1// Copyright 2022 Google LLC.
2// Licensed under the Apache License, Version 2.0 (the "License");
3// you may not use this file except in compliance with the License.
4// You may obtain a copy of the License at
5//
6// https://www.apache.org/licenses/LICENSE-2.0
7//
8// Unless required by applicable law or agreed to in writing, software
9// distributed under the License is distributed on an "AS IS" BASIS,
10// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
11// See the License for the specific language governing permissions and
12// limitations under the License.
13
14// Package client is a cross-platform client for the signer binary (a.k.a."EnterpriseCertSigner").
15//
16// The signer binary is OS-specific, but exposes a standard set of APIs for the client to use.
17package client
18
19import (
20 "crypto"
21 "crypto/ecdsa"
22 "crypto/rsa"
23 "crypto/x509"
24 "encoding/gob"
25 "errors"
26 "fmt"
27 "io"
28 "net/rpc"
29 "os"
30 "os/exec"
31
32 "github.com/googleapis/enterprise-certificate-proxy/client/util"
33)
34
35const signAPI = "EnterpriseCertSigner.Sign"
36const certificateChainAPI = "EnterpriseCertSigner.CertificateChain"
37const publicKeyAPI = "EnterpriseCertSigner.Public"
38const encryptAPI = "EnterpriseCertSigner.Encrypt"
39const decryptAPI = "EnterpriseCertSigner.Decrypt"
40
41// A Connection wraps a pair of unidirectional streams as an io.ReadWriteCloser.
42type Connection struct {
43 io.ReadCloser
44 io.WriteCloser
45}
46
47// Close closes c's underlying ReadCloser and WriteCloser.
48func (c *Connection) Close() error {
49 rerr := c.ReadCloser.Close()
50 werr := c.WriteCloser.Close()
51 if rerr != nil {
52 return rerr
53 }
54 return werr
55}
56
57func init() {
58 gob.Register(crypto.SHA256)
59 gob.Register(crypto.SHA384)
60 gob.Register(crypto.SHA512)
61 gob.Register(&rsa.PSSOptions{})
62 gob.Register(&rsa.OAEPOptions{})
63}
64
65// SignArgs contains arguments for a Sign API call.
66type SignArgs struct {
67 Digest []byte // The content to sign.
68 Opts crypto.SignerOpts // Options for signing. Must implement HashFunc().
69}
70
71// EncryptArgs contains arguments for an Encrypt API call.
72type EncryptArgs struct {
73 Plaintext []byte // The plaintext to encrypt.
74 Opts any // Options for encryption. Ex: an instance of crypto.Hash.
75}
76
77// DecryptArgs contains arguments to for a Decrypt API call.
78type DecryptArgs struct {
79 Ciphertext []byte // The ciphertext to decrypt.
80 Opts crypto.DecrypterOpts // Options for decryption. Ex: an instance of *rsa.OAEPOptions.
81}
82
83// Key implements credential.Credential by holding the executed signer subprocess.
84type Key struct {
85 cmd *exec.Cmd // Pointer to the signer subprocess.
86 client *rpc.Client // Pointer to the rpc client that communicates with the signer subprocess.
87 publicKey crypto.PublicKey // Public key of loaded certificate.
88 chain [][]byte // Certificate chain of loaded certificate.
89}
90
91// CertificateChain returns the credential as a raw X509 cert chain. This contains the public key.
92func (k *Key) CertificateChain() [][]byte {
93 return k.chain
94}
95
96// Close closes the RPC connection and kills the signer subprocess.
97// Call this to free up resources when the Key object is no longer needed.
98func (k *Key) Close() error {
99 if err := k.cmd.Process.Kill(); err != nil {
100 return fmt.Errorf("failed to kill signer process: %w", err)
101 }
102 // Wait for cmd to exit and release resources. Since the process is forcefully killed, this
103 // will return a non-nil error (varies by OS), which we will ignore.
104 _ = k.cmd.Wait()
105 // The Pipes connecting the RPC client should have been closed when the signer subprocess was killed.
106 // Calling `k.client.Close()` before `k.cmd.Process.Kill()` or `k.cmd.Wait()` _will_ cause a segfault.
107 if err := k.client.Close(); err.Error() != "close |0: file already closed" {
108 return fmt.Errorf("failed to close RPC connection: %w", err)
109 }
110 return nil
111}
112
113// Public returns the public key for this Key.
114func (k *Key) Public() crypto.PublicKey {
115 return k.publicKey
116}
117
118// Sign signs a message digest, using the specified signer opts. Implements crypto.Signer interface.
