Crypto Library

A TypeScript SDK for Proxy Re-Encryption (PRE) and cryptographic primitives, enabling secure data sharing directly in the browser.

Overview

This SDK allows users to securely encrypt and share data via a proxy service, without exposing raw data to the proxy. It includes full client-side support for key generation, encryption, and Proxy Re-Encryption (PRE).

This SDK implements the PRE method as detailed in our design spec: Overleaf PRE Design Doc (Work in progress)

Key Features

• ✨ Client-Side Only: All crypto operations are performed in-browser
• 🔐 Key Generation: Generate secure encryption keys with share splitting
• 🔑 Passphrase Protection: Add passphrase security to key shares
• 📁 Data Encryption: Encrypt arbitrary data (files, images, etc.) in the browser
• 🔄 Proxy Re-Encryption: Share encrypted data securely without giving direct access
• 📅 Local Storage Support: Save key shares securely in browser storage

Installation

npm install pre-ts
# or
yarn add pre-ts

Quick Start

import { PreSdk, SecretKey } from "pre-ts";

const client = new PreSdk();
const shares = await client.generateShares();

const data = new Uint8Array([
    /* your data */
]);
const secretKey = SecretKey.fromBytes(await client.pre.combineSecret(shares));
const encrypted = await client.encryptData(secretKey, data);

Usage Guide

1. Key Generation

const client = new PreSdk();
const shares = await client.generateShares();

2. Share Protection (Optional)

const passphrase = "your-secure-passphrase";
const encryptedShare = await encryptShare(shares[0], passphrase);

localStorage.setItem(
    "share1",
    JSON.stringify({
        share: Array.from(new Uint8Array(encryptedShare)),
        hasPassphrase: true,
        passphraseHash: hashPassphrase(passphrase),
    })
);

3. Data Encryption

const secretBytes = await client.pre.combineSecret([share1Array, share2Array]);
const secret = SecretKey.fromBytes(secretBytes);
const encrypted = await client.encryptData(secret, new Uint8Array(dataBuffer));

4. Proxy Re-Encryption

const reKey = client.preClient.generateReEncryptionKey(
    senderSecret.first,
    recipientPublic.second
);

const proxyClient = new pre.ProxyClient();
await proxyClient.store(
    reKey,
    encrypted.encryptedKey,
    encrypted.encryptedMessage,
    "userId"
);

5. Decryption by Recipient

const { firstLevelKey, encryptedData } = await proxyClient.request(
    proxyStoreId
);

const decrypted = await client.preClient.decryptFirstLevel(
    {
        encryptedKey: firstLevelKey,
        encryptedMessage: encryptedData,
    },
    recipientSecretKey
);

API Reference

PreSdk

Methods:

• generateShares(): Promise<Uint8Array[]>
• encryptData(secret: SecretKey, data: Uint8Array): Promise<SecondLevelEncryptionResponse>
• pre: Contains utility methods like combineSecret()

ProxyClient

Handles proxy server communication.

Methods:

• store(reEncryptionKey: G2Point, encryptedKey: Uint8Array, encryptedMessage: Uint8Array, userId: string): Promise<ProxyResponse>
• request(id: string): Promise<{ firstLevelKey: Uint8Array, encryptedData: Uint8Array }>

Security Best Practices

• Use strong, unique passphrases to protect key shares
• Always store shares separately and securely
• Never transmit or store unencrypted secret keys
• Limit proxy access to re-encryption operations only

License

MIT License — see LICENSE for details.

Contributions

PRs and issues welcome! See CONTRIBUTING.md for more info.