TBSCertificateSubject

TBSCertificateSubject is a field within a Transport Layer Security (TLS) certificate, specifically within the X.509 standard. It is a critical component of the certificate that identifies the entity to which the certificate is issued. This entity can be a server, a client, or any other participant in the TLS communication. The TBSCertificateSubject field contains a distinguished name (DN) that provides information about the entity, such as its common name (CN), organization (O), organizational unit (OU), locality (L), state or province (ST), country (C), and other relevant details.

The distinguished name in the TBSCertificateSubject field is structured using a series of attribute-value pairs. Each attribute represents a specific type of information, and the value provides the corresponding data. For example, the common name attribute might contain the fully qualified domain name of a server, while the organization attribute might contain the name of the company that owns the server.

The TBSCertificateSubject field is used by TLS clients to verify the identity of the server they are communicating with. During the TLS handshake process, the client receives the server's certificate and extracts the TBSCertificateSubject field to compare it with the server's domain name. If the names match, the client can proceed with the secure communication. Conversely, if the names do not match, the client may terminate the connection to prevent potential security risks.

In summary, the TBSCertificateSubject field is a vital part of a TLS certificate that provides essential information about the entity to which the certificate is issued. It plays a crucial role in the TLS handshake process, enabling clients to verify the identity of servers and ensure secure communication.