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Circuit Architecture

Circom Circuits

Main Circuits

We provide one main circuit as follows.

email_auth.circom

A circuit to verify that a message in the subject is authorized by a user of an account salt, derived from an email address in the From field and a random field value called account code.

It takes as input the following data:

  1. a padded email header padded_header.
  2. the bytes of the padded email header padded_header_len.
  3. an RSA public key public_key.
  4. an RSA signature signature.
  5. the sender's account code account_code.
  6. a starting position of the From field in the email header from_addr_idx.
  7. a starting position of the Subject field in the email header subject_idx.
  8. a starting position of the email domain in the email address of the From field domain_idx.
  9. a starting position of the timestamp in the email header timestamp_idx.
  10. a starting position of the invitation code in the email header code_idx.

Its instances are as follows:

  1. an email domain domain_name.
  2. a Poseidon hash of the RSA public key public_key_hash.
  3. a nullifier of the email email_nullifier.
  4. a timestamp in the email header timestamp.
  5. a masked subject where characters either in the email address or in the invitation code are replaced with zero masked_subject_str.
  6. an account salt account_salt.
  7. a flag whether the email header contains the invitation code is_code_exist.

How to Use

Build circuits

yarn && yarn build

Run tests

At packages/circuits, make a build directory, download the zip file from the following link, and place its unzipped directory under build. https://drive.google.com/file/d/1TChinAnHr9eV8H_OV9SVReF8Rvu6h1XH/view?usp=sharing

Then, move email_auth.zkey in the unzipped directory params to build.

Then run the following command. yarn test

Generate proving keys and verifier contracts for main circuits

yarn dev-setup

Specification

The email_auth.circom makes constraints and computes the public output as follows.

  1. Assert that signature is valid for padded_header and public_key.
  2. Let public_key_hash be PoseidonHash(public_key).
  3. Let email_nullifier be PoseidonHash(PoseidonHash(signature)).
  4. Let from_addr be padded_header[from_addr_idx:from_addr_idx+256] .
  5. Let subject be padded_header[subject_idx:subject_idx+MAX_SUBJECT_BYTES] .
  6. Let domain_name be padded_header[domain_idx:domain_idx+255] .
  7. Let is_time_exist be 1 if padded_header satisfies the regex of the timestamp field.
  8. Let timestamp_str be padded_header[timestamp_idx:timestamp_idx+10].
  9. If is_time_exist is 1, let timestamp be an integer parsing timestamp_str as a digit string. Otherwise, let timestamp be zero.
  10. Let is_code_exist be 1 if padded_header satisfies the regex of the invitation code.
  11. Let code_str be padded_header[code_idx:code_idx+64].
  12. Let embedded_code be an integer parsing code_str as a hex string.
  13. If is_code_exist is 1, assert that embedded_code is equal to account_code.
  14. Let account_salt be PoseidonHash(from_addr|0..0, account_code, 0).
  15. Let masked_subject be a string that removes code_str, the prefix of the invitation code, and one email address from subject, if they appear in subject.

Note that the email address in the subject is assumbed not to overlap with the invitation code.