Use Recrypt-as-a-Service for Cryptographic Orthogonal Access Control
This is a Mozilla Open Labs project. You can use this software to set up an online service that manages user identity and access authorization for a variety of applications in a manner that protects privacy. The example we gave here is privacy-first file sharing.
Background
The Public Key Infrastructure (PKI), invented over 40 years ago, has been the bed rock for security and privacy on the Internet. While PKI algorithms are behind the most internet security protocols, such as HTTPS and TLS, the idea for individuals to use public keys to exchange data, (eg, PGP), was not adopted in large scale. Traditional PKI is not scalable. It is a O(n*m) complexity problem for an individual to encrypt and send each of her files (n) using the public key from each of the recipients (m).
Centralized file sharing services, such as Dropbox, reduced the problem complexity to O(n+m) as the individual only needs to upload each file once and to manage her contacts list one person at a time. The centralized model has proven scalable but also brings significant privacy implications. The service at the center “sees” all data and can be hacked even if they do not do evil themselves.
In recent years, the proxy re-encryption scheme has emerged as a way to reduce the complexity of privacy-first file sharing to O(n+m). The idea, known as Cryptographic Orthogonal Access Control, is for the individual to encrypt each file once and store the encrypted data on a server. Then, only approved recipients have the ability to download and decrypt the data. A recipient can be added to or removed from the access list at any time.
Use case scenario
Alice creates an identity on the service via a create_identity request. She needs to save the returned UUID and private key values.
$ curl http://127.0.0.1:3000/create_identity
{"uuid":"f9d2ec5a-5f48-4e1b-a0b3-d52b0e0f521f","pk":[8,209,114,217,157,178,185,53,154,42,198,226,108,120,241,24,27,22,244,136,57,40,145,224,234,97,138,58,70,33,116,21]}
# {"uuid":"<Alice UUID>", "pk":"<Alice private key>"}
Bob, Charlie, and others each creates an identity on the service via create_identity requests. They need to save the returned ID and private key values. Here is Bob's UUID and private key.
$ curl http://127.0.0.1:3000/create_identity
{"uuid":"e7a2fc4c-7220-4617-8721-4e67120c63a9","pk":[5,251,27,236,155,82,189,136,54,48,225,95,30,66,96,94,121,155,63,6,207,72,79,9,168,119,2,23,106,36,46,200]}
# {"uuid":"<Bob UUID>", "pk":"<Bob private key>"}
Now, Alice can grant Bob access to all her data via a grant_access request. The request URL takes two parameters. The first is Alice's UUID and the second is Bob's UUID. The request body must be Alice's private key since she is authorizing access.
# curl -d "<Alice private key>" -H 'Content-Type: application/json' -X POST http://127.0.0.1:3000/grant_access/<Alice UUID>/<Bob UUID>
# { ... "signature":"<access signature>" ... }
$ curl -d "[8,209,114,217,157,178,185,53,154,42,198,226,108,120,241,24,27,22,244,136,57,40,145,224,234,97,138,58,70,33,116,21]" -H 'Content-Type: application/json' -X POST http://127.0.0.1:3000/grant_access/f9d2ec5a-5f48-4e1b-a0b3-d52b0e0f521f/e7a2fc4c-7220-4617-8721-4e67120c63a9
{...,"signature":[27,157,189,125,255,133,207,85,122,65,1,4,213,170,221,62,32,34,183,33,83,185,149,84,81,27,219,244,206,31,134,236,177,209,53,190,229,89,31,229,141,198,64,109,81,70,149,229,94,117,49,73,187,220,148,9,135,205,225,107,88,148,37,10]}
When Alice creates a confidential document, she can create a new AES encryption key to encrypt it. She generates the AES key via a create_sym_key request. Alice's UUID is in the URL since this AES key is generated by her and will be shared to people Alice granted access to. Alice notes the key's UUID, and publishes the UUID with her encrypted document.
