go-cert-gen/internal/cert/cert.go

package cert

import (
	"bytes"
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"fmt"
	"log"
	"time"

	"gitlab.com/urkob/go-cert-gen/pkg/ca"

	"gitlab.com/urkob/go-cert-gen/pkg/client"
)

// Creates a new 512bit private key.
func newPrivateKey() (*ecdsa.PrivateKey, error) {
	priv, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		return nil, fmt.Errorf("ecdsa: %s", err)
	}

	return priv, nil
}

// Parse a text PEM file into a x509 cert.
func parseCertificate(data []byte) (*x509.Certificate, error) {
	block, _ := pem.Decode(data)
	if block == nil {
		return nil, fmt.Errorf("parseCertificate (pem.Decode)")
	}
	cert, err := x509.ParseCertificate(block.Bytes)
	if err != nil {
		return nil, fmt.Errorf("parseCertificate: %w", err)
	}
	return cert, nil
}

// Encodes a private key into PEM.
func encodePrivateKey(priv *ecdsa.PrivateKey) ([]byte, error) {
	out := &bytes.Buffer{}
	privBytes, err := x509.MarshalPKCS8PrivateKey(priv)
	if err != nil {
		return nil, fmt.Errorf("marshal: %s", err)
	}
	err = pem.Encode(out, &pem.Block{
		Type:  "PRIVATE KEY",
		Bytes: privBytes,
	})
	return out.Bytes(), err
}

// Create a self-signed certificate.
func newRootCA(config *ca.CaConfig) ([]byte, []byte, error) {
	priv, err := newPrivateKey()
	if err != nil {
		return nil, nil, fmt.Errorf("newPrivateKey: %s", err)
	}

	template := x509.Certificate{
		SerialNumber: config.SerialNumber,
		Subject: pkix.Name{
			Organization: []string{config.Subject.Organization},
			CommonName:   config.Subject.CommonName,
		},
		NotBefore:             time.Now().Add(-time.Minute),
		NotAfter:              time.Now().Add(config.Duration),
		IsCA:                  true,
		KeyUsage:              config.KeyUsage,
		ExtKeyUsage:           config.ExtKeyUsage,
		BasicConstraintsValid: true,
	}
	der, err := x509.CreateCertificate(rand.Reader, &template, &template, &priv.PublicKey, priv)
	if err != nil {
		return nil, nil, fmt.Errorf("x509.CreateCertificate: %s", err)
	}

	out := &bytes.Buffer{}
	err = pem.Encode(out, &pem.Block{Type: "CERTIFICATE", Bytes: der})
	if err != nil {
		return nil, nil, fmt.Errorf("pem.Encode: %s", err)
	}

	caPEM := out.Bytes()
	keyPEM, err := encodePrivateKey(priv)
	if err != nil {
		return nil, nil, fmt.Errorf("encodePrivateKey: %s", err)
	}

	return caPEM, keyPEM, nil
}

func newClientCert(config *client.ClientCertConfig, rootCA *x509.Certificate, rootKeyPEM []byte) ([]byte, []byte, error) {
	template := &x509.Certificate{
		SerialNumber: config.Serial,
		Subject: pkix.Name{
			Organization:  []string{config.Subject.Organization},
			Country:       []string{config.Subject.Country},
			Province:      []string{config.Subject.Province},
			Locality:      []string{config.Subject.Locality},
			StreetAddress: []string{config.Subject.StreetAddress},
			PostalCode:    []string{config.Subject.PostalCode},
		},
		NotBefore:    time.Now(),
		NotAfter:     time.Now().Add(config.Duration),
		SubjectKeyId: config.SubjectKeyId,
		ExtKeyUsage:  config.ExtKeyUsage,
		KeyUsage:     config.KeyUsage,
	}

	block, _ := pem.Decode(rootKeyPEM)
	caPrivKey, err := x509.ParsePKCS8PrivateKey(block.Bytes)
	if err != nil {
		log.Fatalf("x509.ParsePKCS8PrivateKey: %s", err)
	}

	priv, err := newPrivateKey()
	if err != nil {
		return nil, nil, fmt.Errorf("newPrivateKey: %s", err)
	}

	der, err := x509.CreateCertificate(rand.Reader, template, rootCA, &priv.PublicKey, caPrivKey)
	if err != nil {
		return nil, nil, fmt.Errorf("x509.CreateCertificate: %s", err)
	}

	out := &bytes.Buffer{}
	err = pem.Encode(out, &pem.Block{Type: "CERTIFICATE", Bytes: der})
	if err != nil {
		return nil, nil, fmt.Errorf("pem.Encode: %s", err)
	}

	certPEM := out.Bytes()
	keyPEM, err := encodePrivateKey(priv)
	if err != nil {
		return nil, nil, fmt.Errorf("encodePrivateKey: %s", err)
	}

	return certPEM, keyPEM, nil
}

type rootCA struct {
	caPEM  []byte
	keyPEM []byte
}

type clientCert struct {
	certPEM []byte
	keyPEM  []byte
}

func (c *clientCert) Key() []byte {
	return c.keyPEM
}

func (c *clientCert) PEM() []byte {
	return c.certPEM
}

func (r *rootCA) WithClientCert(config *client.ClientCertConfig) (client.ClientCertIface, error) {
	x509RootCA, err := parseCertificate(r.caPEM)
	if err != nil {
		return nil, fmt.Errorf("parseCertificate: %s", err)
	}

	clientCertPEM, clientKeyPEM, err := newClientCert(config, x509RootCA, r.keyPEM)
	if err != nil {
		return nil, fmt.Errorf("newClientCert: %s", err)
	}

	return &clientCert{
		certPEM: clientCertPEM,
		keyPEM:  clientKeyPEM,
	}, nil
}

func (r *rootCA) Key() []byte {
	return r.keyPEM
}

func (r *rootCA) PEM() []byte {
	return r.caPEM
}

func NewRootCA(config *ca.CaConfig) (ca.RootCACertificateIface, error) {
	caPEM, keyPEM, err := newRootCA(config)
	if err != nil {
		return nil, fmt.Errorf("newRootCA: %s", err)
	}

	return &rootCA{
		caPEM:  caPEM,
		keyPEM: keyPEM,
	}, nil
}