Fields within a document can be securely encrypted by the SDK, to support FIPS-140-2 compliance.
Field Level Encryption is normally carried out at a higher level than libcouchbase (LCB). It is not available directly in LCB.
If this is a requirement, we suggest considering a migration to the C++ SDK, which includes Field Level Encryption.
Alternately, take a look at Capella Operational and self-managed Couchbase Server’s Native Encryption at Rest feature.