Keywords

1 Introduction

The contributions presented in this book belong to the broader field of human factors in privacy, usable privacy research, or generally deal with the concept privacy. Usable privacy, in particular, is situated at the intersection of cybersecurity with a focus on privacy and human–computer interaction [9] specifically considering the users’ capabilities and knowledge when interacting with a technology.

The remainder of this chapter particularly focuses on the digital life of individuals and interactions with a digital system, such as a smartphone, personal computer, or Internet-of-Things (IoT) devices. Before we dive into why we need privacy, especially in our digital lives, we first take a look at different privacy definitions and theories that have been described in the literature.

2 Privacy Theories

This section details core privacy theories in the scientific literature. We start historically with the “The Right to Privacy” [23]. Next, the theories of Westin [24], Altman [1, 2], and Solove [22] are summarized. From these theories and further scientific literature, we learn specific properties of privacy and highlight why privacy is a highly individual concept.

The Right to Be Let Alone

An early mention of privacy in the literature is the article “The Right to Privacy” by Warren and Brandeis in 1890 [23]. In this early work, the authors informally define privacy as “the right to be let alone” [23, p. 195].

Warren and Brandeis [23] cite the judge Thomas M. Cooley when making this statement and refer to a section on bodily integrity in his book [6, p. 29] where the original quote reads “The right to one’s person may be said to be a right of complete immunity: to be let alone” [6, p. 29]. However, Cooley mainly refers to the integrity of the human body, specifically to instances of battery, while Warren and Brandeis take “the right to be let alone” to the social domain. Further, Cooley does not attempt to provide a notion of privacy. Also Warren and Brandeis do not attempt to provide a definition of the right to privacy [18], and they argue that privacy should be “part of the more general right to the immunity of the person, – the right to one’s personality” [23, p. 207].

Warren and Brandeis specifically mention early technical devices that allow pictures of individuals to be taken as well as devices that allow eavesdropping conversations from afar mostly referring to the press that might invade people’s private lives. Yet, this leaves room for interpretation what the “the right to be let alone” entails [21]. Nevertheless, this article had quite an impact by motivating privacy laws in the USA because it showed that the tort law did not protect privacy adequately at that time and because privacy violation is an injury to feelings and not to the body [21, 23].

Westin’s Privacy Theory

“The right to be let alone” [23, p. 195] was later on extended to individuals that determine what information about themselves should be known to others [24]. The political scientist and lawyer Alan F. Westin influenced how we understand privacy today.

His privacy theory defines privacy as “the claim of individuals, groups, or institutions to determine for themselves when, how, and to what extent information about them is communicated to others” [24, p. 7]. To show the different reasons “why” individuals might want privacy, Westin describes four privacy functions, which are detailed below:

Westin’s Four Privacy Functions

  1. 1.

    Personal autonomy is the desire of individuals to not be manipulated, dominated, or exposed by others.

  2. 2.

    Emotional release describes a time-out from social demands, such as role demands.

  3. 3.

    Self-evaluation considers processing experiences.

  4. 4.

    Limited and protected communication sets interpersonal boundaries, while protected communication exchanges information with trusted peers.

see [24]

Westin also details different ways on the “hows” to achieve privacy that he denotes as states of privacy [24]. Below, we apply these four states to the analog and digital life and give some examples:

Westin’s Four Privacy States This box gives an overview of Westin’s four privacy states completed with examples from the analog life (denoted as ) and digital life (denoted as ):

  1. 1.

    Solitude means that information is not shared with others, similar to the “right to be let alone” [23, p. 195].

    There is a possibility to physically separate from others.

    A technology provides access control to keep information private.

  2. 2.

    Intimacy refers to information being shared only with specific humans.

    Close relationship between peers based on information exchange.

    A technology provides options to share information only with specific humans, e.g., specific posts can only be shared with “friends” in an online social network.

  3. 3.

    Anonymity means that information cannot be connected to an individual.

    The desire of public privacy.

    A technology offers the possibility to store or submit anonymized data, e.g., in an online election, the identities of the voters are not disclosed.

  4. 4.

    Reserve describes that information disclosures to others are limited.

    The creation of a psychological barrier against unwanted intrusion.

