Zeroize allocated memory blocks for balloon-hash take 2

.github/workflows/balloon-hash.yml

@@ -61,4 +61,6 @@ jobs:
           toolchain: ${{ matrix.rust }}
           override: true
       - run: cargo test --release
+      - run: cargo test --release --no-default-features --features alloc
+      - run: cargo test --release --no-default-features --features alloc,zeroize
       - run: cargo test --release --all-features

balloon-hash/Cargo.toml

@@ -19,6 +19,7 @@ crypto-bigint = { version = "0.4", default-features = false, features = ["generi
 # optional dependencies
 password-hash = { version = "0.4", default-features = false, optional = true }
 rayon = { version = "1.5", optional = true }
+zeroize = { version = "1", default-features = false, optional = true }
 
 [dev-dependencies]
 hex-literal = "0.3"

balloon-hash/src/balloon.rs

@@ -131,7 +131,7 @@ where
     // for m from 1 to s_cost-1:
     for m in 1..s_cost {
         // buf[m] = hash(cnt++, buf[m-1])
-        Digest::update(&mut digest, &cnt.to_le_bytes());
+        Digest::update(&mut digest, cnt.to_le_bytes());
         cnt += 1;
         Digest::update(&mut digest, &buf[m - 1]);
         buf[m] = digest.finalize_reset();
@@ -151,7 +151,7 @@ where
             };
 
             // buf[m] = hash(cnt++, prev, buf[m])
-            Digest::update(&mut digest, &cnt.to_le_bytes());
+            Digest::update(&mut digest, cnt.to_le_bytes());
             cnt += 1;
             Digest::update(&mut digest, prev);
             Digest::update(&mut digest, &buf[m]);
@@ -161,13 +161,13 @@ where
             // for i from 0 to delta-1:
             for i in 0..DELTA {
                 // block_t idx_block = ints_to_block(t, m, i)
-                Digest::update(&mut digest, &t.to_le_bytes());
-                Digest::update(&mut digest, &(m as u64).to_le_bytes());
-                Digest::update(&mut digest, &i.to_le_bytes());
+                Digest::update(&mut digest, t.to_le_bytes());
+                Digest::update(&mut digest, (m as u64).to_le_bytes());
+                Digest::update(&mut digest, i.to_le_bytes());
                 let idx_block = digest.finalize_reset();
 
                 // int other = to_int(hash(cnt++, salt, idx_block)) mod s_cost
-                Digest::update(&mut digest, &cnt.to_le_bytes());
+                Digest::update(&mut digest, cnt.to_le_bytes());
                 cnt += 1;
                 Digest::update(&mut digest, salt);
 
@@ -188,7 +188,7 @@ where
                 );
 
                 // buf[m] = hash(cnt++, buf[m], buf[other])
-                Digest::update(&mut digest, &cnt.to_le_bytes());
+                Digest::update(&mut digest, cnt.to_le_bytes());
                 cnt += 1;
                 Digest::update(&mut digest, &buf[m]);
                 Digest::update(&mut digest, &buf[other]);

balloon-hash/src/lib.rs

@@ -22,6 +22,10 @@
 //! sha2 = "0.9"
 //! ```
 //!
+//! The `zeroize` crate feature will zeroize allocated memory created when
+//! using the [`Balloon::hash`] function. It will do nothing when the `alloc`
+//! crate feature is not active.
+//!
 //! The following example demonstrates the high-level password hashing API:
 //!
 //! ```
@@ -85,6 +89,9 @@ use digest::{Digest, FixedOutputReset};
 #[cfg(all(feature = "alloc", feature = "password-hash"))]
 use password_hash::{Decimal, Ident, ParamsString, Salt};
 
+#[cfg(feature = "zeroize")]
+use zeroize::Zeroize;
+
 /// Balloon context.
 ///
 /// This is the primary type of this crate's API, and contains the following:
@@ -128,7 +135,12 @@ where
         let mut memory = alloc::vec![GenericArray::default(); self.params.s_cost.get() as usize];
         #[cfg(feature = "parallel")]
         let mut memory = alloc::vec![GenericArray::default(); (self.params.s_cost.get() * self.params.p_cost.get()) as usize];
-        self.hash_with_memory(pwd, salt, &mut memory)
+
+        #[cfg_attr(not(feature = "zeroize"), allow(clippy::let_and_return))]
+        let output = self.hash_with_memory(pwd, salt, &mut memory);
+        #[cfg(feature = "zeroize")]
+        memory.iter_mut().for_each(|block| block.zeroize());
+        output
     }
 
     /// Hash a password and associated parameters.