Actually, this contradicts what Luther himself said concerning "the keys."

Luther both taught and acknowledged:  The Pharisees certainly knew that forgiving sins is God’s work and belongs to Him alone... Sins are forgiven in two ways: First, sin is driven out of the heart and grace is poured in; only God does this. Second, the forgiveness of sins is proclaimed; one man does this to another. Christ, however, does both:  All people who are Christians and baptized have this power. so they can say, “Look, dear man! God offers you His grace and forgives all your sins. Be comforted, your sins have been forgiven... Our confidence and boast against sin is that I can say to my brother, who is stuck in the anguish and danger of sin: “Be cheerful and comforted, my brother, because your sins have been forgiven. Even though I cannot give you the Holy Spirit and faith, I can nevertheless proclaim this to you. (Luthers Work v. 79)

So, then we clearly see in Luther's own words the "privilege of man to reassure" forgiveness for sin is predicated solely upon Christ past work, not because of our "power" or authority to grant, but because of permission to declare the reality of what Christ already purchased with his blood, relegating the "power," for lack of any better word, of the church and man to proclamation of what Christ already performed which indeed "squares with Scripture."