feat: add private key viewing for addresses

Add a 'Show private key' button on the address detail view that opens
a dedicated password-prompt screen with a clear warning about key
sensitivity. After correct password entry, the derived private key is
displayed in a read-only well with a copy button.

- Add getPrivateKeyForAddress() to wallet.js
- Add showPrivateKey view with password verification
- Add clipboard policy section to README explaining why we never
  auto-clear the clipboard
- Register new view in helpers.js VIEWS array and wire up in index.js

Closes #19

README.md

@@ -213,6 +213,22 @@ create an address with the same visible characters and trick the user into
 sending funds to it. Showing the complete identifier defeats this class of
 attack.
 
+#### Clipboard Policy
+
+AutistMask never clears or overwrites the user's clipboard. When sensitive data
+such as a private key is copied, it is the user's responsibility to manage their
+clipboard afterwards. We deliberately avoid auto-clearing the clipboard for two
+reasons:
+
+1. **User expectations**: silently modifying the clipboard violates the
+   principle of least surprise. The user initiated the copy and knows the
+   content is sensitive.
+2. **Data safety**: the user may have copied something else important in the
+   intervening time. A timed clipboard clear would destroy that unrelated data.
+
+The warning shown before revealing a private key makes it clear that the key is
+sensitive and that clipboard management is the user's responsibility.
+
 #### Data Model
 
 The core hierarchy is **Wallets → Addresses**:
@@ -316,15 +332,34 @@ transitions.
     - Balance list: ETH + tracked ERC-20 tokens (4 decimal places, USD inline).
       Each balance row is clickable → **AddressToken**
     - Send / Receive / + Token buttons
+    - "Show private key" button
     - Transaction list (with ENS resolution for counterparties)
 - **Transitions**:
     - Tap balance row → **AddressToken** (for that token)
     - "Send" → **Send**
     - "Receive" → **Receive**
     - "+ Token" → **AddToken**
+    - "Show private key" → **ShowPrivateKey**
     - Tap transaction row → **TransactionDetail**
     - "Back" → **Home**
 
+#### ShowPrivateKey
+
+- **When**: User clicked "Show private key" on AddressDetail.
+- **Elements**:
+    - "Back" button
+    - Title: "Display Private Key"
+    - Warning box (lock + money icons) explaining the key controls funds and
+      that the user is responsible for clipboard management
+    - Password input
+    - "Display Private Key" button (with lock + money icons)
+    - After reveal: private key in a read-only well (monospace, select-all),
+      Copy button, Done button
+- **Transitions**:
+    - "Display Private Key" (correct password) → reveals key in-place
+    - "Copy" → copies key to clipboard
+    - "Done" / "Back" → **AddressDetail** (key cleared from DOM)
+
 #### AddressToken
 
 - **When**: User clicked a specific token balance on AddressDetail.

src/popup/index.html

@@ -119,15 +119,6 @@
                         Import private key
                     </button>
                 </div>
-                <div class="mt-1 text-xs text-muted">
-                    Have an extended private key (xprv)?
-                    <button
-                        id="btn-add-wallet-import-xprv"
-                        class="underline cursor-pointer bg-transparent border-none text-fg text-xs font-mono p-0"
-                    >
-                        Import xprv
-                    </button>
-                </div>
             </div>
 
             <!-- ============ IMPORT PRIVATE KEY ============ -->
@@ -179,55 +170,6 @@
                 </button>
             </div>
 
