diff --git a/backend/server/api/devices/[id]/profile.reg.get.ts b/backend/server/api/devices/[id]/profile.reg.get.ts
new file mode 100644
index 0000000..189b934
--- /dev/null
+++ b/backend/server/api/devices/[id]/profile.reg.get.ts
@@ -0,0 +1,48 @@
+import { getProtectedDevice } from "../../../db/protectedDevices";
+import { labelToSlug } from "../../../utils/mobileconfig";
+import { generateWindowsDohRegFile } from "../../../utils/regfile";
+
+/**
+ * GET /api/devices/:id/profile.reg
+ *
+ * PUBLIC — Windows muss ohne Auth-Header zugreifen können.
+ * Der dnsToken im Profil IST die Device-Authentifizierung beim DoH-Server.
+ *
+ * Liefert ein Windows-Registry-File (.reg) das DoH für den ReBreak-DNS-Server
+ * in Windows 11 einrichtet.
+ *
+ * Content-Type: application/octet-stream
+ * Encoding: UTF-16 LE mit BOM (required by regedit.exe)
+ */
+export default defineEventHandler(async (event) => {
+  const id = getRouterParam(event, "id");
+  if (!id) throw createError({ statusCode: 400, data: { error: "ID_REQUIRED" } });
+
+  const device = await getProtectedDevice(id);
+
+  if (!device || device.status === "revoked") {
+    throw createError({ statusCode: 404, data: { error: "DEVICE_NOT_FOUND" } });
+  }
+
+  if (device.platform !== "windows") {
+    throw createError({
+      statusCode: 400,
+      data: { error: "WRONG_PLATFORM", expected: "windows", actual: device.platform },
+    });
+  }
+
+  const regBuffer = generateWindowsDohRegFile({
+    deviceId: device.id,
+    dnsToken: device.dnsToken,
+    label: device.label,
+  });
+
+  const slug = labelToSlug(device.label);
+  const filename = `rebreak-${slug || "schutz"}.reg`;
+
+  setHeader(event, "Content-Type", "application/octet-stream");
+  setHeader(event, "Content-Disposition", `attachment; filename="${filename}"`);
+  setHeader(event, "Cache-Control", "no-store");
+
+  return regBuffer;
+});
diff --git a/backend/server/api/devices/enroll.post.ts b/backend/server/api/devices/enroll.post.ts
index e51ff3b..6881621 100644
--- a/backend/server/api/devices/enroll.post.ts
+++ b/backend/server/api/devices/enroll.post.ts
@@ -65,12 +65,16 @@ export default defineEventHandler(async (event) => {
   const apiBase =
     (config.public as any)?.apiBase ?? "https://api.rebreak.org";
 
+  // Platform-aware download URL: Windows gets .reg, everything else .mobileconfig
+  const profileExt = platform === "windows" ? "reg" : "mobileconfig";
+  const downloadUrl = `${apiBase}/api/devices/${device.id}/profile.${profileExt}`;
+
   return {
     success: true,
     data: {
       deviceId: device.id,
       dnsToken: device.dnsToken,
-      downloadUrl: `${apiBase}/api/devices/${device.id}/profile.mobileconfig`,
+      downloadUrl,
     },
   };
 });
diff --git a/backend/server/utils/regfile.ts b/backend/server/utils/regfile.ts
new file mode 100644
index 0000000..2438693
--- /dev/null
+++ b/backend/server/utils/regfile.ts
@@ -0,0 +1,83 @@
+/**
+ * Windows Registry file generation for DoH (DNS-over-HTTPS) protection setup.
+ *
+ * Windows 11 native DoH client configuration via registry:
+ * - HKLM\SYSTEM\CurrentControlSet\Services\Dnscache\Parameters\DohWellKnownServers
+ * - Subkey per DoH server with DohTemplate + AutoUpgradeFlag
+ *
+ * Registry file encoding: UTF-16 LE with BOM (\xFF\xFE).
+ * Line endings: CRLF (\r\n) — required by regedit.exe.
+ *
+ * Escape rules for .reg string values:
+ *   \  →  \\
+ *   "  →  \"
+ *   (newlines, tabs in string values would also need escaping but label is
+ *    limited to printable user input, so \n/\t coverage is defensive.)
