Devigny Proof of Concept

Devigny is a decentralized identity linking protocol, inspired by the Bluesky Satellite contest. Devigny binds a user's accounts together using zero knowledge proofs such that such links are impossible to forge and are only revealed if a user desires to do so. It derives its operation from the practice of placing public key fingerprints in owned accounts, but adds additional security features.

Protcol

1. The user generates a secret key, sk.
2. The user generates a signature for each account to link. Signatures are derived from sk and are called claims.
3. The user publishes the claims to each account.
4. The user publishes any number of proof books for any subset of accounts they wish to reveal. Proof books contain ZK proofs that claims are derived from the same sk.
5. A verifier gets the user's proof book and checks that the included claims are all derived from sk.

"user" and "verfier" in this context are analogous to DID "subjects" and "verifiers" respectively. Unlike standard DIDs, there is no issuer.

devigny Setup

The devigny tool is a protocol proof of concept.

To install, create a Python virtualenv and install the necessary packages:

$ python3 -m virtualenv -p python3 venv
$ source venv/bin/activate
$ pip install -r requirements.txt
$ ./devigny

In order to verify Twitter accounts, you'll need to set environment variables to a Twitter API key:

export TWITTER_API_KEY=xxx
export TWITTER_API_SECRET_KEY=yyy

Verifier Demo

devigny understands how to fetch data using a few fetch schemes: IPFS, HTTP(S), and TWITTER.

To verify that the IPFS file bafkreih5qw4covu756swv47qgivrbdawhcnhpdefly6ehf6mgvrq4ah6qm, Twitter profile @weschow, and website / git repo https://github.com/wesc/devigny-poc are controlled by a single user, run:

$ ./devigny verify ipfs://bafkreiaqst7ppesyewoui6fkv5fprh74ly6lv5vramagekvylwfudhioji ipfs://bafkreih5qw4covu756swv47qgivrbdawhcnhpdefly6ehf6mgvrq4ah6qm twitter://weschow https://github.com/wesc/devigny-poc
ipfs://bafkreih5qw4covu756swv47qgivrbdawhcnhpdefly6ehf6mgvrq4ah6qm -- OK
twitter://weschow -- OK
https://github.com/wesc/devigny-poc -- OK

Where the first argument, ipfs://bafkreiaqst7ppesyewoui6fkv5fprh74ly6lv5vramagekvylwfudhioji, is the location of that user's proof book. From the output, you can see that the check succeeded for all supplied accounts. The check fails when run against an unclaimed Twitter account:

$ ./devigny verify ipfs://bafkreiaqst7ppesyewoui6fkv5fprh74ly6lv5vramagekvylwfudhioji twitter://jack
twitter://jack -- FAIL, proof of claim CE3va4sKE575MrntLhgnTM9eBpsg861WPkeH5pWgSSpe,e6F8b8Ypo5GZ9K2ozQB4CNSC4gLbR8W6DHuHsZFQoWU must be valid

The check also fails when run against an imposter account. For example, @yesdefwes is most certainly not @weschow, despite claiming to be:

$ ./devigny verify ipfs://bafkreiaqst7ppesyewoui6fkv5fprh74ly6lv5vramagekvylwfudhioji twitter://yesdefwes
twitter://yesdefwes -- FAIL, proof of claim CE3va4sKE575MrntLhgnTM9eBpsg861WPkeH5pWgSSpe,e6F8b8Ypo5GZ9K2ozQB4CNSC4gLbR8W6DHuHsZFQoWU must be valid

A public proof book contains the linked accounts URIs, and so can be checked:

$ ./devigny verify ipfs://bafkreiaqst7ppesyewoui6fkv5fprh74ly6lv5vramagekvylwfudhioji
https://github.com/wesc/devigny-poc -- OK
ipfs://bafkreih5qw4covu756swv47qgivrbdawhcnhpdefly6ehf6mgvrq4ah6qm -- OK
twitter://weschow -- OK

Claims

A user first creates a secret key config:

$ ./devigny init
generating new secret key into config.yaml

The user then creates a claim:

$ ./devigny make-claim
claim: 8dXMQxHDbaYvgUnkNSaaLFdag3Sm8SejSnqSEhbM8Wnu,ERnnbuGtJnTs5aMbqqDrR4HiuKu4X55dbgJMJGpEgWY

The claim needs to be bound to a URI which uniquely specifies an account or piece of content. First, place the signature anywhere on the page:

devigny:[N]:8dXMQxHDbaYvgUnkNSaaLFdag3Sm8SejSnqSEhbM8Wnu,ERnnbuGtJnTs5aMbqqDrR4HiuKu4X55dbgJMJGpEgWY

The devigny: prefix allows the verifier to easily extract a signature. [N] should be set to 0 for the current signature format and can be used to allow for upgrades.

Then, bind the claim to the URI:

$ ./devigny bind-claim 8dXMQxHDbaYvgUnkNSaaLFdag3Sm8SejSnqSEhbM8Wnu,ERnnbuGtJnTs5aMbqqDrR4HiuKu4X55dbgJMJGpEgWY https://demo.com/

Proof Book

To generate a proof book:

$ ./devigny prove-claims > proofs.yaml

(optionally with --public to make a public proof book)

The user should then publish proofs.yaml in any appropriate way, eg to IPFS, a personal website, a publicly maintained directory, blockchain, etc.

Fetch Schemes

A fetch scheme is a method for taking a URI and fetching content where devigny expects to find either a proof book or a claim signature. In the case of IPFS or HTTP(S) this is straightforward: simply retrieve the content and look for the devigny: prefix. For IPFS, the devigny proof of concept tool relies on the ipfs.io gateway, which can sometimes be slow to resolve.

The Twitter fetch scheme is more involved. A natural place to put the signature is the bio field, however this leaves little space for a real bio since the signature is ~100 characters long. Instead, the user publishes the signature in a tweet, and the Twitter fetch protocol searches for the user's most recent tweet with a devigny: prefix. See this tweet for an example.

Theory of Operation

A Devigny claim is a Pedersen commitment to a secret key. A proof book consists of:

1. root commitment
2. proof of knowledge of the root secret key
3. series of ZK proofs that claims are commitments to the same secret key as the root.

To defend against impersonation, Devigny utilizes a specific form of challenge when generating the non-interactive proofs. See theory for details.

Authorship

Wes Chow (Twitter @weschow) authored this readme and all the code in this repo, and here is the claim: devigny:0:81grahS5rhRWyqopWdjjWi9iZEBMQRw1gtiXCQgKaJo3,HXswf5yJyztiW4TSfsh8VN3nS5Bjfe4jTi4DCUUmDTgg