def box(tag, lines)
    lines.unshift "-----BEGIN #{tag}-----"
    lines.push "-----END #{tag}-----"
    lines.join("n")
  end

  def der_to_pem(tag, der)
    box tag, Base64.strict_encode64(der).scan(/.{1,64}/)
  end

  pem = der_to_pementer code here('ENCRYPTED PRIVATE KEY',

  File.read('./file.key'))
  key = OpenSSL::PKey::RSA.new(pem, 'passkey')
  puts key
  puts pem

-----BEGIN RSA PRIVATE KEY-----
MIIEpQIBAAKCAQEAzxy...
...ECYUOVC3zgw23aGcFA8z9ghI=
-----END RSA PRIVATE KEY-----

-----BEGIN ENCRYPTED PRIVATE KEY-----
MIIFDjBABgk...
...Y948X9Zop7aCnxmWI7vHNts=
-----END ENCRYPTED PRIVATE KEY-----

-----BEGIN PRIVATE KEY-----
MIIEvwIBADA...
...ZwUDzP2CEg==
-----END PRIVATE KEY-----

openssl pkcs8 -inform DER -in "./key.key" -passin pass:passkey -out "./key.key.pem"