+ */
+
+/** Escape a string for use inside a .reg double-quoted value. */
+function regEscape(str: string): string {
+  return str
+    .replace(/\\/g, "\\\\") // must be first
+    .replace(/"/g, '\\"')
+    .replace(/\r/g, "\\r")
+    .replace(/\n/g, "\\n")
+    .replace(/\t/g, "\\t");
+}
+
+export interface WindowsDohRegOpts {
+  /** ProtectedDevice.id — not used in file body but available for future use. */
+  deviceId: string;
+  /** 32-char hex DNS token — used in DoH URL. */
+  dnsToken: string;
+  /** User-set device label, e.g. "Büro-PC". */
+  label: string;
+}
+
+/**
+ * Generates the text content of a Windows .reg file that registers a
+ * ReBreak DoH server in the Windows 11 DoH well-known-servers list.
+ *
+ * Returns a UTF-16 LE Buffer with BOM — ready to write as .reg file or send
+ * as HTTP response body. Windows regedit.exe requires this encoding.
+ */
+export function generateWindowsDohRegFile(
+  opts: WindowsDohRegOpts,
+): Buffer {
+  const { dnsToken, label } = opts;
+
+  const tokenPrefix = dnsToken.slice(0, 8);
+  const subkeyName = `rebreak-${tokenPrefix}`;
+  const escapedLabel = regEscape(label);
+
+  // RFC 8484 URI template — {?dns} is the query parameter for GET requests.
+  // Windows DoH client replaces {?dns} with ?dns=<base64url-encoded-query>.
+  const dohTemplate = `https://dns.rebreak.org/api/dns/${dnsToken}/dns-query{?dns}`;
+
+  const isoDate = new Date().toISOString().slice(0, 10);
+
+  const CRLF = "\r\n";
+
+  const lines = [
+    "Windows Registry Editor Version 5.00",
+    "",
+    `; ReBreak DNS-over-HTTPS Filter — Device: ${escapedLabel}`,
+    `; Token: ${tokenPrefix}`,
+    `; Generated: ${isoDate}`,
+    "",
+    "[HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Services\\Dnscache\\Parameters\\DohWellKnownServers]",
+    "",
+    `[HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Services\\Dnscache\\Parameters\\DohWellKnownServers\\${subkeyName}]`,
+    `"DohTemplate"="${regEscape(dohTemplate)}"`,
+    '"AutoUpgradeFlag"=dword:00000001',
+    "",
+  ];
+
+  const text = lines.join(CRLF);
+
+  // UTF-16 LE BOM: 0xFF 0xFE
+  const bom = Buffer.from([0xff, 0xfe]);
+  const body = Buffer.from(text, "utf16le");
+
+  return Buffer.concat([bom, body]);
+}
diff --git a/backend/tests/devices/regfile.test.ts b/backend/tests/devices/regfile.test.ts
new file mode 100644
index 0000000..9019aeb
--- /dev/null
+++ b/backend/tests/devices/regfile.test.ts
@@ -0,0 +1,146 @@
+/**
+ * Tests for generateWindowsDohRegFile + labelToSlug.
+ *
+ * Pure utility — no Prisma, no Nitro globals needed.
+ */
+import { describe, expect, it } from "vitest";
+import { generateWindowsDohRegFile } from "../../server/utils/regfile";
+import { labelToSlug } from "../../server/utils/mobileconfig";
+
+const SAMPLE_TOKEN = "abcdef0123456789abcdef0123456789"; // 32 hex chars
+const SAMPLE_DEVICE_ID = "device-uuid-1234";
+
+describe("generateWindowsDohRegFile", () => {
+  it("output starts with UTF-16 LE BOM (0xFF 0xFE)", () => {
+    const buf = generateWindowsDohRegFile({
+      deviceId: SAMPLE_DEVICE_ID,
+      dnsToken: SAMPLE_TOKEN,
+      label: "Test PC",
+    });
+    expect(buf[0]).toBe(0xff);
+    expect(buf[1]).toBe(0xfe);
+  });
+
+  it("decoded content begins with registry header", () => {
+    const buf = generateWindowsDohRegFile({
+      deviceId: SAMPLE_DEVICE_ID,
+      dnsToken: SAMPLE_TOKEN,
+      label: "Test PC",
+    });
+    // Skip 2-byte BOM, decode remainder as UTF-16 LE
+    const text = buf.slice(2).toString("utf16le");
+    expect(text.startsWith("Windows Registry Editor Version 5.00")).toBe(true);
+  });
+
+  it("contains the full dnsToken in the DohTemplate value", () => {
