Abstract: As part of a security infrastructure based on public-key cryptography, a first digital certificate (200) is issued by a first certification authority (104) to a first subscriber (102) and binds the first subscriber (102) to a first public key (210). The first public key (210) corresponds to a first private key held by the first subscriber (102), and the first public key and the first private key form a key pair for use in public-key cryptography. The first digital certificate (200) is digitally signed by the first certification authority (104) and includes subscriber information (206) pertaining to the first subscriber (102) and related certificate information (216) at least partially identifying a second digital certificate (200). The second digital certificate (200) is issued by a second certification authority (104) to a second subscriber (102) and is digitally signed by the second certification authority (104).