golang - marshal PKCS8 private key?

Question

Is there a way to marshal a PKCS8 private key in go 1.5?
e.g. something similar to or starting from x509.MarshalPKCS1PrivateKey?

Answer 1

Since the above answer was written, go 1.10 has been released with a x509.MarshalPKCS8PrivateKey method.

Answer 2

Funny enough, there are no standard function to do that, but here is a custom solution:

type pkcs8Key struct {
    Version             int
    PrivateKeyAlgorithm []asn1.ObjectIdentifier
    PrivateKey          []byte
}


func rsa2pkcs8(key *rsa.PrivateKey) ([]byte, error) {
    var pkey pkcs8Key
    pkey.Version = 0 
    pkey.PrivateKeyAlgorithm = make([]asn1.ObjectIdentifier, 1)
    pkey.PrivateKeyAlgorithm[0] = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 1}
    pkey.PrivateKey = x509.MarshalPKCS1PrivateKey(key)

    return asn1.Marshal(pkey)
}