Confidentiality ensures that only the intended persons or recipients can access the data.
Integrity aims to ensure that the data cannot be altered; moreover, we can detect any alteration if it occurs.
Availability aims to ensure that the system or service is available when needed.
For example, the CIA as it relates to patient records and related systems:
Confidentiality: According to various laws in modern countries, healthcare providers must ensure and maintain the confidentiality of medical records. Consequently, healthcare providers can be held legally accountable if they illegally disclose their patients’ medical records.
Integrity: If a patient record is accidentally or maliciously altered, it can lead to the wrong treatment being administered, which, in turn, can lead to a life-threatening situation. Hence, the system would be useless and potentially harmful without ensuring the integrity of medical records.
Availability: When a patient visits a clinic to follow up on their medical condition, the system must be available. An unavailable system would mean that the medical practitioner cannot access the patient’s records and consequently won’t know if any current symptoms are related to the patient’s medical history. This situation can make the medical diagnosis more challenging and error-prone.
Going one more step beyond the CIA security triad:
Authenticity: Authentic means not fraudulent or counterfeit. Authenticity is about ensuring that the document/file/data is from the claimed source.
Non-repudiation: Repudiate means refusing to recognize the validity of something. Non-repudiation ensures that the original source cannot deny that they are the source of a particular document/file/data. This characteristic is indispensable for various domains, such as shopping, patient diagnosis, and banking.
These two requirements are closely related. The need to tell authentic files or orders from fake ones is indispensable. Moreover, ensuring that the other party cannot deny being the source is vital for many systems to be usable.