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ca.go
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ca.go
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// Package ca provides easy to use certificate authority related functions.
// This is a lightweight wrapper around "crypto/x509" package for
// creating CA certs, client certs, signing requests, and more.
//
// Any "cert, key []byte" type of function parameters and return types are
// always PEM encoded X.509 certificate and private key pairs.
// You can store the certificate/key pair with standard naming as
// "cert.pem" and "key.pem" in the file system.
//
// This package is mostly based on the example code provided at:
// http://golang.org/src/crypto/tls/generate_cert.go
package ca
import (
"crypto/rand"
"crypto/rsa"
"crypto/tls"
"crypto/x509"
"crypto/x509/pkix"
"encoding/pem"
"errors"
"fmt"
"math/big"
"net"
"strings"
"time"
)
// CertChain is a ready to use certificate chain object, created by GenCertChain function.
// Byte slices are the PEM encoded X.509 certificate and private key pairs.
// ServerTLSConf/ClientTLSConf are tead to use tls.Config objects for a TLS server and client.
type CertChain struct {
RootCACert,
RootCAKey,
IntCACert,
IntCAKey,
ServerCert,
ServerKey,
ClientCert,
ClientKey []byte
ServerTLSConf,
ClientTLSConf *tls.Config
}
// GenCertChain generates an entire certificate chain with the following hierarchy:
// Root CA -> Intermediate CA -> Server Certificate & Client Certificate
//
// name = Certificate name. i.e. FooBar
// host = Comma-separated hostnames and IPs to generate the server certificate for. i.e. "localhost,127.0.0.1"
// hostName = Server host address. i.e. foobar.com
func GenCertChain(name, host, hostName string, validFor time.Duration, keyLength int) (c CertChain, err error) {
// create certificate chain
if c.RootCACert, c.RootCAKey, err = GenCACert(pkix.Name{
Organization: []string{name},
OrganizationalUnit: []string{name + " Certificate Authority"},
CommonName: name + " Root CA",
}, validFor, keyLength, nil, nil); err != nil {
err = fmt.Errorf("Failed to create root CA certificate: %v", err)
return
}
if c.IntCACert, c.IntCAKey, err = GenCACert(pkix.Name{
Organization: []string{name},
OrganizationalUnit: []string{name + " Intermediate Certificate Authority"},
CommonName: name + " Intermadiate CA",
}, validFor, keyLength, c.RootCACert, c.RootCAKey); err != nil {
err = fmt.Errorf("Failed to create intermediate CA certificate: %v", err)
return
}
if c.ServerCert, c.ServerKey, err = GenServerCert(pkix.Name{
Organization: []string{name},
CommonName: hostName,
}, host, validFor, keyLength, c.IntCACert, c.IntCAKey); err != nil {
err = fmt.Errorf("Failed to create server certificate: %v", err)
return
}
if c.ClientCert, c.ClientKey, err = GenClientCert(pkix.Name{
Organization: []string{name},
CommonName: name,
}, validFor, keyLength, c.IntCACert, c.IntCAKey); err != nil {
err = fmt.Errorf("Failed to create client certificate: %v", err)
return
}
// crate server tls.Config object
serverTLSCert, e := tls.X509KeyPair(c.ServerCert, c.ServerKey)
if e != nil {
err = fmt.Errorf("Failed to parse the newly created server certificate or the key: %v", e)
return
}
// parse leaf certificate to facilitate TLS client auth
sc, _ := pem.Decode(c.ServerCert)
if serverTLSCert.Leaf, err = x509.ParseCertificate(sc.Bytes); err != nil {
err = fmt.Errorf("Failed to parse the newly created server certificate: %v", err)
return
}
caCertPool := x509.NewCertPool()
if !caCertPool.AppendCertsFromPEM(c.IntCACert) {
err = errors.New("Failed to parse the newly created intermediate CA certificate.")
return
}
c.ServerTLSConf = &tls.Config{
Certificates: []tls.Certificate{serverTLSCert},
ClientCAs: caCertPool,
ClientAuth: tls.RequireAndVerifyClientCert,
}
// create client tls.Config object
clientTLSCert, e := tls.X509KeyPair(c.ClientCert, c.ClientKey)
if e != nil {
err = fmt.Errorf("Failed to parse the newly created client certificate or the key: %v", e)
return
}
// parse leaf certificate to facilitate TLS client auth
cc, _ := pem.Decode(c.ClientCert)
if clientTLSCert.Leaf, err = x509.ParseCertificate(cc.Bytes); err != nil {
err = fmt.Errorf("Failed to parse the newly created client certificate: %v", err)
return
}
c.ClientTLSConf = &tls.Config{
Certificates: []tls.Certificate{clientTLSCert},
RootCAs: caCertPool,
}
return
}
// GenCACert generates a CA certificate.
// If signingCert and signingKey are not provided, the certificate is created as a self-signed root CA.
// If signingCert and signingKey are provided, the certificate is created as an intermediate CA, signed with provided certificate.
// The generated certificate can only be used for signing other certificates and CRLs.
