code: func SerializeSN(sn *big.Int) ([]byte, error) {
  	blob, err := sn.GobEncode()
  	if err != nil {
  		return nil, fmt.Errorf("can't encode SN - %s", err)
  	}
  	return blob, nil
  }
docs: // SerializeSN converts a certificate serial number to a byte blob.