What were the powers of the Keys as understood in the West in earlier days?
The Clavis Potentiae and the Clavis Scientiae
The Key of Power and the Key of Knowledge
The Catholic Encyclopedia has an article The Power of the Keys
where it seems that up until the 14th or 15th century
the power of the keys was not understood in the limited modern Catholic understanding. The understanding for the first millennium and a half in the West was centred on the power of all the clergy to judge penitents and forgive their sins.
The idea that the Keys symbolise the power of Peter and the Petrine office and the Vatican is relatively new, only about 500 years old. It is not the primary interpretation of Scripture; it is merely a secondary and later interpretation of Scripture.
This is a tantalisingly short article and it would be great to find a fuller source.http://www.newadvent.org/cathen/08631b.htm
"The meaning attached to the term [the power of the keys] by the older Scholastics was, however, different from this. They followed the patristic tradition, and confined its significance to the judicial authority exercised in the Sacrament of Penance.
"The power of the keys, St. Thomas tells us (Summa Theologica Supp:17:2, ad 1um), is a necessary consequence of the sacerdotal character. It is, in fact, identical in essence with the power to consecrate and to offer the Holy Sacrifice of the Mass. The one sacerdotal gift is applied to different ends in the different sacraments.
Such, too, appears to be the teaching of Pope John XXII [died 1334] in a well-known passage dealing with this subject. The definition, "The keys are a special power of binding and loosing by which the ecclesiastical judge [the confessor] should receive the worthy [into the kingdom of heaven] and exclude the unworthy therefrom", generally accepted in the Scholastic period (Peter. Lombard, John XXII, St. Thomas Aquinas), might seem indeed to include jurisdiction in the external as well as in the internal forum.
"But in point of fact it was not so understood. The distinction between the clavis potentiae [key of power]and the clavis scientiae [key of knowledge] was employed here. By the clavis scientiae was understood the priestly authority to interrogate the penitent and thus obtain cognizance of the facts of the case; by the clavis potentiae, the authority to grant or refuse absolution."
[For easier readibility I have taken the Latin sentences out of this extract, but of course left the English. I don't believe that anything has been distorted by this but please read the article on the website if you want to see the Latin.]