pinentry-qt
• or apt-get install pinentry-gtk2
• or apt-get install pinentry-gnome3
• or apt-get install pinentry-fltk

(or anything equivalent to apt-get install on your OS)

Installation

pip3 install pwdsphinx should get you started.

API

sphinxlib is a ctypes-based python wrapper around libsphinx, so you can build whatever you fancy immediately in python. The interface exposed wraps the 3 sphinx functions from the library like this:

def challenge(pwd)

returns bfac and chal

def respond(chal, secret)

return the response

def finish(pwd, bfac, resp)

returns the raw 32 byte password.

Server/Client

Since the sphinx protocol only makes sense if the "device" is somewhere else than where you type your password, pwdsphinx comes with a server implemented in py3 which you can host off-site from your usual desktop/smartphone. Also a client is supplied which is able to communicate with the server and manage passwords.

Both the client and the server can be configured by any of the following files:

• /etc/sphinx/config
• ~/.sphinxrc
• ~/.config/sphinx/config
• ./sphinx.cfg

Files are parsed in this order, this means global settings can be overridden by per-user and per-directory settings.

oracle - the server

pwdsphinx comes with a python reference implementation of a extended sphinx server called oracle.

The server can be "configured" by changing the variables in the [server] section of the config file.

The address is the IP address on which the server is listening, default is localhost - you might want to change that.

The port where the server is listening is by default 2355.

datadir specifies the data directory where all the device "secrets" are stored, this defaults to "data/" in the current directory. You might want to back up this directory from time to time to an encrypted medium.

verbose enables logging to standard output.

timeout sets the timeout for any connection the server keeps open.

max_kids sets the number maximum requests handled in parallel. The timeout config variable makes sure that all handlers are recycled in predictable time.

rl_decay specifies the number of seconds after which a ratelimit level decays to an easier difficulty.

rl_threshold increase the difficulty of ratelimit puzzles if not decaying.

rl_gracetime gracetime in seconds added to the expcted time to solve a rate-limiting puzzle.

Change these settings to fit your needs. Starting the server can be done simply by:

oracle

sphinx - the client

This is the client that connects to the oracle to manage passwords using the extended sphinx protocol.

Client Configuration

Like the server, the client can be configured changing the settings in the [client] section of the config file. The host and port should match what you set in the oracle.

The datadir (default: ~/.sphinx) variable holds the location for your client parameters. Particularly it contains a masterkey which is used to derive secrets. The master key - if not available - is generated by issuing an init command. You should back up and encrypt this master key.

rwd_keys toggles if the master password is required for authentication of management operations. If it is False it protects against offline master password bruteforce attacks - which is also a security guarantee of the original SPHINX protocol. The drawback is that for known (host,username) tuples the seeds/blobs can be changed/deleted by an attacker if the clients masterkey is available to them. But neither the master nor the account password can leak this way. This is merely a denial-of-service vector. If rwd_keys is True, then this eliminates the denial-of-service vector, but instead eliminates the offline-bruteforce guarantee of the SPHINX protocol. Note that the oracle is oblivious to this setting, this is purely a client-side toggle, in theory it is possible to have different settings for different "records" on the oracle.

validate_password Stores a check digit of 5 bits in on the oracle, this helps to notice most typos of the master password, while decreasing security slightly.

Operations

The client provides the following operations: Create, Get, Change, Commit, Undo, List and Delete. All operations need a username and a site this password belongs to, even if they're only empty strings.

Create password

Creating a new password for a site is easy, pass your "master" password on standard input to the client, and provide parameters like in this example:

echo -n 'my master password' | sphinxy create username example.com ulsd 0 ' !"#$%&\'()*+,-./:;<=>?@[\\]^_`{|}~'

The parameters to the client are create for the operation, then username for the username on the site example.com then a combination of the letters ulsd and the 0 for the size of the final password. The letters ulsd stand in order for the following character classes: u upper-case letters, l lower-case letters, s symbols and d for digits. The s is a short-cut to allow all of the symbols, if you have a stupid server that limits some symbols, you can specify the allowed symbols explicitly. Currently these are the symbols supported (note the leading space char):

 !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~

Be careful, if you specify these on the command-line you'll have to escape the quotes you use for enclosing this list and possibly the backslash char that is also part of this list. In the create username example above the symbols are correctly escaped, in case you need to copy/paste them.

