fix: wipe the exported private key from the DOM on any view leave (closes #221)

src/popup/views/exportPrivkey.js

@@ -0,0 +1,174 @@
+// Private key export for a single address.
+//
+// The key controls the address outright — anyone holding it can move every
+// token in it, from any device, forever — so this screen is handled under
+// the same rules as the recovery phrase screen (./showPhrase.js):
+//
+//   1. Nothing is decrypted, no key is derived, and nothing is written into
+//      the DOM until decryptWithPassword has accepted the password.
+//   2. Leaving the screen by any path wipes it, via the onViewLeave hook,
+//      and a decrypt still in flight when that happens is discarded
+//      instead of written (revealGeneration).
+//   3. The key never reaches the logger. This module deliberately does not
+//      import src/shared/log.js.
+//
+// The key is also never assigned to `state`, so it cannot be persisted to
+// extension storage, and "export-privkey" is excluded from RESTORABLE_VIEWS
+// so the popup can never reopen onto it.
+
+const {
+    $,
+    showView,
+    showFlash,
+    flashCopyFeedback,
+    goBack,
+    onViewLeave,
+    pushCurrentView,
+    renderAddressHtml,
+    attachCopyHandlers,
+} = require("./helpers");
+const { state } = require("../../shared/state");
+const { decryptWithPassword } = require("../../shared/vault");
+const { getSignerForAddress } = require("../../shared/wallet");
+const makeBlockie = require("ethereum-blockies-base64");
+
+const VIEW = "export-privkey";
+
+let walletIndex = null;
+let addressIndex = null;
+
+// Bumped by every clear(), which is what leaving the screen runs. reveal()
+// captures it before awaiting the decrypt and refuses to touch the DOM if
+// it has moved: a decrypt still in flight when the screen is left would
+// otherwise write the key *after* the wipe, with nothing scheduled to wipe
+// it again, leaving it in the hidden view for the life of the popup.
+let revealGeneration = 0;
+
+// True only if the reveal that captured `generation` is still the live one:
+// the screen has not been left, cleared, or re-entered for another address
+// since it started.
+function isCurrentReveal(generation) {
+    return (
+        generation === revealGeneration &&
+        walletIndex !== null &&
+        addressIndex !== null &&
+        state.currentView === VIEW
+    );
+}
+
+function fail(message) {
+    $("export-privkey-flash").textContent = message;
+    $("export-privkey-flash").style.visibility = "visible";
+}
+
+// Wipe every trace of the key and drop the address selection. Safe to call
+// when nothing was ever revealed, and safe to call twice.
+function clear() {
+    walletIndex = null;
+    addressIndex = null;
+    revealGeneration += 1;
+    $("export-privkey-value").textContent = "";
+    $("export-privkey-password").value = "";
+    $("export-privkey-result").classList.add("hidden");
+    $("export-privkey-password-section").classList.remove("hidden");
+    $("export-privkey-flash").textContent = "";
+    $("export-privkey-flash").style.visibility = "hidden";
+}
+
+function show(walletIdx, addrIdx) {
+    const wallet = state.wallets[walletIdx];
+    const addr = wallet && wallet.addresses[addrIdx];
+    if (!addr) {
+        showFlash("That address is no longer available.");
+        return;
+    }
+    clear();
+    walletIndex = walletIdx;
+    addressIndex = addrIdx;
+
+    const blockieEl = $("export-privkey-jazzicon");
+    blockieEl.innerHTML = "";
+    const img = document.createElement("img");
+    img.src = makeBlockie(addr.address);
+    img.width = 48;
+    img.height = 48;
+    img.style.imageRendering = "pixelated";
+    img.style.borderRadius = "50%";
+    blockieEl.appendChild(img);
+
+    $("export-privkey-title").textContent =
+        wallet.name + " — Address " + (addrIdx + 1);
+    const addrContainer = $("export-privkey-dot").parentElement;
+    addrContainer.innerHTML = renderAddressHtml(addr.address);
+    attachCopyHandlers(addrContainer);
+
+    // Pushed here rather than by the caller: this function can return
+    // without navigating, and a push that happened anyway would leave an
+    // entry on the stack that no screen transition matches.
+    pushCurrentView();
+    showView(VIEW);
+}
+
+async function reveal() {
+    const password = $("export-privkey-password").value;
+    if (!password) {
+        fail("Password is required.");
+        return;
+    }
+    if (walletIndex === null) {
+        fail("No address is selected.");
+        return;
+    }
+    const wallet = state.wallets[walletIndex];
+
+    const btn = $("btn-export-privkey-confirm");
+    btn.disabled = true;
+    btn.classList.add("text-muted");
+    const generation = revealGeneration;
+    try {
+        const secret = await decryptWithPassword(
+            wallet.encryptedSecret,
+            password,
+        );
+        // The only suspension point in this view, and the gate on the only
+        // place a secret is written: if the screen was left while the
+        // decrypt ran, the wipe has already happened, so the key is not
+        // even derived, let alone written.
+        if (!isCurrentReveal(generation)) return;
+        const signer = getSignerForAddress(wallet, addressIndex, secret);
+        $("export-privkey-password").value = "";
+        $("export-privkey-password-section").classList.add("hidden");
+        $("export-privkey-value").textContent = signer.privateKey;
+        $("export-privkey-result").classList.remove("hidden");
+        $("export-privkey-flash").textContent = "";
+        $("export-privkey-flash").style.visibility = "hidden";
+    } catch {
+        if (!isCurrentReveal(generation)) return;
+        fail("That password is not correct. Please try again.");
+    } finally {
+        btn.disabled = false;
+        btn.classList.remove("text-muted");
+    }
+}
+
+function init() {
+    onViewLeave(VIEW, clear);
+
+    // No wipe here: goBack() routes through showView(), which runs the
+    // leave hook. A per-button wipe would only cover this one path.
+    $("btn-export-privkey-back").addEventListener("click", () => {
+        goBack();
+    });
+
+    $("btn-export-privkey-confirm").addEventListener("click", reveal);
+
+    $("export-privkey-value").addEventListener("click", () => {
+        const key = $("export-privkey-value").textContent;
+        if (!key) return;
+        navigator.clipboard.writeText(key);
+        showFlash("Copied!");
+        flashCopyFeedback($("export-privkey-value"));
+    });
+}
+
+module.exports = { init, show };