ZK-Regex

A library to do regex verification in circom. It will also generate lookup tables compatible with halo2-regex soon.

Introduction

This library provides circom circuits that enables you to prove that

  • the input string satisfies regular expressions (regexes) specified in the chip.

  • the substrings are correctly extracted from the input string according to substring definitions.

This is a JS/Rust adaptation of the Python regex-to-circom work done by sampriti and yush_g, along with sorasue's decomposed specifications. You can generate your own regexes via our no-code tool at https://www.zkregex.com

In addition to the original work, this library also supports the following features:

  • CLI to dynamically generate regex circuit based on regex argument

  • Extended regex circuit template supporting:

    • group and negation regexes.

    • a decomposed regex definition, which is the easiest way to define your regex.

You can define a regex to be proved and its substring patterns to be revealed. Specifically, there are two ways to define them:

  1. (manual way) converting the regex into an equivalent determistic finite automaton (DFA), selecting state transitions for each substring pattern, and writing the transitions in a json file.

  2. (automatic way) writing a decomposed version of the regex in a json file with specifying which part of the regex is revealed.

  3. (no code way) put the regex into zkregex.com > tool, highlight your chosen part, and copy the generated circuit While the manual way supports more kinds of regexes than the automatic way, the latter is easier and sufficient for most regexes.

Theory

To understand the theory behind the regex circuit compiler, please checkout this blog post (edits in progress). You can also look at the original regex description and how it ties into the original zk email work at the original zk-email blog post regex overview.

How to use

Install

Install yarn v1, or run yarn set version classic to set the version. Also make sure that circom is installed.

Clone the repo and install the dependencies:

yarn install

Compiler CLI

zk-regex is a CLI to compile a user-defined regex to the corresponding regex circuit. It provides two commands: raw and decomposed

zk-regex decomposed -d <DECOMPOSED_REGEX_PATH> -c <CIRCOM_FILE_PATH> -t <TEMPLATE_NAME> -g <GEN_SUBSTRS (true/false)>

This command generates a regex circom from a decomposed regex definition. For example, if you want to verify the regex of email was meant for @(a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z)+. and reveal alphabets after @, you can define the decomposed regex as follows.

{
     "parts":[
         {
             "is_public": false,
             "regex_def": "email was meant for @"
         },
         {
             "is_public": true,
             "regex_def": "[a-z]+"
         },
         {
             "is_public": false,
             "regex_def": "."
         }
     ]
}

Note that the is_public field in the second part is true since it is a substring to be revealed. You can generate its regex circom as follows.

  1. Make the above json file at ./simple_regex_decomposed.json.

  2. Run zk-regex decomposed -d ./simple_regex_decomposed.json -c ./simple_regex.circom -t SimpleRegex -g true. It outputs a circom file at ./simple_regex.circom that has a SimpleRegex template.

zk-regex raw -r <RAW_REGEX> -s <SUBSTRS_JSON_PATH> -c <CIRCOM_FILE_PATH> -t <TEMPLATE_NAME> -g <GEN_SUBSTRS (true/false)>

This command generates a regex circom from a raw string of the regex definition and a json file that defines state transitions in DFA to be revealed. For example, to verify the regex 1=(a|b) (2=(b|c)+ )+d and reveal its alphabets,

  1. Visualize DFA of the regex using this website.

  2. Find state transitions matching with the substrings to be revealed. In this case, they are 2->3 for the alphabets after 1=, 6->7 and 7->7 for those after 2=, and 8->9 for d.

  3. Make a json file at ./simple_regex_substrs.json that defines the state transitions. For example,

    {
        "transitions": [
            [
                [
                    2,
                    3
                ]
            ],
            [
                [
                    6,
                    7
                ],
                [
                    7,
                    7
                ]
            ],
            [
                [
                    8,
                    9
                ]
            ]
        ]
    }
  4. Run zk-regex raw -r "1=(a|b) (2=(b|c)+ )+d" -s ./simple_regex_substrs.json -c ./simple_regex.circom -t SimpleRegex -g true. It outputs a circom file at ./simple_regex.circom that has a SimpleRegex template.

Circuit Usage

The generated circuit has

  • 1 template arguments:

    • msg_bytes: the number of characters for the input string.

  • 1 input signals:

    • msg[msg_bytes]: the input message to match against

  • 1 + (the number of substring patterns) output signals:

    • out: a bit flag to identify whether the substring of the input string matches with the defined regex.

    • reveal(i)[msg_bytes]: The masked version of msg[msg_bytes]. Each character in msg[msg_bytes] is turned to zero in reveal(i)[msg_bytes] if it does not belong to the i-th substring pattern.

For more examples in action, please checkout the test cases in the ./packages/circom/circuits/common folder.

Helper APIs

A package in ./packages/apis provides nodejs/rust apis helpful to generate inputs of the regex circuits.

Development

Welcome any questions, suggestions or PRs!

Testing

yarn test

Cite this Work

Use this bibtex citation.

@misc{zk-regex,
  author = {Gupta, Aayush and Panda, Sampriti and Suegami, Sora},
  title = {zk-regex},
  year = {2022},
  publisher = {GitHub},
  journal = {GitHub repository},
  howpublished = {\url{https://github.com/zkemail/zk-regex/}},
}

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