diff --git a/src/main/kotlin/dev/usbharu/httpsignature/common/DefaultSignatureBase.kt b/src/main/kotlin/dev/usbharu/httpsignature/common/DefaultSignatureBase.kt
new file mode 100644
index 0000000..bf53fe7
--- /dev/null
+++ b/src/main/kotlin/dev/usbharu/httpsignature/common/DefaultSignatureBase.kt
@@ -0,0 +1,39 @@
+package dev.usbharu.httpsignature.common
+
+class DefaultSignatureBase : SignatureBase {
+
+    private val list = mutableListOf<Component>()
+
+    fun addComponent(component: Component) {
+        if (list.indexOf(component) != -1) {
+            throw IllegalArgumentException("Component with identifier ${component.componentIdentifier} already exists.")
+        }
+        list.add(component)
+    }
+
+    override fun generateSignatureBase(signatureParameters: List<SignatureParameter>): String {
+        val signatureBase =
+            list.joinToString(
+                separator = "",
+                postfix = "\n"
+            ) { component -> "${component.componentIdentifier}: ${component.componentValue}" }
+
+        val signatureParams = "\"@signature-params\": " + generateSignatureParameterString(signatureParameters)
+
+        return signatureBase + signatureParams
+    }
+
+    override fun generateSignatureParameterString(signatureParameters: List<SignatureParameter>): String {
+        return (listOf(
+            list.joinToString(
+                " ",
+                "(",
+                ")"
+            ) { it.componentIdentifier }
+        ) + signatureParameters.map { "${it.name}=${it.value}" }).joinToString(";")
+    }
+
+    override fun coveredComponents(): List<String> {
+        return list.map { it.componentIdentifier }
+    }
+}
diff --git a/src/main/kotlin/dev/usbharu/httpsignature/common/SignatureBase.kt b/src/main/kotlin/dev/usbharu/httpsignature/common/SignatureBase.kt
index dc8ac71..392abb3 100644
--- a/src/main/kotlin/dev/usbharu/httpsignature/common/SignatureBase.kt
+++ b/src/main/kotlin/dev/usbharu/httpsignature/common/SignatureBase.kt
@@ -1,39 +1,7 @@
 package dev.usbharu.httpsignature.common
 
-class SignatureBase() {
-
-    private val list = mutableListOf<Component>()
-
-    fun addComponent(component: Component) {
-        if (list.indexOf(component) != -1) {
-            throw IllegalArgumentException("Component with identifier ${component.componentIdentifier} already exists.")
-        }
-        list.add(component)
-    }
-
-    fun generateSignatureBase(signatureParameters: List<SignatureParameter>): String {
-        val signatureBase =
-            list.joinToString(
-                separator = "",
-                postfix = "\n"
-            ) { component -> "${component.componentIdentifier}: ${component.componentValue}" }
-
-        val signatureParams = "\"@signature-params\": " + generateSignatureParameterString(signatureParameters)
-
-        return signatureBase + signatureParams
-    }
-
-    fun generateSignatureParameterString(signatureParameters: List<SignatureParameter>): String {
-        return (listOf(
-            list.joinToString(
-                " ",
-                "(",
-                ")"
-            ) { it.componentIdentifier }
-        ) + signatureParameters.map { "${it.name}=${it.value}" }).joinToString(";")
-    }
-
-    fun coveredComponents(): List<String> {
-        return list.map { it.componentIdentifier }
-    }
-}
+interface SignatureBase {
+    fun generateSignatureBase(signatureParameters: List<SignatureParameter>): String
+    fun generateSignatureParameterString(signatureParameters: List<SignatureParameter>): String
+    fun coveredComponents(): List<String>
+}
\ No newline at end of file
diff --git a/src/main/kotlin/dev/usbharu/httpsignature/common/SignatureBaseBuilder.kt b/src/main/kotlin/dev/usbharu/httpsignature/common/SignatureBaseBuilder.kt
index bc04e3f..6111e52 100644
--- a/src/main/kotlin/dev/usbharu/httpsignature/common/SignatureBaseBuilder.kt
+++ b/src/main/kotlin/dev/usbharu/httpsignature/common/SignatureBaseBuilder.kt
@@ -5,9 +5,9 @@ import java.net.http.HttpRequest
 import kotlin.jvm.optionals.getOrNull
 
 class SignatureBaseBuilder {
-    private val signatureBase = SignatureBase()
+    private val signatureBase = DefaultSignatureBase()
 
-    fun build(): SignatureBase {
+    fun build(): DefaultSignatureBase {
         return signatureBase
     }