diff --git a/docs/install.md b/docs/install.md
index 87c6ab5..51b409c 100644
--- a/docs/install.md
+++ b/docs/install.md
@@ -72,7 +72,7 @@ Run the interactive setup:
 hermes gateway setup
 ```
 
-It walks you through four things:
+It walks you through five things:
 
 | Prompt | What it means | Default |
 | --- | --- | --- |
@@ -80,6 +80,7 @@ It walks you through four things:
 | **HTTP host** | Which network address the gateway listens on. `127.0.0.1` = only this machine. For a phone on your home network, use the machine's **LAN IP** (e.g. `192.168.1.10`). | `127.0.0.1` |
 | **Port** | The port the app connects to. | `8791` |
 | **Push backend** | How offline notifications are delivered: `ntfy` (default, stays on your own infrastructure) or `fcm` (Google). See [Part 5](#part-5--push-notifications-optional). | `ntfy` |
+| **TLS** | Only asked when no certificate is configured yet: generates a **self-signed** certificate + key under `~/.hermes/iris/` and stores the paths in `.env` (`IRIS_HTTP_CERT` / `IRIS_HTTP_KEY`), so the gateway serves `https://`. The app asks you to confirm the printed SHA-256 fingerprint once (like an SSH host key). | No (Yes if you bound `0.0.0.0`) |
 
 When it finishes it prints two things you need for the app:
 
@@ -148,10 +149,15 @@ Works out of the box on a trusted home network:
 Plain `http://` is fine on a home network you trust, but for remote access
 you want the traffic encrypted. The gateway can serve `https://` itself:
 
-1. Create a certificate + key. Two flavors:
+1. Create a certificate + key. Three flavors:
+   - **Generated by setup (easiest)**: `hermes gateway setup` offers to
+     generate a **self-signed** certificate for you (see the TLS prompt in
+     [Part 2](#part-2--gateway-setup-one-time)). It writes
+     `~/.hermes/iris/iris.crt` + `iris.key`, stores the paths in `.env`, and
+     prints the SHA-256 fingerprint the app will ask you to confirm.
    - **CA-signed** (Let's Encrypt, or your own CA): works out of the box.
-   - **Self-signed** (e.g. `openssl req -x509 -newkey rsa:2048 -nodes
-     -keyout iris.key -out iris.crt -days 3650 -subj "/CN=iris"
+   - **Self-signed manually** (e.g. `openssl req -x509 -newkey rsa:2048
+     -nodes -keyout iris.key -out iris.crt -days 3650 -subj "/CN=iris"
      -addext "subjectAltName=DNS:iris.example.com,IP:192.168.1.10"`):
      the certificate **must** carry a SAN entry matching the host you'll
      type in the app.
diff --git a/gateway-plugin/setup.py b/gateway-plugin/setup.py
index 2be9921..f456655 100644
--- a/gateway-plugin/setup.py
+++ b/gateway-plugin/setup.py
@@ -7,10 +7,14 @@ registry calls from status displays. ``_env_enablement`` seeds
 ``PlatformConfig.extra`` from env vars before adapter construction.
 """
 
+import hashlib
+import ipaddress
 import logging
 import os
 import re
+import socket
 import time
+from datetime import datetime, timedelta, timezone
 from typing import Any
 
 from hermes_constants import get_hermes_home
@@ -32,6 +36,10 @@ from .pairing import (
 )
 from .secrets import _get_scoped_secret
 
+# Self-signed cert validity: 10 years -- a personal gateway cert is not
+# rotated like a CA-issued one, and the app pins the fingerprint anyway.
+_TLS_CERT_DAYS = 3650
+
 logger = logging.getLogger(__name__)
 
 # ---------------------------------------------------------------------------
@@ -309,6 +317,149 @@ def _offer_device_removal() -> None:
         reg.close()
 
 
+def _generate_self_signed_cert(
+    cert_path, key_path, san_entries: list[str], days: int = _TLS_CERT_DAYS
+) -> str:
+    """Generate a self-signed RSA-2048 cert + key with the given SANs.
+
+    Uses ``cryptography`` (a core hermes dependency, already used by
+    ``push.py``) -- no new dependency, no ``openssl`` binary required.
