Direct Anonymous Attestation involves a Signer using a credential supplied by an Issuer to anonymously prove to a Verifier, on the basis of a public key of the Issuer, the Issuer's attestation to the Signer's membership of a particular group. To facilitate membership revocation, the Issuer updates the public key at intervals, and also effects a complementary updating to the Signer's credential unless the Signer has ceased to be a legitimate group member. A non-updated credential is inadequate to enable the Signer to prove its Issuer attested group membership to a Verifier on the basis of the updated Issuer public key.