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examples/features/encryption/README.md

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+# Encryption
+
+The example for encryption includes three individual examples for TLS, ALTS
+and mTLS encryption mechanism respectively.
+
+## Try it
+
+In each example's subdirectory:
+
+```
+go run server/main.go
+```
+
+```
+go run client/main.go
+```
+
+## Explanation
+
+### TLS
+
+TLS is a commonly used cryptographic protocol to provide end-to-end
+communication security. In the example, we show how to set up a server
+authenticated TLS connection to transmit RPC.
+
+In our `grpc/credentials` package, we provide several convenience methods to
+create grpc
+[`credentials.TransportCredentials`](https://godoc.org/google.golang.org/grpc/credentials#TransportCredentials)
+base on TLS. Refer to the
+[godoc](https://godoc.org/google.golang.org/grpc/credentials) for details.
+
+In our example, we use the public/private keys created ahead:
+* "server_cert.pem" contains the server certificate (public key).
+* "server_key.pem" contains the server private key.
+* "ca_cert.pem" contains the certificate (certificate authority)
+that can verify the server's certificate.
+
+On server side, we provide the paths to "server_cert.pem" and "server_key.pem" to
+configure TLS and create the server credential using
+[`credentials.NewServerTLSFromFile`](https://godoc.org/google.golang.org/grpc/credentials#NewServerTLSFromFile).
+
+On client side, we provide the path to the "ca_cert.pem" to configure TLS and create
+the client credential using
+[`credentials.NewClientTLSFromFile`](https://godoc.org/google.golang.org/grpc/credentials#NewClientTLSFromFile).
+Note that we override the server name with "x.test.example.com", as the server
+certificate is valid for *.test.example.com but not localhost. It is solely for
+the convenience of making an example.
+
+Once the credentials have been created at both sides, we can start the server
+with the just created server credential (by calling
+[`grpc.Creds`](https://godoc.org/google.golang.org/grpc#Creds)) and let client dial
+to the server with the created client credential (by calling
+[`grpc.WithTransportCredentials`](https://godoc.org/google.golang.org/grpc#WithTransportCredentials))
+
+And finally we make an RPC call over the created `grpc.ClientConn` to test the secure
+connection based upon TLS is successfully up.
+
+### ALTS
+NOTE: ALTS currently needs special early access permission on GCP. You can ask
+about the detailed process in https://groups.google.com/forum/#!forum/grpc-io.
+
+ALTS is the Google's Application Layer Transport Security, which supports mutual
+authentication and transport encryption. Note that ALTS is currently only
+supported on Google Cloud Platform, and therefore you can only run the example
+successfully in a GCP environment. In our example, we show how to initiate a
+secure connection that is based on ALTS.
+
+Unlike TLS, ALTS makes certificate/key management transparent to user. So it is
+easier to set up.
+
+On server side, first call
+[`alts.DefaultServerOptions`](https://godoc.org/google.golang.org/grpc/credentials/alts#DefaultServerOptions)
+to get the configuration for alts and then provide the configuration to
+[`alts.NewServerCreds`](https://godoc.org/google.golang.org/grpc/credentials/alts#NewServerCreds)
+to create the server credential based upon alts.
+
+On client side, first call
+[`alts.DefaultClientOptions`](https://godoc.org/google.golang.org/grpc/credentials/alts#DefaultClientOptions)
+to get the configuration for alts and then provide the configuration to
+[`alts.NewClientCreds`](https://godoc.org/google.golang.org/grpc/credentials/alts#NewClientCreds)
+to create the client credential based upon alts.
+
+Next, same as TLS, start the server with the server credential and let client
+dial to server with the client credential.
+
+Finally, make an RPC to test the secure connection based upon ALTS is
+successfully up.
+
+### mTLS
+
+In mutual TLS (mTLS), the client and the server authenticate each other. gRPC
+allows users to configure mutual TLS at the connection level.
+
+In this example, we use the following public/private keys created ahead of time:
+
+* "server_cert.pem" contains the server's certificate (public key).
+* "server_key.pem" contains the server's private key.
+* "ca_cert.pem" contains the certificate of the certificate authority that can
+  verify the server's certificate.
+* "client_cert.pem" contains the client's certificate (public key).
+* "client_key.pem" contains the client's private key.
+* "client_ca_cert.pem" contains the certificate of the certificate authority
+  that can verify the client's certificate.
+
+In normal TLS, the server is only concerned with presenting the server
+certificate for clients to verify. In mutual TLS, the server also loads in a
+list of trusted CA files for verifying the client's presented certificates.
+This is done by setting
+[`tls.Config.ClientCAs`](https://pkg.go.dev/crypto/tls#Config.ClientCAs)
+to the list of trusted CA files,
+and setting
+[`tls.config.ClientAuth`](https://pkg.go.dev/crypto/tls#Config.ClientAuth)
+to
+[`tls.RequireAndVerifyClientCert`](https://pkg.go.dev/crypto/tls#RequireAndVerifyClientCert).
+
+In normal TLS, the client is only concerned with authenticating the server by
+using one or more trusted CA file. In mutual TLS, the client also presents its
+client certificate to the server for authentication. This is done by setting
+[`tls.Config.Certificates`](https://pkg.go.dev/crypto/tls#Config.Certificates).