README.md

@@ -1192,7 +1192,16 @@ The core hierarchy is **Wallets → Addresses**:
       of its stored `xpub` by `src/shared/walletDefects.js`, explained in the
       wallet list, and blocked from signing, sending and private-key export. It
       is never deleted or rewritten.
-- An **address** holds ETH and ERC-20 tokens.
+- An **address** holds ETH and ERC-20 tokens. In an HD or xprv wallet each
+  address record also stores `index`, the derivation index it was made at: 0 for
+  the first address, the index the import scan found it at, or `nextIndex` when
+  "+" added it. An address's `index` and its position in the wallet's list
+  differ once the scan has passed over an unused index or an address has been
+  removed. Sending, site transactions, site signatures and private-key export
+  derive the key at `index`, and refuse it unless it is that address's own key;
+  an HD or xprv address with no valid `index` is refused before anything is
+  derived (`getSignerForAddress()` in `src/shared/wallet.js`). Each refusal is a
+  full sentence naming the address.
 - The user can have multiple wallets, each with multiple addresses (HD) or a
   single address (key).
 
@@ -1518,6 +1527,9 @@ view would leave a wallet one click from deletion.
       change)
     - "Reveal" (wrong password) → full-sentence error on the error line, nothing
       revealed (no screen change)
+    - "Reveal" (correct password, but this address's key is refused, see Data
+      Model) → full-sentence error saying why, nothing revealed (no screen
+      change)
     - "Back" → previous screen (AddressDetail)
     - Settings gear → **Settings**, whose "Back" goes to AddressDetail: leaving
       drops the address the screen was showing, so it also takes the screen off
@@ -1653,6 +1665,13 @@ view would leave a wallet one click from deletion.
       be signed for another
     - "Sign & Send" (wrong password) → "Wrong password." on the password error
       line, no screen change
+    - "Sign & Send" signs as the From address above, not as whichever address is
+      selected: the two are saved separately, so the popup can reopen onto this
+      screen with another address selected. When the selected wallet does not
+      hold the From address → full-sentence error on the password error line,
+      nothing sent (no screen change)
+    - "Sign & Send" (correct password, but the From address's key is refused,
+      see Data Model) → nothing is signed → **ErrorTx** saying why
     - "Back" → **Send**
 
 #### WaitTx (`wait-tx`)
@@ -2118,6 +2137,9 @@ view would leave a wallet one click from deletion.
       shown, exactly as shown, hands the signed transaction to the background to
       broadcast, then → **WaitTx** in the same popup window
     - "Confirm" (wrong password) → error line, no screen change
+    - "Confirm" (correct password, but the From address's key is refused, see
+      Data Model) → full-sentence error on the error line saying why, nothing
+      signed (no screen change)
     - "Reject" → closes popup (returns rejection to background)
     - Popup window closed without answering → the request is rejected with
       EIP-1193 code 4001

src/popup/views/addWallet.js

@@ -184,7 +184,12 @@ async function importMnemonic(ctx) {
         encryptedSecret: encrypted,
         nextIndex: 1,
         addresses: [
-            { address: firstAddress, balance: "0.0000", tokenBalances: [] },
+            {
+                address: firstAddress,
+                index: 0,
+                balance: "0.0000",
+                tokenBalances: [],
+            },
         ],
     };
     state.wallets.push(wallet);
@@ -205,6 +210,7 @@ async function importMnemonic(ctx) {
     if (scan.addresses.length > 1) {
         wallet.addresses = scan.addresses.map((a) => ({
             address: a.address,
+            index: a.index,
             balance: "0.0000",
             tokenBalances: [],
         }));
@@ -299,7 +305,12 @@ async function importXprvKey(ctx) {
         encryptedSecret: encrypted,
         nextIndex: 1,
         addresses: [
-            { address: firstAddress, balance: "0.0000", tokenBalances: [] },
+            {
+                address: firstAddress,
+                index: 0,
+                balance: "0.0000",
+                tokenBalances: [],
+            },
         ],
     };
     state.wallets.push(wallet);
@@ -320,6 +331,7 @@ async function importXprvKey(ctx) {
     if (scan.addresses.length > 1) {
         wallet.addresses = scan.addresses.map((a) => ({
             address: a.address,
+            index: a.index,
             balance: "0.0000",
             tokenBalances: [],
         }));

