Auditable Credential Based on Privacy-Preserving Smart Contract

| Overview | Workflow | Architecture | Functionality | Evaluation | Proofs | Resource |

Overview

This project is a privacy-focused blind credential framework powered by blockchain technology; in particular, it employs Oasis Env as the privacy-preserving smart contract execution platform. It allows an issuer to release a credential blindly and make the verifier to reveal this blindness by interacting with the privacy-preserving smart contract. Since the calling progress with the privacy-preserving smart contract is transparent, the project makes the blindness showing traceable.

Workflow

A user firstly interacts with a privacy-preserving smart contract through a secure communication channel to negotiate the parameters; an issuer blindly issues a credential to the user; the user shows the issued credential and the verifier confirms the credential; the corresponding entities such as issuer and verifier invoke the blockchain bearing an auditable transaction to reveal the blindness.

This process is implemented as five main functionalities in our system: parameter preparation, credential issuing, credential verifying, identity tracing and credential tracing. Among them, the protocols of identity tracing and credential tracing are executed on blockchain, while the protocols of credential issuing and credential verifying are executed locally(independent of blockchain). The details are shown as follows:

Functionality	Description	Remark
Parameter preparation	Preparing the parameters such the p q and the order of the Group.	on-line blockchain
Credential issuing	Blindly issuing credentials without knowing users' identity.	off-line blockchain
Credential verifying	Verifying credentials by the Verifier	off-line blockchain
Identity tracing	Tracing identity by giving the credential.	on-line blockchain
Credential tracing	Tracing credential by giving the credential identity.	on-line blockchain

Architecture

Two architectures are given in our implementation: the integration server and micro service.

Integration server

An integration server [2] is a type of server that enables the integration and interaction of different operating systems, application and services within an enterprise IT environment. It enables applications and services to communicate with each other, regardless of their underlying platform. It eliminates compatibility and interoperability issues between different platforms.

As it is shown below, the server is built with express, which is one of the most popular frameworks for web developers. In terms of cryptosystems, a powerful framework called charm is employed. To share data between these two different modules, we utilize thrift (a lightweight RPC framework) for inter data communication.

We suggest using docker to deploy the integration server.

docker pull aowatchsea/blindca
docker run -t -i -p 443:8080 aowatchsea/blindca
start.sh

Micro service

Microservice [2] architecture allows the system to be implemented in different programming languages and be deployed independently. As it is shown in the following illustration, the microservice architecture is represented as two independent services collaborating as one system: Credential issuing/verifying service and Credential tracing service. Credential issuing/verifying service is implemented by Python, while credential tracing service is implemented by NodeJs.

Evaluation

Performance testing

This table shows the average testing time (in seconds) for each procedure (1000 rounds) under different security parameters (Elliptic Curves 192, Elliptic Curves 256, Integers Group 256, Integers Group 1024).

All experiments are conducted on a Dell precision 3630 tower with 16GB of RAM and one 3.7GHz six core i7-8700K processors running Ubuntu 18.04.

For more details, we refer the reader to Elliptic_Curves_192_result, Elliptic_Curves_256_result, Integers_Group_256_result, Integers_Group_1024_result.

	Parameter preparation	Credential issuing	Credential verifying	Identity tracing	Credential tracing
Elliptic Curves 192	0.00052	0.00454	0.00141	0.00391	0.00216
Elliptic Curves 256	0.00084	0.00740	0.00232	0.00455	0.00306
Integers Group 256	0.02839	0.000245	0.00008	0.00041	0.00038
Integers Group 1024	2.28698	0.006368	0.00296	×	×

We use a simulation-based testing approach to test the code execution in a smart contract. We first simulate the network request and response time NT1 with calling an empty function in the smart contract. Then, we simulate the network request and response time NT2 with calling a function that covers the code. Lastly, the code execution time is represented as NT2 getting rid of NT1. The below picture shows the part of the test record according to our new testing method.

Latency testing

Latency is an essential consideration for adopting a blockchain based system - too much latency may discourage the user from employing such kind of system. In our prototype, the latency time includes blockchain confirming time T2 and the network request time T1 and response time T3 which is shown as follows:

Latency testing of credential issuing and credential verifying are not covered in the table since these operations are executed independently from blockchain.

	Contract deployment	Parameter preparation	Identity tracing	Credential tracing
Elliptic Curves 192	14.104	12.346	16.678	16.052
Elliptic Curves 256	15.213	14.781	17.538	18.905
Integers Group 256	12.563	11.327	12.870	15.659
Integers Group 1024	13.263	×	×	×

Cost testing

Our project is based on Oasis Env. In this stage their coin is used at no costs. However, the gas of the related operations is still evaluated to prove that this cost is acceptable even if it will have intrinsic value in the future.

Similar to the above latency testing, the cost testing of credential issuing and credential verifying are not covered in the table since these operations are executed independently from blockchain.

	Contract deployment	Parameter preparation	Identity tracing	Credential tracing
Elliptic Curves 192	0.000264	0.00020	0.002930	0.002979
Elliptic Curves 256	0.000264	0.00020	0.003889	0.003902
Integers Group 256	0.000157	0.000139	0.000060	0.000051
Integers Group 1024	0.000157	×	×	×

Proofs

Game based Cryptographic Proofs

Resource

1. Project page auditable-credential-webpage
2. Documentation auditable-credential-documentation
3. Performance testing records
   • Elliptic Curves version Elliptic_Curves_192_result, Elliptic_Curves_256_result.
   • Integers Group version Integers_Group_256_result, Integers_Group_1024_result.
4. Delay & Cost testing records transactions in Oasis Devnet

Reference

[1] https://searchcio.techtarget.com/definition/integration-server
[2] https://microservices.io/