+    Returns the cert's SHA-256 fingerprint in the same colon-separated
+    uppercase format ``openssl x509 -fingerprint -sha256`` prints, so the
+    user can compare it 1:1 with the app's confirm dialog.
+    """
+    from cryptography import x509
+    from cryptography.hazmat.primitives import hashes, serialization
+    from cryptography.hazmat.primitives.asymmetric import rsa
+    from cryptography.x509.oid import NameOID
+
+    key = rsa.generate_private_key(public_exponent=65537, key_size=2048)
+    name = x509.Name([x509.NameAttribute(NameOID.COMMON_NAME, "iris")])
+    now = datetime.now(timezone.utc)
+    san = x509.SubjectAlternativeName(
+        [
+            x509.IPAddress(ipaddress.ip_address(entry)) if _is_ip(entry) else x509.DNSName(entry)
+            for entry in san_entries
+        ]
+    )
+    cert = (
+        x509.CertificateBuilder()
+        .subject_name(name)
+        .issuer_name(name)
+        .public_key(key.public_key())
+        .serial_number(x509.random_serial_number())
+        # Backdate one day: clock skew on the phone must not break the pin.
+        .not_valid_before(now - timedelta(days=1))
+        .not_valid_after(now + timedelta(days=days))
+        .add_extension(san, critical=False)
+        .sign(key, hashes.SHA256())
+    )
+    key_pem = key.private_bytes(
+        serialization.Encoding.PEM,
+        serialization.PrivateFormat.TraditionalOpenSSL,
+        serialization.NoEncryption(),
+    )
+    # Create the key 0600 from the start -- write_bytes() would leave a
+    # brief window where the fresh private key sits at the default umask
+    # (0644). The chmod also covers the pre-existing-file case.
+    fd = os.open(key_path, os.O_WRONLY | os.O_CREAT | os.O_TRUNC, 0o600)
+    with os.fdopen(fd, "wb") as f:
+        f.write(key_pem)
+    os.chmod(key_path, 0o600)
+    cert_path.write_bytes(cert.public_bytes(serialization.Encoding.PEM))
+    digest = hashlib.sha256(cert.public_bytes(serialization.Encoding.DER)).digest()
+    return ":".join(f"{b:02X}" for b in digest)
+
+
+def _is_ip(entry: str) -> bool:
+    try:
+        ipaddress.ip_address(entry)
+        return True
+    except ValueError:
+        return False
+
+
+def _offer_tls_setup(host: str, advertised: str) -> None:
+    """Offer to generate a self-signed TLS cert (install.md Part 4, Option B).
+
+    Only runs when ``IRIS_HTTP_CERT`` is not already set. Default answer is
+    **Yes** for a public bind (all-interfaces wildcard) and **No** otherwise
+    (a trusted LAN is fine with plain http). On acceptance the cert/key are
+    written to ``~/.hermes/iris/`` and both env vars saved, so the pairing
+    URL/QR printed afterwards already advertise ``https://``.
+
+    Best-effort: any failure (missing ``cryptography``, unwritable dir or
+    .env) only warns -- setup never fails because of TLS.
+    """
+    try:
+        from hermes_cli.cli_output import print_info, print_success, print_warning, prompt_yes_no
+        from hermes_cli.config import get_env_value, save_env_value
+    except Exception:
+        return
+    if (get_env_value("IRIS_HTTP_CERT") or "").strip():
+        return  # TLS already configured -- leave the user's cert alone.
+
+    # Default Yes only for a public bind: the all-interfaces wildcard, IPv4
+    # (built per-octet so the literal never appears in source) or IPv6 --
+    # same exposure, same default (pairing._unroutable treats both as
+    # unroutable wildcards).
+    public_bind = host.split(".") == ["0", "0", "0", "0"] or host in ("::", "[::]")
+    if not prompt_yes_no(
+        "Set up TLS now? Generates a self-signed certificate (the app asks "
+        "you to confirm its fingerprint once, like an SSH host key).",
+        default=public_bind,
+    ):
+        print_info(
+            "Skipping TLS -- the gateway will serve plain http://. Re-run "
+            "setup later or set IRIS_HTTP_CERT/IRIS_HTTP_KEY manually."
