diff --git a/draft-irtf-cfrg-vdaf.md b/draft-irtf-cfrg-vdaf.md index bcd0e9fb..01782b82 100644 --- a/draft-irtf-cfrg-vdaf.md +++ b/draft-irtf-cfrg-vdaf.md @@ -4562,17 +4562,16 @@ scheme would not allow key rotation over the lifetime of a task. ## Requirements for the Nonce {#nonce-requirements} The sharding and preparation steps of VDAF execution depend on a nonce -associated with the Client's report. To ensure privacy of the underlying -measurement, the Client MUST generate this nonce using a CSPRNG. This is -required in order to leverage security analysis for the privacy definition of -{{DPRS23}}, which assumes the nonce is chosen at random prior to generating the -report. +associated with the Client's report. To leverage the security analysis for the +privacy definition of {{DPRS23}}, which assumes the nonce is chosen at random +prior to generating the report, the client MUST generate this nonce using a +CSPRNG and the aggregators MUST verify that nonces are never re-used. Other security considerations may require the nonce to be non-repeating. For example, to achieve differential privacy it is necessary to avoid "over -exposing" a measurement by including it too many times in a single batch or -across multiple batches. It is RECOMMENDED that the nonce generated by the -Client be used by the Aggregators for replay protection. +exposing" a report by including it too many times in a single batch or across +multiple batches. It is RECOMMENDED that the nonce generated by the Client be +used by the Aggregators for replay protection. ## Requirements for the Aggregation Parameters