cert.go

/*
Copyright 2014 The Kubernetes 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 cert

import (
	"bytes"
	"crypto"
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	cryptorand "crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"errors"
	"fmt"
	"math"
	"math/big"
	"net"
	"os"
	"path"
	"strings"
	"time"
)

const (
	rsaKeySize   = 2048
	duration365d = time.Hour * 24 * 365
)

// Config contains the basic fields required for creating a certificate
type Config struct {
	CommonName   string
	Organization []string
	AltNames     AltNames
	Usages       []x509.ExtKeyUsage
	Duration     time.Duration
}

func (cfg Config) GetDuration() time.Duration {
	if cfg.Duration > 0 {
		return cfg.Duration
	}
	return duration365d
}

// AltNames contains the domain names and IP addresses that will be added
// to the API Server's x509 certificate SubAltNames field. The values will
// be passed directly to the x509.Certificate object.
type AltNames struct {
	DNSNames []string
	IPs      []net.IP
}

// NewPrivateKey creates an RSA private key
func NewPrivateKey() (*rsa.PrivateKey, error) {
	return rsa.GenerateKey(cryptorand.Reader, rsaKeySize)
}

// NewSelfSignedCACert creates a CA certificate
func NewSelfSignedCACert(cfg Config, key crypto.Signer) (*x509.Certificate, error) {
	now := time.Now()
	tmpl := x509.Certificate{
		SerialNumber: new(big.Int).SetInt64(0),
		Subject: pkix.Name{
			CommonName:   cfg.CommonName,
			Organization: cfg.Organization,
		},
		NotBefore:             now.UTC(),
		NotAfter:              now.Add(cfg.GetDuration() * 10).UTC(),
		KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature | x509.KeyUsageCertSign,
		BasicConstraintsValid: true,
		IsCA:                  true,
	}

	certDERBytes, err := x509.CreateCertificate(cryptorand.Reader, &tmpl, &tmpl, key.Public(), key)
	if err != nil {
		return nil, err
	}
	return x509.ParseCertificate(certDERBytes)
}

// NewSignedCert creates a signed certificate using the given CA certificate and key
func NewSignedCert(cfg Config, key crypto.Signer, caCert *x509.Certificate, caKey crypto.Signer) (*x509.Certificate, error) {
	serial, err := rand.Int(rand.Reader, new(big.Int).SetInt64(math.MaxInt64))
	if err != nil {
		return nil, err
	}
	if len(cfg.CommonName) == 0 {
		return nil, errors.New("must specify a CommonName")
	}
	if len(cfg.Usages) == 0 {
		return nil, errors.New("must specify at least one ExtKeyUsage")
	}

	certTmpl := x509.Certificate{
		Subject: pkix.Name{
			CommonName:   cfg.CommonName,
			Organization: cfg.Organization,
		},
		DNSNames:     cfg.AltNames.DNSNames,
		IPAddresses:  cfg.AltNames.IPs,
		SerialNumber: serial,
		NotBefore:    caCert.NotBefore,
		NotAfter:     time.Now().Add(cfg.GetDuration()).UTC(),
		KeyUsage:     x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
		ExtKeyUsage:  cfg.Usages,
	}
	certDERBytes, err := x509.CreateCertificate(cryptorand.Reader, &certTmpl, caCert, key.Public(), caKey)
	if err != nil {
		return nil, err
	}
	return x509.ParseCertificate(certDERBytes)
}

// MakeEllipticPrivateKeyPEM creates an ECDSA private key
func MakeEllipticPrivateKeyPEM() ([]byte, error) {
	privateKey, err := ecdsa.GenerateKey(elliptic.P256(), cryptorand.Reader)
	if err != nil {
		return nil, err
	}

	derBytes, err := x509.MarshalECPrivateKey(privateKey)
	if err != nil {
		return nil, err
	}

	privateKeyPemBlock := &pem.Block{
		Type:  ECPrivateKeyBlockType,
		Bytes: derBytes,
	}
	return pem.EncodeToMemory(privateKeyPemBlock), nil
}

// GenerateSelfSignedCertKey creates a self-signed certificate and key for the given host.
// Host may be an IP or a DNS name
// You may also specify additional subject alt names (either ip or dns names) for the certificate.
func GenerateSelfSignedCertKey(host string, alternateIPs []net.IP, alternateDNS []string) ([]byte, []byte, error) {
	return GenerateSelfSignedCertKeyWithFixtures(host, alternateIPs, alternateDNS, "")
}

// GenerateSelfSignedCertKeyWithFixtures creates a self-signed certificate and key for the given host.
// Host may be an IP or a DNS name. You may also specify additional subject alt names (either ip or dns names)
// for the certificate.
//
// If fixtureDirectory is non-empty, it is a directory path which can contain pre-generated certs. The format is:
// <host>_<ip>-<ip>_<alternateDNS>-<alternateDNS>.crt
// <host>_<ip>-<ip>_<alternateDNS>-<alternateDNS>.key
// Certs/keys not existing in that directory are created.
func GenerateSelfSignedCertKeyWithFixtures(host string, alternateIPs []net.IP, alternateDNS []string, fixtureDirectory string) ([]byte, []byte, error) {
	validFrom := time.Now().Add(-time.Hour) // valid an hour earlier to avoid flakes due to clock skew
	maxAge := time.Hour * 24 * 365          // one year self-signed certs

