Which aspect is NOT supported by Public Key Infrastructure (PKI)?

Public Key Infrastructure (PKI) primarily focuses on enabling secure communication through the use of public and private keys, which facilitate various security services such as authentication, integrity, and non-repudiation.

In this context, availability does not fall under the direct support provided by PKI. While PKI components, such as Certificate Authorities (CAs) and registration authorities, contribute to maintaining the trustworthiness of the system, they do not inherently address the availability of data or services. Availability refers to the readiness of the systems and data for access and use when needed, which is more a function of network design, redundancy, and operational management rather than cryptographic processes like those provided by PKI.

In contrast, distribution is crucial since PKI must effectively distribute public keys generated by users. Integrity checks are supported through digital signatures, which verify that the data has not been altered in transit. Non-repudiation is also an essential part of PKI, as it uses digital signatures to ensure that a sender cannot deny sending a message, providing a clear audit trail.

Therefore, while PKI is adept at securing communications and establishing trust, it does not directly ensure that systems or data remain available for access at all times.