This project defines the software for building a secure physical lock using the Vanadium stack, along with a commmand-line tool for interacting with the lock. The software runs on a Raspberry Pi and interacts with the locks's switches and sensors using GPIO. It runs a Vanadium RPC service that allows clients to send lock and unlock requests.
Before describing the design in detail we highlight its key distinguishing aspects:
Decentralized: There is no single authority on all the locks, no cloud server that controls access to all locks from a particular manufacturer. All secrets and credentials pertaining to a particular lock are solely held by the lock and its clients. Huge compute farms run by hackers all over the world have no single point of attack that can compromise the security of multiple locks.
No Internet Connectivity Required: The lock does not require internet connectivity to function. When you’re right in front of the device, you can communicate with it directly without going through the cloud or a third-party service.
Audited: The lock can keep track of who opened the door, when and how they got access.
An out-of-box lock device exposes the UnclaimedLock interface on startup.
type UnclaimedLock interface {
Claim(name string) (security.WireBlessings | error)
}
This interface has a single method Claim that can be used to claim the device with a specific name and obtain credentials that grant authorization for subsequently interacting with the lock. Once claimed, the device exposes the Lock interface.
type Lock interface {
// Lock locks the lock.
Lock() error
// Unlock unlocks the lock.
Unlock() error
// Status returns the current status (locked or unlocked) of the
// lock.
Status() (LockStatus | error)
}
Clients that possess the appropriate authorization credentials can interact with the device and send it requests to lock, unlock or determine the status.
An out-of-box lock device comes with pre-installed credentials (private key and blessings) from its manufacturer. For instance, it may have blessings of the form <lock manufacturer>/<serial no>. The UnclaimedLock interface exposed by it is accessible to everyone.
When the lock is claimed with a specific name, it blesses itseld under the name and uses that blessing to subsequently authenticate to clients. It also creates a blessing for the claimer by extending this (self) blessing with the extension key. For e.g., a lock claimed with the name front-door will subsequently authenticate with the blessing front-door, and grant the blessing front-door/key to the claimer.
The blessing granted to the claimer is the key to the lock. It provides access to the methods on the Lock interface exposed by a claimed lock device. Furthermore, all extensions of this key blessing are also authorized to access the Lock interface.
Access to the lock can be shared with other principals by blessing them with the key blessing. Appropriate caveats may be added to this blessing to limit the scope of use. For e.g., the key front-door/key can be shared with a house guest for a limited period by extending it as front-door/key/houseguest with an expiration caveat.
Both claimed and unclaimed lock devices advertise their endpoints using MDNS to allow clients to discover them without going through the cloud or a third-party Mounttable. All lock devices advertise themselves with names that are prefixed with lock-. This prefix allows clients to easily filter MDNS advertisements for lock devices.
An unclaimed lock device advertises under a name of the form lock-unclaimed-lock-xxxxxx where xxxxxx is a random number generated by the lock device. A claimed lock device advertises itself under the name lock-<claimed name>.
Currently we don't have any protection for preventing a rogue device from impersonating the MDNS name of a lock device. This is something we plan to add in the future. Note that impersonating the MDNS name of a lock device may lead to denial of service but does not compromise the security of the lock.
The Lock interface has methods to lock, unlock and determine the status of the lock device. The device logs the blessings of the caller for all method requests thereby maintaining an audit trail. Internally, these methods set or unset certain GPIO pins on the Raspberry Pi based on the circuitory described below.
Apologies for this unconventional, possibly unreadable circuit representation. Putting it down so that the author can remember! TODO(ashankar): Clean it up!
The pin number assignments here work both for RaspberryPi Model B/B+ and RaspberryPi2-ModelB.
---(Pin 1)-------/\/\(10KΩ)/\/\---------(COM port of magnetic switch)
\
\----/\/\(1KΩ)/\/\---------(Pin 15 = GPIO22)
\
\----(LED)-----|
|
|
(N.O. port of magnetic switch)--|
|
|
(-ve terminal of active buzzer)--|
|
|
|
(Pin 6 = GND)--|
---(Pin 11 = GPIO17)-----------(+ terminal of active buzzer)
The above ciruit is meant to be a simulation of an actual lock device wherein locking and unlocking simply makes a buzzer ring. In particular the Lock and Unlock calls update the status of the pin GPIO17, and the Status call checks the status of the ping GPIO22.