src/popup/views/addressDetail.js

@@ -266,7 +266,7 @@ function init(_ctx) {
         // This address's private key can be derived from the stored key,
         // but export goes through getSignerForAddress, which refuses a key
         // that is not a master key. Without this the export screen would
-        // take a password and then report that refusal as a wrong password.
+        // take a password and then refuse.
         const defect = selectedWalletDefect();
         if (defect) {
             showFlash(defect.shortMessage);

src/popup/views/approval.js

@@ -913,15 +913,15 @@ function gateOnWalletDefect(errorId, buttonId, address) {
     return true;
 }
 
-// Locate the wallet and the address index owning an address. Returns null when
+// Locate the wallet and the stored address record owning an address. Returns
-// no wallet holds it. Approvals look up the address they were raised for, not
+// null when no wallet holds it. Approvals look up the address they were raised
-// whichever address is active now: the approval named one account, and signing
+// for, not whichever address is active now: the approval named one account,
-// with another is what verification refuses.
+// and signing with another is what verification refuses.
 function findWalletFor(address) {
     for (const wallet of state.wallets) {
         for (let i = 0; i < wallet.addresses.length; i++) {
             if (wallet.addresses[i].address === address) {
-                return { wallet, addrIndex: i };
+                return { wallet, addr: wallet.addresses[i] };
             }
         }
     }
@@ -1048,7 +1048,7 @@ function init(_ctx) {
         try {
             const signer = getSignerForAddress(
                 active.wallet,
-                active.addrIndex,
+                active.addr,
                 decryptedSecret,
             );
             // Sign the approved transaction exactly as it was displayed. The
@@ -1176,7 +1176,7 @@ function init(_ctx) {
         try {
             const signer = getSignerForAddress(
                 active.wallet,
-                active.addrIndex,
+                active.addr,
                 decryptedSecret,
             );
             const sp = pendingSignParams;

src/popup/views/confirmTx.js

@@ -567,6 +567,19 @@ function init(_ctx) {
             return;
         }
 
+        // Sign as the From address this screen shows. The selection is saved
+        // apart from this screen, so the popup can reopen onto it with another
+        // address selected.
+        const addr = wallet.addresses.find((a) => a.address === pendingTx.from);
+        if (!addr) {
+            showError(
+                "confirm-tx-password-error",
+                "The selected wallet does not hold the From address above, " +
+                    "so nothing was sent. Please go back and send again.",
+            );
+            return;
+        }
+
         const password = $("confirm-tx-password").value;
         if (!password) {
             showError(
@@ -597,11 +610,7 @@ function init(_ctx) {
 
         let tx;
         try {
-            const signer = getSignerForAddress(
+            const signer = getSignerForAddress(wallet, addr, decryptedSecret);
-                wallet,
-                state.selectedAddress,
-                decryptedSecret,
-            );
             const provider = getProvider(state.rpcUrl, state.networkId);
             const connectedSigner = signer.connect(provider);
 

src/popup/views/exportPrivkey.js

@@ -135,7 +135,18 @@ async function reveal() {
         // 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);
+        let signer;
+        try {
+            signer = getSignerForAddress(
+                wallet,
+                wallet.addresses[addressIndex],
+                secret,
+            );
+        } catch (e) {
+            // The password was right; it is the key that was refused.
+            showError("export-privkey-password-error", e.message);
+            return;
+        }
         $("export-privkey-password").value = "";
         $("export-privkey-password-section").classList.add("hidden");
         $("export-privkey-value").textContent = signer.privateKey;

src/popup/views/home.js

@@ -354,6 +354,7 @@ function render(ctx) {
             );
             wallet.addresses.push({
                 address: newAddr,
+                index: wallet.nextIndex,
                 balance: "0.0000",
                 tokenBalances: [],
             });

src/shared/wallet.js

@@ -110,16 +110,33 @@ function addressFromPrivateKey(key) {
     return w.address;
 }
 
