return buildString {
      append("-----BEGIN RSA PRIVATE KEY-----\n")
      encodeBase64Lines(pkcs1Bytes())
      append("-----END RSA PRIVATE KEY-----\n")
    }
  }

  private fun pkcs1Bytes(): ByteString {
    val decoded = CertificateAdapters.privateKeyInfo.fromDer(keyPair.private.encoded.toByteString())
    return decoded.privateKey
  }