022.1 Lesson 2

Public Key Infrastructure (PKI) is pivotal in establishing trust and securing digital communications. At its core, PKI provides a structured framework for managing digital certificates and public-private key pairs, which are essential for verifying identities and securing data exchanges over the internet. When two entities, such as a user and a website, need to communicate securely, PKI ensures that each party can be confident of the other’s identity and the integrity of the data being shared.

PKI allows secure communication through the management of public and private key pairs. Entities such as websites, servers, or individuals are issued a digital certificate that links their identity to a public key.

Digital certificates serve as an electronic “passport” for an entity — whether it’s a person, device, or service. This certificate is issued by a trusted third party known as a Certificate Authority (CA).

Before issuing a certificate, the CA performs a thorough verification process to confirm the legitimacy of the entity’s identity. This process prevents malicious actors from falsely claiming to be someone else. Once the certificate is issued, it can be used to encrypt data with the entity’s public key. Only the corresponding private key, which is securely held by the entity, can decrypt this data, ensuring that sensitive information remains confidential and accessible only to the intended recipient.

At the heart of PKI are Certificate Authorities and Trusted Root Certificate Authorities, which form the backbone of the chain of trust that underpins the security of digital certificates used in web browsing, secure email, and other applications.

CAs play a critical role in PKI by issuing, validating, and managing digital certificates. Once issued, the certificate can be trusted by other users or systems that rely on the CA’s authority.

Root CAs form the top of the trust hierarchy in PKI. Root CAs issue certificates to intermediate CAs, creating a chain of trust that extends to the end-user certificates. Root certificates are pre-installed in operating systems and web browsers, providing the foundation for all certificates issued in the hierarchy.

This chain of trust is essential, creating a hierarchical relationship between Root CAs, intermediate CAs, and the entities they issue certificates to. Each certificate in the chain is validated by the one above it, ultimately leading back to a trusted Root CA. This hierarchical model ensures that users and systems can trust the certificates they encounter in digital interactions.

Here is an example of a chain of trust involving a Root CA, an intermediate CA, and end-entity certificates.

X.509 certificates are the standard digital certificate format used in Public Key Infrastructure (PKI) and are essential for verifying the identity of entities in secure communications. Often referred to as “digital passports,” these certificates establish a reliable association between an entity’s identity and its public key through certification by a trusted Certificate Authority (CA).

Each X.509 certificate contains fields that detail the entity’s public key, the name of the issuing CA, and specific identity information, such as the entity’s domain name or organization name. This standardized format ensures that X.509 certificates provide a consistent and trusted method for authenticating entities across a wide range of digital applications.

Understanding the role of X.509 certificates is essential because they are used to facilitate secure connections in many applications, including HTTPS for secure web browsing, SSL/TLS for data encryption, and digital signatures for verifying the authenticity and integrity of electronic documents.

The certificate contains a digital signature generated by the CA using its private key, which binds the public key to the entity’s identity. This digital signature can be verified by anyone using the CA’s public key, ensuring that the certificate has not been tampered with and that it indeed originates from the trusted CA.

There are dozens of CAs around the world, most of which offer paid certificate issuance services. Well-known CAs include Let’s Encrypt, which provides free, automated SSL/TLS certificates and promotes the widespread adoption of HTTPS.

Let’s Encrypt has transformed the process of obtaining and managing X.509 certificates by offering free, automated SSL/TLS certificates. This initiative promotes the widespread adoption of HTTPS, making the internet more secure by lowering the barriers to encryption.

Before Let’s Encrypt, obtaining SSL/TLS certificates was often a costly and technically complex process. Let’s Encrypt simplifies this by automating the certificate issuance and renewal process, allowing websites to secure their communications easily and at no cost.

Let’s Encrypt has played a significant role in increasing the adoption of HTTPS, improving security and privacy across the web. However, it is important to note that Let’s Encrypt issues Domain Validated (DV) certificates, which verify domain ownership but do not provide the same level of assurance as Organization Validated (OV) or Extended Validation (EV) certificates.

Let’s Encrypt certificates are valid for only 90 days. This short validity period ensures that certificates are regularly updated, reducing the risk of misuse in the event of compromise. Because of the short lifetime of Let’s Encrypt certificates, automatic renewal is crucial to maintaining security.