-            <!-- ============ IMPORT XPRV ============ -->
-            <div id="view-import-xprv" class="view hidden">
-                <button
-                    id="btn-import-xprv-back"
-                    class="border border-border px-2 py-1 hover:bg-fg hover:text-bg cursor-pointer mb-2"
-                >
-                    &lt; Back
-                </button>
-                <h2 class="font-bold mb-2">Import Extended Private Key</h2>
-                <p class="mb-2">
-                    Paste your extended private key (xprv) below. This will
-                    import the HD wallet and scan for used addresses.
-                </p>
-                <div class="mb-2">
-                    <input
-                        type="password"
-                        id="import-xprv-key"
-                        class="border border-border p-1 w-full font-mono text-sm bg-bg text-fg"
-                        placeholder="xprv..."
-                    />
-                </div>
-                <div class="mb-2" id="import-xprv-password-section">
-                    <label class="block mb-1">Choose a password</label>
-                    <p class="text-xs text-muted mb-1">
-                        This password encrypts your key on this device. You will
-                        need it to send funds.
-                    </p>
-                    <input
-                        type="password"
-                        id="import-xprv-password"
-                        class="border border-border p-1 w-full font-mono text-sm bg-bg text-fg"
-                    />
-                </div>
-                <div class="mb-2" id="import-xprv-password-confirm-section">
-                    <label class="block mb-1">Confirm password</label>
-                    <input
-                        type="password"
-                        id="import-xprv-password-confirm"
-                        class="border border-border p-1 w-full font-mono text-sm bg-bg text-fg"
-                    />
-                </div>
-                <button
-                    id="btn-import-xprv-confirm"
-                    class="border border-border px-2 py-1 hover:bg-fg hover:text-bg cursor-pointer"
-                >
-                    Import
-                </button>
-            </div>
-
             <!-- ============ MAIN VIEW: ALL WALLETS & ADDRESSES ============ -->
             <div id="view-main" class="view hidden">
                 <!-- active address headline -->
@@ -365,6 +307,15 @@
                     </button>
                 </div>
 
+                <div class="mb-3">
+                    <button
+                        id="btn-show-private-key"
+                        class="border border-border px-2 py-1 hover:bg-fg hover:text-bg cursor-pointer text-xs"
+                    >
+                        &#128274; Show private key
+                    </button>
+                </div>
+
                 <!-- transactions -->
                 <div class="mt-3">
                     <div class="border-b border-border pb-1 mb-1">
@@ -376,6 +327,77 @@
                 </div>
             </div>
 
+            <!-- ============ SHOW PRIVATE KEY ============ -->
+            <div id="view-show-private-key" class="view hidden">
+                <button
+                    id="btn-show-pk-back"
+                    class="border border-border px-2 py-1 hover:bg-fg hover:text-bg cursor-pointer mb-2"
+                >
+                    &lt; Back
+                </button>
+                <h2 class="font-bold mb-2">Display Private Key</h2>
+
+                <!-- password prompt section -->
+                <div id="show-pk-prompt">
+                    <div
+                        class="border border-border border-dashed p-3 mb-3 text-xs"
+                    >
+                        <p class="mb-1">
+                            &#128274;&#128176; Your private key controls this
+                            address and all its funds. Anyone who has it can
+                            spend your tokens.
+                        </p>
+                        <p>
+                            Do not share it. Do not paste it into websites. If
+                            you copy it, you are responsible for clearing your
+                            clipboard when you are done.
+                        </p>
+                    </div>
+                    <div class="mb-2">
+                        <label class="block mb-1">Password</label>
+                        <input
+                            type="password"
+                            id="show-pk-password"
+                            class="border border-border p-1 w-full font-mono text-sm bg-bg text-fg"
+                            placeholder="Enter your password"
+                        />
+                    </div>
+                    <div
+                        id="show-pk-error"
+                        class="text-xs mb-2 border border-border border-dashed p-1 hidden"
+                    ></div>
+                    <button
+                        id="btn-show-pk-reveal"
+                        class="border border-border px-2 py-1 hover:bg-fg hover:text-bg cursor-pointer"
+                    >
+                        &#128274;&#128176; Display Private Key
+                    </button>
+                </div>
+
+                <!-- revealed key section -->
+                <div id="show-pk-key-well" class="hidden">
+                    <div
+                        class="bg-well p-3 mx-1 mb-3 break-all font-mono text-xs select-all"
+                    >
+                        <span id="show-pk-key-value"></span>
+                    </div>
+                    <div class="flex gap-2">
+                        <button
+                            id="btn-show-pk-copy"
+                            class="border border-border px-2 py-1 hover:bg-fg hover:text-bg cursor-pointer"
+                        >
+                            Copy
+                        </button>
+                        <button
+                            id="btn-show-pk-done"
+                            class="border border-border px-2 py-1 hover:bg-fg hover:text-bg cursor-pointer"
+                        >
+                            Done
+                        </button>
+                    </div>
+                </div>
+            </div>
+
             <!-- ============ ADDRESS-TOKEN DETAIL VIEW ============ -->
             <div id="view-address-token" class="view hidden">
                 <button