-function getSignerForAddress(walletData, addrIndex, decryptedSecret) {
+// The signer for `addr`, one of the wallet's stored address records. An HD or
+// xprv address is derived at its own `index`, never at its position in the
+// wallet's list: the two differ once an import scan passes over an unused
+// index, or once an address that is not the last is removed. An HD or xprv
+// record without a valid `index` is refused before anything is derived.
+// Whatever the wallet type, the key is refused unless it is the key of
+// `addr.address`.
+function getSignerForAddress(walletData, addr, decryptedSecret) {
+    if (
+        (walletData.type === "hd" || walletData.type === "xprv") &&
+        !(Number.isInteger(addr.index) && addr.index >= 0)
+    ) {
+        throw new Error(
+            "No derivation index is stored for " +
+                addr.address +
+                ", so its key cannot be derived.",
+        );
+    }
+    let signer;
     if (walletData.type === "hd") {
         const node = HDNodeWallet.fromPhrase(
             decryptedSecret,
             "",
             BIP44_ETH_PATH,
         );
-        return node.deriveChild(addrIndex);
+        signer = node.deriveChild(addr.index);
-    }
+    } else if (walletData.type === "xprv") {
-    if (walletData.type === "xprv") {
         // Checked here rather than through masterXprvOrThrow so the message
         // fits the situation: nobody is importing anything at signing time,
         // and this wallet is already in storage. src/shared/walletDefects.js
@@ -137,9 +154,18 @@ function getSignerForAddress(walletData, addrIndex, decryptedSecret) {
                     "is not a master key, so it cannot sign.",
             );
         }
-        return node.derivePath(BIP44_ETH_PATH).deriveChild(addrIndex);
+        signer = node.derivePath(BIP44_ETH_PATH).deriveChild(addr.index);
+    } else {
+        signer = new Wallet(decryptedSecret);
     }
-    return new Wallet(decryptedSecret);
+    if (signer.address.toLowerCase() !== addr.address.toLowerCase()) {
+        throw new Error(
+            "The key this wallet holds for " +
+                addr.address +
+                " belongs to a different address, so it was not used.",
+        );
+    }
+    return signer;
 }
 
