From 20bc9200b2c28172cb5e04ccbd1cde5a6e47fa79 Mon Sep 17 00:00:00 2001
From: Christopher Patton <cpatton@cloudflare.com>
Date: Mon, 13 Jan 2025 13:03:26 -0800
Subject: [PATCH] Move `szk` module from `flp` to `vdaf::mastic`

Some of the implementation details of SZK are, for the moment, specific
to Mastic. For example, the domain separation tag for each XOF
invocation is prefixed by `b"mastic"`. It therefore makes sense to move
this module to `mastic` until such time we need to refactor in order to
use SZK in multiple places.
---
 src/flp.rs                      |  2 --
 src/vdaf.rs                     |  4 ++--
 src/vdaf/mastic.rs              | 15 ++++++++-------
 src/{flp => vdaf/mastic}/szk.rs |  0
 4 files changed, 10 insertions(+), 11 deletions(-)
 rename src/{flp => vdaf/mastic}/szk.rs (100%)

diff --git a/src/flp.rs b/src/flp.rs
index a34f3cf0..d6e1bdf8 100644
--- a/src/flp.rs
+++ b/src/flp.rs
@@ -57,8 +57,6 @@ use std::convert::TryFrom;
 use std::fmt::Debug;
 
 pub mod gadgets;
-#[cfg(all(feature = "crypto-dependencies", feature = "experimental"))]
-pub mod szk;
 pub mod types;
 
 /// Errors propagated by methods in this module.
diff --git a/src/vdaf.rs b/src/vdaf.rs
index c992869b..c76bf456 100644
--- a/src/vdaf.rs
+++ b/src/vdaf.rs
@@ -8,10 +8,10 @@
 #[cfg(feature = "experimental")]
 use crate::dp::DifferentialPrivacyStrategy;
 #[cfg(all(feature = "crypto-dependencies", feature = "experimental"))]
-use crate::flp::szk::SzkError;
-#[cfg(all(feature = "crypto-dependencies", feature = "experimental"))]
 use crate::idpf::IdpfError;
 #[cfg(all(feature = "crypto-dependencies", feature = "experimental"))]
+use crate::vdaf::mastic::szk::SzkError;
+#[cfg(all(feature = "crypto-dependencies", feature = "experimental"))]
 use crate::vidpf::VidpfError;
 use crate::{
     codec::{CodecError, Decode, Encode, ParameterizedDecode},
diff --git a/src/vdaf/mastic.rs b/src/vdaf/mastic.rs
index f0bf9a4a..0b165552 100644
--- a/src/vdaf/mastic.rs
+++ b/src/vdaf/mastic.rs
@@ -8,10 +8,7 @@ use crate::{
     bt::BinaryTree,
     codec::{CodecError, Decode, Encode, ParameterizedDecode},
     field::{decode_fieldvec, FieldElement, FieldElementWithInteger},
-    flp::{
-        szk::{Szk, SzkInputShare, SzkJointShare, SzkQueryShare, SzkQueryState},
-        Type,
-    },
+    flp::Type,
     vdaf::{
         poplar1::{Poplar1, Poplar1AggregationParam},
         xof::{Seed, Xof},
@@ -24,6 +21,8 @@ use crate::{
     },
 };
 
+use szk::{Szk, SzkInputShare, SzkJointShare, SzkQueryShare, SzkQueryState};
+
 use rand::prelude::*;
 use std::io::{Cursor, Read};
 use std::ops::BitAnd;
@@ -33,6 +32,8 @@ use subtle::{Choice, ConstantTimeEq};
 
 use super::xof::XofTurboShake128;
 
+pub(crate) mod szk;
+
 pub(crate) const SEED_SIZE: usize = 32;
 pub(crate) const NONCE_SIZE: usize = 16;
 
@@ -319,9 +320,9 @@ impl<T: Type> Client<16> for Mastic<T> {
 
 /// Mastic preparation state.
 ///
-/// State held by an aggregator waiting for a message during Mastic preparation. Includes intermediate
-/// state for [`Szk`] verification, the output shares currently being validated, and
-/// parameters of Mastic used for encoding.
+/// State held by an aggregator waiting for a message during Mastic preparation. Includes
+/// intermediate state for the evaluation check, the range check (if applicable) verification, and
+/// the output shares currently being validated.
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub struct MasticPrepareState<F: FieldElement> {
     /// The counter and truncated weight for each candidate prefix.
diff --git a/src/flp/szk.rs b/src/vdaf/mastic/szk.rs
similarity index 100%
rename from src/flp/szk.rs
rename to src/vdaf/mastic/szk.rs