src/popup/index.js

@@ -11,7 +11,6 @@ const home = require("./views/home");
 const welcome = require("./views/welcome");
 const addWallet = require("./views/addWallet");
 const importKey = require("./views/importKey");
-const importXprv = require("./views/importXprv");
 const addressDetail = require("./views/addressDetail");
 const addressToken = require("./views/addressToken");
 const send = require("./views/send");
@@ -20,6 +19,7 @@ const txStatus = require("./views/txStatus");
 const transactionDetail = require("./views/transactionDetail");
 const receive = require("./views/receive");
 const addToken = require("./views/addToken");
+const showPrivateKey = require("./views/showPrivateKey");
 const settings = require("./views/settings");
 const settingsAddToken = require("./views/settingsAddToken");
 const approval = require("./views/approval");
@@ -56,8 +56,8 @@ const ctx = {
     doRefreshAndRender,
     showAddWalletView: () => addWallet.show(),
     showImportKeyView: () => importKey.show(),
-    showImportXprvView: () => importXprv.show(),
     showAddressDetail: () => addressDetail.show(),
+    showPrivateKey: () => showPrivateKey.show(),
     showAddressToken: () => addressToken.show(),
     showAddTokenView: () => addToken.show(),
     showConfirmTx: (txInfo) => confirmTx.show(txInfo),
@@ -212,9 +212,9 @@ async function init() {
     welcome.init(ctx);
     addWallet.init(ctx);
     importKey.init(ctx);
-    importXprv.init(ctx);
     home.init(ctx);
     addressDetail.init(ctx);
+    showPrivateKey.init(ctx);
     addressToken.init(ctx);
     send.init(ctx);
     confirmTx.init(ctx);

src/popup/views/addWallet.js

@@ -124,11 +124,6 @@ function init(ctx) {
         "click",
         ctx.showImportKeyView,
     );
-
-    $("btn-add-wallet-import-xprv").addEventListener(
-        "click",
-        ctx.showImportXprvView,
-    );
 }
 
 module.exports = { init, show };

src/popup/views/addressDetail.js

@@ -261,6 +261,10 @@ function init(_ctx) {
     });
 
     $("btn-add-token").addEventListener("click", ctx.showAddTokenView);
+
+    $("btn-show-private-key").addEventListener("click", () => {
+        ctx.showPrivateKey();
+    });
 }
 
 module.exports = { init, show };

src/popup/views/helpers.js

@@ -16,6 +16,7 @@ const VIEWS = [
     "import-key",
     "main",
     "address",
+    "show-private-key",
     "address-token",
     "send",
     "confirm-tx",

src/popup/views/home.js

@@ -230,7 +230,7 @@ function render(ctx) {
         html += `<div>`;
         html += `<div class="flex justify-between items-center bg-section py-1 px-2" style="margin:0 -0.5rem">`;
         html += `<span class="font-bold cursor-pointer wallet-name underline decoration-dashed" data-wallet="${wi}">${wallet.name}</span>`;
-        if (wallet.type === "hd" || wallet.type === "xprv") {
+        if (wallet.type === "hd") {
             html += `<button class="btn-add-address border border-border px-1 hover:bg-fg hover:text-bg cursor-pointer text-xs" data-wallet="${wi}" title="Add another address to this wallet">+</button>`;
         }
         html += `</div>`;

