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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.
// pkcs11 provides helpers for working with certificates via PKCS#11 APIs
// provided by go-pkcs11
package pkcs11
import (
"crypto"
"crypto/ecdsa"
"crypto/rand"
"crypto/rsa"
"crypto/sha1"
"crypto/sha256"
"errors"
"fmt"
"hash"
"io"
"strconv"
"strings"
"github.com/google/go-pkcs11/pkcs11"
)
// ParseHexString parses hexadecimal string into uint32
func ParseHexString(str string) (i uint32, err error) {
stripped := strings.Replace(str, "0x", "", -1)
resultUint64, err := strconv.ParseUint(stripped, 16, 32)
if err != nil {
return 0, err
}
return uint32(resultUint64), nil
}
// Cred returns a Key wrapping the first valid certificate in the pkcs11 module
// matching a given slot and label.
func Cred(pkcs11Module string, slotUint32Str string, label string, userPin string) (*Key, error) {
module, err := pkcs11.Open(pkcs11Module)
if err != nil {
return nil, err
}
slotUint32, err := ParseHexString(slotUint32Str)
if err != nil {
return nil, err
}
kslot, err := module.Slot(slotUint32, pkcs11.Options{PIN: userPin})
if err != nil {
return nil, err
}
certs, err := kslot.Objects(pkcs11.Filter{Class: pkcs11.ClassCertificate, Label: label})
if err != nil {
return nil, err
}
if len(certs) < 1 {
return nil, fmt.Errorf("No certificate object was found with label %s.", label)
}
cert, err := certs[0].Certificate()
if err != nil {
return nil, err
}
x509, err := cert.X509()
if err != nil {
return nil, err
}
var kchain [][]byte
kchain = append(kchain, x509.Raw)
pubKeys, err := kslot.Objects(pkcs11.Filter{Class: pkcs11.ClassPublicKey, Label: label})
if err != nil {
return nil, err
}
if len(pubKeys) < 1 {
return nil, fmt.Errorf("No public key object was found with label %s.", label)
}
pubKey, err := pubKeys[0].PublicKey()
if err != nil {
return nil, err
}
privkeys, err := kslot.Objects(pkcs11.Filter{Class: pkcs11.ClassPrivateKey, Label: label})
if err != nil {
return nil, err
}
if len(privkeys) < 1 {
return nil, fmt.Errorf("No private key object was found with label %s.", label)
}
privKey, err := privkeys[0].PrivateKey(pubKey)
if err != nil {
return nil, err
}
ksigner, ok := privKey.(crypto.Signer)
if !ok {
return nil, errors.New("PrivateKey does not implement crypto.Signer")
}
kdecrypter, ok := privKey.(crypto.Decrypter)
if !ok {
return nil, errors.New("PrivateKey does not implement crypto.Decrypter")
}
defaultHash := crypto.SHA256
return &Key{
slot: kslot,
signer: ksigner,
chain: kchain,
privKey: privKey,
label: label,
module: *module,
hash: defaultHash,
decrypter: kdecrypter,
}, nil
}
// Key is a wrapper around the pkcs11 module and uses it to
// implement signing-related methods.
type Key struct {
slot *pkcs11.Slot
signer crypto.Signer
chain [][]byte
privKey crypto.PrivateKey
label string
module pkcs11.Module
hash crypto.Hash
decrypter crypto.Decrypter
}
// CertificateChain returns the credential as a raw X509 cert chain. This
// contains the public key.
func (k *Key) CertificateChain() [][]byte {
return k.chain
}
// Close releases resources held by the credential.
func (k *Key) Close() {
k.slot.Close()
k.module.Close()
}
// Public returns the corresponding public key for this Key.
func (k *Key) Public() crypto.PublicKey {
return k.signer.Public()
}
// Sign signs a message.
func (k *Key) Sign(_ io.Reader, digest []byte, opts crypto.SignerOpts) ([]byte, error) {
return k.signer.Sign(nil, digest, opts)
}
// Encrypt encrypts a plaintext message digest using the public key. Here, we use standard golang API.
func (k *Key) Encrypt(plaintext []byte, opts any) ([]byte, error) {
if hash, ok := opts.(crypto.Hash); ok {
k.hash = hash
} else {
return nil, fmt.Errorf("Unsupported encrypt opts: %v", opts)
}
publicKey := k.Public()
_, ok := publicKey.(*rsa.PublicKey)
if ok {
return k.encryptRSA(plaintext)
}
_, ok = publicKey.(*ecdsa.PublicKey)
if ok {
// TODO: Implement encryption for ec keys - https://github.com/googleapis/enterprise-certificate-proxy/issues/95
return nil, errors.New("encrypt error: EC keys not yet supported")
}
return nil, errors.New("encrypt error: Unsupported key type")
}
// Decrypt decrypts a ciphertext message digest using the private key. Here, we pass off the decryption to pkcs11 library.
func (k *Key) Decrypt(msg []byte, opts crypto.DecrypterOpts) ([]byte, error) {
if oaepOpts, ok := opts.(*rsa.OAEPOptions); ok {
k.hash = oaepOpts.Hash
} else {
return nil, fmt.Errorf("Unsupported DecrypterOpts: %v", opts)
}
publicKey := k.Public()
_, ok := publicKey.(*rsa.PublicKey)
if ok {
return k.decryptRSAWithPKCS11(msg)
}
_, ok = publicKey.(*ecdsa.PublicKey)
if ok {
// TODO: Implement decryption for ec keys - https://github.com/googleapis/enterprise-certificate-proxy/issues/95
return nil, errors.New("decrypt error: EC keys not yet supported")
}
return nil, errors.New("decrypt error: Unsupported key type")
}
func (k *Key) encryptRSA(data []byte) ([]byte, error) {
publicKey := k.Public()
rsaPubKey := publicKey.(*rsa.PublicKey)
hash, err := cryptoHashToHash(k.hash)
if err != nil {
return nil, err
}
return rsa.EncryptOAEP(hash, rand.Reader, rsaPubKey, data, nil)
}
func (k *Key) decryptRSAWithPKCS11(encryptedData []byte) ([]byte, error) {
opts := &rsa.OAEPOptions{Hash: k.hash}
return k.decrypter.Decrypt(nil, encryptedData, opts)
}
func (k *Key) WithHash(hash crypto.Hash) *Key {
k.hash = hash
return k
}
func cryptoHashToHash(hash crypto.Hash) (hash.Hash, error) {
switch hash {
case crypto.SHA256:
return sha256.New(), nil
case crypto.SHA1:
return sha1.New(), nil
default:
return nil, errors.New("hash conversion error: Unsupported hash")
}
}
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