通過Go語言建立CA與簽發證書

Cylon發表於2022-07-01
Go

本篇文章中，將描述如何使用go建立CA，並使用CA簽署證書。在使用openssl建立證書時，遵循的步驟是 建立祕鑰 > 建立CA > 生成要頒發證書的祕鑰 > 使用CA簽發證書。這種步驟，那麼我們現在就來嘗試下。

建立證書的頒發機構

首先，會從將從建立 CA 開始。CA 會被用來簽署其他證書

// 對證書進行簽名
ca := &x509.Certificate{
	SerialNumber: big.NewInt(2019),
	Subject: pkix.Name{
        CommonName:    "domain name",
		Organization:  []string{"Company, INC."},
		Country:       []string{"US"},
		Province:      []string{""},
		Locality:      []string{"San Francisco"},
		StreetAddress: []string{"Golden Gate Bridge"},
		PostalCode:    []string{"94016"},
	},
	NotBefore:             time.Now(),  // 生效時間
	NotAfter:              time.Now().AddDate(10, 0, 0), // 過期時間 年月日
	IsCA:                  true, // 表示用於CA
    // openssl 中的 extendedKeyUsage = clientAuth, serverAuth 欄位
	ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth, x509.ExtKeyUsageServerAuth},
    // openssl 中的 keyUsage 欄位
	KeyUsage:              x509.KeyUsageDigitalSignature | x509.KeyUsageCertSign,
	BasicConstraintsValid: true,
}

接下來需要對證書生成公鑰和私鑰

caPrivKey, err := rsa.GenerateKey(rand.Reader, 4096)
if err != nil {
	return err
}

然後生成證書：

caBytes, err := x509.CreateCertificate(rand.Reader, ca, ca, &caPrivKey.PublicKey, caPrivKey)
if err != nil {
	return err
}

我們看到的證書內容是PEM編碼後的，現在caBytes我們有了生成的證書，我們將其進行 PEM 編碼以供以後使用：

caPEM := new(bytes.Buffer)
pem.Encode(caPEM, &pem.Block{
	Type:  "CERTIFICATE",
	Bytes: caBytes,
})

caPrivKeyPEM := new(bytes.Buffer)
pem.Encode(caPrivKeyPEM, &pem.Block{
	Type:  "RSA PRIVATE KEY",
	Bytes: x509.MarshalPKCS1PrivateKey(caPrivKey),
})

建立證書

證書的 x509.Certificate 與CA的 x509.Certificate 屬性有稍微不同，需要進行一些修改

cert := &x509.Certificate{
	SerialNumber: big.NewInt(1658),
	Subject: pkix.Name{
        CommonName:    "domain name",
		Organization:  []string{"Company, INC."},
		Country:       []string{"US"},
		Province:      []string{""},
		Locality:      []string{"San Francisco"},
		StreetAddress: []string{"Golden Gate Bridge"},
		PostalCode:    []string{"94016"},
	},
    IPAddresses:  []net.IP{}, // 這裡就是openssl配置檔案中 subjectAltName 裡的 IP:/IP=
    DNSNames:     []string{}, // 這裡就是openssl配置檔案中 subjectAltName 裡的 DNS:/DNS=
	NotBefore:    time.Now(),
	NotAfter:     time.Now().AddDate(10, 0, 0),
	SubjectKeyId: []byte{1, 2, 3, 4, 6},
    // 這裡就是openssl中的extendedKeyUsage 
	ExtKeyUsage:  []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth, x509.ExtKeyUsageServerAuth},
	KeyUsage:     x509.KeyUsageDigitalSignature,
}

注：這裡會在證書中特別新增了 DNS 和 IP （這個不是必須的），這個選項的增加代表的我們的證書可以支援多域名

為該證書建立私鑰和公鑰：

certPrivKey, err := rsa.GenerateKey(rand.Reader, 4096)
if err != nil {
	return err
}

使用CA簽署證書

有了上述的內容後，可以建立證書並用CA進行簽名

certBytes, err := x509.CreateCertificate(rand.Reader, cert, ca, &certPrivKey.PublicKey, caPrivKey)
if err != nil {
	return err
}

要儲存成證書格式需要做PEM編碼

certPEM := new(bytes.Buffer)
pem.Encode(certPEM, &pem.Block{
	Type:  "CERTIFICATE",
	Bytes: certBytes,
})

certPrivKeyPEM := new(bytes.Buffer)
pem.Encode(certPrivKeyPEM, &pem.Block{
	Type:  "RSA PRIVATE KEY",
	Bytes: x509.MarshalPKCS1PrivateKey(certPrivKey),
})

把上面內容融合為一起

建立一個 ca.go 裡面是建立ca和頒發證書的邏輯

package main

import (
	"bytes"
	cr "crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"math/big"
	"math/rand"
	"net"
	"os"
	"time"
)

type CERT struct {
	CERT       []byte
	CERTKEY    *rsa.PrivateKey
	CERTPEM    *bytes.Buffer
	CERTKEYPEM *bytes.Buffer
	CSR        *x509.Certificate
}

func CreateCA(sub *pkix.Name, expire int) (*CERT, error) {
	var (
		ca  = new(CERT)
		err error
	)

	if expire < 1 {
		expire = 1
	}
	// 為ca生成私鑰
	ca.CERTKEY, err = rsa.GenerateKey(cr.Reader, 4096)
	if err != nil {
		return nil, err
	}