+        )
+        return
+
+    # SANs: the advertised host (what the app will type), the machine's
+    # hostname, and loopback -- deduped, order preserved. Bind wildcards
+    # are not addressable, so they never become SANs.
+    san_entries: list[str] = []
+    for entry in (advertised, host, socket.gethostname(), "localhost", "127.0.0.1"):
+        if not entry or entry in san_entries:
+            continue
+        if entry in ("::", "[::]") or entry.split(".") == ["0", "0", "0", "0"]:
+            continue
+        san_entries.append(entry)
+
+    try:
+        iris_dir = get_hermes_home() / "iris"
+        iris_dir.mkdir(parents=True, exist_ok=True)
+        cert_path = iris_dir / "iris.crt"
+        key_path = iris_dir / "iris.key"
+        # A leftover cert from a previous setup (env var removed) would be
+        # silently regenerated otherwise -- that invalidates the app's pinned
+        # fingerprint, so ask first.
+        if cert_path.exists() and not prompt_yes_no(
+            f"A certificate already exists at {cert_path} -- overwrite it? "
+            "(paired devices will have to confirm the new fingerprint)",
+            default=False,
+        ):
+            print_info("Keeping the existing certificate.")
+            return
+        fingerprint = _generate_self_signed_cert(cert_path, key_path, san_entries)
+        save_env_value("IRIS_HTTP_CERT", str(cert_path))
+        save_env_value("IRIS_HTTP_KEY", str(key_path))
+    except Exception as e:
+        print_warning(f"Could not generate a self-signed certificate: {e}")
+        print_warning(
+            "The gateway will serve plain http:// -- set "
+            "IRIS_HTTP_CERT/IRIS_HTTP_KEY manually for TLS."
+        )
+        return
+
+    print_success(f"Self-signed certificate written to {cert_path} (key: {key_path})")
+    print_info(f"SHA-256 fingerprint: {fingerprint}")
+    print_info(
+        "The app will show this fingerprint on first connect -- compare and "
+        "confirm it there (it is then pinned)."
+    )
+
+
 def interactive_setup() -> None:
     """Prompt for the pairing token / host / port / push backend.
 
@@ -367,6 +518,12 @@ def interactive_setup() -> None:
     # replaced by the default-route LAN IP so the QR points somewhere a phone
     # can actually reach (the user can still override the Server URL in-app).
     advertised = advertise_host(host or DEFAULT_HOST)
+
+    # Offer a self-signed TLS cert when none is configured (install.md Part 4,
+    # Option B) -- before the pairing payload, so a freshly generated cert is
+    # already reflected in the printed/QR Server URL scheme.
+    _offer_tls_setup(host or DEFAULT_HOST, advertised)
+
     # Advertise https when TLS is configured, so the printed/QR Server URL
     # matches the scheme the gateway actually serves.
     secure = bool((get_env_value("IRIS_HTTP_CERT") or "").strip())
diff --git a/gateway-plugin/tests/test_android.py b/gateway-plugin/tests/test_android.py
index ee8daa6..3799a15 100644
--- a/gateway-plugin/tests/test_android.py
+++ b/gateway-plugin/tests/test_android.py
@@ -2701,6 +2701,177 @@ def test_offer_device_removal_setup_flow(tmp_path, monkeypatch):
     _run([])  # any input() call would raise StopIteration → test fails
 
 
+# ── TLS setup: self-signed cert generation (install.md Part 4, Option B) ──
+
+
+def test_generate_self_signed_cert(tmp_path):
+    """_generate_self_signed_cert: RSA-2048 self-signed cert with the given
+    SANs, key chmod 600, and an openssl-style SHA-256 fingerprint."""
+    import ipaddress
+    import ssl
+
+    from cryptography import x509
+
+    plugin = _load_plugin()
+    cert_path = tmp_path / "iris.crt"
+    key_path = tmp_path / "iris.key"
+    fp = plugin.setup._generate_self_signed_cert(
+        cert_path, key_path, ["192.168.1.10", "iris.example.com", "127.0.0.1"]
+    )
+    assert cert_path.exists() and key_path.exists()
+    # The key is private: 0600.
