Authenticity vs integrity

Most people do not use the terms “authenticity” and “integrity” as synonyms, but the differences between the two concepts as used in security research differ in varied and often confusing ways. A message is authentic when its origin claim is true: e.g., a painting is authentic if when it says “I was painted by Picasso”, then it was really painted by Picasso. Integrity usually means that the message was not altered in transfer: e.g., the integrity of a painting can be destroyed if it is changed in restoration. The integrity of a voting ballot can be destroyed if the tamper protections on it are damaged, since we cannot be sure any more whether the vote was altered or not. Some people call the process of establishing authenticity “entity authentication”, and the process of establishing integrity “message authentication”. Both processes require that something that we observe (e.g. a painting) allows us to draw conclusions about something that we cannot observe (who made the painting). Deriving what is unobservable from what is observable is a formidable logical task: in a sense, both science and religion are can be viewed as methods for authentication. More about this later.

Secrecy vs confidentiality

The terms “secrecy” and “confidentiality” are also used in subtly different ways, but they both express restrictions on some undesired information flows. E.g., a medical file is confidential, in the sense that its contents can only be disclosed to the patient and to the physician, although everyone knows that the file surely exists; an intelligence file about a suspect is secret, in the sense that even its existence cannot be disclosed. To make it more complicated, even the term “privacy” is often used in related senses: e.g.,  contrast a private ceremony with a secret ceremony.

Think about concepts, not words

Without the formal definitions, the security terminology is used freely and imprecisely in everyday life, and there is nothing wrong with that. In security research, though, it is useful to fix some definitions, to assign some words to some concepts, and to stick with them even if other people may use the words differently. Our goal is not to study the ways people use the words “confidentiality” and “integrity”, but to understand and develop some methods to restrict the undesired data flows, and to establish the desired data flows.

So lets stick with the taxonomy of the security concepts, proposed in this post.


In many security courses and overviews, you will encounter the CIA triad, referring to Confidentiality, Integrity and Availability. This triad consists of three of the four basic security concepts that we spelled out in SecSci taxonomy. They are displayed on a triangle, clarified by examples, and often related with other concepts, such as trustworthiness or reliability, assumed to be intuitively clearer than confidentiality, integrity. or availability. Students often wonder why are these three more important, and whether there might be other important security properties that we still didn’t encounter, and some authors extend the triad by their favorites, such as Non-repudiation, so that CIA becomes CIAN. Then the students ask whether there might still other important security properties, and there is no obvious reason why the list should ever end.

The taxonomy above can be viewed as the triad extended by Authorization, so that CIA became CIAA. What is the point of that? Well, if security research is concerned with what-you-know (information) or what-you-have (resources), and its goals are either to prevent bad things or to provide good things, then there are just 4 security goals: Confidentiality and Integrity of what-you-know, and Authorization and Availability of what-you-have. And you know that the CIAA list is complete and exhaustive, and that any imaginable security must be a combination of those 4.

Spelling out the informal security concepts and the principles tried out in practice has been a useful and important strategy in the engineering approach to security, where we gather experience to build better and better systems. But a scientific approach to security, necessary for dealing with systems that combine engineered and natural processes, requires that we precisely define the subject of our science. To do that, we need an exhaustive list of security properties: a taxonomy which covers not only the properties that we have encountered, but also the properties that we have not yet thought about, but may encounter in the future. The good-things/bad-things taxonomy seems like a good candiate for that purpose. It played a similar role in software science, so maybe it will get us ahead in security science as well.

So whenever you encounter the CIA triad, then either expand it to CIAA, or maybe even ignore the whole thing.

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