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// Copyright 2022 Google LLC.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// signer.go is a net/rpc server that listens on stdin/stdout, exposing
// mock methods for testing client.go.
package main
import (
"crypto"
"crypto/tls"
"crypto/x509"
"io"
"log"
"net/rpc"
"os"
"time"
)
// SignArgs encapsulate the parameters for the Sign method.
type SignArgs struct {
Digest []byte
Opts crypto.SignerOpts
}
// EnterpriseCertSigner exports RPC methods for signing.
type EnterpriseCertSigner struct {
cert *tls.Certificate
}
// Connection wraps a pair of unidirectional streams as an io.ReadWriteCloser.
type Connection struct {
io.ReadCloser
io.WriteCloser
}
// Close closes c's underlying ReadCloser and WriteCloser.
func (c *Connection) Close() error {
rerr := c.ReadCloser.Close()
werr := c.WriteCloser.Close()
if rerr != nil {
return rerr
}
return werr
}
// CertificateChain returns the credential as a raw X509 cert chain. This
// contains the public key.
func (k *EnterpriseCertSigner) CertificateChain(ignored struct{}, certificateChain *[][]byte) error {
*certificateChain = k.cert.Certificate
return nil
}
// Public returns the first public key for this Key, in ASN.1 DER form.
func (k *EnterpriseCertSigner) Public(ignored struct{}, publicKey *[]byte) (err error) {
if len(k.cert.Certificate) == 0 {
return nil
}
cert, err := x509.ParseCertificate(k.cert.Certificate[0])
if err != nil {
return err
}
*publicKey, err = x509.MarshalPKIXPublicKey(cert.PublicKey)
return err
}
// Sign signs a message digest.
func (k *EnterpriseCertSigner) Sign(args SignArgs, resp *[]byte) (err error) {
*resp = args.Digest
return nil
}
func main() {
enterpriseCertSigner := new(EnterpriseCertSigner)
data, err := os.ReadFile(os.Args[1])
if err != nil {
log.Fatalf("Error reading certificate: %v", err)
}
cert, _ := tls.X509KeyPair(data, data)
enterpriseCertSigner.cert = &cert
if err := rpc.Register(enterpriseCertSigner); err != nil {
log.Fatalf("Error registering net/rpc: %v", err)
}
// If the parent process dies, we should exit.
// We can detect this by periodically checking if the PID of the parent
// process is 1 (https://stackoverflow.com/a/2035683).
go func() {
for {
if os.Getppid() == 1 {
log.Fatalln("Parent process died, exiting...")
}
time.Sleep(time.Second)
}
}()
rpc.ServeConn(&Connection{os.Stdin, os.Stdout})
}
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