  In this note, we remark that the aggregation property of the BLS signature
scheme yields an efficient Content Extraction Signature (CES). This
construction can be used to build digital credentials that support selective
disclosure in various settings. Interestingly, this construction is efficient
and well suited to build credential issuance schemes with various applications
in the client-server or in the distributed ledger models. Finally, we sketch a
protocol that combines the CES with the use of a NIZK which allows to prove
predicate satisfaction on claims extracted from a credential, while keeping the
data secret.
