Which format is most commonly used for digital certificates?

The most commonly used format for digital certificates is x.509. This format is a standard that defines the structure of public key certificates, enabling entities to exchange secure information over a network. x.509 certificates contain essential details, such as the public key, the identity of the certificate holder, the issuer of the certificate, and a digital signature that verifies the authenticity of the certificate.

x.509's widespread use is due to its incorporation into various security frameworks and protocols, such as SSL/TLS for secure transactions on the internet and other public key infrastructure (PKI) applications. This makes it a cornerstone of modern digital security, ensuring that communications remain confidential and trustworthy.

While formats such as PEM, p12, and DER are associated with the handling and storage of certificates, they are essentially encapsulations or encodings of x.509 certificates. PEM is a base64-encoded format often used for certificate files; p12 (or PKCS#12) is a binary format that can contain multiple certificates and private keys; and DER is a binary encoding of x.509 certificates. Therefore, x.509 stands out as the foundational standard that ensures compatibility and security across multiple platforms and applications.