    A technology offers options to limit information disclosures, e.g., IoT devices do not capture specific information.

see [24]

Altman’s Privacy Regulation Theory

Similar like Westin, the social psychologist Irwin Altman also impacted our understanding of the concept privacy. He concisely defines privacy as “the selective control of access to the self” [1, p. 24], yet also captures more nuanced aspects of privacy in his work.

Altman states that privacy involves a dynamic process of boundary control between individuals [1]. Within this process, the desired level of privacy wanted by an individual might not match the achieved level in reality. To better describe this, he models privacy as a non-monotonic function with three different privacy levels: (1) optimal level where the desired level matches reality, (2), too much privacy, i.e., the desired level is lower than reality, and (3) too little privacy, i.e., the desired level is higher than reality. This function also shows several important aspects that Altman detailed in his later work: privacy, in principal, is a social process, which is why an in-depth understanding of psychological aspects is needed [2]. Too much privacy might result in social isolation, while too little might alter the behavior of individuals. We will talk about that in more details in the next section. An interesting extension of Altman’s theory that specifically considers online communication is the Communication Privacy Management (CPM) by Petronio [17].

Solove’s Privacy Taxonomy

While Westin and Altman discuss privacy as a rather positive concept that enables individuals to exert control, Solove specifically considers the negative side of privacy invasions [22]. He first dives into different existing privacy theories mainly demonstrating that those are “too narrow, too broad, or too vague” [22, p. 8]. Then, he identifies four types of privacy problems that he uses to build a four-layered taxonomy. Each layer contains a different number of specific activities that can be done to harm the privacy of individuals:

Solove’s Taxonomy

  1. 1.

    Information collection: surveillance and interrogation

  2. 2.

    Information processing: aggregation (combining different data pieces), identification (linking information to individuals), insecurity (not protect stored information adequately), secondary use (using collected information for a different purpose), and exclusion (not informing individuals properly about data handling)

  3. 3.

    Information dissemination: breach of confidentiality, disclosure, exposure (revealing nudity, grief, or bodily functions of individuals), increased accessibility, blackmail, appropriation (identity misuse), and distortion (propagating false information)

  4. 4.

    Invasions: intrusion (i.e., disturbing one’s tranquility or solitude), and decisional interference (i.e., impact on private decisions by governments)

see [22]

It should be noted that each action by itself might not impose any harm on individuals as long as consent is given [22].

2.1 How (Not) to Define Privacy

Even though several attempts have been made to define privacy later on, no overall definition has been agreed on so far. Solove discussed different existing privacy theories concluding that they mainly are “too narrow, too broad, or too vague” [22, p. 8], and later in his book, he compares the term privacy to the ambiguity of the term animal to highlight how problematic ambiguity can be [22]. The reason for that lies in the complexity of privacy as an umbrella term for different concepts within different disciplines and scopes [22]. Further, privacy has a quite challenging property: it is a highly individual and elastic concept meaning each individual decides what kind of information they wish to keep private [15]. Something that is private information for one individual might be happily shared by another.

Further, there are differences in privacy perceptions based on specific contexts, such as culture [15]. Hence, there are different spheres that can impact privacy norms on different levels, such as political, socio-cultural, and personal levels [25].

The definition considers the possibility for individuals to exert control on when and how personal information about them is collected and processed by others [7, 8, 23, 24]. Consequently, it is a personal good that also protects individuals. One must also mention that sometimes, privacy is considered as a value that can be traded against specific benefits [5], such as financial benefits or services that are free of charge. The chapter “From the Privacy Calculus to Crossing the Rubicon: An Introduction to Theoretical Models of User Privacy Behavior” specifically describes theories and behavioral models that aim to explain privacy behavior.

Finally, it is also challenging to separate privacy from related concepts, such as secrecy or anonymity. Especially in the legal context, privacy can be defined as secrecy, and there are several disagreements on the specific boundaries between privacy and its related concepts [12]. A core aspect of privacy, however, is that it is a highly individual concept. Individual differences also make it particularly challenging to implement one specific overall solution that fits the needs of each and every individual. Consequently, specific technologies ideally offer a possibility for individuals to configure it according to their privacy needs. Privacy, furthermore, can fulfill different functions.