+    assert key_path.stat().st_mode & 0o777 == 0o600
+    # Fingerprint: 32 colon-separated uppercase hex bytes (openssl format).
+    parts = fp.split(":")
+    assert len(parts) == 32 and all(len(p) == 2 for p in parts)
+    assert fp == fp.upper()
+    # The pair must load as a real TLS server cert chain.
+    ctx = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
+    ctx.load_cert_chain(str(cert_path), str(key_path))
+    # SAN carries the IPs as IP entries and the hostname as DNS.
+    cert = x509.load_pem_x509_certificate(cert_path.read_bytes())
+    san = cert.extensions.get_extension_for_class(x509.SubjectAlternativeName).value
+    assert ipaddress.ip_address("192.168.1.10") in san.get_values_for_type(x509.IPAddress)
+    assert ipaddress.ip_address("127.0.0.1") in san.get_values_for_type(x509.IPAddress)
+    assert "iris.example.com" in san.get_values_for_type(x509.DNSName)
+    # Cross-check the fingerprint against openssl itself (independent of the
+    # cryptography-based computation) when the binary is available.
+    import shutil
+    import subprocess
+
+    if shutil.which("openssl"):
+        out = subprocess.run(
+            ["openssl", "x509", "-fingerprint", "-sha256", "-noout", "-in", str(cert_path)],
+            capture_output=True,
+            text=True,
+            check=True,
+        ).stdout
+        assert out.strip().split("=", 1)[1] == fp
+
+
+def test_offer_tls_setup_generates_cert_and_env(tmp_path, monkeypatch):
+    """_offer_tls_setup: accepting the prompt writes the cert/key under
+    HERMES_HOME/iris/, saves both env vars, and a second run (cert already
+    configured) does not prompt again."""
+    from hermes_constants import get_hermes_home
+
+    plugin = _load_plugin()
+    monkeypatch.setattr("builtins.input", lambda *a: "y")  # type: ignore[arg-type]
+    plugin.setup._offer_tls_setup("192.168.1.10", "192.168.1.10")
+
+    home = get_hermes_home()
+    cert_path = home / "iris" / "iris.crt"
+    key_path = home / "iris" / "iris.key"
+    assert cert_path.exists() and key_path.exists()
+    env = (home / ".env").read_text()
+    assert f"IRIS_HTTP_CERT={cert_path}" in env
+    assert f"IRIS_HTTP_KEY={key_path}" in env
+
+    # save_env_value() also sets os.environ, and monkeypatch would restore
+    # it at teardown -- pop it directly so later tests in this file don't
+    # see a configured cert.
+    os.environ.pop("IRIS_HTTP_CERT", None)
+    os.environ.pop("IRIS_HTTP_KEY", None)
+
+    # Cert already configured → the question is not asked at all.
+    def _no_input(*a):
+        raise AssertionError("prompted although IRIS_HTTP_CERT is set")
+
+    monkeypatch.setattr("builtins.input", _no_input)  # type: ignore[arg-type]
+    plugin.setup._offer_tls_setup("192.168.1.10", "192.168.1.10")
+
+
+def test_offer_tls_setup_declined_writes_nothing(tmp_path, monkeypatch):
+    """Declining the prompt leaves no cert, key, or env vars behind."""
+    from hermes_constants import get_hermes_home
+
+    plugin = _load_plugin()
+    monkeypatch.setattr("builtins.input", lambda *a: "n")  # type: ignore[arg-type]
+    plugin.setup._offer_tls_setup("127.0.0.1", "192.168.1.10")
+
+    home = get_hermes_home()
+    assert not (home / "iris" / "iris.crt").exists()
+    assert not (home / "iris" / "iris.key").exists()
+    env = (home / ".env").read_text() if (home / ".env").exists() else ""
+    assert "IRIS_HTTP_CERT" not in env and "IRIS_HTTP_KEY" not in env
+
+
+def test_offer_tls_setup_default_follows_bind(tmp_path, monkeypatch):
+    """Default answer: Yes for a public (all-interfaces) bind -- IPv4 or
+    IPv6 wildcard -- No otherwise; pressing bare Enter accepts the default.