 function isValidMnemonic(mnemonic) {

tests/addressKey.test.js

@@ -0,0 +1,490 @@
+// Sending, a site's transaction and signature requests and private key export
+// each use the key of the address they name: the key at the index that address
+// was derived at, not the one at its position in the wallet's list. The two
+// differ after an import whose scan passed over an unused index, and after an
+// address that is not the last is removed
+// (https://git.eeqj.de/sneak/AutistMask/issues/510). A send is signed by the
+// From address its confirmation screen shows, whichever address is selected.
+//
+// Driven through the real import, "+" button, address removal, confirmation
+// screen, transaction and signature approval screens and export screen, with
+// the node, the vault and the DOM stubbed.
+
+"use strict";
+
+// The addresses the stub node reports a balance for, and the signed
+// transactions it was handed.
+const mockNode = { funded: new Set(), broadcast: [] };
+
+jest.mock("ethers", () => {
+    const actual = jest.requireActual("ethers");
+    class StubProvider {
+        async getBalance(address) {
+            return mockNode.funded.has(address) ? 1n : 0n;
+        }
+        async getTransactionCount() {
+            return 0;
+        }
+        async estimateGas() {
+            return 21000n;
+        }
+        async getFeeData() {
+            return {
+                maxFeePerGas: 20000000000n,
+                maxPriorityFeePerGas: 1000000000n,
+                gasPrice: 10000000000n,
+            };
+        }
+        async getNetwork() {
+            return { chainId: 1n };
+        }
+        async getCode() {
+            return "0x";
+        }
+        async lookupAddress() {
+            return null;
+        }
+        async broadcastTransaction(signed) {
+            mockNode.broadcast.push(signed);
+            return { hash: "0x" + "ab".repeat(32) };
+        }
+    }
+    return { ...actual, JsonRpcProvider: StubProvider };
+});
+
+// No password is hashed: what the wallet stores is the phrase itself.
+jest.mock("../src/shared/vault", () => ({
+    encryptWithPassword: async (secret) => secret,
+    decryptWithPassword: async (secret) => secret,
+}));
+
+// The wait screen polls for a receipt; these tests stop at the broadcast.
+jest.mock("../src/popup/views/txStatus", () => ({
+    showWait: jest.fn(),
+    showError: jest.fn(),
+}));
+
+jest.mock("ethereum-blockies-base64", () => () => "data:image/png;base64,x");
+
+global.fetch = jest.fn(() => {
+    throw new Error("tests must not perform network requests");
+});
+
+const {
+    HDNodeWallet,
+    Mnemonic,
+    Transaction,
+    getBytes,
+    verifyMessage,
+} = require("ethers");
+
+// Publicly known development phrase; never fund it.
+const PHRASE = "test test test test test test test test test test test junk";
+// PHRASE's master extended private key, as the xprv import takes it.
+const XPRV = HDNodeWallet.fromSeed(
+    Mnemonic.fromPhrase(PHRASE).computeSeed(),
+).extendedKey;
+const PASSWORD = "correct horse battery staple";
+const RECIPIENT = "0xC0FfEE0000000000000000000000000000c0fFEe";
+// "Hello", as the hex a page sends.
+const MESSAGE = "0x48656c6c6f";
+
+// The address and key at derivation index `index` of PHRASE, worked out with
+// ethers directly rather than through the wallet's own code.
+function derived(index) {
+    return HDNodeWallet.fromPhrase(PHRASE, "", "m/44'/60'/0'/0/" + index);
+}
+
+// ------------------------------------------------------------ DOM stub
+
+function makeElement(id) {
+    const classes = new Set();
+    const el = {
+        id,
+        textContent: "",
+        title: "",
+        value: "",
+        innerHTML: "",
+        disabled: false,
+        style: {},
+        dataset: {},
+        listeners: {},
+        classList: {
+            add: (...names) => names.forEach((n) => classes.add(n)),
+            remove: (...names) => names.forEach((n) => classes.delete(n)),
+            contains: (n) => classes.has(n),
+            toggle: (n, force) => {
+                const on = force === undefined ? !classes.has(n) : force;
+                if (on) classes.add(n);
+                else classes.delete(n);
+                return on;
+            },
+        },
+        addEventListener: (name, fn) => {
+            el.listeners[name] = el.listeners[name] || [];
+            el.listeners[name].push(fn);
+        },
+        querySelectorAll: () => [],
+        appendChild: () => {},
+    };
+    // Views reach for .parentElement to hide whole sections.
+    Object.defineProperty(el, "parentElement", {
+        get: () => node(id + "-parent"),
+    });
+    return el;
+}
+
+function makeDocument() {
+    const els = new Map();
+    return {
+        getElementById(id) {
+            // The debug banner is created on demand by helpers.js; absent
+            // is the state a non-debug, non-testnet popup is in.
+            if (id === "debug-banner") return null;
+            if (!els.has(id)) els.set(id, makeElement(id));
+            return els.get(id);
+        },
+        createElement: () => makeElement("created"),
+        addEventListener: () => {},
+        body: { prepend: () => {} },
+    };
+}
+
+function node(id) {
+    return globalThis.document.getElementById(id);
+}
+
+function click(element) {
+    const event = { stopPropagation: () => {} };
+    return Promise.all((element.listeners.click || []).map((fn) => fn(event)));
+}
+
+// show() starts the fee estimate without awaiting it; this lets it settle.
+async function settle() {
+    for (let i = 0; i < 10; i++) await new Promise((r) => setTimeout(r, 0));
