According a Catholic interpretation of the natural law, do individuals posses a right to privacy?

Secret/private vs. open is distinguished in moral theology. For example:

• Backbiting/detraction (detractio),

  the blackening of another's good name (fama) by words uttered in secret
  _{—St. Albert the Great, Sum. Theol. II 117, quoted in St. Thomas Aquinas, Summa Theologica II-II q. 73 a. 1 arg. 1}

  It's a serious sin because one has a right to his good reputation (fama):

  of all temporal things a man's good name (fama) seems the most precious
  _{—ibid. a. 2 co.}

vs.

• railing/reviling (contumelia)
  

  the same [as backbiting], but done openly, to his face (ibid.)

"Privacy rights" would seem to help protect one's reputation against detractors, but it also would seem to protect detractors in their detracting.

This is reminiscent of the supposed "right" to freedom of press, where one is allowed to spread both lies and truths; or the supposed "right" to freedom of conscience and religious liberty, where one is allowed both to worship the True God and false gods (an "insanity", according to Popes Gregory XVI and Pius IX, Quanta Cura §3).

Pope Gregory XVI's 1832 encyclical on Liberalism and Religious Indifferentism, Mirari Vos §15, gave an illustrative analogy, in the context of the supposed freedom to publish:

Is there any sane man who would say poison [e.g., dangerous books] ought to be distributed, sold publicly, stored, and even drunk because some antidote [e.g., orthodox books] is available and those who use it may be snatched from death again and again?

In Catholic Republic written by author Timothy Gordon (page 38ff), he outlines there are only 3 rights directly under Natural Law: Right to Life, Right to Liberty and Right to Property, so one cannot directly say that according to natural law one has a right to privacy. However, that doesn't mean that from Natural Law, it would be perfectly moral to "pry into details" or "keep things" to yourself; it just isn't a "right"

Where human rights come from

Catholic understanding of natural law is the law that God implants in every human being when He creates human nature as opposed to animal nature. The human soul then is equipped with a conscience that informs reason to act according to what is proper to human nature. When someone thinks, feels, wills, or acts against human nature, he/she is always breaking natural law by definition.

Catholic understanding of human right in relation to natural law can then be simply defined as the dignity, blessing, and privileges proper to the human soul so the person can achieve one possible end / telos fit for human nature. This is a right given by God (who created each human soul) by the simple virtue of his/her existence. Whether sinner or saint, damned or saved, rich or poor, baby or adult, this human right is a gift from God not earned by anyone, and therefore the withholding of this right by another human being is an offence against the giver, God. The victim can then appeal to God as his/her prosecutor. All celebration in the Psalms about God's justice (such as Psalm 98) is the expectation that God will eventually punish the perpetrator and restore what was "stolen" to those who "cry out" to Him.

Criteria of human laws to be consistent with natural law

We also have to consider our participation in a country (through an implicit social contract), a country with human law that we need to obey. Aquinas defined the validity of human law as possessing 4 properties:

1. Ordination of reason (i.e. follow natural law principles)
2. For the common good (i.e. not corrupt, or end up injuring the common good)
3. By one who has care for the community (i.e. by justly elected / appointed official having jurisdiction)
4. Promulgated (i.e. published through a channel that everyone has access to; no surprises, no secrets)

Therefore if a government creates a "social distancing" / "contact tracing" rule which has the above 4 properties, natural law will not have a problem with it. This is even though the rule does limit freedom of movement or does require giving up some private location and social connection. But this giving up for the sake of contact tracing is consistent with our dignity because this rule is for the common good (property #2) so we willingly give up some freedom (NOT giving up right, which is not ours in the first place, but God's) as a "give and take" (benefiting from the common good created by the laws of the country while voluntarily relinquishing some freedom).

There are only positive rights under Thomistic natural law

Because it is God who gave us all human rights through our nature, all human rights are then positive rights, framed as existential rights for us to grow to fulfill our end / telos. To the person who receive this gift from God he/she is responsible to cultivate it in a certain direction as a farmer cultivates land to produce crops, or as in the Parable of Talents. The rights should then be seen as the foundation and raw material for producing goals consistent with human nature, rather than entitlement we can use for something that would not please God.

In Thomistic natural law, negative commandments like "Do not murder", "Do not steal", etc. do not create rights but serve as a hedge of protection to preserve the integrity of existential rights of individuals living in a society. They should then be part of the fabric of laws derived from social contracts which in turn are "insured" by the power of a government. In other words, a social contract which respects natural law creates those "negative rights" to protect the inalienable "positive right" granted by God to individual human beings.

From individual perspective, a human being exercising his/her God-given right can freely enter into a social contract. Even though entering the social contract restricts some of his/her freedom & privacy, it's consistent with natural law because by nature human being is a "political animal", needing a society to develop his/her potential.

No right to privacy under natural law, but right to dignity & flourishing

How then should we construe the "right" to privacy? As explained above, in Thomistic natural law principle there is no "right to privacy" per se, only right to human dignity and right to "flourish in relative freedom" under God, our giver. Because human nature has a social component, what's good for our community will be good for us. Therefore, when in times of hardship some regulations / laws are enacted which reduce our freedom (social distancing) and privacy (contact tracing), as long as this rule is reasonable (property #1), is for the common good (property #2), is enacted & enforced by lawful official (property #3), and is clear & stable (property #4), this temporary reduction is consistent with natural law.

