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//
// Copyright 2021 The Sigstore 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 cryptoutils implements support for working with encoded certificates, public keys, and private keys
package cryptoutils
import (
"bytes"
"crypto/rand"
"crypto/x509"
"encoding/pem"
"errors"
"fmt"
"io"
"math/big"
"time"
)
const (
// CertificatePEMType is the string "CERTIFICATE" to be used during PEM encoding and decoding
CertificatePEMType PEMType = "CERTIFICATE"
)
// MarshalCertificateToPEM converts the provided X509 certificate into PEM format
func MarshalCertificateToPEM(cert *x509.Certificate) ([]byte, error) {
if cert == nil {
return nil, errors.New("nil certificate provided")
}
return PEMEncode(CertificatePEMType, cert.Raw), nil
}
// MarshalCertificatesToPEM converts the provided X509 certificates into PEM format
func MarshalCertificatesToPEM(certs []*x509.Certificate) ([]byte, error) {
buf := bytes.Buffer{}
for _, cert := range certs {
pemBytes, err := MarshalCertificateToPEM(cert)
if err != nil {
return nil, err
}
_, _ = buf.Write(pemBytes)
}
return buf.Bytes(), nil
}
// UnmarshalCertificatesFromPEM extracts one or more X509 certificates from the provided
// byte slice, which is assumed to be in PEM-encoded format.
func UnmarshalCertificatesFromPEM(pemBytes []byte) ([]*x509.Certificate, error) {
result := []*x509.Certificate{}
remaining := pemBytes
remaining = bytes.TrimSpace(remaining)
for len(remaining) > 0 {
var certDer *pem.Block
certDer, remaining = pem.Decode(remaining)
if certDer == nil {
return nil, errors.New("error during PEM decoding")
}
cert, err := x509.ParseCertificate(certDer.Bytes)
if err != nil {
return nil, err
}
result = append(result, cert)
}
return result, nil
}
// UnmarshalCertificatesFromPEMLimited extracts one or more X509 certificates from the provided
// byte slice, which is assumed to be in PEM-encoded format. Fails after a specified
// number of iterations. A reasonable limit is 10 iterations.
func UnmarshalCertificatesFromPEMLimited(pemBytes []byte, iterations int) ([]*x509.Certificate, error) {
result := []*x509.Certificate{}
remaining := pemBytes
remaining = bytes.TrimSpace(remaining)
count := 0
for len(remaining) > 0 {
if count == iterations {
return nil, errors.New("too many certificates specified in PEM block")
}
var certDer *pem.Block
certDer, remaining = pem.Decode(remaining)
if certDer == nil {
return nil, errors.New("error during PEM decoding")
}
cert, err := x509.ParseCertificate(certDer.Bytes)
if err != nil {
return nil, err
}
result = append(result, cert)
count++
}
return result, nil
}
// LoadCertificatesFromPEM extracts one or more X509 certificates from the provided
// io.Reader.
func LoadCertificatesFromPEM(pem io.Reader) ([]*x509.Certificate, error) {
fileBytes, err := io.ReadAll(pem)
if err != nil {
return nil, err
}
return UnmarshalCertificatesFromPEM(fileBytes)
}
func formatTime(t time.Time) string {
return t.UTC().Format(time.RFC3339)
}
// CheckExpiration verifies that epoch is during the validity period of
// the certificate provided.
//
// It returns nil if issueTime < epoch < expirationTime, and error otherwise.
func CheckExpiration(cert *x509.Certificate, epoch time.Time) error {
if cert == nil {
return errors.New("certificate is nil")
}
if cert.NotAfter.Before(epoch) {
return fmt.Errorf("certificate expiration time %s is before %s", formatTime(cert.NotAfter), formatTime(epoch))
}
if cert.NotBefore.After(epoch) {
return fmt.Errorf("certificate issued time %s is before %s", formatTime(cert.NotBefore), formatTime(epoch))
}
return nil
}
// ParseCSR parses a PKCS#10 PEM-encoded CSR.
func ParseCSR(csr []byte) (*x509.CertificateRequest, error) {
derBlock, _ := pem.Decode(csr)
if derBlock == nil || derBlock.Bytes == nil {
return nil, errors.New("no CSR found while decoding")
}
correctType := false
acceptedHeaders := []string{"CERTIFICATE REQUEST", "NEW CERTIFICATE REQUEST"}
for _, v := range acceptedHeaders {
if derBlock.Type == v {
correctType = true
}
}
if !correctType {
return nil, fmt.Errorf("DER type %v is not of any type %v for CSR", derBlock.Type, acceptedHeaders)
}
return x509.ParseCertificateRequest(derBlock.Bytes)
}
// GenerateSerialNumber creates a compliant serial number as per RFC 5280 4.1.2.2.
// Serial numbers must be positive, and can be no longer than 20 bytes.
// The serial number is generated with 159 bits, so that the first bit will always
// be 0, resulting in a positive serial number.
func GenerateSerialNumber() (*big.Int, error) {
// Pick a random number from 0 to 2^159.
serial, err := rand.Int(rand.Reader, (&big.Int{}).Exp(big.NewInt(2), big.NewInt(159), nil))
if err != nil {
return nil, errors.New("error generating serial number")
}
return serial, nil
}
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