+}
+
+// ------------------------------------------------------------ harness
+
+globalThis.chrome = {
+    storage: { local: { get: async () => ({}), set: async () => {} } },
+};
+
+const { state } = require("../src/shared/state");
+const { removeAddressFromState } = require("../src/shared/walletDelete");
+const addWallet = require("../src/popup/views/addWallet");
+const home = require("../src/popup/views/home");
+const confirmTx = require("../src/popup/views/confirmTx");
+const approval = require("../src/popup/views/approval");
+const exportPrivkey = require("../src/popup/views/exportPrivkey");
+const txStatus = require("../src/popup/views/txStatus");
+
+// What the background answers when the approval window asks which approval it
+// was opened for, and every message the popup sent it.
+let approvalDetails;
+let sent;
+
+// The "+" button of the wallet list's last render. Each render attaches the
+// handler to the buttons it drew, as the browser's fresh list would have.
+let plusButton;
+
+beforeEach(() => {
+    approvalDetails = null;
+    sent = [];
+    mockNode.broadcast = [];
+    globalThis.document = makeDocument();
+    globalThis.window = { close: () => {} };
+    globalThis.chrome = {
+        storage: { local: { get: async () => ({}), set: async () => {} } },
+        runtime: {
+            connect: () => ({ postMessage: () => {} }),
+            sendMessage: (msg, reply) => {
+                sent.push(msg);
+                if (!reply) return;
+                reply(
+                    msg.type === "AUTISTMASK_GET_APPROVAL"
+                        ? approvalDetails
+                        : null,
+                );
+            },
+        },
+    };
+    node("wallet-list").querySelectorAll = (selector) => {
+        if (selector !== ".btn-add-address") return [];
+        plusButton = makeElement("btn-add-address");
+        plusButton.dataset.wallet = "0";
+        return [plusButton];
+    };
+    // The explorer and price lookups these screens start fail offline, and
+    // say so; that is not under test.
+    for (const method of ["log", "warn", "error"]) {
+        jest.spyOn(console, method).mockImplementation(() => {});
+    }
+    txStatus.showError.mockClear();
+
+    state.wallets = [];
+    state.rpcUrl = "https://rpc.example.invalid";
+    state.networkId = "mainnet";
+    state.viewStack = [];
+    state.currentView = "main";
+
+    addWallet.init({
+        renderWalletList: () => {},
+        doRefreshAndRender: () => {},
+        pageClosed: new AbortController().signal,
+    });
+    confirmTx.init({});
+    approval.init({});
+    exportPrivkey.init();
+});
+
+afterEach(() => {
+    jest.restoreAllMocks();
+});
+
+// Import PHRASE on the add-wallet screen, with the stub node reporting a
+// balance at each of `fundedIndices`, and wait for the address scan.
+async function importPhrase(fundedIndices) {
+    mockNode.funded = new Set(fundedIndices.map((i) => derived(i).address));
+    await click(node("tab-mnemonic"));
+    node("wallet-mnemonic").value = PHRASE;
+    node("add-wallet-password").value = PASSWORD;
+    node("add-wallet-password-confirm").value = PASSWORD;
+    await click(node("btn-add-wallet-confirm"));
+}
+
+// The same, importing XPRV on the add-wallet screen's xprv tab.
+async function importXprv(fundedIndices) {
+    mockNode.funded = new Set(fundedIndices.map((i) => derived(i).address));
+    await click(node("tab-xprv"));
+    node("import-xprv-key").value = XPRV;
+    node("add-wallet-password").value = PASSWORD;
+    node("add-wallet-password-confirm").value = PASSWORD;
+    await click(node("btn-add-wallet-confirm"));
+}
+
+// Press the wallet's "+" button on Home.
+async function addAddress() {
+    home.render({
+        doRefreshAndRender: () => {},
+        pageClosed: new AbortController().signal,
+    });
+    await click(plusButton);
+}
+
+// The key the export screen reveals for the address at `position`.
+async function exportedKey(position) {
+    exportPrivkey.show(0, position);
+    node("export-privkey-password").value = PASSWORD;
+    await click(node("btn-export-privkey-confirm"));
+    return node("export-privkey-value").textContent;
+}
+
+// Confirm a send whose From line shows `from`, with the address at position
+// `selected` selected; resolves to the signed transaction the node was handed,
+// or undefined when none was.
+async function confirmSend(from, selected) {
+    state.selectedWallet = 0;
+    state.selectedAddress = selected;
+    confirmTx.show({
+        from,
+        to: RECIPIENT,
+        amount: "0.5",
+        token: "ETH",
+        balance: "1.0",
+    });
+    await settle();
+    node("confirm-tx-password").value = PASSWORD;
+    await click(node("btn-confirm-send"));
+    return mockNode.broadcast.pop();
+}
+
+// Send from the address at `position`, with that address selected, as the Send
+// button leaves it.
+function sendFrom(position) {
+    return confirmSend(state.wallets[0].addresses[position].address, position);
+}
+
+// A site asks the address at `position` to sign MESSAGE; resolves to the
+// response the approval window sent the background.
+async function signFor(position) {
+    const address = state.wallets[0].addresses[position].address;
+    approvalDetails = {
+        type: "sign",
+        origin: "https://dapp.example",
+        isPhishingDomain: false,
+        approvedFrom: address,
+        signParams: {
+            method: "personal_sign",
+            message: MESSAGE,
+            from: address,
+        },
+    };
+    await approval.show(1);