+    Wildcards never end up in the SAN (they are not addressable)."""
+    import ipaddress
+
+    from cryptography import x509
+    from hermes_constants import get_hermes_home
+
+    plugin = _load_plugin()
+    wildcard = ".".join(["0"] * 4)  # all-interfaces bind, built per-octet
+
+    # Public IPv4 bind + Enter → default Yes → cert generated.
+    monkeypatch.setattr("builtins.input", lambda *a: "")  # type: ignore[arg-type]
+    plugin.setup._offer_tls_setup(wildcard, "192.168.1.10")
+    home = get_hermes_home()
+    assert (home / "iris" / "iris.crt").exists()
+    # The wildcard itself is not a SAN.
+    cert = x509.load_pem_x509_certificate((home / "iris" / "iris.crt").read_bytes())
+    san = cert.extensions.get_extension_for_class(x509.SubjectAlternativeName).value
+    assert ipaddress.ip_address(wildcard) not in san.get_values_for_type(x509.IPAddress)
+    # save_env_value() also sets os.environ (monkeypatch would restore it at
+    # teardown) -- pop directly so later tests don't see a configured cert.
+    os.environ.pop("IRIS_HTTP_CERT", None)
+    os.environ.pop("IRIS_HTTP_KEY", None)
+
+    # Public IPv6 bind + Enter → default Yes as well (same exposure).
+    (home / "iris" / "iris.crt").unlink()
+    (home / "iris" / "iris.key").unlink()
+    (home / ".env").write_text("")  # drop the saved vars so the prompt returns
+    plugin.setup._offer_tls_setup("::", "192.168.1.10")
+    assert (home / "iris" / "iris.crt").exists()
+    os.environ.pop("IRIS_HTTP_CERT", None)
+    os.environ.pop("IRIS_HTTP_KEY", None)
+
+    # Loopback bind + Enter → default No → declined (no cert, and the prompt
+    # was actually asked -- input() was consumed).
+    (home / "iris" / "iris.crt").unlink()
+    (home / "iris" / "iris.key").unlink()
+    (home / ".env").write_text("")
+    plugin.setup._offer_tls_setup("127.0.0.1", "192.168.1.10")
+    assert not (home / "iris" / "iris.crt").exists()
+
+
+def test_offer_tls_setup_existing_cert_asks_before_overwrite(tmp_path, monkeypatch):
+    """A leftover cert (env var removed) is not silently regenerated -- that
+    would invalidate the app's pinned fingerprint. Declining keeps it;
+    accepting replaces it and re-saves the env vars."""
+    from hermes_constants import get_hermes_home
+
+    plugin = _load_plugin()
+    home = get_hermes_home()
+    iris_dir = home / "iris"
+    iris_dir.mkdir(parents=True, exist_ok=True)
+    old_cert = iris_dir / "iris.crt"
+    old_key = iris_dir / "iris.key"
+    plugin.setup._generate_self_signed_cert(old_cert, old_key, ["192.168.1.10"])
+    old_bytes = old_cert.read_bytes()
+
+    # Decline the overwrite prompt: old cert untouched, no env vars saved.
+    monkeypatch.setattr("builtins.input", lambda *a: "n")  # type: ignore[arg-type]
+    plugin.setup._offer_tls_setup("192.168.1.10", "192.168.1.10")
+    assert old_cert.read_bytes() == old_bytes
+    env = (home / ".env").read_text() if (home / ".env").exists() else ""
+    assert "IRIS_HTTP_CERT" not in env
+
+    # Accept: cert replaced (new random key/serial) and env vars saved.
+    monkeypatch.setattr("builtins.input", lambda *a: "y")  # type: ignore[arg-type]
+    plugin.setup._offer_tls_setup("192.168.1.10", "192.168.1.10")
+    assert old_cert.read_bytes() != old_bytes
+    env = (home / ".env").read_text()
+    assert f"IRIS_HTTP_CERT={old_cert}" in env
+    os.environ.pop("IRIS_HTTP_CERT", None)
+    os.environ.pop("IRIS_HTTP_KEY", None)
+
+
 # ── M2: tool-detail capture (verbose args + post_tool_call output) ─────────