Encryption Service

A lightweight library to use E2EE

🚀 Installation

From npm

npm install @amirafa/encryption-service

From yarn

yarn add @amirafa/encryption-service

From pnpm

pnpm add @amirafa/encryption-service

---

🧩 Import and Usage

import { EncryptionService } from "@amirafa/encryption-service";

const enc = EncryptionService();

// generate user keys
await enc.generateAndStoreIdentityKeyPair("alice");
await enc.generateAndStoreECDHKeyPair("alice");

// example: encrypt and decrypt a message
const alicePriv = await enc.importPrivateKey(localStorage.getItem("alice-privateKey")!);
const bobPub = await enc.importPublicKey(localStorage.getItem("bob-publicKey")!);

const sharedKey = await enc.deriveSharedKey(alicePriv, bobPub);

const { encryptedMessage, iv } = await enc.encryptMessageAES("Hello Bob!", sharedKey);
const plain = await enc.decryptMessageAES(encryptedMessage, sharedKey, iv);

console.log(plain); // "Hello Bob!"

---

Full Flow & Backend Schema

This document describes how the EncryptionServiceClass implements end-to-end encryption (E2EE) for a secure chat system and how the backend should store and handle related data.

---

🧩 Architecture Overview

The system uses three cryptographic layers:

1. ECDSA (Identity) — for signing and verifying identity keys.
2. ECDH (Shared Key) — for deriving a mutual secret key between two users.
3. AES-GCM (Message Encryption) — for encrypting and decrypting messages.

All encryption/decryption logic happens in the browser (client-side).
The backend only stores public keys, signatures, and encrypted data — never plaintext or private keys.

---

🧱 Function Reference (Client-Side)

generateAndStoreIdentityKeyPair(username)

Generates an ECDSA key pair (identity keys) and stores both in localStorage.

await enc.generateAndStoreIdentityKeyPair("alice");

Stored keys:

alice-id-publicKey
alice-id-privateKey

---

generateAndStoreECDHKeyPair(username)

Generates an ECDH key pair for secure message key exchange.

await enc.generateAndStoreECDHKeyPair("alice");

Stored keys:

alice-publicKey
alice-privateKey

---

signEcdhPublicKey(identityPriv, ecdhPub)

Signs the ECDH public key using the identity private key (ECDSA).

const sig = await enc.signEcdhPublicKey(aliceIdPriv, aliceEcdhPub);

---

verifyEcdhPublicKeySignature(identityPub, ecdhPub, signature)

Verifies that an ECDH public key truly belongs to a given identity.

const ok = await enc.verifyEcdhPublicKeySignature(bobIdPub, bobEcdhPub, sig);

---

deriveSharedKey(privateKey, publicKey)

Derives a shared AES key using your private ECDH key and the other user’s public ECDH key.

const aesKey = await enc.deriveSharedKey(alicePrivEcdh, bobPubEcdh);

Both sides independently derive the same AES key.

---

encryptMessageAES(message, aesKey)

Encrypts a plaintext message using AES-GCM.

const { encryptedMessage, iv } = await enc.encryptMessageAES("Hello Bob", aesKey);

iv (Initialization Vector) must be sent along with the ciphertext.

---

decryptMessageAES(encryptedMessage, aesKey, iv)

Decrypts a message using the same AES key and IV.

const plain = await enc.decryptMessageAES(encryptedMessage, aesKey, iv);

---

getIdentityFingerprint(identityPub)

Generates a SHA-256 fingerprint of an identity key for display and manual verification (TOFU).

const fpr = await enc.getIdentityFingerprint(aliceIdentityPub);
console.log("Alice fingerprint:", fpr);

---

🧭 Full Message Exchange Flow

1️⃣ Key Generation (first time only)

await enc.generateAndStoreIdentityKeyPair("alice");
await enc.generateAndStoreECDHKeyPair("alice");

await enc.generateAndStoreIdentityKeyPair("bob");
await enc.generateAndStoreECDHKeyPair("bob");

---

2️⃣ Alice signs her ECDH key

const idPriv = await enc.importIdentityPrivateKey(localStorage.getItem("alice-id-privateKey")!);
const ecdhPub = await enc.importPublicKey(localStorage.getItem("alice-publicKey")!);
const signature = await enc.signEcdhPublicKey(idPriv, ecdhPub);

const alicePackage = {
  identityPublicKey: localStorage.getItem("alice-id-publicKey")!,
  ecdhPublicKey: localStorage.getItem("alice-publicKey")!,
  signature
};

Alice sends this JSON package to Bob via the server.

