code/unchat/crypt-unchat.go

package unchat

import (
	"crypto/rand"
	"crypto/rsa"
	"crypto/sha256"
	"crypto/x509"
	"encoding/pem"
	"fmt"
	"log"
)

func main() {
	key_pk, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		log.Fatalf("could not generate keypair %s", err)
	}

	pub_key := &key_pk.PublicKey

	msg := []byte("this is a new message to be encrypted")
	label := []byte("")
	hash := sha256.New()

	cipher_text, err := rsa.EncryptOAEP(
		hash,
		rand.Reader,
		pub_key,
		msg,
		label)

	if err != nil {
		log.Fatalf("could not encrypt message %s", err)
	}

	fmt.Printf("message encrypted: \n%x\n", cipher_text)

	plain_text, err := rsa.DecryptOAEP(
		hash,
		rand.Reader,
		key_pk,
		cipher_text,
		label)
	if err != nil {
		log.Fatalf("could not decrypt message %s", err)
	}
	fmt.Printf("message decrypted: \n%s\n", plain_text)

	pem := ExportPrivKeyAsPEM(key_pk)
	fmt.Printf("PEM Priv Key \n%s\n", pem)

	ParsePrivKeyFromPEM(pem)

}

func ExportPrivKeyAsPEM(privKey *rsa.PrivateKey) string {
	privkey_bytes := x509.MarshalPKCS1PrivateKey(privKey)
	privkey_pem := pem.EncodeToMemory(
		&pem.Block{
			Type:  "RSA PRIVATE KEY",
			Bytes: privkey_bytes,
		},
	)
	return string(privkey_pem)
}

func ParsePrivKeyFromPEM(pemKey string) (*rsa.PrivateKey, error) {
	block, _ := pem.Decode([]byte(pemKey))
	if block == nil {
		return nil, fmt.Errorf("could not read pem string")
	}
	priv, err := x509.ParsePKCS1PrivateKey(block.Bytes)
	if err != nil {
		return nil, err
	}
	return priv, nil
}