3 Why Do We Need Privacy?

Now that we introduced the concept of privacy, different theories, and its functions, we discuss why privacy is needed in the first place. Solove’s taxonomy detailed above already provides a list of negative consequences of privacy invasions [22]. In the remainder of this chapter, we provide three specific reasons why privacy is important:

  1. 1.

    Missing Privacy Can Bias Decisions: Early research in the field of psychology showed that sacrificing privacy is not a viable solution. It has repeatedly been demonstrated that people alter their behavior when observed by others [3, 10, 19]. For instance, Asch studied the extent to which the opinions and behavior of a majority could affect individual decisions and judgments of individuals [3]. Therefore, he performed a series of experiments that became known under the terms elevator test and line test. Both experiments share that one participant is confronted with a group of actors. In the elevator test, the group performs unexpected actions, such as facing the elevator’s wall instead of the door. In the line test, the participants received a card with a line and have to pick a line that matches the line length on the received card from a set. The actors chose a line from the set that was obviously not matching the one on the card. Asch’s results indicate that individuals conformed to the majority’s opinion even when the correct answer was obvious. Thus, social influence can make people question their own decision under the supervision of a contradicting majority. This is also one reason for a central principle of modern democracies: vote privacy. In summary, the need for privacy comes from the presence of society and other individuals around us [14]. Without that, we would not need privacy [14].

  2. 2.

    Missing Privacy Allows Others to Control Us: The amount of information that another entity holds about individuals can also be used to influence that specific individual without the presence of other humans. This also relates to Westin’s privacy function personal autonomy described above [24]. Zuboff coins the term surveillance capitalism [29] to describe the influence on humans by massively using data captured about them. More specifically, she describes it as a “new economic order that claims human experience as free raw material for hidden commercial practices of extraction, prediction, and sales” [29, p. 1]. The idea behind this is that any kind of data created by human experiences, such as sharing pictures or purchasing products, is fed into algorithms that aim to subtly influence actions of humans, e.g., going to a specific restaurant. Such influence can occur via targeted advertisements, but also via coupons or even games. While individuals might benefits from such data analysis, many mechanisms are designed in a way that do not keep individuals in control, and there is a fine line between benefit and exploitation. A possible solution to that would be not to process data about individuals.

  3. 3.

    Missing Privacy Can Impact Mental Health: Privacy is an integral human need. Each individual has different kinds of personal boundaries. In this context, privacy serves as a boundary control that enables individuals to regulate contact and information exchange with other individuals on several levels. Too much information (or contact) is perceived as an invasion of the self [16]. Complete withdrawal of others, however, can result in feelings of loneliness [16]. Therefore, privacy regulation is essential for mental health [11].

    The reasons outlined above are just a fraction of the reasons to motivate a need for privacy. Privacy in the digital world is particularly challenging. In the analog world, humans can use physical restrictions to protect personal information from others. Until the early two-thousands, the majority of information had been in analog format. To interact with analog information, humans either needed to be in the vicinity of the information or had to make a physical copy. To enforce restrictions based on privacy preferences, humans could physically limit access to analog information about them. In doing so, humans can decide which information they share with others. Translating such physical limitations into the digital world, however, is not trivial.

    The ongoing digital transformation is fundamentally changing how humans interact with information and the kind of information they share with others. At the beginning of the digital transformation, computers were obvious standalone devices, and users always intentionally interacted with them. Thus, privacy did not require much added extra effort. Just two decades later, in 2023, the majority of information is digital data. Networks, such as the Internet, serve as an infrastructure to interact with data that are stored remotely. Computational capabilities and sensors for collecting data are integrated into everyday objects connected to the Internet—the so-called Internet of Things (IoT) [4]. This has numerous benefits for users, such as availability or convenience of everyday life [13, 26]. However, the ubiquitous abilities of digital services and the IoT devices they are connected with raised several privacy challenges because digital services generate, collect, store, and analyze data about people’s private lives (cf. [20, 27, 28]). As Warren and Brandeis already feared in 1890, technology can now penetrate our very private places and eavesdrop on our private conversations [23].

    In summary, privacy is a highly individual concept. Missing privacy can impact mental health, social decisions, and our lives in general. Privacy in the digital world is challenging for several reasons demanding a need for more in-depth research in this field and novel solutions that better help protecting the essential need of our society.