Use JcaPEMWriter to export PEM file?

Issue

I am trying to figure out how to export private key from the X509Certificate instance as a PEM string encoded.

What I have done to far is to export certificate as PEM encoded:

import org.bouncycastle.jce.provider.BouncyCastleProvider
import org.bouncycastle.openssl.jcajce.JcaPEMWriter
import java.io.StringWriter
import java.security.KeyPairGenerator
import java.security.Security
import java.security.spec.ECGenParameterSpec


fun main(args: Array<String>) {
    Security.addProvider(BouncyCastleProvider())

    val kpGen = KeyPairGenerator.getInstance("EC", "BC")
    kpGen.initialize(ECGenParameterSpec("P-256"))

    val keyPair = kpGen.generateKeyPair()
    val cert = SelfSignedCertGenerator().generate(keyPair, "SHA512WithECDSA", "localhost", 730)
    val sw = StringWriter()

    JcaPEMWriter(sw).use { jpw ->
        jpw.writeObject(cert)
    }


    println(sw.toString())


}

the output shows the expected result:

-----BEGIN CERTIFICATE-----
MIIBcDCCARWgAwIBAgIGAYHjRWOUMAoGCCqGSM49BAMEMBQxEjAQBgNVBAMMCWxv
Y2FsaG9zdDAeFw0yMjA3MDkxNDAzMDRaFw0yNDA3MDgxNDAzMDRaMBQxEjAQBgNV
BAMMCWxvY2FsaG9zdDBZMBMGByqGSM49AgEGCCqGSM49AwEHA0IABF+G+CHHQ56C
AgWN2G9PUemJTNGVdefWWuPVA5Oruepm9yOM69H5tPia0V/BCDlVHQrJ8Q0yC4Fa
uuM3HP42VJ6jUzBRMB0GA1UdDgQWBBTYf15PsEN2DaNaG3YFDL84SgXZvTAfBgNV
HSMEGDAWgBTYf15PsEN2DaNaG3YFDL84SgXZvTAPBgNVHRMBAf8EBTADAQH/MAoG
CCqGSM49BAMEA0kAMEYCIQCr9MrSGW3eimfDodqC6a4nxbusOUQcFz2+DHYFrZTx
AAIhAPRJ70basMDBOBdOQnN2DgxbGSHzsixZ7qajakRTlKKz
-----END CERTIFICATE-----

The question is how to export the generated private key as PEM encoded?

Solution

Just pass your private key to the JcaPEMWriter::writeObject :

JcaPEMWriter(sw).use {
    w -> w.writeObject(keyPair.private)
}


println(sw.toString())

which gives :

-----BEGIN EC PRIVATE KEY-----
MHcCAQEEIK2XWix+f1aRSh7sH4NSYQeCBsCfOBjFATKiJLnD4UPdoAoGCCqGSM49
AwEHoUQDQgAEIQAArKsROcQ8l2aZUO+a3zm+03+a9ToTrpE+Ysi9Pm5+oQoy1Oro
kLiJxihn2rgQFspUuQ0cRdwj8HKo2MsIzQ==
-----END EC PRIVATE KEY-----

Answered By - Michał Krzywański