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@shaneutt
Last active April 14, 2024 00:52
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Golang: Demonstrate creating a CA Certificate, and Creating and Signing Certs with the CA
package main
import (
"bytes"
"crypto/rand"
"crypto/rsa"
"crypto/tls"
"crypto/x509"
"crypto/x509/pkix"
"encoding/pem"
"fmt"
"io/ioutil"
"math/big"
"net"
"net/http"
"net/http/httptest"
"strings"
"time"
)
func main() {
// get our ca and server certificate
serverTLSConf, clientTLSConf, err := certsetup()
if err != nil {
panic(err)
}
// set up the httptest.Server using our certificate signed by our CA
server := httptest.NewUnstartedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
fmt.Fprintln(w, "success!")
}))
server.TLS = serverTLSConf
server.StartTLS()
defer server.Close()
// communicate with the server using an http.Client configured to trust our CA
transport := &http.Transport{
TLSClientConfig: clientTLSConf,
}
http := http.Client{
Transport: transport,
}
resp, err := http.Get(server.URL)
if err != nil {
panic(err)
}
// verify the response
respBodyBytes, err := ioutil.ReadAll(resp.Body)
if err != nil {
panic(err)
}
body := strings.TrimSpace(string(respBodyBytes[:]))
if body == "success!" {
fmt.Println(body)
} else {
panic("not successful!")
}
}
func certsetup() (serverTLSConf *tls.Config, clientTLSConf *tls.Config, err error) {
// set up our CA certificate
ca := &x509.Certificate{
SerialNumber: big.NewInt(2019),
Subject: pkix.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(),
NotAfter: time.Now().AddDate(10, 0, 0),
IsCA: true,
ExtKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth, x509.ExtKeyUsageServerAuth},
KeyUsage: x509.KeyUsageDigitalSignature | x509.KeyUsageCertSign,
BasicConstraintsValid: true,
}
// create our private and public key
caPrivKey, err := rsa.GenerateKey(rand.Reader, 4096)
if err != nil {
return nil, nil, err
}
// create the CA
caBytes, err := x509.CreateCertificate(rand.Reader, ca, ca, &caPrivKey.PublicKey, caPrivKey)
if err != nil {
return nil, nil, err
}
// pem encode
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),
})
// set up our server certificate
cert := &x509.Certificate{
SerialNumber: big.NewInt(2019),
Subject: pkix.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{net.IPv4(127, 0, 0, 1), net.IPv6loopback},
NotBefore: time.Now(),
NotAfter: time.Now().AddDate(10, 0, 0),
SubjectKeyId: []byte{1, 2, 3, 4, 6},
ExtKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth, x509.ExtKeyUsageServerAuth},
KeyUsage: x509.KeyUsageDigitalSignature,
}
certPrivKey, err := rsa.GenerateKey(rand.Reader, 4096)
if err != nil {
return nil, nil, err
}
certBytes, err := x509.CreateCertificate(rand.Reader, cert, ca, &certPrivKey.PublicKey, caPrivKey)
if err != nil {
return nil, nil, err
}
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),
})
serverCert, err := tls.X509KeyPair(certPEM.Bytes(), certPrivKeyPEM.Bytes())
if err != nil {
return nil, nil, err
}
serverTLSConf = &tls.Config{
Certificates: []tls.Certificate{serverCert},
}
certpool := x509.NewCertPool()
certpool.AppendCertsFromPEM(caPEM.Bytes())
clientTLSConf = &tls.Config{
RootCAs: certpool,
}
return
}
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In jurisdictions that recognize copyright laws, the author or authors
of this software dedicate any and all copyright interest in the
software to the public domain. We make this dedication for the benefit
of the public at large and to the detriment of our heirs and
successors. We intend this dedication to be an overt act of
relinquishment in perpetuity of all present and future rights to this
software under copyright law.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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@yakuter
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yakuter commented Feb 16, 2022

Yeah I got it. Thanks for the explanation @shaneutt

@Ran-Xing
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Ran-Xing commented Feb 26, 2022

h := "127.0.0.1"
certificate := &x509.Certificate{
	Subject: pkix.Name{
		CommonName:   commonName,
	},
+	IPAddresses: []net.IP{net.ParseIP(h)},
}
if net.ParseIP(h) != nil {
-	certificate.IPAddresses = []net.IP{net.ParseIP(h)}
}

I found many cases in the gist and found that IPAddresses cannot be added @ certificate.IPAddresses = []net.IP{net.ParseIP(h)}
Do you know why this is? @shaneutt

@shaneutt
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Author

@XRSec not sure if I'm understanding the problem: using net.ParseIP("127.0.0.1") should be equivalent to the example I provided above that uses net.IPv4(127, 0, 0, 1), e.g.:

gore> :import net
gore> :import reflect
gore> a := net.ParseIP("127.0.0.1")
net.IP{
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0x7f, 0x00, 0x00, 0x01,
}
gore> b := net.IPv4(127,0,0,1)
net.IP{
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0x7f, 0x00, 0x00, 0x01,
}
gore> reflect.DeepEqual(a,b)
true

What are you seeing that suggests to you that it can't be added, are you receiving some kind of error?

For some simple testing you can manually verify whether the IP address you add to an x509 certificate in Go is included in the SAN using the openssl command line. For instance I ran the following by connecting to the httptest server using the exact code from above:

$ openssl s_client -connect localhost:39781 | openssl x509 -noout -text |grep -B 1 'IP Address'
            X509v3 Subject Alternative Name: 
                IP Address:127.0.0.1, IP Address:0:0:0:0:0:0:0:1

@dipankardas011
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dipankardas011 commented Dec 16, 2023

Thanks @shaneutt for this blog. it is helping me to automate certificate generation to be used for etcd cluster for my project ksctl 😄

@albertjin
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This code helps a lot! Note that Safari may reject a certificate filled NotBefore as time.Now() displaying that "xxx certificate is not standards compliant". Changing it to time.Now().Add(-1 * time.Hour) solves the problem.

@aceeric
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aceeric commented Mar 9, 2024

hey @shaneutt thank you for this - I was able to use it to build unit tests: https://github.com/aceeric/ociregistry/blob/main/impl/upstream/queue_test.go - thanks!

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