# curl http://127.0.0.1:3000/create_sym_key/<Alice UUID>
# {"uuid":"<Key UUID>","sk":"<AES key in HEX>"}
$ curl http://127.0.0.1:3000/create_sym_key/f9d2ec5a-5f48-4e1b-a0b3-d52b0e0f521f
{"uuid":"9ebc843e-c82a-4c72-88b5-d8401f640cc7","sk":"83177a48b4c97ed4b0d8f0fd0f34f549b4d2987582d59397e67294566c481ad2"}
When Bob wants to decrypt the document, he asks for Alice's AES key via a get_sym_key request. The URL has Bob's UUID, Alice's UUID, and the AES key's UUID. The request body is Bob's private key to prove this is really Bob. The return value is the AES key that can decrypt Alice's documents.
# curl -d "<Bob private key>" -H 'Content-Type: application/json' -X POST http://127.0.0.1:3000/get_sym_key/<Bob UUID>/<Alice UUID>/<Key UUID>
# <AES key in HEX>
$ curl -d "[5,251,27,236,155,82,189,136,54,48,225,95,30,66,96,94,121,155,63,6,207,72,79,9,168,119,2,23,106,36,46,200]" -H 'Content-Type: application/json' -X POST http://127.0.0.1:3000/get_sym_key/e7a2fc4c-7220-4617-8721-4e67120c63a9/f9d2ec5a-5f48-4e1b-a0b3-d52b0e0f521f/9ebc843e-c82a-4c72-88b5-d8401f640cc7
83177a48b4c97ed4b0d8f0fd0f34f549b4d2987582d59397e67294566c481ad2
Now Bob received Alice's AES key and decrypted her documents. Alice can create more documents and more AES keys. She shares the key UUID to everyone she grant_access to and they will all be able to retrieve the key themselves. If Alice does not grant_access to Charlie, the above get_sym_key operaton with Charlie's UUID and private key will fail.
Finally, Alice can revoke access for Bob. She does so by posting the signature value returned from grant_access to a revoke_access request.
# curl -d "<access signature>" -H 'Content-Type: application/json' -X POST http://127.0.0.1:3000/revoke_access/<Alice UUID>/<Bob UUID>
$ curl -d "[27,157,189,125,255,133,207,85,122,65,1,4,213,170,221,62,32,34,183,33,83,185,149,84,81,27,219,244,206,31,134,236,177,209,53,190,229,89,31,229,141,198,64,109,81,70,149,229,94,117,49,73,187,220,148,9,135,205,225,107,88,148,37,10]" -H 'Content-Type: application/json' -X POST http://127.0.0.1:3000/revoke_access/f9d2ec5a-5f48-4e1b-a0b3-d52b0e0f521f/e7a2fc4c-7220-4617-8721-4e67120c63a9
[Success]
Bob cannot get any of Alice's published AES key anymore.
# curl -d "<Bob private key>" -H 'Content-Type: application/json' -X POST http://127.0.0.1:3000/get_sym_key/<Bob UUID>/<Alice UUID>/<Key UUID>
$ curl -d "[5,251,27,236,155,82,189,136,54,48,225,95,30,66,96,94,121,155,63,6,207,72,79,9,168,119,2,23,106,36,46,200]" -H 'Content-Type: application/json' -X POST http://127.0.0.1:3000/get_sym_key/e7a2fc4c-7220-4617-8721-4e67120c63a9/f9d2ec5a-5f48-4e1b-a0b3-d52b0e0f521f/9ebc843e-c82a-4c72-88b5-d8401f640cc7
[Error]
Building and running the service
Our service incorporates Ironcore Labs' Rust-based proxy re-encryption library Recrypt.rs.
Prerequisite
$ sudo apt-get update
$ sudo apt-get -y upgrade
$ sudo apt install build-essential curl wget git vim libboost-all-dev
$ curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
$ source $HOME/.cargo/env
$ curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.35.3/install.sh | bash
$ export NVM_DIR="$HOME/.nvm"
$ [ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh"
$ [ -s "$NVM_DIR/bash_completion" ] && \. "$NVM_DIR/bash_completion"
$ nvm install v10.19.0
$ nvm use v10.19.0
$ npm install -g ssvmup # Append --unsafe-perm if permission denied
$ npm install ssvm
$ npm install uuid
$ npm install express
Build the application
$ ssvmup build
Start the service
$ cd node
$ node app.js