In whilelist-based authentication, a first device (102) in a system (100) authenticates itself to a second device (103) using a group certificate identifying a range of non-revoked device identifiers, said range encompassing the device identifier of the first device (102). Preferably the device identifiers correspond to leaf nodes in a hierarchically ordered tree, and the group certificate identifies a node (202-207) in the tree representing a subtree in which the leaf nodes correspond to said range. The group certificate can also identify a further node (308, 310, 312) in the subtree which represents a sub-subtree in which the leaf nodes correspond to revoked device identifiers. Alternatively, the device identifiers are selected from a sequentially ordered range, and the group certificate identifies a subrange of the sequentially ordered range, said subrange encompassing the whitelisted device identifiers.