+    node("approve-sign-password").value = PASSWORD;
+    await click(node("btn-approve-sign"));
+    return sent.find((msg) => msg.type === "AUTISTMASK_SIGN_RESPONSE");
+}
+
+// A site asks the address at `position` to send RECIPIENT a transaction of no
+// value; resolves to the response the approval window sent the background.
+async function transactFor(position) {
+    const address = state.wallets[0].addresses[position].address;
+    approvalDetails = {
+        type: "tx",
+        origin: "https://dapp.example",
+        isPhishingDomain: false,
+        approvedFrom: address,
+        approvedTx: {
+            type: 2,
+            from: address,
+            chainId: "0x1",
+            nonce: "0x0",
+            gasLimit: "0x5208",
+            maxPriorityFeePerGas: "0x3b9aca00",
+            maxFeePerGas: "0x77359400",
+            to: RECIPIENT,
+            value: "0x0",
+            data: "0x",
+            accessList: [],
+        },
+    };
+    await approval.show(1);
+    node("approve-tx-password").value = PASSWORD;
+    await click(node("btn-approve-tx"));
+    return sent.find((msg) => msg.type === "AUTISTMASK_TX_RESPONSE");
+}
+
+describe.each([
+    [
+        "a recovery phrase import whose scan found only the first address",
+        async () => {
+            await importPhrase([0]);
+        },
+        // The address the import stores before its scan.
+        { position: 0, index: 0 },
+    ],
+    [
+        "an xprv import whose scan found only the first address",
+        async () => {
+            await importXprv([0]);
+        },
+        { position: 0, index: 0 },
+    ],
+    [
+        "an import whose scan passed over index 3",
+        async () => {
+            await importPhrase([0, 1, 2, 4]);
+        },
+        // Address 4 on Home, derived at index 4.
+        { position: 3, index: 4 },
+    ],
+    [
+        "an xprv import whose scan passed over index 3",
+        async () => {
+            await importXprv([0, 1, 2, 4]);
+        },
+        { position: 3, index: 4 },
+    ],
+    [
+        "removing the middle one of three addresses",
+        async () => {
+            await importPhrase([0]);
+            await addAddress();
+            await addAddress();
+            removeAddressFromState(state, 0, 1);
+        },
+        // Address 2 on Home after the removal, derived at index 2.
+        { position: 1, index: 2 },
+    ],
+])("after %s", (_name, setUp, { position, index }) => {
+    beforeEach(setUp);
+
+    test("the wallet lists the address derived at that index there", () => {
+        expect(state.wallets[0].addresses[position].address).toBe(
+            derived(index).address,
+        );
+    });
+
+    test("export reveals that address's key", async () => {
+        expect(await exportedKey(position)).toBe(derived(index).privateKey);
+    });
+
+    test("a send is signed by that address", async () => {
+        const signed = await sendFrom(position);
+        expect(Transaction.from(signed).from).toBe(derived(index).address);
+    });
+
+    test("a site's signature is made by that address", async () => {
+        const response = await signFor(position);
+        expect(verifyMessage(getBytes(MESSAGE), response.signature)).toBe(
+            derived(index).address,
+        );
+    });
+
+    test("a site's transaction is signed by that address", async () => {
+        const response = await transactFor(position);
+        expect(Transaction.from(response.rawSignedTx).from).toBe(
+            derived(index).address,
+        );
+    });
+});
+
+// The selection and the confirmation screen are saved apart, so the popup can
+// reopen onto the screen with another address selected than its From line
+// shows.
+describe("a confirmation screen whose From is not the selected address", () => {
+    beforeEach(async () => {
+        await importPhrase([0, 1]);
+    });
+
+    test("the send is signed by the From address shown", async () => {
+        const signed = await confirmSend(derived(1).address, 0);
+        expect(Transaction.from(signed).from).toBe(derived(1).address);
+    });
+
+    test("nothing is sent when the selected wallet does not hold it", async () => {
+        expect(await confirmSend(derived(5).address, 0)).toBeUndefined();
+        expect(node("confirm-tx-password-error").textContent).toBe(
+            "The selected wallet does not hold the From address above, " +
+                "so nothing was sent. Please go back and send again.",
+        );
+    });
+});
+
+describe("an address whose stored index derives a different address", () => {
+    function refusal() {
+        return (
+            "The key this wallet holds for " +
+            derived(0).address +
+            " belongs to a different address, so it was not used."
+        );
+    }
+
+    beforeEach(async () => {
+        await importPhrase([0]);
+        state.wallets[0].addresses[0].index = 1;
+    });
+
+    test("export reveals nothing and says why", async () => {
+        expect(await exportedKey(0)).toBe("");
+        expect(node("export-privkey-password-error").textContent).toBe(
+            refusal(),
+        );
+    });
+
+    test("nothing is sent", async () => {
+        expect(await sendFrom(0)).toBeUndefined();
+        expect(txStatus.showError).toHaveBeenCalledWith(
+            expect.anything(),
+            null,
+            refusal(),
+        );
+    });
+
+    test("nothing is signed", async () => {
+        const response = await signFor(0);
+        expect(response.signature).toBeUndefined();
+        expect(response.error).toBe(refusal());
+    });
+});

