There's some sort of a four digit code, maybe a birthday.

有某种四位数代码，也许是生日。

This is similar, this is more like a simplified version of Nintendo spread coding system, because it is a six digit code, I think it's sure.

这种方式似曾相识，更像是一个简化版本的任天堂扩展编码系统，因为它是6位数的密码，我很确信。