sync-server-example/demo/experimental/encrypted-client.ts

import { subtle, getRandomValues } from 'node:crypto';
import { fromExtendedJson, toExtendedJson } from '@xo-cash/utils';
import { sha256, binToBase64 } from '@bitauth/libauth';

import { BaseSyncClient, type ResourcesRecord } from '../../source/shared/base-client.js';

/**
 * Encrypts every resource with a single shared key.
 */
export class EncryptedClient<T = unknown> extends BaseSyncClient<T> {
    private readonly encryptionKey: Uint8Array;

    constructor(
        private readonly client: BaseSyncClient<string>,
        encryptionKey: Uint8Array | string,
    ) {
        super();

        // Hash the encryption key into 32 bytes if it is a string
        this.encryptionKey = typeof encryptionKey === 'string' ? sha256.hash(new TextEncoder().encode(encryptionKey)) : encryptionKey;

        this.client.on('resource-instance-updated', async (message) => {
            try {
                this.emit('resource-instance-updated', {
                    ...message,
                    value: (await EncryptedClient.decrypt(this.encryptionKey, message.value)) as T,
                });
            } catch (error) {
                this.emit('error', error instanceof Error ? error : new Error(String(error)));
            }
        });
    }

    /**
     * Decrypts every instance of every resource in a record.
     * @param resources - The encrypted resources record
     * @returns The resources record with decrypted values
     */
    private async decryptResources(resources: ResourcesRecord<string>): Promise<ResourcesRecord<T>> {
        const entries = await Promise.all(
            Object.entries(resources).map(async ([resourceId, resource]) => {
                const instances = await Promise.all(
                    resource.instances.map(async (instance) => ({
                        ...instance,
                        value: (await EncryptedClient.decrypt(this.encryptionKey, instance.value)) as T,
                    })),
                );

                return [resourceId, { ...resource, instances }] as const;
            }),
        );

        return Object.fromEntries(entries);
    }

    public async connect(): Promise<void> {
        return this.client.connect();
    }

    public async disconnect(): Promise<void> {
        return this.client.disconnect();
    }

    public async readMany(resourceIds: string[]): Promise<ResourcesRecord<T>> {
        const encryptedResources = await this.client.readMany(resourceIds);

        return this.decryptResources(encryptedResources);
    }

    public async writeMany(resources: Record<string, T>): Promise<ResourcesRecord<T>> {
        const encryptedEntries = await Promise.all(
            Object.entries(resources).map(async ([resourceId, value]) => {
                return [resourceId, await EncryptedClient.encrypt(this.encryptionKey, value)] as const;
            }),
        );

        const response = await this.client.writeMany(Object.fromEntries(encryptedEntries));

        return this.decryptResources(response);
    }

    public async subscribe(resourceId: string): Promise<void> {
        return this.client.subscribe(resourceId);
    }

    public async unsubscribe(resourceId: string): Promise<void> {
        return this.client.unsubscribe(resourceId);
    }

    /**
     * Imports raw key material as an AES-GCM key
     * @param keyMaterial - The 32 byte key material
     * @returns The AES-GCM CryptoKey
     */
    private static importKey(keyMaterial: Uint8Array) {
        return subtle.importKey('raw', Buffer.from(keyMaterial), { name: 'AES-GCM' }, false, ['encrypt', 'decrypt']);
    }

    /**
     * Encrypts a value using AES-GCM with a random 12 byte IV
     * @param keyMaterial - The encryption key material
     * @param value - The value to encrypt
     * @returns The IV and ciphertext as a base64 string
     */
    public static async encrypt(keyMaterial: Uint8Array, value: unknown): Promise<string> {
        const key = await this.importKey(keyMaterial);
        const iv = getRandomValues(new Uint8Array(12));

        // Encode the value as extended JSON and then to UTF-8 bytes
        const encodedValue = new TextEncoder().encode(toExtendedJson(value));

        const encrypted = await subtle.encrypt({ name: 'AES-GCM', iv }, key, encodedValue);

        // Prepend the IV so it can be recovered when decrypting
        return binToBase64(Buffer.concat([iv, new Uint8Array(encrypted)]));
    }

    /**
     * Decrypts a value encrypted by `encrypt`
     * @param keyMaterial - The encryption key material
     * @param value - The IV and ciphertext as a base64 string
     * @returns The decrypted value
     */
    public static async decrypt(keyMaterial: Uint8Array, value: string): Promise<unknown> {
        const key = await this.importKey(keyMaterial);

        // Decode the base64 first: the IV is 12 bytes, not 12 base64 characters
        const bytes = Buffer.from(value, 'base64');
        const iv = bytes.subarray(0, 12);
        const encryptedValue = bytes.subarray(12);

        const decrypted = await subtle.decrypt({ name: 'AES-GCM', iv }, key, encryptedValue);

        return fromExtendedJson(new TextDecoder().decode(decrypted));
    }
}