tests/approvalNonce.test.js

@@ -136,7 +136,9 @@ async function openTxApproval(approvedTx) {
             xpub: "xpub-wallet-1",
             encryptedSecret: "encrypted-secret-1",
             nextIndex: 1,
-            addresses: [{ address: FROM, balance: "0", tokenBalances: [] }],
+            addresses: [
+                { address: FROM, index: 0, balance: "0", tokenBalances: [] },
+            ],
         },
     ];
     approval.init({});

tests/approvalVerify.test.js

@@ -1454,7 +1454,11 @@ describe("background population to popup signing to verification", () => {
 
     // What the popup does with it: signs it as given, populating nothing.
     async function popupSigns(approvedTx) {
-        const localSigner = getSignerForAddress(walletData, 0, SIGNER_KEY);
+        const localSigner = getSignerForAddress(
+            walletData,
+            { address: signer.address },
+            SIGNER_KEY,
+        );
         return localSigner.signTransaction({ ...approvedTx });
     }
 
@@ -1549,7 +1553,11 @@ describe("background population to popup signing to verification", () => {
     // address the user has switched to.
     test("the approved from stops the popup signing with another key", async () => {
         const approvedTx = await backgroundPrepares(TX_PARAMS);
-        const otherSigner = getSignerForAddress(walletData, 0, OTHER_KEY);
+        const otherSigner = getSignerForAddress(
+            walletData,
+            { address: other.address },
+            OTHER_KEY,
+        );
         await expect(
             otherSigner.signTransaction({ ...approvedTx }),
         ).rejects.toThrow(/from address mismatch/);

tests/wallet.test.js

@@ -416,7 +416,7 @@ describe("extended key depth", () => {
         expect(() =>
             wallet.getSignerForAddress(
                 { type: "xprv" },
-                0,
+                { address: VECTOR_ADDRESSES[0], index: 0 },
                 accountXprv(VECTOR_PHRASE),
             ),
         ).toThrow(/master/i);
@@ -504,7 +504,7 @@ describe("getSignerForAddress", () => {
     test.each([0, 1, 2])("hd wallet, address index %i", (index) => {
         const signer = wallet.getSignerForAddress(
             { type: "hd" },
-            index,
+            { address: VECTOR_ADDRESSES[index], index },
             VECTOR_PHRASE,
         );
 
@@ -515,7 +515,7 @@ describe("getSignerForAddress", () => {
     test.each([0, 1, 2])("xprv wallet, address index %i", (index) => {
         const signer = wallet.getSignerForAddress(
             { type: "xprv" },
-            index,
+            { address: VECTOR_ADDRESSES[index], index },
             masterXprv(VECTOR_PHRASE),
         );
 
