quak/test/crypto/stream.test.ts

/**
 * Tests for `crypto.initStreamPull` and `crypto.pullStreamChunk`.
 *
 * Ente encrypts file content with libsodium's secretstream construction
 * (XChaCha20-Poly1305) in chunked mode. Each plaintext chunk is at most
 * `STREAM_CHUNK_SIZE` bytes (4 MiB); each ciphertext chunk is exactly 17
 * bytes longer than its plaintext (16-byte Poly1305 tag plus a 1-byte
 * secretstream tag).
 *
 * The decryption header is delivered separately from the encrypted body in
 * the file metadata (`file.file.decryptionHeader`). Once `initStreamPull`
 * has consumed it, the body is read in order, one ciphertext chunk at a
 * time, and each chunk is fed to `pullStreamChunk`. The library exposes
 * the secretstream tag on each pulled chunk so the caller can verify the
 * stream ended on a `TAG_FINAL` chunk and was therefore not truncated.
 *
 * These tests pin:
 *   - The chunk-size constants match Ente's expectations, and the
 *     re-exported `streamTagFinal()` matches the tag a real final chunk
 *     carries.
 *   - The pull state can decrypt a multi-chunk stream produced by
 *     sodium.crypto_secretstream_xchacha20poly1305_push, in order.
 *   - The tag byte is propagated to the caller.
 *   - Tampered or out-of-order ciphertext is rejected.
 */

import sodium from "libsodium-wrappers-sumo";
import { beforeAll, describe, expect, it } from "vitest";
import {
    init,
    initStreamPull,
    pullStreamChunk,
    STREAM_CHUNK_OVERHEAD,
    STREAM_CHUNK_SIZE,
    streamTagFinal,
} from "../../src/crypto/index.js";

describe("crypto stream constants", () => {
    /**
     * These constants match the values hard-coded into Ente's web client
     * and Go CLI. If Ente ever changes them server-side, every client
     * must change in lockstep.
     */
    it("STREAM_CHUNK_SIZE is 4 MiB", () => {
        expect(STREAM_CHUNK_SIZE).toBe(4 * 1024 * 1024);
    });

    it("STREAM_CHUNK_OVERHEAD is 17 bytes", () => {
        expect(STREAM_CHUNK_OVERHEAD).toBe(17);
    });

    /**
     * `streamTagFinal()` is re-exported so callers can detect a truncated
     * stream (a body that ended on a non-final chunk) without importing
     * libsodium themselves.
     *
     * It is a function, not a constant, and that is load-bearing: libsodium
     * attaches its own constants to the module object only after
     * `sodium.ready` resolves, which is long after this library's modules are
     * evaluated. Reading the value at call time yields libsodium's number;
     * reading it at module scope would yield `undefined`, and every
     * truncation check downstream would then compare against `undefined` and
     * reject good downloads. This test pins the behaviour end to end — it
     * compares against the tag observed on a real final chunk pulled back off
     * the wire format, so it fails if the accessor is ever made eager.
     */
    it("streamTagFinal() is the tag carried by a real final chunk", async () => {
        await init();
        await sodium.ready;

        const key = sodium.crypto_secretstream_xchacha20poly1305_keygen();
        const push =
            sodium.crypto_secretstream_xchacha20poly1305_init_push(key);
        const ciphertext = sodium.crypto_secretstream_xchacha20poly1305_push(
            push.state,
            new TextEncoder().encode("last chunk"),
            null,
            sodium.crypto_secretstream_xchacha20poly1305_TAG_FINAL,
        );

        const state = initStreamPull(push.header, key);
        expect(pullStreamChunk(state, ciphertext).tag).toBe(streamTagFinal());
    });
});

describe("crypto.initStreamPull / pullStreamChunk", () => {
    beforeAll(async () => {
        await init();
        await sodium.ready;
    });

    /**
     * Helper: encrypt a sequence of plaintext chunks with sodium's push
     * API and return the header plus the encrypted chunks. Marks the
     * final chunk with `TAG_FINAL` (3); intermediate chunks use
     * `TAG_MESSAGE` (0).
     */
    const encryptChunks = (
        key: Uint8Array,
        chunks: Uint8Array[],
    ): { header: Uint8Array; encrypted: Uint8Array[] } => {
        const push =
            sodium.crypto_secretstream_xchacha20poly1305_init_push(key);
        const encrypted: Uint8Array[] = [];
        for (let i = 0; i < chunks.length; i++) {
            const isLast = i === chunks.length - 1;
            const tag = isLast
                ? sodium.crypto_secretstream_xchacha20poly1305_TAG_FINAL
                : sodium.crypto_secretstream_xchacha20poly1305_TAG_MESSAGE;
            encrypted.push(
                sodium.crypto_secretstream_xchacha20poly1305_push(
                    push.state,
                    chunks[i]!,
                    null,
                    tag,
                ),
            );
        }
        return { header: push.header, encrypted };
    };

    it("decrypts a single-chunk stream marked TAG_FINAL", () => {
        const key = sodium.crypto_secretstream_xchacha20poly1305_keygen();
        const plaintext = new TextEncoder().encode("a small file's contents");
        const { header, encrypted } = encryptChunks(key, [plaintext]);

        const state = initStreamPull(header, key);
        const result = pullStreamChunk(state, encrypted[0]!);
        expect(result.plaintext).toEqual(plaintext);
        expect(result.tag).toBe(
            sodium.crypto_secretstream_xchacha20poly1305_TAG_FINAL,
        );
    });

    it("decrypts a multi-chunk stream in order, exposing tags per chunk", () => {
        const key = sodium.crypto_secretstream_xchacha20poly1305_keygen();
        const plaintexts = [
            new Uint8Array([1, 2, 3]),
            new Uint8Array([4, 5, 6, 7, 8]),
            new Uint8Array([9, 10]),
        ];
        const { header, encrypted } = encryptChunks(key, plaintexts);

        const state = initStreamPull(header, key);
        const results = encrypted.map((c) => pullStreamChunk(state, c));

        // Plaintext is recovered chunk-for-chunk, in order.
        expect(results.map((r) => r.plaintext)).toEqual(plaintexts);

        // Intermediate chunks carry TAG_MESSAGE; the last carries TAG_FINAL.
        // The caller can use this to detect a truncated stream: if the
        // last chunk seen does not have TAG_FINAL, the body was cut off.
        const TAG_MESSAGE =
            sodium.crypto_secretstream_xchacha20poly1305_TAG_MESSAGE;
        const TAG_FINAL =
            sodium.crypto_secretstream_xchacha20poly1305_TAG_FINAL;
        expect(results[0]!.tag).toBe(TAG_MESSAGE);
        expect(results[1]!.tag).toBe(TAG_MESSAGE);
        expect(results[2]!.tag).toBe(TAG_FINAL);
    });

    it("rejects a tampered ciphertext chunk", () => {
        const key = sodium.crypto_secretstream_xchacha20poly1305_keygen();
        const { header, encrypted } = encryptChunks(key, [
            new Uint8Array([1, 2, 3]),
        ]);
        encrypted[0]![0] = encrypted[0]![0]! ^ 0x01;

        const state = initStreamPull(header, key);
        expect(() => pullStreamChunk(state, encrypted[0]!)).toThrow();
    });

    it("rejects a chunk decrypted with the wrong key", () => {
        const key = sodium.crypto_secretstream_xchacha20poly1305_keygen();
        const wrongKey = sodium.crypto_secretstream_xchacha20poly1305_keygen();
        const { header, encrypted } = encryptChunks(key, [
            new Uint8Array([1, 2, 3]),
        ]);
        const state = initStreamPull(header, wrongKey);
        expect(() => pullStreamChunk(state, encrypted[0]!)).toThrow();
    });

    it("rejects chunks pulled out of order", () => {
        // The secretstream construction binds each chunk to its position in
        // the stream. Feeding chunk 1's ciphertext after chunk 0 was
        // skipped, or in the wrong order, must fail authentication.
        const key = sodium.crypto_secretstream_xchacha20poly1305_keygen();
        const { header, encrypted } = encryptChunks(key, [
            new Uint8Array([1, 2, 3]),
            new Uint8Array([4, 5, 6]),
        ]);
        const state = initStreamPull(header, key);
        // Skip chunk 0 entirely and try to pull chunk 1 first.
        expect(() => pullStreamChunk(state, encrypted[1]!)).toThrow();
    });

    it("ciphertext chunks are exactly STREAM_CHUNK_OVERHEAD longer than plaintext", () => {
        // Sanity check on the overhead constant. If libsodium ever changes
        // this (it won't), the constant in our crypto module must change
        // with it.
        const key = sodium.crypto_secretstream_xchacha20poly1305_keygen();
        const plaintext = new Uint8Array(123).fill(0x55);
        const { encrypted } = encryptChunks(key, [plaintext]);
        expect(encrypted[0]!.length).toBe(
            plaintext.length + STREAM_CHUNK_OVERHEAD,
        );
    });
});