What type of electronic document contains a public key?

The correct answer is a digital certificate. A digital certificate is an electronic document used to prove the ownership of a public key. It typically contains information about the key, information about the identity of the key owner (such as the entity's name and email address), as well as metadata such as the certificate's expiration date and details about the issuing authority.

Digital certificates are an essential component of public key infrastructure (PKI), enabling secure communication over the internet by verifying that a public key belongs to the stated owner. This verification helps establish trust in digital transactions and communications, ensuring that the sender's and recipient's public keys are valid and recognized.

In contrast, a smart card is a physical device that can store keys and perform cryptographic operations but does not primarily function as a document for holding public keys like a digital certificate. A digital signature is a cryptographic mechanism used to verify the authenticity of a message or document, whereas the authentication token refers to a device or software that generates a code for user authentication. Neither of these directly serves the purpose of containing a public key within a formalized structure like a digital certificate does.