+    const buf = generateWindowsDohRegFile({
+      deviceId: SAMPLE_DEVICE_ID,
+      dnsToken: SAMPLE_TOKEN,
+      label: "Test PC",
+    });
+    const text = buf.slice(2).toString("utf16le");
+    expect(text).toContain(SAMPLE_TOKEN);
+  });
+
+  it("uses token prefix (first 8 chars) in the subkey name and comment", () => {
+    const buf = generateWindowsDohRegFile({
+      deviceId: SAMPLE_DEVICE_ID,
+      dnsToken: SAMPLE_TOKEN,
+      label: "Test PC",
+    });
+    const text = buf.slice(2).toString("utf16le");
+    const prefix = SAMPLE_TOKEN.slice(0, 8); // "abcdef01"
+    expect(text).toContain(`rebreak-${prefix}`);
+    expect(text).toContain(`Token: ${prefix}`);
+  });
+
+  it("contains AutoUpgradeFlag as dword:00000001", () => {
+    const buf = generateWindowsDohRegFile({
+      deviceId: SAMPLE_DEVICE_ID,
+      dnsToken: SAMPLE_TOKEN,
+      label: "Test PC",
+    });
+    const text = buf.slice(2).toString("utf16le");
+    expect(text).toContain('"AutoUpgradeFlag"=dword:00000001');
+  });
+
+  it("uses CRLF line endings throughout", () => {
+    const buf = generateWindowsDohRegFile({
+      deviceId: SAMPLE_DEVICE_ID,
+      dnsToken: SAMPLE_TOKEN,
+      label: "Test PC",
+    });
+    const text = buf.slice(2).toString("utf16le");
+    // Every newline must be preceded by \r
+    const lines = text.split("\r\n");
+    // Rejoining with \r\n and comparing proves all endings were CRLF
+    expect(lines.join("\r\n")).toBe(text);
+    // And there must be multiple lines
+    expect(lines.length).toBeGreaterThan(5);
+  });
+
+  describe("label escaping", () => {
+    it('escapes double-quote in label', () => {
+      const buf = generateWindowsDohRegFile({
+        deviceId: SAMPLE_DEVICE_ID,
+        dnsToken: SAMPLE_TOKEN,
+        label: 'My "Gaming" PC',
+      });
+      const text = buf.slice(2).toString("utf16le");
+      // In comment line the label appears escaped
+      expect(text).toContain('My \\"Gaming\\" PC');
+    });
+
+    it("escapes backslash in label", () => {
+      const buf = generateWindowsDohRegFile({
+        deviceId: SAMPLE_DEVICE_ID,
+        dnsToken: SAMPLE_TOKEN,
+        label: "C:\\Users\\PC",
+      });
+      const text = buf.slice(2).toString("utf16le");
+      expect(text).toContain("C:\\\\Users\\\\PC");
+    });
+
+    it("escapes newline in label", () => {
+      const buf = generateWindowsDohRegFile({
+        deviceId: SAMPLE_DEVICE_ID,
+        dnsToken: SAMPLE_TOKEN,
+        label: "Line1\nLine2",
+      });
+      const text = buf.slice(2).toString("utf16le");
+      expect(text).toContain("Line1\\nLine2");
+    });
+  });
+
+  it("contains the correct HKLM registry path for DohWellKnownServers", () => {
+    const buf = generateWindowsDohRegFile({
+      deviceId: SAMPLE_DEVICE_ID,
+      dnsToken: SAMPLE_TOKEN,
+      label: "Test PC",
+    });
+    const text = buf.slice(2).toString("utf16le");
+    expect(text).toContain(
+      "HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Services\\Dnscache\\Parameters\\DohWellKnownServers",
+    );
+  });
+});
+
+describe("labelToSlug", () => {
+  it("lowercases and replaces non-alphanumeric with hyphens", () => {
+    expect(labelToSlug("Mein PC")).toBe("mein-pc");
+    expect(labelToSlug("Büro-PC 2024")).toBe("b-ro-pc-2024");
+  });
+
+  it("strips leading and trailing hyphens", () => {
+    expect(labelToSlug("  --test--  ")).toBe("test");
+  });
+
+  it("truncates to 40 characters", () => {
+    const long = "a".repeat(50);
+    expect(labelToSlug(long)).toHaveLength(40);
+  });
+
+  it("returns empty string for label with no alphanumeric chars", () => {
+    expect(labelToSlug("---")).toBe("");
+  });
+});