I have no other evidence to back this up

Never occurred to me that Paul might have gotten his inspiration from the Psalms.

Psalm 18.30-36:
As for God, His way is blameless;
The word of the Lord is tried;
He is a shield to all who take refuge in Him.
For who is God, but the Lord?
And who is a rock, except our God,
The God who girds me with strength
And makes my way blameless?
He makes my feet like hinds’ feet,
And sets me upon my high places.
He trains my hands for battle,
So that my arms can bend a bow of bronze.
You have also given me the shield of Your salvation,
And Your right hand upholds me;
And Your gentleness makes me great.
You enlarge my steps under me,
And my feet have not slipped.

Ephesians 6.10-17:
Finally, be strong in the Lord and in the strength of His might. Put on the full armor of God, so that you will be able to stand firm against the schemes of the devil. For our struggle is not against flesh and blood, but against the rulers, against the powers, against the world forces of this darkness, against the spiritual forces of wickedness in the heavenly places. Therefore, take up the full armor of God, so that you will be able to resist in the evil day, and having done everything, to stand firm. Stand firm therefore, having girded your loins with truth, and having put on the breastplate of righteousness, and having shod your feet with the preparation of the gospel of peace; in addition to all, taking up the shield of faith with which you will be able to extinguish all the flaming arrows of the evil one. And take the helmet of salvation, and the sword of the Spirit, which is the word of God.