---

3️⃣ Bob verifies Alice’s identity

const aliceIdPub = await enc.importIdentityPublicKey(alicePackage.identityPublicKey);
const aliceEcdhPub = await enc.importPublicKey(alicePackage.ecdhPublicKey);
const valid = await enc.verifyEcdhPublicKeySignature(aliceIdPub, aliceEcdhPub, alicePackage.signature);
if (!valid) throw new Error("Fake Alice detected!");

---

4️⃣ Both derive the shared AES key

const bobPriv = await enc.importPrivateKey(localStorage.getItem("bob-privateKey")!);
const sharedKey = await enc.deriveSharedKey(bobPriv, aliceEcdhPub);

Both parties now hold the same symmetric AES key.

---

5️⃣ Alice encrypts and sends the message

const { encryptedMessage, iv } = await enc.encryptMessageAES("Hi Bob!", sharedKey);
const chatEntry = {
  sender: "alice",
  recipient: "bob",
  message: Array.from(new Uint8Array(encryptedMessage)),
  iv: Array.from(iv)
};
// send chatEntry to server

---

6️⃣ Bob receives and decrypts

const msgBuf = new Uint8Array(chatEntry.message).buffer;
const ivBuf = new Uint8Array(chatEntry.iv);
const plain = await enc.decryptMessageAES(msgBuf, sharedKey, ivBuf);
console.log("Decrypted:", plain); // "Hi Bob!"

---

🗄 Recommended Database Schema (Backend)

Users Table

{
  username: string,
  identityPublicKey: string,
  ecdhPublicKey: string,
  signature: string
}

Messages Table

{
  sender: string,
  recipient: string,
  message: number[],
  iv: number[]
}

---

💾 SQL Implementation Example

users

CREATE TABLE users (
  id SERIAL PRIMARY KEY,
  username VARCHAR(50) UNIQUE NOT NULL,
  identity_public_key TEXT NOT NULL,
  ecdh_public_key TEXT NOT NULL,
  signature TEXT NOT NULL,
  created_at TIMESTAMP DEFAULT NOW()
);

messages

CREATE TABLE messages (
  id SERIAL PRIMARY KEY,
  sender VARCHAR(50) NOT NULL,
  recipient VARCHAR(50) NOT NULL,
  message BYTEA NOT NULL,
  iv BYTEA NOT NULL,
  created_at TIMESTAMP DEFAULT NOW(),
  FOREIGN KEY (sender) REFERENCES users(username),
  FOREIGN KEY (recipient) REFERENCES users(username)
);

---

🔄 Example API Flow

Client → Server (Send Message)

{
  "sender": "alice",
  "recipient": "bob",
  "message": "BASE64_ENCRYPTED_DATA",
  "iv": "BASE64_IV"
}

Server → Client (Retrieve Message)

{
  "sender": "alice",
  "message": "BASE64_ENCRYPTED_DATA",
  "iv": "BASE64_IV"
}

Client Decrypts

const msg = await enc.decryptMessageAES(
  base64ToArrayBuffer(message),
  aesKey,
  base64ToUint8Array(iv)
);
console.log(msg); // "Hello Bob!"

---

🔒 Security Notes

• The server stores only public keys and encrypted data.
• Private keys and plaintext never leave the user’s device.
• Messages must be delivered only to their intended recipient.
• The backend is zero-knowledge — even a data leak reveals nothing readable.

---

✅ Summary

Component	Responsibility	Location
ECDSA	Identity and signature	Client
ECDH	Shared key derivation	Client
AES-GCM	Message encryption/decryption	Client
Key & message storage	Persistence only	Backend
Plaintext visibility	Sender & recipient devices only	—

---

🧾 License

MIT © 2025 — Encryption Service by Amirafa
Feel free to use, modify, and distribute under the terms of the MIT license.

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Changelog

[Version 1.0.6] - 2025-10-28

• Add git repository

[Version 1.0.5] - 2025-10-26

• Update README.md
• Add logo

[Version 1.0.3] - 2025-10-26

• Add type declaration
• Update README.md

[Version 1.0.2] - 2025-10-26

• Add README.md

[Version 1.0.1] - 2025-10-26

• Minor fixes

[Version 1.0.0] - 2025-10-26

• published @amirafa/encryption-service