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certs.go
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certs.go
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/*
Copyright 2016 SPIFFE Authors
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
http://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 utils
import (
"bytes"
"crypto"
"crypto/ecdsa"
"crypto/rand"
"crypto/rsa"
"crypto/x509"
"crypto/x509/pkix"
"encoding/pem"
"math/big"
"time"
"github.com/gravitational/trace"
log "github.com/sirupsen/logrus"
)
// ParseSigningKeyStore parses signing key store from PEM encoded key pair
func ParseSigningKeyStorePEM(keyPEM, certPEM string) (*SigningKeyStore, error) {
_, err := ParseCertificatePEM([]byte(certPEM))
if err != nil {
return nil, trace.Wrap(err)
}
key, err := ParsePrivateKeyPEM([]byte(keyPEM))
if err != nil {
return nil, trace.Wrap(err)
}
rsaKey, ok := key.(*rsa.PrivateKey)
if !ok {
return nil, trace.BadParameter("key of type %T is not supported, only RSA keys are supported for signatures")
}
certASN, _ := pem.Decode([]byte(certPEM))
if certASN == nil {
return nil, trace.BadParameter("expected PEM-encoded block")
}
return &SigningKeyStore{privateKey: rsaKey, cert: certASN.Bytes}, nil
}
// SigningKeyStore is used to sign using X509 digital signatures
type SigningKeyStore struct {
privateKey *rsa.PrivateKey
cert []byte
}
func (ks *SigningKeyStore) GetKeyPair() (*rsa.PrivateKey, []byte, error) {
return ks.privateKey, ks.cert, nil
}
// GenerateSelfSignedSigningCert generates self-signed certificate used for digital signatures
func GenerateSelfSignedSigningCert(entity pkix.Name, dnsNames []string, ttl time.Duration) ([]byte, []byte, error) {
priv, err := rsa.GenerateKey(rand.Reader, 2048)
if err != nil {
return nil, nil, trace.Wrap(err)
}
// to account for clock skew
notBefore := time.Now().Add(-2 * time.Minute)
notAfter := notBefore.Add(ttl)
serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
if err != nil {
return nil, nil, trace.Wrap(err)
}
template := x509.Certificate{
SerialNumber: serialNumber,
Issuer: entity,
Subject: entity,
NotBefore: notBefore,
NotAfter: notAfter,
KeyUsage: x509.KeyUsageDigitalSignature,
BasicConstraintsValid: true,
DNSNames: dnsNames,
}
derBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, &priv.PublicKey, priv)
if err != nil {
return nil, nil, trace.Wrap(err)
}
keyPEM := pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(priv)})
certPEM := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: derBytes})
return keyPEM, certPEM, nil
}
// ParseCertificateRequestPEM parses PEM-encoded certificate signing request
func ParseCertificateRequestPEM(bytes []byte) (*x509.CertificateRequest, error) {
block, _ := pem.Decode(bytes)
if block == nil {
return nil, trace.BadParameter("expected PEM-encoded block")
}
csr, err := x509.ParseCertificateRequest(block.Bytes)
if err != nil {
return nil, trace.BadParameter(err.Error())
}
return csr, nil
}
// ParseCertificatePEM parses PEM-encoded certificate
func ParseCertificatePEM(bytes []byte) (*x509.Certificate, error) {
block, _ := pem.Decode(bytes)
if block == nil {
return nil, trace.BadParameter("expected PEM-encoded block")
}
cert, err := x509.ParseCertificate(block.Bytes)
if err != nil {
return nil, trace.BadParameter(err.Error())
}
return cert, nil
}
// ParsePrivateKeyPEM parses PEM-encoded private key
func ParsePrivateKeyPEM(bytes []byte) (crypto.Signer, error) {
block, _ := pem.Decode(bytes)
if block == nil {
return nil, trace.BadParameter("expected PEM-encoded block")
}
return ParsePrivateKeyDER(block.Bytes)
}
// ParsePrivateKeyDER parses unencrypted DER-encoded private key
func ParsePrivateKeyDER(der []byte) (crypto.Signer, error) {
generalKey, err := x509.ParsePKCS8PrivateKey(der)
if err != nil {
generalKey, err = x509.ParsePKCS1PrivateKey(der)
if err != nil {
generalKey, err = x509.ParseECPrivateKey(der)
if err != nil {
log.Errorf("failed to parse key: %v", err)
return nil, trace.BadParameter("failed parsing private key")
}
}
}
switch generalKey.(type) {
case *rsa.PrivateKey:
return generalKey.(*rsa.PrivateKey), nil
case *ecdsa.PrivateKey:
return generalKey.(*ecdsa.PrivateKey), nil
}
return nil, trace.BadParameter("unsupported private key type")
}
// VerifyCertificateChain reads in chain of certificates and makes sure the
// chain from leaf to root is valid. This ensures that clients (web browsers
// and CLI) won't have problem validating the chain.
func VerifyCertificateChain(certificateBytes []byte) error {
// build the certificate chain next
var certificateBlock *pem.Block
var remainingBytes []byte = certificateBytes
var certificateChain [][]byte
for {
certificateBlock, remainingBytes = pem.Decode(remainingBytes)
certificateChain = append(certificateChain, certificateBlock.Bytes)
if len(remainingBytes) == 0 {
break
}
}
// build a concatenated certificate chain
var buf bytes.Buffer
for _, cc := range certificateChain {
_, err := buf.Write(cc)
if err != nil {
return trace.Wrap(err)
}
}
// parse the chain and get a slice of x509.Certificates.
x509Chain, err := x509.ParseCertificates(buf.Bytes())
if err != nil {
return trace.Wrap(err)
}
// extract intermediates and leaf certificate chains
intermediates := x509.NewCertPool()
if len(certificateChain) > 1 {
for _, v := range x509Chain[1:len(x509Chain)] {
intermediates.AddCert(v)
}
}
leaf := x509Chain[0]
// verify the entire chain using system roots. if we want to support
// validating the name presented on the certificate in the future we should
// pass in DNSName here.
opts := x509.VerifyOptions{
Intermediates: intermediates,
}
_, err = leaf.Verify(opts)
if err != nil {
return trace.Wrap(err)
}
return nil
}