去ListenAndServeTLS

Im currently trying to use this function for my http server. I already have the cert.pem and the private.key but I am getting this error

crypto/tls: failed to parse private key

No idea what is wrong. This is the correct key because any other key will just throw

private key does not match public key

They are both on the same folder

Since I am not sure how risky is to expose the key. It starts with this

-----BEGIN RSA PRIVATE KEY-----
Proc-Type: 4,ENCRYPTED
DEK-Info: DES-EDE3-CBC,D353D2D8ACDA5320
....
---END RSA PRIVATE KEY-----

The code I am using

err := http.ListenAndServeTLS(":80", "mycert.pem", "private.key", router)
if err != nil {
    log.Fatal(err)
}