diff --git a/osi/sign.go b/osi/sign.go
new file mode 100644
index 0000000..c89a0da
--- /dev/null
+++ b/osi/sign.go
@@ -0,0 +1,30 @@
+package osi
+
+import (
+	"crypto/md5"
+	"encoding/hex"
+)
+
+type HeaderInput struct {
+	OrgCode  string
+	DeviceSN string
+	UserName string
+	Ask      string
+	TS       string
+}
+
+func SignPassword(ts, ask string) string {
+	sum := md5.Sum([]byte("ts=" + ts + "&ask=" + ask))
+	return hex.EncodeToString(sum[:])
+}
+
+func BuildHeaders(input HeaderInput) map[string]string {
+	return map[string]string{
+		"Content-Type": "application/json",
+		"orgCode":      input.OrgCode,
+		"deviceSN":     input.DeviceSN,
+		"ts":           input.TS,
+		"userName":     input.UserName,
+		"password":     SignPassword(input.TS, input.Ask),
+	}
+}
diff --git a/osi/sign_test.go b/osi/sign_test.go
new file mode 100644
index 0000000..6e1f027
--- /dev/null
+++ b/osi/sign_test.go
@@ -0,0 +1,43 @@
+package osi
+
+import "testing"
+
+func TestSignPasswordMatchesPythonScriptVector(t *testing.T) {
+	got := SignPassword("1700000000123", "secret-key")
+	want := "008aceff8247cb42d2a99b2c48d0ac88"
+	if got != want {
+		t.Fatalf("SignPassword() = %q, want %q", got, want)
+	}
+}
+
+func TestBuildHeadersIncludesSignatureFields(t *testing.T) {
+	headers := BuildHeaders(HeaderInput{
+		OrgCode:  "12441625456962881G",
+		DeviceSN: "device-001",
+		UserName: "dyytgw",
+		Ask:      "secret-key",
+		TS:       "1700000000123",
+	})
+
+	if headers["Content-Type"] != "application/json" {
+		t.Fatalf("Content-Type = %q", headers["Content-Type"])
+	}
+	if headers["orgCode"] != "12441625456962881G" {
+		t.Fatalf("orgCode = %q", headers["orgCode"])
+	}
+	if headers["deviceSN"] != "device-001" {
+		t.Fatalf("deviceSN = %q", headers["deviceSN"])
+	}
+	if headers["ts"] != "1700000000123" {
+		t.Fatalf("ts = %q", headers["ts"])
+	}
+	if headers["userName"] != "dyytgw" {
+		t.Fatalf("userName = %q", headers["userName"])
+	}
+	if headers["password"] != "008aceff8247cb42d2a99b2c48d0ac88" {
+		t.Fatalf("password = %q", headers["password"])
+	}
+	if _, ok := headers["ask"]; ok {
+		t.Fatal("headers must not include ask")
+	}
+}