diff --git a/csharp/keys/Google.Protobuf.snk b/csharp/keys/Google.Protobuf.snk
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index 00000000..7515443c
Binary files /dev/null and b/csharp/keys/Google.Protobuf.snk differ
diff --git a/csharp/keys/README.md b/csharp/keys/README.md
index 1a014198..f6f27e80 100644
--- a/csharp/keys/README.md
+++ b/csharp/keys/README.md
@@ -2,4 +2,8 @@ Contents
 --------
 
 - Google.Protobuf.public.snk:
-  Public key to verify strong name of Google.Protobuf assemblies.
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+  Public key to verify strong name of Google.Protobuf assemblies.
+- Google.Protobuf.snk:
+  Signing key to provide strong name of Google.Protobuf assemblies.
+  As per https://msdn.microsoft.com/en-us/library/wd40t7ad(v=vs.110).aspx
+  signing key should be checked into the repository.
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