Encrypt the message with the key - go

Question

I need to use a public key to encrypt the message "Message" and save it as a file ciphertext.txt by converting pre-received data in HEX encoding. I do not need the public key to be generated, I already have a ready-made public key. Using this public key, you need to encrypt the message.
Here's what I was able to do:
package main
import (
"crypto/rand"
"crypto/rsa"
"crypto/sha256"
"crypto/x509"
"encoding/pem"
"errors"
"log"
"os"
)
func main() {
publicKeyBytes, err := os.ReadFile("publicik.key")
if err!= nil {
return
}
publicKey, err := decodepublicKey(publicKeyBytes)
if err != nil {
return
}
plaintext := []byte("Message")
ciphertext, err := rsa.EncryptOAEP(sha256.New(), rand.Reader, publicKey, plaintext, nil)
if err != nil {
return
}
log.Printf( "%x", ciphertext)
privateKeyBytes, err := os.ReadFile("private.key")
if err != nil {
return
}
privateKey, err := decodePrivateKey(privateKeyBytes)
if err != nil {
return
}
decryptedtext, err := rsa.DecryptOAEP(sha256.New(), rand.Reader, privateKey,ciphertext, nil)
if err != nil {
return
}
log.Printf("%s", decryptedtext)
}
func decodepublicKey(key []byte) (*rsa.PublicKey, error) {
block, _:= pem.Decode(key)
if block == nil {
return nil, errors.New("can't decode pem block")
}
publicKey, err := x509.ParsePKCS1PublicKey(block.Bytes)
if err != nil {
return nil, err
}
return publicKey, nil
}
func decodePrivateKey(key []byte) (*rsa.PrivateKey,error) { block, _ := pem.Decode(key)
if block == nil {
return nil, errors.New("can't decode pem block")
}
privateKey, err := x509.ParsePKCS1PrivateKey(block.Bytes)
if err != nil {
return nil, err
}
return privateKey, nil
}
Then I don’t know how to solve this problem?
Please help with solving this problem

Answer 1

I debugged your code and found 2 potential issues:
Double check whether you need to use x509.ParsePKCS1PublicKey() or x509.ParsePKIXPublicKey(). This depends on the format of your public key. More here: https://stackoverflow.com/a/54775627/9698467
You may need to type assert the public key in your decodepublicKey function: return publicKey.(*rsa.PublicKey), nil.