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Generate SSH RSA Private/Public Key pair with Golang
// This shows an example of how to generate a SSH RSA Private/Public key pair and save it locally
package main
import (
"crypto/rand"
"crypto/rsa"
"crypto/x509"
"encoding/pem"
"golang.org/x/crypto/ssh"
"io/ioutil"
"log"
)
func main() {
savePrivateFileTo := "./id_rsa_test"
savePublicFileTo := "./id_rsa_test.pub"
bitSize := 4096
privateKey, err := generatePrivateKey(bitSize)
if err != nil {
log.Fatal(err.Error())
}
publicKeyBytes, err := generatePublicKey(&privateKey.PublicKey)
if err != nil {
log.Fatal(err.Error())
}
privateKeyBytes := encodePrivateKeyToPEM(privateKey)
err = writeKeyToFile(privateKeyBytes, savePrivateFileTo)
if err != nil {
log.Fatal(err.Error())
}
err = writeKeyToFile([]byte(publicKeyBytes), savePublicFileTo)
if err != nil {
log.Fatal(err.Error())
}
}
// generatePrivateKey creates a RSA Private Key of specified byte size
func generatePrivateKey(bitSize int) (*rsa.PrivateKey, error) {
// Private Key generation
privateKey, err := rsa.GenerateKey(rand.Reader, bitSize)
if err != nil {
return nil, err
}
// Validate Private Key
err = privateKey.Validate()
if err != nil {
return nil, err
}
log.Println("Private Key generated")
return privateKey, nil
}
// encodePrivateKeyToPEM encodes Private Key from RSA to PEM format
func encodePrivateKeyToPEM(privateKey *rsa.PrivateKey) []byte {
// Get ASN.1 DER format
privDER := x509.MarshalPKCS1PrivateKey(privateKey)
// pem.Block
privBlock := pem.Block{
Type: "RSA PRIVATE KEY",
Headers: nil,
Bytes: privDER,
}
// Private key in PEM format
privatePEM := pem.EncodeToMemory(&privBlock)
return privatePEM
}
// generatePublicKey take a rsa.PublicKey and return bytes suitable for writing to .pub file
// returns in the format "ssh-rsa ..."
func generatePublicKey(privatekey *rsa.PublicKey) ([]byte, error) {
publicRsaKey, err := ssh.NewPublicKey(privatekey)
if err != nil {
return nil, err
}
pubKeyBytes := ssh.MarshalAuthorizedKey(publicRsaKey)
log.Println("Public key generated")
return pubKeyBytes, nil
}
// writePemToFile writes keys to a file
func writeKeyToFile(keyBytes []byte, saveFileTo string) error {
err := ioutil.WriteFile(saveFileTo, keyBytes, 0600)
if err != nil {
return err
}
log.Printf("Key saved to: %s", saveFileTo)
return nil
}
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