diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..969ab85
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module gitea.drjosh.dev/josh/plugctl
+
+go 1.19
diff --git a/plug.go b/plug.go
new file mode 100644
index 0000000..293a427
--- /dev/null
+++ b/plug.go
@@ -0,0 +1,76 @@
+// Package plugctl provides an API for Kasa smart home switches.
+package plugctl
+
+import (
+	"io"
+	"net"
+)
+
+// Plug provides an API for a single Kasa smart home switch.
+type Plug struct {
+	Addr net.TCPAddr
+}
+
+type msg struct {
+	System *systemMsg `json:"system,omitempty"`
+	EMeter *eMeterMsg `json:"emeter,omitempty"`
+}
+
+type eMeterMsg struct {
+	GetRealtime *getRealtimeMsg `json:"get_realtime"`
+}
+
+type getRealtimeMsg struct{}
+
+type systemMsg struct {
+	GetSysInfo    *getSysInfoMsg    `json:"get_sysinfo"`
+	SetRelayState *setRelayStateMsg `json:"set_relay_state,omitempty"`
+}
+
+type getSysInfoMsg struct{}
+
+type setRelayStateMsg struct {
+	State int `json:"state"`
+}
+
+type decryptReader struct {
+	r io.Reader
+	c byte
+}
+
+func newDecrypter(r io.Reader) *decryptReader {
+	return &decryptReader{
+		r: r,
+		c: 0xab,
+	}
+}
+
+func (d *decryptReader) Read(b []byte) (int, error) {
+	n, err := d.r.Read(b)
+	for i, x := range b {
+		b[i] = d.c ^ x
+		d.c = x
+	}
+	return n, err
+}
+
+type encryptWriter struct {
+	w io.Writer
+	c byte
+}
+
+func newEncrypter(w io.Writer) *encryptWriter {
+	return &encryptWriter{
+		w: w,
+		c: 0xab,
+	}
+}
+
+func (e *encryptWriter) Write(b []byte) (int, error) {
+	eb := make([]byte, len(b))
+	for i, x := range b {
+		e.c ^= x
+		eb[i] = e.c
+	}
+	return e.w.Write(eb)
+}
diff --git a/plug_test.go b/plug_test.go
new file mode 100644
index 0000000..110a16a
--- /dev/null
+++ b/plug_test.go
@@ -0,0 +1,54 @@
+package plugctl
+
+import (
+	"bytes"
+	"encoding/base64"
+	"io"
+	"testing"
+)
+
+func TestDecrypt(t *testing.T) {
+	// on message from hs100.sh
+	in64 := "AAAAKtDygfiL/5r31e+UtsWg1Iv5nPCR6LfEsNGlwOLYo4HyhueT9tTu36Lfog=="
+	in, err := base64.StdEncoding.DecodeString(in64)
+	if err != nil {
+		t.Fatalf("base64.DecodeString(%q) error: %v", in64, err)
+	}
+	in = in[4:]
+	want := []byte(`{"system":{"set_relay_state":{"state":1}}}`)
+	dec := newDecrypter(bytes.NewReader(in))
+	got, err := io.ReadAll(dec)
+	if err != nil {
+		t.Fatalf("io.ReadAll(decryptReader) error: %v", err)
+	}
+	if !bytes.Equal(got, want) {
+		t.Errorf("decrypt(%02x) = %q, want %q", in, got, want)
+	}
+}
+
+func TestEncrypt(t *testing.T) {
+	// on message from hs100.sh
+	want64 := "AAAAKtDygfiL/5r31e+UtsWg1Iv5nPCR6LfEsNGlwOLYo4HyhueT9tTu36Lfog=="
+	want, err := base64.StdEncoding.DecodeString(want64)
+	if err != nil {
+		t.Fatalf("base64.DecodeString(%q) error: %v", want64, err)
+	}
+	want = want[4:]
+	in := []byte(`{"system":{"set_relay_state":{"state":1}}}`)
+	var buf bytes.Buffer
+	newEncrypter(&buf).Write(in)
+
+	if got := buf.Bytes(); !bytes.Equal(got, want) {
+		t.Errorf("encrypt(%q) = %02x, want %02x", in, got, want)
+	}
+}
+
+// func TestEncryptDecrypt(t *testing.T) {
+// 	want := make([]byte, 64)
+// 	if _, err := rand.Read(want); err != nil {
+// 		t.Fatalf("rand.Read(want) error: %v", err)
+// 	}
+// 	if got := decrypt(encrypt(want)); !bytes.Equal(got, want) {
+// 		t.Errorf("decrypt(encrypt(%02x)) = %02x, want %02x", want, got, want)
+// 	}
+// }