src/popup/views/importXprv.js

@@ -1,106 +0,0 @@
-const { $, showView, showFlash } = require("./helpers");
-const { hdWalletFromXprv, isValidXprv } = require("../../shared/wallet");
-const { encryptWithPassword } = require("../../shared/vault");
-const { state, saveState } = require("../../shared/state");
-const { scanForAddresses } = require("../../shared/balances");
-
-function show() {
-    $("import-xprv-key").value = "";
-    $("import-xprv-password").value = "";
-    $("import-xprv-password-confirm").value = "";
-    showView("import-xprv");
-}
-
-function init(ctx) {
-    $("btn-import-xprv-confirm").addEventListener("click", async () => {
-        const xprv = $("import-xprv-key").value.trim();
-        if (!xprv) {
-            showFlash("Please enter your extended private key.");
-            return;
-        }
-        if (!isValidXprv(xprv)) {
-            showFlash("Invalid extended private key.");
-            return;
-        }
-        let result;
-        try {
-            result = hdWalletFromXprv(xprv);
-        } catch (e) {
-            showFlash("Invalid extended private key.");
-            return;
-        }
-        const { xpub, firstAddress } = result;
-        const duplicate = state.wallets.find(
-            (w) =>
-                (w.type === "hd" || w.type === "xprv") &&
-                w.addresses[0] &&
-                w.addresses[0].address.toLowerCase() ===
-                    firstAddress.toLowerCase(),
-        );
-        if (duplicate) {
-            showFlash("This key is already added (" + duplicate.name + ").");
-            return;
-        }
-        const pw = $("import-xprv-password").value;
-        const pw2 = $("import-xprv-password-confirm").value;
-        if (!pw) {
-            showFlash("Please choose a password.");
-            return;
-        }
-        if (pw.length < 12) {
-            showFlash("Password must be at least 12 characters.");
-            return;
-        }
-        if (pw !== pw2) {
-            showFlash("Passwords do not match.");
-            return;
-        }
-        const encrypted = await encryptWithPassword(xprv, pw);
-        const walletNum = state.wallets.length + 1;
-        const wallet = {
-            type: "xprv",
-            name: "Wallet " + walletNum,
-            xpub: xpub,
-            encryptedSecret: encrypted,
-            nextIndex: 1,
-            addresses: [
-                { address: firstAddress, balance: "0.0000", tokenBalances: [] },
-            ],
-        };
-        state.wallets.push(wallet);
-        state.hasWallet = true;
-        await saveState();
-        ctx.renderWalletList();
-        showView("main");
-
-        // Scan for used HD addresses beyond index 0.
-        showFlash("Scanning for addresses...", 30000);
-        const scan = await scanForAddresses(xpub, state.rpcUrl);
-        if (scan.addresses.length > 1) {
-            wallet.addresses = scan.addresses.map((a) => ({
-                address: a.address,
-                balance: "0.0000",
-                tokenBalances: [],
-            }));
-            wallet.nextIndex = scan.nextIndex;
-            await saveState();
-            ctx.renderWalletList();
-            showFlash("Found " + scan.addresses.length + " addresses.");
-        } else {
-            showFlash("Ready.", 1000);
-        }
-
-        ctx.doRefreshAndRender();
-    });
-
-    $("btn-import-xprv-back").addEventListener("click", () => {
-        if (!state.hasWallet) {
-            showView("welcome");
-        } else {
-            ctx.renderWalletList();
-            showView("main");
-        }
-    });
-}
-
-module.exports = { init, show };

