From 313607f06ac439cb1f5d277f021a6b9931921af2 Mon Sep 17 00:00:00 2001
From: Isis Lovecruft <isis@torproject.org>
Date: Thu, 30 Nov 2017 22:04:47 +0000
Subject: [PATCH] Remove decaf fuzzer and change scalar fuzzer.

 * REMOVE fuzz/fuzz_targets/decaf.rs
 * RENAME fuzz/fuzz_targets/scalar_constructor_accepts_256bit_values.rs
   to fuzz/fuzz_targets/scalar_constructors_and_reduction.rs
 * CHANGE scalar_constructors_and_reduction fuzz target to test
   reduction after using the 255-bit constructor versus constructor
   mod order.
 * FIXES #91: https://github.com/isislovecruft/curve25519-dalek/issues/91
---
 fuzz/Cargo.toml                               |  4 ----
 fuzz/fuzz_targets/decaf.rs                    | 21 -------------------
 ...s => scalar_constructors_and_reduction.rs} | 14 +++++--------
 3 files changed, 5 insertions(+), 34 deletions(-)
 delete mode 100644 fuzz/fuzz_targets/decaf.rs
 rename fuzz/fuzz_targets/{scalar_constructor_accepts_256bit_values.rs => scalar_constructors_and_reduction.rs} (63%)

diff --git a/fuzz/Cargo.toml b/fuzz/Cargo.toml
index ceb067b..0dccf7b 100644
--- a/fuzz/Cargo.toml
+++ b/fuzz/Cargo.toml
@@ -23,10 +23,6 @@ git = "https://github.com/rust-fuzz/libfuzzer-sys.git"
 [workspace]
 members = ["."]
 
-[[bin]]
-name = "decaf"
-path = "fuzz_targets/decaf.rs"
-
 [[bin]]
 name = "scalar_constructor_accepts_256bit_values"
 path = "fuzz_targets/scalar_constructor_accepts_256bit_values.rs"
diff --git a/fuzz/fuzz_targets/decaf.rs b/fuzz/fuzz_targets/decaf.rs
deleted file mode 100644
index 5199183..0000000
--- a/fuzz/fuzz_targets/decaf.rs
+++ /dev/null
@@ -1,21 +0,0 @@
-#![no_main]
-#[macro_use] extern crate libfuzzer_sys;
-extern crate curve25519_dalek;
-
-use curve25519_dalek::curve::ValidityCheck;
-use curve25519_dalek::decaf::DecafPoint;
-use curve25519_dalek::field::FieldElement;
-
-fuzz_target!(|data: &[u8]| {
-    if data.len() != 32 {
-        return;
-    }
-    let mut field_bytes = [0u8; 32];
-    for (by, data) in field_bytes.iter_mut().zip(data.iter()) {
-        *by = *data;
-    }
-    let fe = FieldElement::from_bytes(&field_bytes);
-    let p = DecafPoint::elligator_decaf_flavour(&fe);
-    assert!(p.0.is_valid());
-    p.compress();
-});
diff --git a/fuzz/fuzz_targets/scalar_constructor_accepts_256bit_values.rs b/fuzz/fuzz_targets/scalar_constructors_and_reduction.rs
similarity index 63%
rename from fuzz/fuzz_targets/scalar_constructor_accepts_256bit_values.rs
rename to fuzz/fuzz_targets/scalar_constructors_and_reduction.rs
index 38bba88..fc3eba9 100644
--- a/fuzz/fuzz_targets/scalar_constructor_accepts_256bit_values.rs
+++ b/fuzz/fuzz_targets/scalar_constructors_and_reduction.rs
@@ -4,10 +4,10 @@ extern crate curve25519_dalek;
 
 use curve25519_dalek::scalar::Scalar;
 
-/// Check that the Scalar constructor accepts 256-bit input values and
+/// Check that the Scalar constructor accepts 255-bit input values and
 /// behaves correctly on them.
 ///
-/// Specifically, we take 256-bit values `a` and `b` from the fuzzer
+/// Specifically, we take 255-bit values `a` and `b` from the fuzzer
 /// input data and check that `(a mod l) * (b mod l) == (a * b) mod l`.
 fuzz_target!(|data: &[u8]| {
     if data.len() != 64 {
@@ -21,15 +21,11 @@ fuzz_target!(|data: &[u8]| {
     b_bytes.copy_from_slice(&data[32..64]);
 
     // Compute c = a*b (mod l)
-    let c1 = &Scalar(a_bytes) * &Scalar(b_bytes);
+    let c1 = (&Scalar::from_bits(a_bytes) * &Scalar::from_bits(b_bytes)).reduce();
 
     // Compute c = (a mod l) * (b mod l)
-    let mut tmp = [0u8; 64];
-    tmp[0..32].copy_from_slice(&a_bytes[..]);
-    let a_mod_l = Scalar::reduce(&tmp);
-    tmp[0..32].copy_from_slice(&b_bytes[..]);
-    let b_mod_l = Scalar::reduce(&tmp);
-
+    let a_mod_l = Scalar::from_bytes_mod_order(a_bytes);
+    let b_mod_l = Scalar::from_bytes_mod_order(b_bytes);
     let c2 = &a_mod_l * &b_mod_l;
 
     assert_eq!(c1, c2);