	baseName := fmt.Sprintf("%s_%s_%s", host, strings.Join(ipsToStrings(alternateIPs), "-"), strings.Join(alternateDNS, "-"))
	certFixturePath := path.Join(fixtureDirectory, baseName+".crt")
	keyFixturePath := path.Join(fixtureDirectory, baseName+".key")
	if len(fixtureDirectory) > 0 {
		cert, err := os.ReadFile(certFixturePath)
		if err == nil {
			key, err := os.ReadFile(keyFixturePath)
			if err == nil {
				return cert, key, nil
			}
			return nil, nil, fmt.Errorf("cert %s can be read, but key %s cannot: %v", certFixturePath, keyFixturePath, err)
		}
		maxAge = 100 * time.Hour * 24 * 365 // 100 years fixtures
	}

	caKey, err := rsa.GenerateKey(cryptorand.Reader, 2048)
	if err != nil {
		return nil, nil, err
	}

	caTemplate := x509.Certificate{
		SerialNumber: big.NewInt(1),
		Subject: pkix.Name{
			CommonName: fmt.Sprintf("%s-ca@%d", host, time.Now().Unix()),
		},
		NotBefore: validFrom,
		NotAfter:  validFrom.Add(maxAge),

		KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature | x509.KeyUsageCertSign,
		BasicConstraintsValid: true,
		IsCA:                  true,
	}

	caDERBytes, err := x509.CreateCertificate(cryptorand.Reader, &caTemplate, &caTemplate, &caKey.PublicKey, caKey)
	if err != nil {
		return nil, nil, err
	}

	caCertificate, err := x509.ParseCertificate(caDERBytes)
	if err != nil {
		return nil, nil, err
	}

	priv, err := rsa.GenerateKey(cryptorand.Reader, 2048)
	if err != nil {
		return nil, nil, err
	}

	template := x509.Certificate{
		SerialNumber: big.NewInt(2),
		Subject: pkix.Name{
			CommonName: fmt.Sprintf("%s@%d", host, time.Now().Unix()),
		},
		NotBefore: validFrom,
		NotAfter:  validFrom.Add(maxAge),

		KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
		BasicConstraintsValid: true,
	}

	if ip := net.ParseIP(host); ip != nil {
		template.IPAddresses = append(template.IPAddresses, ip)
	} else {
		template.DNSNames = append(template.DNSNames, host)
	}

	template.IPAddresses = append(template.IPAddresses, alternateIPs...)
	template.DNSNames = append(template.DNSNames, alternateDNS...)

	derBytes, err := x509.CreateCertificate(cryptorand.Reader, &template, caCertificate, &priv.PublicKey, caKey)
	if err != nil {
		return nil, nil, err
	}

	// Generate cert, followed by ca
	certBuffer := bytes.Buffer{}
	if err := pem.Encode(&certBuffer, &pem.Block{Type: CertificateBlockType, Bytes: derBytes}); err != nil {
		return nil, nil, err
	}
	if err := pem.Encode(&certBuffer, &pem.Block{Type: CertificateBlockType, Bytes: caDERBytes}); err != nil {
		return nil, nil, err
	}

	// Generate key
	keyBuffer := bytes.Buffer{}
	if err := pem.Encode(&keyBuffer, &pem.Block{Type: RSAPrivateKeyBlockType, Bytes: x509.MarshalPKCS1PrivateKey(priv)}); err != nil {
		return nil, nil, err
	}

	if len(fixtureDirectory) > 0 {
		if err := os.WriteFile(certFixturePath, certBuffer.Bytes(), 0644); err != nil {
			return nil, nil, fmt.Errorf("failed to write cert fixture to %s: %v", certFixturePath, err)
		}
		if err := os.WriteFile(keyFixturePath, keyBuffer.Bytes(), 0644); err != nil {
			return nil, nil, fmt.Errorf("failed to write key fixture to %s: %v", certFixturePath, err)
		}
	}

	return certBuffer.Bytes(), keyBuffer.Bytes(), nil
}

// FormatBytesCert receives byte array certificate and formats in human-readable format
func FormatBytesCert(cert []byte) (string, error) {
	block, _ := pem.Decode(cert)
	c, err := x509.ParseCertificate(block.Bytes)
	if err != nil {
		return "", fmt.Errorf("failed to parse certificate [%v]", err)
	}
	return FormatCert(c), nil
}

// FormatCert receives certificate and formats in human-readable format
func FormatCert(c *x509.Certificate) string {
	var ips []string
	for _, ip := range c.IPAddresses {
		ips = append(ips, ip.String())
	}
	altNames := append(ips, c.DNSNames...)
	res := fmt.Sprintf(
		"Issuer: CN=%s | Subject: CN=%s | CA: %t\n",
		c.Issuer.CommonName, c.Subject.CommonName, c.IsCA,
	)
	res += fmt.Sprintf("Not before: %s Not After: %s", c.NotBefore, c.NotAfter)
	if len(altNames) > 0 {
		res += fmt.Sprintf("\nAlternate Names: %v", altNames)
	}
	return res
}

func ipsToStrings(ips []net.IP) []string {
	ss := make([]string, 0, len(ips))
	for _, ip := range ips {
		ss = append(ss, ip.String())
	}
	return ss
}