119func (k *Key) Sign(_ io.Reader, digest []byte, opts crypto.SignerOpts) (signed []byte, err error) {
120 if opts != nil && opts.HashFunc() != 0 && len(digest) != opts.HashFunc().Size() {
121 return nil, fmt.Errorf("Digest length of %v bytes does not match Hash function size of %v bytes", len(digest), opts.HashFunc().Size())
122 }
123 err = k.client.Call(signAPI, SignArgs{Digest: digest, Opts: opts}, &signed)
124 return
125}
126
127// Encrypt encrypts a plaintext msg into ciphertext, using the specified encrypt opts.
128func (k *Key) Encrypt(_ io.Reader, msg []byte, opts any) (ciphertext []byte, err error) {
129 err = k.client.Call(encryptAPI, EncryptArgs{Plaintext: msg, Opts: opts}, &ciphertext)
130 return
131}
132
133// Decrypt decrypts a ciphertext msg into plaintext, using the specified decrypter opts. Implements crypto.Decrypter interface.
134func (k *Key) Decrypt(_ io.Reader, msg []byte, opts crypto.DecrypterOpts) (plaintext []byte, err error) {
135 err = k.client.Call(decryptAPI, DecryptArgs{Ciphertext: msg, Opts: opts}, &plaintext)
136 return
137}
138
139// ErrCredUnavailable is a sentinel error that indicates ECP Cred is unavailable,
140// possibly due to missing config or missing binary path.
141var ErrCredUnavailable = errors.New("Cred is unavailable")
142
143// Cred spawns a signer subprocess that listens on stdin/stdout to perform certificate
144// related operations, including signing messages with the private key.
145//
146// The signer binary path is read from the specified configFilePath, if provided.
147// Otherwise, use the default config file path.
148//
149// The config file also specifies which certificate the signer should use.
150func Cred(configFilePath string) (*Key, error) {
151 if configFilePath == "" {
152 envFilePath := util.GetConfigFilePathFromEnv()
153 if envFilePath != "" {
154 configFilePath = envFilePath
155 } else {
156 configFilePath = util.GetDefaultConfigFilePath()
157 }
158 }
159 enterpriseCertSignerPath, err := util.LoadSignerBinaryPath(configFilePath)
160 if err != nil {
161 if errors.Is(err, util.ErrConfigUnavailable) {
162 return nil, ErrCredUnavailable
163 }
164 return nil, err
165 }
166 k := &Key{
167 cmd: exec.Command(enterpriseCertSignerPath, configFilePath),
168 }
169
170 // Redirect errors from subprocess to parent process.
171 k.cmd.Stderr = os.Stderr
172
173 // RPC client will communicate with subprocess over stdin/stdout.
174 kin, err := k.cmd.StdinPipe()
175 if err != nil {
176 return nil, err
177 }
178 kout, err := k.cmd.StdoutPipe()
179 if err != nil {
180 return nil, err
181 }
182 k.client = rpc.NewClient(&Connection{kout, kin})
183
184 if err := k.cmd.Start(); err != nil {
185 return nil, fmt.Errorf("starting enterprise cert signer subprocess: %w", err)
186 }
187
188 if err := k.client.Call(certificateChainAPI, struct{}{}, &k.chain); err != nil {
189 return nil, fmt.Errorf("failed to retrieve certificate chain: %w", err)
190 }
191
192 var publicKeyBytes []byte
193 if err := k.client.Call(publicKeyAPI, struct{}{}, &publicKeyBytes); err != nil {
194 return nil, fmt.Errorf("failed to retrieve public key: %w", err)
195 }
196
197 publicKey, err := x509.ParsePKIXPublicKey(publicKeyBytes)
198 if err != nil {
199 return nil, fmt.Errorf("failed to parse public key: %w", err)
200 }
201
202 var ok bool
203 k.publicKey, ok = publicKey.(crypto.PublicKey)
204 if !ok {
205 return nil, fmt.Errorf("invalid public key type: %T", publicKey)
206 }
207
208 switch pub := k.publicKey.(type) {
209 case *rsa.PublicKey:
210 if pub.Size() < 256 {
211 return nil, fmt.Errorf("RSA modulus size is less than 2048 bits: %v", pub.Size()*8)
212 }
213 case *ecdsa.PublicKey:
214 default:
215 return nil, fmt.Errorf("unsupported public key type: %v", pub)
216 }
217
218 return k, nil
219}