diff --git a/core/constants/network-crypto.go b/core/constants/network-crypto.go
new file mode 100644
index 0000000..5a140d2
--- /dev/null
+++ b/core/constants/network-crypto.go
@@ -0,0 +1,49 @@
+package constants
+
+import (
+	"encoding/json"
+	"fmt"
+)
+
+type CryptoType int
+
+const (
+	CryptoTypeTLS CryptoType = iota
+)
+
+var (
+	cryptoTypeID = map[CryptoType]string{
+		CryptoTypeTLS: "TLS",
+	}
+
+	cryptoTypeName = map[string]CryptoType{
+		"TLS": CryptoTypeTLS,
+	}
+)
+
+func (ct CryptoType) String() string {
+	return cryptoTypeID[ct]
+}
+
+func (ct CryptoType) MarshalJSON() ([]byte, error) {
+	value, ok := cryptoTypeID[ct]
+	if !ok {
+		return nil, fmt.Errorf("Invalid EnumType[%s] value", ct)
+	}
+	return json.Marshal(value)
+}
+
+func (ct CryptoType) UnmarshalJSON(b []byte) error {
+	var s string
+	err := json.Unmarshal(b, &s)
+	if err != nil {
+		return err
+	}
+
+	value, ok := cryptoTypeName[s]
+	if !ok {
+		return fmt.Errorf("Invalid EnumType[%s] value", s)
+	}
+	ct = value
+	return nil
+}
diff --git a/core/constants/network.go b/core/constants/network-port.go
similarity index 100%
rename from core/constants/network.go
rename to core/constants/network-port.go
diff --git a/discovery/model/Port.go b/discovery/model/Port.go
index cbc02a2..2ae3097 100644
--- a/discovery/model/Port.go
+++ b/discovery/model/Port.go
@@ -5,15 +5,16 @@ import (
 
 	"github.com/google/gopacket"
 
+	"git.loafle.net/overflow/commons-go/core/constants"
 	"git.loafle.net/overflow/commons-go/core/util"
 )
 
 type Port struct {
 	Host *Host `json:"host,omitempty"`
 
-	ID         json.Number `json:"id,Number,omitempty"`
-	PortType   string      `json:"portType,omitempty"`
-	PortNumber json.Number `json:"portNumber,omitempty"`
+	ID         json.Number        `json:"id,Number,omitempty"`
+	PortType   constants.PortType `json:"portType,omitempty"`
+	PortNumber json.Number        `json:"portNumber,omitempty"`
 
 	DiscoveredDate util.Timestamp `json:"discoveredDate,omitempty"`
 
diff --git a/discovery/model/Service.go b/discovery/model/Service.go
index 437978e..08a4b07 100644
--- a/discovery/model/Service.go
+++ b/discovery/model/Service.go
@@ -3,15 +3,16 @@ package model
 import (
 	"encoding/json"
 
+	"git.loafle.net/overflow/commons-go/core/constants"
 	"git.loafle.net/overflow/commons-go/core/util"
 )
 
 type Service struct {
 	Port *Port `json:"port,omitempty"`
 
-	ID          json.Number `json:"id,Number,omitempty"`
-	CryptoType  string      `json:"cryptoType,omitempty"`
-	ServiceName string      `json:"serviceName,omitempty"`
+	ID          json.Number          `json:"id,Number,omitempty"`
+	CryptoType  constants.CryptoType `json:"cryptoType,omitempty"`
+	ServiceName string               `json:"serviceName,omitempty"`
 
 	DiscoveredDate util.Timestamp `json:"discoveredDate,omitempty"`
 }