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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.
// Package client is a cross-platform client for the signer binary (a.k.a."EnterpriseCertSigner").
//
// The signer binary is OS-specific, but exposes a standard set of APIs for the client to use.
package client
import (
"crypto"
"crypto/ecdsa"
"crypto/rsa"
"crypto/x509"
"encoding/gob"
"errors"
"fmt"
"io"
"net/rpc"
"os"
"os/exec"
"github.com/googleapis/enterprise-certificate-proxy/client/util"
)
const signAPI = "EnterpriseCertSigner.Sign"
const certificateChainAPI = "EnterpriseCertSigner.CertificateChain"
const publicKeyAPI = "EnterpriseCertSigner.Public"
// A 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
}
func init() {
gob.Register(crypto.SHA256)
gob.Register(&rsa.PSSOptions{})
}
// SignArgs contains arguments to a crypto Signer.Sign method.
type SignArgs struct {
Digest []byte // The content to sign.
Opts crypto.SignerOpts // Options for signing, such as Hash identifier.
}
// Key implements credential.Credential by holding the executed signer subprocess.
type Key struct {
cmd *exec.Cmd // Pointer to the signer subprocess.
client *rpc.Client // Pointer to the rpc client that communicates with the signer subprocess.
publicKey crypto.PublicKey // Public key of loaded certificate.
chain [][]byte // Certificate chain of loaded certificate.
}
// CertificateChain returns the credential as a raw X509 cert chain. This contains the public key.
func (k *Key) CertificateChain() [][]byte {
return k.chain
}
// Close closes the RPC connection and kills the signer subprocess.
// Call this to free up resources when the Key object is no longer needed.
func (k *Key) Close() error {
if err := k.cmd.Process.Kill(); err != nil {
return fmt.Errorf("failed to kill signer process: %w", err)
}
// Wait for cmd to exit and release resources. Since the process is forcefully killed, this
// will return a non-nil error (varies by OS), which we will ignore.
_ = k.cmd.Wait()
// The Pipes connecting the RPC client should have been closed when the signer subprocess was killed.
// Calling `k.client.Close()` before `k.cmd.Process.Kill()` or `k.cmd.Wait()` _will_ cause a segfault.
if err := k.client.Close(); err.Error() != "close |0: file already closed" {
return fmt.Errorf("failed to close RPC connection: %w", err)
}
return nil
}
// Public returns the public key for this Key.
func (k *Key) Public() crypto.PublicKey {
return k.publicKey
}
// Sign signs a message digest, using the specified signer options.
func (k *Key) Sign(_ io.Reader, digest []byte, opts crypto.SignerOpts) (signed []byte, err error) {
if opts != nil && opts.HashFunc() != 0 && len(digest) != opts.HashFunc().Size() {
return nil, fmt.Errorf("Digest length of %v bytes does not match Hash function size of %v bytes", len(digest), opts.HashFunc().Size())
}
err = k.client.Call(signAPI, SignArgs{Digest: digest, Opts: opts}, &signed)
return
}
// ErrCredUnavailable is a sentinel error that indicates ECP Cred is unavailable,
// possibly due to missing config or missing binary path.
var ErrCredUnavailable = errors.New("Cred is unavailable")
// Cred spawns a signer subprocess that listens on stdin/stdout to perform certificate
// related operations, including signing messages with the private key.
//
// The signer binary path is read from the specified configFilePath, if provided.
// Otherwise, use the default config file path.
//
// The config file also specifies which certificate the signer should use.
func Cred(configFilePath string) (*Key, error) {
if configFilePath == "" {
configFilePath = util.GetDefaultConfigFilePath()
}
enterpriseCertSignerPath, err := util.LoadSignerBinaryPath(configFilePath)
if err != nil {
if errors.Is(err, util.ErrConfigUnavailable) {
return nil, ErrCredUnavailable
}
return nil, err
}
k := &Key{
cmd: exec.Command(enterpriseCertSignerPath, configFilePath),
}
// Redirect errors from subprocess to parent process.
k.cmd.Stderr = os.Stderr
// RPC client will communicate with subprocess over stdin/stdout.
kin, err := k.cmd.StdinPipe()
if err != nil {
return nil, err
}
kout, err := k.cmd.StdoutPipe()
if err != nil {
return nil, err
}
k.client = rpc.NewClient(&Connection{kout, kin})
if err := k.cmd.Start(); err != nil {
return nil, fmt.Errorf("starting enterprise cert signer subprocess: %w", err)
}
if err := k.client.Call(certificateChainAPI, struct{}{}, &k.chain); err != nil {
return nil, fmt.Errorf("failed to retrieve certificate chain: %w", err)
}
var publicKeyBytes []byte
if err := k.client.Call(publicKeyAPI, struct{}{}, &publicKeyBytes); err != nil {
return nil, fmt.Errorf("failed to retrieve public key: %w", err)
}
publicKey, err := x509.ParsePKIXPublicKey(publicKeyBytes)
if err != nil {
return nil, fmt.Errorf("failed to parse public key: %w", err)
}
var ok bool
k.publicKey, ok = publicKey.(crypto.PublicKey)
if !ok {
return nil, fmt.Errorf("invalid public key type: %T", publicKey)
}
switch pub := k.publicKey.(type) {
case *rsa.PublicKey:
if pub.Size() < 256 {
return nil, fmt.Errorf("RSA modulus size is less than 2048 bits: %v", pub.Size()*8)
}
case *ecdsa.PublicKey:
default:
return nil, fmt.Errorf("unsupported public key type: %v", pub)
}
return k, nil
}
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