// The returned slices are the PEM encoded X.509 certificate and private key pair.
func GenCACert(subject pkix.Name, validFor time.Duration, keyLength int, signingCert, signingKey []byte) (cert, key []byte, err error) {
var (
sc, c *x509.Certificate
sk, k *rsa.PrivateKey
)
if c, k, err = createBaseCert(subject, validFor, keyLength); err != nil {
return
}
if signingCert == nil || signingKey == nil {
sc = c
sk = k
} else if sc, sk, err = parseCertAndKey(signingCert, signingKey); err != nil {
return
}
c.KeyUsage = x509.KeyUsageCertSign | x509.KeyUsageCRLSign
c.IsCA = true
cert, key, err = signAndEncodeCert(sc, sk, c, k)
return
}
// GenServerCert generates a hosting certificate for TLS servers.
// host = Comma-separated hostnames and IPs to generate a certificate for. i.e. "localhost,127.0.0.1"
// The returned slices are the PEM encoded X.509 certificate and private key pair.
func GenServerCert(subject pkix.Name, host string, validFor time.Duration, keyLength int, signingCert, signingKey []byte) (cert, key []byte, err error) {
var (
sc, c *x509.Certificate
sk, k *rsa.PrivateKey
)
if sc, sk, err = parseCertAndKey(signingCert, signingKey); err != nil {
return
}
if c, k, err = createBaseCert(subject, validFor, keyLength); err != nil {
return
}
c.KeyUsage = x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature
c.ExtKeyUsage = []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth, x509.ExtKeyUsageClientAuth}
c.IsCA = false
setHosts(host, c)
cert, key, err = signAndEncodeCert(sc, sk, c, k)
return
}
// GenClientCert generates a client certificate.
// The generated certificate will have its extended key usage set to 'client authentication' and will be ready for use in TLS client authentication.
// The returned slices are the PEM encoded X.509 certificate and private key pair.
func GenClientCert(subject pkix.Name, validFor time.Duration, keyLength int, signingCert, signingKey []byte) (cert, key []byte, err error) {
var (
sc, c *x509.Certificate
sk, k *rsa.PrivateKey
)
if sc, sk, err = parseCertAndKey(signingCert, signingKey); err != nil {
return
}
if c, k, err = createBaseCert(subject, validFor, keyLength); err != nil {
return
}
c.KeyUsage = x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature
c.ExtKeyUsage = []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth}
c.IsCA = false
cert, key, err = signAndEncodeCert(sc, sk, c, k)
return
}
// createBaseCert creates and returns x509.Certificate (unsigned) and rsa.PrivateKey objects with basic paramters set.
func createBaseCert(subject pkix.Name, validFor time.Duration, keyLength int) (*x509.Certificate, *rsa.PrivateKey, error) {
privKey, err := rsa.GenerateKey(rand.Reader, keyLength)
if err != nil {
return nil, nil, fmt.Errorf("failed to generate certificate private key using RSA: %v", err)
}
notBefore := time.Now()
notAfter := notBefore.Add(validFor)
serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
if err != nil {
return nil, nil, fmt.Errorf("failed to generate the certificate serial number: %v", err)
}
cert := x509.Certificate{
SerialNumber: serialNumber,
Subject: subject,
NotBefore: notBefore,
NotAfter: notAfter,
BasicConstraintsValid: true,
}
return &cert, privKey, nil
}
// setHosts parses the comma separated host name / IP list and adds them to Subject Alternate Name list of a server/hosting certificate.
func setHosts(host string, cert *x509.Certificate) {
hosts := strings.Split(host, ",")
for _, h := range hosts {
if ip := net.ParseIP(h); ip != nil {
cert.IPAddresses = append(cert.IPAddresses, ip)
} else {
cert.DNSNames = append(cert.DNSNames, h)
}
}
}
// Parses PEM encoded X.509 certificate and private key pair into x509.Certificate and rsa.PrivateKey objects.
func parseCertAndKey(cert, key []byte) (c *x509.Certificate, k *rsa.PrivateKey, err error) {
pc, _ := pem.Decode(cert)
if c, err = x509.ParseCertificate(pc.Bytes); err != nil {
err = fmt.Errorf("Failed to parse private key with error: %v", err)
return
}
pk, _ := pem.Decode(key)
if k, err = x509.ParsePKCS1PrivateKey(pk.Bytes); err != nil {
err = fmt.Errorf("Failed to parse certificate with error: %v", err)
return
}
return
}
// signAndEncodeCert signs a given certificate with given signing cert/key pair and encodes resulting signed cert and private key in PEM format and returns.
func signAndEncodeCert(signingCert *x509.Certificate, signingKey *rsa.PrivateKey, c *x509.Certificate, k *rsa.PrivateKey) (cert, key []byte, err error) {
certDerBytes, err := x509.CreateCertificate(rand.Reader, c, signingCert, &k.PublicKey, signingKey)
if err != nil {
return
}
cert = pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: certDerBytes})
key = pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(k)})
return
}