src/popup/views/showPrivateKey.js

@@ -0,0 +1,79 @@
+const { $, showView, showFlash, showError, hideError } = require("./helpers");
+const { state } = require("../../shared/state");
+const { decryptWithPassword } = require("../../shared/vault");
+const { getPrivateKeyForAddress } = require("../../shared/wallet");
+
+let ctx;
+let revealed = false;
+
+function show() {
+    revealed = false;
+    $("show-pk-password").value = "";
+    $("show-pk-key-well").classList.add("hidden");
+    $("show-pk-key-value").textContent = "";
+    $("show-pk-prompt").classList.remove("hidden");
+    hideError("show-pk-error");
+    showView("show-private-key");
+}
+
+function init(_ctx) {
+    ctx = _ctx;
+
+    $("btn-show-pk-back").addEventListener("click", () => {
+        clearKey();
+        ctx.showAddressDetail();
+    });
+
+    $("btn-show-pk-reveal").addEventListener("click", async () => {
+        const pw = $("show-pk-password").value;
+        if (!pw) {
+            showError("show-pk-error", "Please enter your password.");
+            return;
+        }
+
+        const wallet = state.wallets[state.selectedWallet];
+        let decryptedSecret;
+        try {
+            decryptedSecret = await decryptWithPassword(
+                wallet.encryptedSecret,
+                pw,
+            );
+        } catch (_e) {
+            showError("show-pk-error", "Wrong password.");
+            return;
+        }
+
+        const privateKey = getPrivateKeyForAddress(
+            wallet,
+            state.selectedAddress,
+            decryptedSecret,
+        );
+
+        revealed = true;
+        $("show-pk-prompt").classList.add("hidden");
+        $("show-pk-key-well").classList.remove("hidden");
+        $("show-pk-key-value").textContent = privateKey;
+        hideError("show-pk-error");
+    });
+
+    $("btn-show-pk-copy").addEventListener("click", () => {
+        const key = $("show-pk-key-value").textContent;
+        if (key) {
+            navigator.clipboard.writeText(key);
+            showFlash("Copied!");
+        }
+    });
+
+    $("btn-show-pk-done").addEventListener("click", () => {
+        clearKey();
+        ctx.showAddressDetail();
+    });
+}
+
+function clearKey() {
+    revealed = false;
+    $("show-pk-key-value").textContent = "";
+    $("show-pk-password").value = "";
+}
+
+module.exports = { init, show };

src/shared/wallet.js

@@ -24,25 +24,6 @@ function hdWalletFromMnemonic(mnemonic) {
     return { xpub, firstAddress };
 }
 
-function hdWalletFromXprv(xprv) {
-    const node = HDNodeWallet.fromExtendedKey(xprv);
-    if (!node.privateKey) {
-        throw new Error("Not an extended private key (xprv).");
-    }
-    const xpub = node.neuter().extendedKey;
-    const firstAddress = node.deriveChild(0).address;
-    return { xpub, firstAddress };
-}
-
-function isValidXprv(key) {
-    try {
-        const node = HDNodeWallet.fromExtendedKey(key);
-        return !!node.privateKey;
-    } catch {
-        return false;
-    }
-}
-
 function addressFromPrivateKey(key) {
     const w = new Wallet(key);
     return w.address;
@@ -57,13 +38,21 @@ function getSignerForAddress(walletData, addrIndex, decryptedSecret) {
         );
         return node.deriveChild(addrIndex);
     }
-    if (walletData.type === "xprv") {
-        const node = HDNodeWallet.fromExtendedKey(decryptedSecret);
-        return node.deriveChild(addrIndex);
-    }
     return new Wallet(decryptedSecret);
 }
 
+function getPrivateKeyForAddress(walletData, addrIndex, decryptedSecret) {
+    if (walletData.type === "hd") {
+        const node = HDNodeWallet.fromPhrase(
+            decryptedSecret,
+            "",
+            BIP44_ETH_PATH,
+        );
+        return node.deriveChild(addrIndex).privateKey;
+    }
+    return decryptedSecret;
+}
+
 function isValidMnemonic(mnemonic) {
     return Mnemonic.isValidMnemonic(mnemonic);
 }
@@ -72,9 +61,8 @@ module.exports = {
     generateMnemonic,
     deriveAddressFromXpub,
     hdWalletFromMnemonic,
-    hdWalletFromXprv,
-    isValidXprv,
     addressFromPrivateKey,
     getSignerForAddress,
+    getPrivateKeyForAddress,
     isValidMnemonic,
 };