特此证明用英语怎么说?

特此奉告 we have the honour to apprise you; have the honour of informing you
特此告知 we acquaint you that
特此函复 in reply
特此函告 this is to acquaint you
特此声明 we state
特此通知 1.It is hereby announced that ... ; notice is hereby given; ....
特此作证 in testimony whereof; in witness whereof; 1.in test....
..., 特此奉告 we have the honour to inform you of
..., 特此函告 permit us to communicate to you

一般我们开证明的时候最后会写一句“特此证明”，可是用英语怎么说呢？查到了 Hereby prove, 但是好像不对，感觉还缺点什么。
多谢多谢！

This is for certification only.

This is hereby to certify that

It is hereby cetify that