Adopt prio::vdaf::dummy::Vdaf everywhere (#2692)

...and remove the dummy VDAF we had in Janus itself. This is a step
toward implementing support for VDAFs that use an aggregation parameter
(#225). We could use Poplar1, of course, but what's _really_ interesting
is Mastic, which besides using an aggregation parameter, is a
single-round VDAF. I want to be able to contrast the implementation
complexity of VDAFs with an aggregation parameter and ones that also
take multiple rounds, and the dummy VDAF is most expedient way to wire
up the former.

Also adopts `prio` 0.16.1, to pick up some bug fixes to the dummy VDAF.

Cargo.toml

@@ -47,7 +47,7 @@ k8s-openapi = { version = "0.20.0", features = ["v1_26"] }  # keep this version
 kube = { version = "0.87.2", default-features = false, features = ["client", "rustls-tls"] }
 opentelemetry = { version = "0.21", features = ["metrics"] }
 opentelemetry_sdk = { version = "0.21", features = ["metrics"] }
-prio = { version = "0.16.0", features = ["multithreaded", "experimental"] }
+prio = { version = "0.16.1", features = ["multithreaded", "experimental"] }
 serde = { version = "1.0.196", features = ["derive"] }
 serde_json = "1.0.113"
 serde_test = "1.0.175"

aggregator/src/aggregator.rs

@@ -39,8 +39,6 @@ use janus_aggregator_core::{
     task::{self, AggregatorTask, VerifyKey},
     taskprov::PeerAggregator,
 };
-#[cfg(feature = "test-util")]
-use janus_core::test_util::dummy_vdaf;
 #[cfg(feature = "fpvec_bounded_l2")]
 use janus_core::vdaf::Prio3FixedPointBoundedL2VecSumBitSize;
 use janus_core::{
@@ -71,7 +69,7 @@ use opentelemetry::{
 #[cfg(feature = "fpvec_bounded_l2")]
 use prio::vdaf::prio3::Prio3FixedPointBoundedL2VecSumMultithreaded;
 #[cfg(feature = "test-util")]
-use prio::vdaf::{PrepareTransition, VdafError};
+use prio::vdaf::{dummy, PrepareTransition, VdafError};
 use prio::{
     codec::{Decode, Encode, ParameterizedDecode},
     dp::DifferentialPrivacyStrategy,
@@ -943,11 +941,11 @@ impl<C: Clock> TaskAggregator<C> {
             }
 
             #[cfg(feature = "test-util")]
-            VdafInstance::Fake => VdafOps::Fake(Arc::new(dummy_vdaf::Vdaf::new())),
+            VdafInstance::Fake => VdafOps::Fake(Arc::new(dummy::Vdaf::new(1))),
 
             #[cfg(feature = "test-util")]
             VdafInstance::FakeFailsPrepInit => VdafOps::Fake(Arc::new(
-                dummy_vdaf::Vdaf::new().with_prep_init_fn(|_| -> Result<(), VdafError> {
+                dummy::Vdaf::new(1).with_prep_init_fn(|_| -> Result<(), VdafError> {
                     Err(VdafError::Uncategorized(
                         "FakeFailsPrepInit failed at prep_init".to_string(),
                     ))
@@ -956,8 +954,8 @@ impl<C: Clock> TaskAggregator<C> {
 
             #[cfg(feature = "test-util")]
             VdafInstance::FakeFailsPrepStep => {
-                VdafOps::Fake(Arc::new(dummy_vdaf::Vdaf::new().with_prep_step_fn(
-                    || -> Result<PrepareTransition<dummy_vdaf::Vdaf, 0, 16>, VdafError> {
+                VdafOps::Fake(Arc::new(dummy::Vdaf::new(1).with_prep_step_fn(
+                    |_| -> Result<PrepareTransition<dummy::Vdaf, 0, 16>, VdafError> {
                         Err(VdafError::Uncategorized(
                             "FakeFailsPrepStep failed at prep_step".to_string(),
                         ))
@@ -1181,7 +1179,7 @@ enum VdafOps {
         VerifyKey<VERIFY_KEY_LENGTH>,
     ),
     #[cfg(feature = "test-util")]
-    Fake(Arc<dummy_vdaf::Vdaf>),
+    Fake(Arc<dummy::Vdaf>),
 }
 
 /// Emits a match block dispatching on a [`VdafOps`] object. Takes a `&VdafOps` as the first
@@ -1314,7 +1312,7 @@ macro_rules! vdaf_ops_dispatch {
             crate::aggregator::VdafOps::Fake(vdaf) => {
                 let $vdaf = vdaf;
                 let $verify_key = &VerifyKey::new([]);
-                type $Vdaf = ::janus_core::test_util::dummy_vdaf::Vdaf;
+                type $Vdaf = ::prio::vdaf::dummy::Vdaf;
                 const $VERIFY_KEY_LENGTH: usize = 0;
                 type $DpStrategy = janus_core::dp::NoDifferentialPrivacy;
                 let $dp_strategy = &Arc::new(janus_core::dp::NoDifferentialPrivacy);