Building the lock service for the RaspberryPi
v23 go get -u github.com/davecheney/gpio V23_PROFILE=arm v23 go install v.io/x/lock/lockd scp $V23_ROOT/release/projects/physical-lock/go/bin/lockd <rpi_scp_location>
If building without the arm profile, there are no physical switches/relays and instead a simulated hardware is used that uses the interrupt signal (SIGINT) to simulate locking/unlocking externally.
The lock service can be started by running the following command in the directory where the lockd binary was copied.
lockd --v23.credentials=<creds dir> --config-dir=<config dir>
The --config-dir flag specifies a path to a directory where configuration files can be saved, and the --v23.credentials flag specifies a path to the Vanadium credentials directory for lockd. The configuration directory must be persisted accross restarts; emptying it would amount to a “factory reset”.
We describe a few commands for discovering and interacting with a lock device.
The first step is to build the command-line tool.
v23 go install v.io/x/lock/lock
In the rest of this section, we specify all commands relative to the directory containing the lock tool.
All commands must be run under an agent that has a blessing from dev.v.io. This can be achieved by starting bash under an agent and using the principal tool to obtain a blessing from dev.v.io.
v23 go install v.io/x/ref/cmd/principal v23 go install v.io/x/ref/services/agent/... $V23_ROOT/release/go/bin/agent --v23.credentials=<creds> bash $V23_ROOT/release/go/bin/principal seekblessings
Above, <creds> points to a directory where the tool's Vanadium credentials would be persisted.
Find the names of nearby lock devices (on the same network as this tool)
lock scan
This command prints out the names of nearby lock devices. The name of an unclaimed lock device always begins with unclaimed-, and the name of a claimed lock device is the name under which it was claimed.
The claim command can be used to claim an unclaimed device. For instance, the following command claims the device unclaimed-lock-xxxxxx with the name front-door. (Here unclaimed-lock-xxxxxx is the name of the unclaimed lock device obtained from the scan command.)
lock claim unclaimed-lock-xxxxxx front-door
The lock would now authenticate with the name front-door and a subsequent invocation of scan should print the name front-door.
The listkeys command lists the set of available physical-lock keys and the names of the locks to which they apply.
lock listkeys
For example, as a result of the previous claim, the key front-door/key would show up as being available to this tool for the lock front-door.
The lock front-door can be locked using
lock lock front-door
and unlocked using
lock unlock front-door
The status command can be used to determine the current status of the lock.
lock status front-door
The lock tool can also be used to share keys with nearby users (on the same network as this tool). This involves the following steps.
First, the receiver must run the recvkeys command on their lock tool.
// At the receiver lock recvkeys
As a result of this command, the receiver's lock tool would start a server for receiving keys and advertise the endpoint of the server over MDNS.
Next, the sender must then search its neighborhood for users waiting to receiving keys
// At the sender lock users
This command would print the email addresses of all users waiting to receive keys. Once the email address of the receiver is visible then this command can be stopped and sendkey command can be used to send a key.
For instance, the following command sends the key for lock front-door to the user john.smith@gmail.com that is only valid for 10 minutes.
// At the sender lock sendkey --for=10m front-door john.smith@gmail.com friend
Above, friend is the category used to classify the receiver.
The sendkey command would cause the receiver to see a prompt specifying the name of the key received and the blessings of the sender. Once the receiver confirms saving the key, he/she would be able to use it to interact with the lock front-door for next 10 minutes. Executing the listkeys command would reveal the key front-door/key/friend along with its expiration time.
AuditLog(startTime, endTime time.Time) []AuditLog | error
type AuditLog struct {
Blessing string
Action LockStatus
Timestamp time.Time
}
We'd also have to work out how to control access to this AuditLog. One option is to use caveats - so when “making” a new key one can choose to insert the “noadmin” caveat?
sendkey command only supports expiration commands. In the future, we would like to support at least the following caveats: