feat(security): verify binaries with pinned Ed25519 signature on SHA256SUMS

Replace the same-origin checksum with a detached Ed25519 signature
(SHA256SUMS.sig) verified against a pinned public key before extraction,
closing #308: a compromised download mirror can no longer certify a
tampered binary. The signed manifest also binds the release version,
rejecting a forced downgrade to an older signed build.

Verification is mandatory and non-bypassable on the official download path;
custom CLOAKBROWSER_DOWNLOAD_URL mirrors keep the legacy skippable checksum.
Silent auto-update is preserved for everyone because only a constant public
key is pinned, not per-version hashes. Older installed wrappers are
unaffected — the version= line is ignored by their checksum parser.

Python uses cryptography; JS uses node:crypto. Adds tamper, downgrade, and
fail-closed tests in both languages.

js/tests/signature.test.ts

@@ -0,0 +1,234 @@
+import { describe, it, expect, vi, afterEach } from "vitest";
+import { sign as cryptoSign, createPrivateKey, createHash } from "node:crypto";
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+
+// Generate a throwaway signing keypair BEFORE the config mock is hoisted, then
+// pin its public key so verifySignature accepts signatures we produce here.
+const h = vi.hoisted(() => {
+  // eslint-disable-next-line @typescript-eslint/no-var-requires
+  const crypto = require("node:crypto");
+  const { publicKey, privateKey } = crypto.generateKeyPairSync("ed25519");
+  const otherPub = crypto.generateKeyPairSync("ed25519").publicKey;
+  const rawB64 = (pk: any) =>
+    Buffer.from(pk.export({ format: "jwk" }).x, "base64url").toString("base64");
+  return {
+    pinnedPubB64: rawB64(publicKey),
+    otherPubB64: rawB64(otherPub),
+    privPem: privateKey.export({ type: "pkcs8", format: "pem" }) as string,
+  };
+});
+
+vi.mock("../src/config.js", async (importActual) => {
+  const actual = await importActual<typeof import("../src/config.js")>();
+  return { ...actual, BINARY_SIGNING_PUBKEYS: [h.pinnedPubB64] };
+});
+
+import {
+  fetchSignedManifest,
+  parseChecksums,
+  parseManifestVersion,
+  verifyDownloadChecksum,
+  verifySignature,
+} from "../src/download.js";
+import { getArchiveName, getChromiumVersion } from "../src/config.js";
+
+/** Produce SHA256SUMS.sig content (base64 text bytes) for a manifest. */
+function sign(manifest: Uint8Array): Uint8Array {
+  const priv = createPrivateKey(h.privPem);
+  const sig = cryptoSign(null, manifest, priv); // raw 64-byte Ed25519 signature
+  return new TextEncoder().encode(sig.toString("base64"));
+}
+
+const enc = (s: string) => new TextEncoder().encode(s);
+
+describe("verifySignature", () => {
+  it("accepts a valid signature", () => {
+    const manifest = enc("abc  cloakbrowser-linux-x64.tar.gz\n");
+    expect(() => verifySignature(manifest, sign(manifest))).not.toThrow();
+  });
+
+  it("rejects a tampered manifest", () => {
+    const manifest = enc("abc  cloakbrowser-linux-x64.tar.gz\n");
+    const sig = sign(manifest);
+    const tampered = enc("xyz  cloakbrowser-linux-x64.tar.gz\n");
+    expect(() => verifySignature(tampered, sig)).toThrow(/signature verification failed/);
+  });
+
+  it("rejects malformed base64 in the .sig", () => {
+    expect(() => verifySignature(enc("data\n"), enc("!!!not base64!!!")))
+      .toThrow(/Malformed/);
+  });
+
+  it("rejects a signature from a non-pinned key", async () => {
+    // Re-mock config so ONLY the other key is pinned, then the signature
+    // (made with the real key) must fail.
+    vi.resetModules();
+    vi.doMock("../src/config.js", async (importActual) => {
+      const actual = await importActual<typeof import("../src/config.js")>();
+      return { ...actual, BINARY_SIGNING_PUBKEYS: [h.otherPubB64] };
+    });
+    const { verifySignature: vs } = await import("../src/download.js");
+    const manifest = enc("data\n");
+    expect(() => vs(manifest, sign(manifest))).toThrow(/signature verification failed/);
+    vi.doUnmock("../src/config.js");
+    vi.resetModules();
+  });
+
+  it("accepts a signature under the new key during rotation", async () => {
+    // Pin BOTH keys (old + new) and sign with the real (new) key — must pass.
+    vi.resetModules();
+    vi.doMock("../src/config.js", async (importActual) => {
+      const actual = await importActual<typeof import("../src/config.js")>();
+      return { ...actual, BINARY_SIGNING_PUBKEYS: [h.otherPubB64, h.pinnedPubB64] };
+    });
+    const { verifySignature: vs } = await import("../src/download.js");
+    const manifest = enc("rotated\n");
+    expect(() => vs(manifest, sign(manifest))).not.toThrow();
+    vi.doUnmock("../src/config.js");
+    vi.resetModules();
+  });
+});
+
+describe("verifyDownloadChecksum (official path, fail-closed)", () => {
+  afterEach(() => {
+    vi.restoreAllMocks();
+    delete process.env.CLOAKBROWSER_DOWNLOAD_URL;
+    delete process.env.CLOAKBROWSER_SKIP_CHECKSUM;
+  });
+
+  function tmpFile(bytes: Buffer): string {
+    const p = path.join(os.tmpdir(), `cloak-sig-${process.pid}-${bytes.length}-${bytes[0]}`);
+    fs.writeFileSync(p, bytes);
+    return p;
+  }
+
+  /** Mock fetch to serve a signed manifest for the official URLs. */
+  function mockManifest(manifestBytes: Uint8Array) {
+    const sig = sign(manifestBytes);
+    vi.spyOn(globalThis, "fetch").mockImplementation(async (input) => {
+      const url = typeof input === "string" ? input : (input as URL).toString();
+      const body = url.endsWith(".sig") ? sig : manifestBytes;
+      return { ok: true, arrayBuffer: async () => body.buffer } as Response;
+    });
+  }
+
+  /** Manifest body with the bound version line prepended (defaults to current). */
+  const body = (lines: string, version = getChromiumVersion()) =>
+    enc(`version=${version}\n${lines}`);
+
+  it("passes when signature is valid and hash matches", async () => {
+    const data = Buffer.from("the real binary");
+    const file = tmpFile(data);
+    const hash = createHash("sha256").update(data).digest("hex");
+    mockManifest(body(`${hash}  ${getArchiveName()}\n`));
+    await expect(verifyDownloadChecksum(file)).resolves.toBeUndefined();
+  });
+
+  it("fails when the binary is tampered (hash mismatch)", async () => {
+    const file = tmpFile(Buffer.from("a malicious binary"));
+    const goodHash = createHash("sha256").update(Buffer.from("the real binary")).digest("hex");
+    mockManifest(body(`${goodHash}  ${getArchiveName()}\n`));
+    await expect(verifyDownloadChecksum(file)).rejects.toThrow(/Checksum verification failed/);
+  });
+
+  it("fails on a signed manifest for the wrong version (downgrade)", async () => {
+    const data = Buffer.from("the real binary");
+    const file = tmpFile(data);
+    const hash = createHash("sha256").update(data).digest("hex");
+    // Genuinely signed, but declares an old version we did not request.
+    mockManifest(body(`${hash}  ${getArchiveName()}\n`, "1.0.0.0"));
+    await expect(verifyDownloadChecksum(file)).rejects.toThrow(/Version mismatch/);
+  });
+
+  it("fails when the version line is missing (binding required)", async () => {
+    const data = Buffer.from("the real binary");
+    const file = tmpFile(data);
+    const hash = createHash("sha256").update(data).digest("hex");
+    mockManifest(enc(`${hash}  ${getArchiveName()}\n`)); // no version= line
+    await expect(verifyDownloadChecksum(file)).rejects.toThrow(/Version mismatch/);
+  });
+
+  it("fails closed when no signed manifest can be fetched", async () => {
+    const file = tmpFile(Buffer.from("x"));
+    vi.spyOn(globalThis, "fetch").mockResolvedValue({ ok: false, status: 404 } as Response);
+    await expect(verifyDownloadChecksum(file)).rejects.toThrow(/signed SHA256SUMS/);
+  });
+
+  it("fails when the signed manifest has no entry for this platform", async () => {
+    const file = tmpFile(Buffer.from("x"));
+    const someHash = "0".repeat(64);
+    mockManifest(body(`${someHash}  some-other-file.tar.gz\n`));
+    await expect(verifyDownloadChecksum(file)).rejects.toThrow(/no entry for/);
+  });
+
+  it("custom download URL keeps the legacy skippable path (no signature fetch)", async () => {
+    const file = tmpFile(Buffer.from("x"));
+    process.env.CLOAKBROWSER_DOWNLOAD_URL = "https://my-mirror.test";
+    process.env.CLOAKBROWSER_SKIP_CHECKSUM = "true";
+    const spy = vi.spyOn(globalThis, "fetch");
+    await expect(verifyDownloadChecksum(file)).resolves.toBeUndefined();
+    expect(spy).not.toHaveBeenCalled();
+  });
+});
+
+describe("version binding", () => {
+  it("reads the version= line", () => {
+    expect(
+      parseManifestVersion("version=146.0.7680.177.5\nabc  file.tar.gz\n")
+    ).toBe("146.0.7680.177.5");
+  });
+
+  it("returns null when absent", () => {
+    expect(parseManifestVersion("abc  file.tar.gz\n")).toBeNull();
+  });
+
+  it("old parseChecksums ignores the version line", () => {
+    const result = parseChecksums(
+      `version=146.0.7680.177.5\n${"a".repeat(64)}  cloakbrowser-linux-x64.tar.gz\n`
+    );
+    expect(result.size).toBe(1);
+    expect(result.has("cloakbrowser-linux-x64.tar.gz")).toBe(true);
+  });
+});
+
+describe("fetchSignedManifest", () => {
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  const mockPair = (manifest: string, sig: string, failPrimarySig = false) =>
+    vi.spyOn(globalThis, "fetch").mockImplementation(async (input) => {
+      const url = typeof input === "string" ? input : (input as URL).toString();
+      const isSig = url.endsWith(".sig");
+      if (url.includes("cloakbrowser.dev") && isSig && failPrimarySig) {
+        return { ok: false, status: 404 } as Response;
+      }
+      return {
+        ok: true,
+        arrayBuffer: async () =>
+          new TextEncoder().encode(isSig ? sig : manifest).buffer,
+      } as Response;
+    });
+
+  it("returns manifest + sig from the primary origin", async () => {
+    mockPair("MANIFEST", "U0lH");
+    const result = await fetchSignedManifest("1.2.3.4");
+    expect(new TextDecoder().decode(result!.manifestBytes)).toBe("MANIFEST");
+    expect(new TextDecoder().decode(result!.sigBytes)).toBe("U0lH");
+  });
+
+  it("falls back to GitHub when the primary .sig is missing", async () => {
+    const spy = mockPair("MANIFEST", "U0lH", true);
+    const result = await fetchSignedManifest("1.2.3.4");
+    expect(result).not.toBeNull();
+    // primary SHA256SUMS + primary .sig (404) + github SHA256SUMS + github .sig
+    expect(spy.mock.calls.length).toBeGreaterThanOrEqual(3);
+  });
+
+  it("returns null when everything fails", async () => {
+    vi.spyOn(globalThis, "fetch").mockRejectedValue(new Error("network"));
+    expect(await fetchSignedManifest("1.2.3.4")).toBeNull();
+  });
+});