diff --git a/.gitignore b/.gitignore
index 57a1574..85a2891 100644
--- a/.gitignore
+++ b/.gitignore
@@ -194,3 +194,4 @@ FakesAssemblies/
 
 # Visual Studio 6 workspace options file
 *.opt
+/acme-key.xml
diff --git a/src/Oocx.ACME.Common/ILog.cs b/src/Oocx.ACME.Common/ILog.cs
new file mode 100644
index 0000000..8c27a1d
--- /dev/null
+++ b/src/Oocx.ACME.Common/ILog.cs
@@ -0,0 +1,13 @@
+namespace Oocx.ACME.Common
+{
+    public interface ILog
+    {
+        void Verbose(string message, params object[] args);
+
+        void Info(string message, params object[] args);
+
+        void Warning(string message, params object[] args);
+
+        void Error(string message, params object[] args);
+    }
+}