Assure vs Certify - What's the difference?

In transitive terms the difference between assure and certify

is that assure is to make sure and secure while certify is to attest to as the truth or meeting a standard.

(assur)

To make sure and secure.

To give (someone) confidence in the trustworthiness of (something).

I assure you that the program will work smoothly when we demonstrate it to the client.

He assured of his commitment to her happiness.

(obsolete) To guarantee, promise (to do something).

* 1590 , Edmund Spenser, The Faerie Queene , II.ii:

That as a law for euer should endure; / Which to obserue in word of knights they did assure .

To reassure.

to attest to as the truth or meeting a standard

* (to attest as to) attest, witness, vouch for, approve, confirm

* certifiable * decertify