	// 對證書進行簽名
	ca.CSR = &x509.Certificate{
		SerialNumber: big.NewInt(rand.Int63n(2000)),
		Subject:      *sub,
		NotBefore:    time.Now(),                       // 生效時間
		NotAfter:     time.Now().AddDate(expire, 0, 0), // 過期時間
		IsCA:         true,                             // 表示用於CA
		// openssl 中的 extendedKeyUsage = clientAuth, serverAuth 欄位
		ExtKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth, x509.ExtKeyUsageServerAuth},
		// openssl 中的 keyUsage 欄位
		KeyUsage:              x509.KeyUsageDigitalSignature | x509.KeyUsageCertSign,
		BasicConstraintsValid: true,
	}
	// 建立證書
	// caBytes 就是生成的證書
	ca.CERT, err = x509.CreateCertificate(cr.Reader, ca.CSR, ca.CSR, &ca.CERTKEY.PublicKey, ca.CERTKEY)
	if err != nil {
		return nil, err
	}
	ca.CERTPEM = new(bytes.Buffer)
	pem.Encode(ca.CERTPEM, &pem.Block{
		Type:  "CERTIFICATE",
		Bytes: ca.CERT,
	})
	ca.CERTKEYPEM = new(bytes.Buffer)
	pem.Encode(ca.CERTKEYPEM, &pem.Block{
		Type:  "RSA PRIVATE KEY",
		Bytes: x509.MarshalPKCS1PrivateKey(ca.CERTKEY),
	})

	// 進行PEM編碼，編碼就是直接cat證書裡面內容顯示的東西
	return ca, nil
}

func Req(ca *x509.Certificate, sub *pkix.Name, expire int, dns []string, ip []net.IP) (*CERT, error) {
	var (
		cert = &CERT{}
		err  error
	)
	cert.CERTKEY, err = rsa.GenerateKey(cr.Reader, 4096)
	if err != nil {
		return nil, err
	}
	if expire < 1 {
		expire = 1
	}
	cert.CSR = &x509.Certificate{
		SerialNumber: big.NewInt(rand.Int63n(2000)),
		Subject:      *sub,
		IPAddresses:  ip,
		DNSNames:     dns,
		NotBefore:    time.Now(),
		NotAfter:     time.Now().AddDate(expire, 0, 0),
		SubjectKeyId: []byte{1, 2, 3, 4, 6},
		ExtKeyUsage:  []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth, x509.ExtKeyUsageServerAuth},
		KeyUsage:     x509.KeyUsageDigitalSignature,
	}

	cert.CERT, err = x509.CreateCertificate(cr.Reader, cert.CSR, ca, &cert.CERTKEY.PublicKey, cert.CERTKEY)
	if err != nil {
		return nil, err
	}

	cert.CERTPEM = new(bytes.Buffer)
	pem.Encode(cert.CERTPEM, &pem.Block{
		Type:  "CERTIFICATE",
		Bytes: cert.CERT,
	})
	cert.CERTKEYPEM = new(bytes.Buffer)
	pem.Encode(cert.CERTKEYPEM, &pem.Block{
		Type:  "RSA PRIVATE KEY",
		Bytes: x509.MarshalPKCS1PrivateKey(cert.CERTKEY),
	})
	return cert, nil
}

func Write(cert *CERT, file string) error {
	keyFileName := file + ".key"
	certFIleName := file + ".crt"
	kf, err := os.Create(keyFileName)
	if err != nil {
		return err
	}
	defer kf.Close()

	if _, err := kf.Write(cert.CERTKEYPEM.Bytes()); err != nil {
		return err
	}

	cf, err := os.Create(certFIleName)
	if err != nil {
		return err
	}
	if _, err := cf.Write(cert.CERTPEM.Bytes()); err != nil {
		return err
	}
	return nil
}

如果需要使用的話，可以引用這些函式

package main

import (
	"crypto/x509/pkix"
	"log"
	"net"
)

func main() {
	subj := &pkix.Name{
		CommonName:    "chinamobile.com",
		Organization:  []string{"Company, INC."},
		Country:       []string{"US"},
		Province:      []string{""},
		Locality:      []string{"San Francisco"},
		StreetAddress: []string{"Golden Gate Bridge"},
		PostalCode:    []string{"94016"},
	}
	ca, err := CreateCA(subj, 10)
	if err != nil {
		log.Panic(err)
	}

	Write(ca, "./ca")

	crt, err := Req(ca.CSR, subj, 10, []string{"test.default.svc", "test"}, []net.IP{})

	if err != nil {
		log.Panic(err)
	}

	Write(crt, "./tls")
}

遇到的問題

panic: x509: unsupported public key type: rsa.PublicKey

這裡是因為 x509.CreateCertificate 的引數 privatekey 需要傳入引用變數，而傳入的是一個普通變數

注：x509: only RSA and ECDSA public keys supported

一些引數的意思

extendedKeyUsage ：增強型金鑰用法(參見"new_oids"欄位)：伺服器身份驗證、客戶端身份驗證、時間戳。

extendedKeyUsage = critical,serverAuth, clientAuth, timeStamping

keyUsage ： 金鑰用法，防否認(nonRepudiation)、數字簽名(digitalSignature)、金鑰加密(keyEncipherment)。

keyUsage = nonRepudiation, digitalSignature, keyEncipherment

Reference

golang ca and signed cert go

package x509

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