If you do not provide password rules, they will be defaulting to 'ulsd' and length as long as possible.

If the command runs successfully - the resulting new high-entropy password according to the given rules is printed to the console.

In case for some reason you cannot use random passwords with your account, or you want to store a "password" that you cannot change, like a PIN code for example, or a passphrase shared with your colleagues, you can specify a maximuxm 38 characte long password, that will be generated by the SPHINX client for you. In that case the command line looks like this (note the same syntax also works for the change operation)

echo -n 'my master password' | sphinx create username example.com "correct_battery-horse#staple"

In this case you cannot specify neither the accepted character classes, nor the size, nor symbols.

Note1, since the master password is not used to encrypt anything, you can actually use different "master" passwords for different user/site combinations.

Note2, using echo is only for demonstration, you should use something like this instead (or even directly getpwd from the contrib directory):

echo GETPIN | pinentry | grep '^D' | cut -c3- | sphinx create username example.com ulsd 0

Using pinentry you can go fancy and do double password input, and even have something checking password quality for you, check it out, it's quite versatile.

Get password

Getting a password from the sphinx oracle works by running the following command:

echo -n 'my master password' | sphinx get username example.com

Here again you supply your master password on standard input, provide the get operation as the first parameter, your username as the 2nd and the site as the 3rd parameter. The resulting password is returned on standard output.

Change password

You might want to (or are forced to regularly) change your password, this is easy while you can keep your master password the unchanged (or you can change it too, if you want). The command is this:

echo -en 'my master password\nnew masterpassword' | sphinx change username example.com 'ulsd' 0 ' !"#$%&\'()*+,-./:;<=>?@[\\]^_`{|}~'

Here again you supply your master password on standard input, but separated by a new-line you also provide the new master password. The new master password can be the same as the old, but can also be a new password if you want to change also the master password. You provide the change operation as the first parameter to the client, your username as the 2nd and the site as the 3rd parameter. You also can provide similar password generation rule parameters that were also used to create the original password, in case your account has new password rules and you want/have to accomodate them. Your new new password is returned on standard output.

Committing a changed password

After changing the password, you will still get the old password when running get. To switch to use the new password you have to commit the changes with

echo -n 'my master password' | sphinx commit username example.com

Undoing a password commit

If you somehow messed up and have to go back to use the old password, you can undo committing your password using:

echo -n 'my master password' | sphinx undo username example.com

Deleting passwords

In case you want to delete a password, you can do using the following command:

echo -n "my master password" | sphinx delete username example.com

You provide the delete operation as the first parameter to the client, your username as the 2nd and the site as the 3rd parameter. This command does not provide anything on standard output in case everything goes well.

QR code config

In case you want to use phone with the same sphinx server, you need to export your config to the phone via a QR code.

sphinx qr

Will display a QR code containing only public information - like the server host and port, and if you use rwd_keys. This is mostly useful if you want to share your setup with a friend or family.

If you want to connect your own phone to the setup used with pwdsphinx, you also need to export your client secret in the QR code:

sphinx qr key

This contains your client secret, and you should keep this QR code confidential. Make sure there is no cameras making copies of this while this QR code is displayed on your screen.

If for whatever reason you want to display the QR code as an SVG, just append the svg keyword to the end of the sphinx qr command.

X11 frontend

You can find a bunch of shell-scripts that are based on pinentry-(gtk|qt), xinput, xdotool and dmenu, the top-level entry to these is the dmenu-sphinx.sh script, which stores its history of entered hostnames in ~/.sphinx-hosts - if the hosts are in any way sensitive, you might want to link this file to /dev/null. The contrib/README.md should give you an idea of how else to combine these scripts.

Credits

This project was funded through the NGI0 PET Fund, a fund established by NLnet with financial support from the European Commission's Next Generation Internet programme, under the aegis of DG Communications Networks, Content and Technology under grant agreement No 825310.