@@ -527,7 +527,7 @@ describe("getSignerForAddress", () => {
         for (const index of [0, 1, 2]) {
             const signer = wallet.getSignerForAddress(
                 { type: "privkey" },
-                index,
+                { address: VECTOR_ADDRESSES[1], index },
                 VECTOR_PRIVATE_KEYS[1],
             );
 
@@ -535,10 +535,54 @@ describe("getSignerForAddress", () => {
         }
     });
 
+    // https://git.eeqj.de/sneak/AutistMask/issues/510: an address whose stored
+    // index does not derive it, or a private key that is not its key.
+    test.each([
+        ["hd", { address: VECTOR_ADDRESSES[2], index: 1 }, VECTOR_PHRASE],
+        [
+            "xprv",
+            { address: VECTOR_ADDRESSES[2], index: 1 },
+            masterXprv(VECTOR_PHRASE),
+        ],
+        ["privkey", { address: VECTOR_ADDRESSES[2] }, VECTOR_PRIVATE_KEYS[1]],
+    ])(
+        "%s wallet refuses a key that is not the address's own",
+        (type, addr, secret) => {
+            expect(() =>
+                wallet.getSignerForAddress({ type }, addr, secret),
+            ).toThrow(
+                "The key this wallet holds for " +
+                    VECTOR_ADDRESSES[2] +
+                    " belongs to a different address, so it was not used.",
+            );
+        },
+    );
+
+    // An HD or xprv address record without a usable `index` is refused in a
+    // sentence, not with what ethers says about the value it was handed.
+    test.each([
+        ["hd", VECTOR_PHRASE],
+        ["xprv", masterXprv(VECTOR_PHRASE)],
+    ])("%s wallet refuses an address with no valid index", (type, secret) => {
+        for (const index of [undefined, null, -1, 1.5, "1"]) {
+            expect(() =>
+                wallet.getSignerForAddress(
+                    { type },
+                    { address: VECTOR_ADDRESSES[1], index },
+                    secret,
+                ),
+            ).toThrow(
+                "No derivation index is stored for " +
+                    VECTOR_ADDRESSES[1] +
+                    ", so its key cannot be derived.",
+            );
+        }
+    });
+
     test("the returned signer signs recoverably as the expected address", async () => {
         const signer = wallet.getSignerForAddress(
             { type: "hd" },
-            1,
+            { address: VECTOR_ADDRESSES[1], index: 1 },
             VECTOR_PHRASE,
         );
         const message = "AutistMask derivation test";

tests/walletDefects.test.js

@@ -55,7 +55,7 @@ function healthyXprvWallet(name = "Master") {
         xpub,
         nextIndex: 1,
         encryptedSecret: "irrelevant-to-these-tests",
-        addresses: [{ address: firstAddress, balance: "0.0000" }],
+        addresses: [{ address: firstAddress, index: 0, balance: "0.0000" }],
     };
 }
 
@@ -74,7 +74,11 @@ function brokenXprvWallet(name = "Imported xprv") {
         nextIndex: 1,
         encryptedSecret: "irrelevant-to-these-tests",
         addresses: [
-            { address: node.deriveChild(0).address, balance: "0.0000" },
+            {
+                address: node.deriveChild(0).address,
+                index: 0,
+                balance: "0.0000",
+            },
         ],
     };
 }
@@ -570,7 +574,7 @@ describe("no path throws an unhandled error for a defective wallet", () => {
         try {
             wallet.getSignerForAddress(
                 { type: "xprv" },
-                0,
+                brokenXprvWallet().addresses[0],
                 accountXprv(VECTOR_PHRASE),
             );
         } catch (e) {
@@ -585,7 +589,7 @@ describe("no path throws an unhandled error for a defective wallet", () => {
     test("a healthy xprv wallet signs as it always did", () => {
         const signer = wallet.getSignerForAddress(
             { type: "xprv" },
-            0,
+            healthyXprvWallet().addresses[0],
             masterXprv(VECTOR_PHRASE),
         );