Absorb elements from the validated input slice

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- Read the `Sponge::absorb` input through a single `as_ref` call
 - Wipe old output allocations before growth, including when continuing cloned sponges [#37]
 - Return an error and invalidate the sponge when output allocation fails [#37]
 - Wipe encryption/decryption temporary vectors on error and unwinding [#37]

src/sponge.rs

@@ -207,7 +207,8 @@ where
             return Err(Error::IOPatternViolation);
         }
         // Check that input yields enough elements
-        if input.as_ref().len() < len {
+        let input = input.as_ref();
+        if input.len() < len {
             self.zeroize();
             return Err(Error::TooFewInputElements);
         }
@@ -224,7 +225,7 @@ where
 
         // Absorb `len` elements into the state, calling [`permute`] when the
         // absorb-position reached the rate.
-        for element in input.as_ref().iter().take(len) {
+        for element in input.iter().take(len) {
             if self.pos_absorb == Self::RATE {
                 self.safe.permute(&mut self.state);
 

tests/sponge.rs

@@ -4,6 +4,8 @@
 //
 // Copyright (c) DUSK NETWORK. All rights reserved.
 
+use core::cell::Cell;
+
 use dusk_bls12_381::BlsScalar;
 use dusk_safe::{Call, Error, Safe, Sponge};
 use zeroize::Zeroize;
@@ -41,6 +43,23 @@ impl Rotate {
     }
 }
 
+#[test]
+fn absorb_uses_the_validated_slice() {
+    struct Input<'a>(Cell<&'a [BlsScalar]>);
+    impl AsRef<[BlsScalar]> for Input<'_> {
+        fn as_ref(&self) -> &[BlsScalar] {
+            self.0.replace(&[])
+        }
+    }
+    let input = [BlsScalar::from(7), BlsScalar::from(9)];
+    let mut sponge =
+        Sponge::start(Rotate::new(), [Call::Absorb(2), Call::Squeeze(1)], 0)
+            .unwrap();
+    sponge.absorb(2, Input(Cell::new(&input))).unwrap();
+    sponge.squeeze(1).unwrap();
+    assert_eq!(sponge.finish().unwrap(), [input[1]]);
+}
+
 #[test]
 fn failures_are_terminal() {
     for case in 0..9 {