Golang RSA Key Generation

keys.go

/*
 * Genarate rsa keys.
 */

package main

import (
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"encoding/asn1"
	"encoding/gob"
	"encoding/pem"
	"fmt"
	"os"
)

func main() {
	reader := rand.Reader
	bitSize := 2048

	key, err := rsa.GenerateKey(reader, bitSize)
	checkError(err)

	publicKey := key.PublicKey

	saveGobKey("private.key", key)
	savePEMKey("private.pem", key)

	saveGobKey("public.key", publicKey)
	savePublicPEMKey("public.pem", publicKey)
}

func saveGobKey(fileName string, key interface{}) {
	outFile, err := os.Create(fileName)
	checkError(err)
	defer outFile.Close()

	encoder := gob.NewEncoder(outFile)
	err = encoder.Encode(key)
	checkError(err)
}

func savePEMKey(fileName string, key *rsa.PrivateKey) {
	outFile, err := os.Create(fileName)
	checkError(err)
	defer outFile.Close()

	var privateKey = &pem.Block{
		Type:  "PRIVATE KEY",
		Bytes: x509.MarshalPKCS1PrivateKey(key),
	}

	err = pem.Encode(outFile, privateKey)
	checkError(err)
}

func savePublicPEMKey(fileName string, pubkey rsa.PublicKey) {
	asn1Bytes, err := asn1.Marshal(pubkey)
	checkError(err)

	var pemkey = &pem.Block{
		Type:  "PUBLIC KEY",
		Bytes: asn1Bytes,
	}

	pemfile, err := os.Create(fileName)
	checkError(err)
	defer pemfile.Close()

	err = pem.Encode(pemfile, pemkey)
	checkError(err)
}

func checkError(err error) {
	if err != nil {
		fmt.Println("Fatal error ", err.Error())
		os.Exit(1)
	}
}

Nice, but fails when using the generated public key to verify jwt token with https://github.com/dgrijalva/jwt-go. @xeoncross comment fixes the error.

@sdorra Why does the code example generate same private and public key while the code is executing one more time ?

@muratsplat If you run it on play.golang.org it will always produce the same result. If you don't check the errors you might find that O_CREATE fails on the second run because the file already exists.

Sorry I forgot the test result is cached on the test. That reason make to show same result. You are right.

@xeoncross thanks for feedback..

Amazing! This and the comments saved me a bunch of time implementing this, especially @ugokoli's comment about jwt-go

For PKCS#1 Formatting, the lable should be starts with RSA PRIVATE KEY instead of PRIVATE KEY. Nice code snippets 😃

var privateKey = &pem.Block{
    Type:  "RSA PRIVATE KEY",
    Bytes: x509.MarshalPKCS1PrivateKey(key),
}

yo man, after a single look at your code i felt like it's really beatiful and ... i love u bruh thx for that implementation!

You can also replace asn1Bytes, err := asn1.Marshal(pubkey) with asn1Bytes, err := x509.MarshalPKIXPublicKey(&pubkey) if you want DER-encoded PKIX format.

Thanks a lot