Right to privacy derived from social contract

BUT we DO have a "right to privacy" in the social contract realm, which maybe framed as "negative right" (I don't know the details), through the available constitutional means. Natural law theorist would not see privacy as an end in itself, but only as a means to ensure the dignity and flourishing goals of a human being. Thus privacy has limits that should be connected with what makes sense for that society in a particular situation so the society can creates a best-possible condition for individuals in it to flourish. The classic examples are 1) the "freedom" to say "fire" in a crowded indoor theatre, or 2) the "privacy right" to not provide the password of a smartphone to a law enforcement official acting under a lawful order which fulfills the 4 properties above.

Combining natural law and social contract, what we Christians can do is to advocate for our elected / appointed officials to use their wisdom to create and implement contact tracing in a way that minimizes the reduction of privacy according to the 4 principles above. We Christians (especially those in IT) can contribute our technical ingenuity to offer ways to do contact tracing that is more secure, revocable, limit access to authorized officials, and having as little privacy-divulging footprint as possible. We can also maximize our "rights" as parties in the social contract to use 1) legal means (lawsuit) if we feel the privacy reduction unreasonable (against property #1), 2) "freedom of speech" to promote our view, and 3) lawful participation for political change.

According a Catholic interpretation of the natural law, do individuals posses a right to privacy?

The short answer is yes.

To start with I am going to begin with the Natural Law in Catholic Social Teachings:

Catholic Social Teachings

Catholic social teachings from Leo XIII through John Paul II have been influenced in various ways, either by way of agreement or by way of disagreement, by these natural law tra­ditions. They have selectively incorporated, sometimes to the consternation of purists, both modern natural rights theories as well as the older views of medieval jurists and Scholastic theologians. For purposes of convenience, Catholic social teachings are often divided into two main periods: one preceding Gaudium et spes and the second following from it. Litera­ture from the former period was primarily philosophical and its theological claims gener­ally drew from the doctrine of creation. It employed natural law argumentation in an explicit, direct, and fairly consistent manner; its philosophical framework was neoscholastic. Literature from the more recent period has been explicitly biblical and its claims are drawn more often from the doctrine of Christ; it pre­sumes the existence of the natural law but uses it in a more restricted, indirect, and selective fnshion. Its philosophical matrix has attempted to combine neoscholasticism with continental philosophy, and particularly existentialism, per­sonalism, and phenomenology.

Vatican II: Gaudium et spes

John XXIII's attempt to "read the signs of the times" was adopted by Vatican II (1962-65). Gaudium et spes began by declaring its intent to read "the signs of the times" in light of the gospel. These simple words signaled a very fun­ damental transformation of the character of Catholic social teachings that took place at the time. We can mention briefly four of its impor­ tant features: a new openness to the modern world, a heightened attentiveness to historical context and development, a return to scripture and Christology, and a special emphasis on the dignity of the person.

First, the Council's openness to the modern world contrasted with the distance and some­ times strong suspicions of popes earlier in the century. It recognized "the proper autonomy of the creature," that "by the very nature of cre­ation, all things are endowed with their own solidity, truth, and goodness, their own laws and logic" (GS 36). This fundamental affirma­tion of "created autonomy" expressed both the Council's reaffirmation of the substance of the classical natural law tradition and its ability to distinguish the core of the vital tradition from its naive and outmoded particular expres­sions.

Aquinas wrote most extensively about natural law. He stated, "the light of reason is placed by nature in every man to guide him in his acts." Therefore, human beings, alone among God’s creatures, use reason to lead their lives. This is natural law.

The main principle of the natural law, as St. Thomas Aquinas points out is that "good is to be done and pursued and evil avoided." Aquinas stated that reason reveals particular natural laws that are good for humans such as self-preservation, marriage and family, and the desire to know God. Reason, he taught, also enables humans to understand things that are evil such as adultery, suicide, and lying.

While natural law applied to all humans and was unchanging, human law could vary with time, place, and circumstance. Aquinas defined this last type of law as "an ordinance of reason for the common good" made and enforced by a ruler or government. He warned, however, that people were not bound to obey laws made by humans that conflicted with natural law.

Privacy is part of our natural rights and freedoms as pertaining to the human race.

The Common Good (Catechism of the Catholic Church)

1907 First, the common good presupposes respect for the person as such. In the name of the common good, public authorities are bound to respect the fundamental and inalienable rights of the human person. Society should permit each of its members to fulfill his vocation. In particular, the common good resides in the conditions for the exercise of the natural freedoms indispensable for the development of the human vocation, such as "the right to act according to a sound norm of conscience and to safeguard . . . privacy, and rightful freedom also in matters of religion.”

Thus the Council Fathers in Vatican II spoke thus in regards to privacy in Gaudium et spes, which is written in light of St. Thomas’ teaching on the subject of the natural law. This is well explained in the Natural Law in Catholic Social Teachings.

Every day human interdependence grows more tightly drawn and spreads by degrees over the whole world. As a result the common good, that is, the sum of those conditions of social life which allow social groups and their individual members relatively thorough and ready access to their own fulfillment, today takes on an increasingly universal complexion and consequently involves rights and duties with respect to the whole human race. Every social group must take account of the needs and legitimate aspirations of other groups, and even of the general welfare of the entire human family.

At the same time, however, there is a growing awareness of the exalted dignity proper to the human person, since he stands above all things, and his rights and duties are universal and inviolable. Therefore, there must be made available to all men everything necessary for leading a life truly human, such as food, clothing, and shelter; the right to choose a state of life freely and to found a family, the right to education, to employment, to a good reputation, to respect, to appropriate information, to activity in accord with the upright norm of one's own conscience, to protection of privacy and rightful freedom even in matters religious. - Gaudium et spes (26)