ascon-xof128: replace implementation of CustomizedInit with TryCustomizedInit (#859)

Author: newpavlov

ascon-xof128/CHANGELOG.md

@@ -8,8 +8,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Changed
 - Internal implementation by removing unnecessary buffering ([#849])
 - Serialization format used by `SerializableState` implementations ([#849])
+- Replaced implementation of `CustomizedInit` with `TryCustomizedInit` ([#857])
 
 [#849]: https://github.com/RustCrypto/hashes/pull/849
+[#857]: https://github.com/RustCrypto/hashes/pull/857
 
 ## 0.1.0 (2026-04-24)
 - Initial release ([#841])

ascon-xof128/Cargo.toml

@@ -13,12 +13,12 @@ categories = ["cryptography", "no-std"]
 description = "Implementation of Ascon-XOF128 and Ascon-СXOF128"
 
 [dependencies]
-digest = { version = "0.11", default-features = false }
+digest = { version = "0.11.3", default-features = false }
 ascon = "0.5"
 sponge-cursor = "0.1"
 
 [dev-dependencies]
-digest = { version = "0.11", default-features = false, features = ["dev"] }
+digest = { version = "0.11.3", default-features = false, features = ["dev"] }
 hex-literal = "1"
 
 [features]

ascon-xof128/README.md

@@ -30,10 +30,10 @@ assert_eq!(dst, hex!("8C7DD114A0"));
 Ascon-CXOF128 works similarly, but you must specify a customization string to initialize it:
 
 ```rust
-use ascon_xof128::{AsconCxof128, CustomizedInit, ExtendableOutput, Update, XofReader};
+use ascon_xof128::{AsconCxof128, ExtendableOutput, TryCustomizedInit, Update, XofReader};
 use hex_literal::hex;
 
-let mut xof = AsconCxof128::new_customized(b"some customization string");
+let mut xof = AsconCxof128::try_new_customized(b"some customization string").unwrap();
 xof.update(b"some bytes");
 let mut reader = xof.finalize_xof();
 let mut dst = [0u8; 5];
@@ -45,8 +45,8 @@ Note that the NIST specifies that:
 
 >The length of the customization string **shall** be at most 2048 bits (i.e., 256 bytes).
 
-This limit is not enforced by the `new_customized` method; users must ensure their customization
-strings meet the size requirement if they intend to claim conformance to the standard.
+Implementation of the `TryCustomizedInit` trait for this type returns `InvalidCustomizationError`
+for longer customization strings.
 
 See the [`digest`] crate docs for additional examples.
 

ascon-xof128/src/cxof.rs

@@ -1,36 +1,45 @@
 use ascon::State;
+use core::fmt;
 use digest::{
-    CollisionResistance, CustomizedInit, ExtendableOutput, HashMarker, OutputSizeUser, Update,
-    common::AlgorithmName,
-    common::hazmat::{DeserializeStateError, SerializableState, SerializedState},
+    CollisionResistance, ExtendableOutput, HashMarker, OutputSizeUser, TryCustomizedInit, Update,
+    common::{
+        AlgorithmName,
+        hazmat::{DeserializeStateError, SerializableState, SerializedState},
+    },
     consts::{U16, U32, U41},
 };
 use sponge_cursor::SpongeCursor;
 
 use crate::{AsconXof128Reader, consts::CXOF_INIT_STATE};
 
+const MAX_CUSTOMIZATION_LEN: usize = 256;
+
 /// Ascon-CXOF128 hasher.
 ///
 /// Note that NIST SP 800-232 specifies the following:
 ///
 /// >The length of the customization string **shall** be at most 2048 bits (i.e., 256 bytes).
 ///
-/// We do not check this condition as part of [`CustomizedInit::new_customized`] and
-/// consider it the user's responsibility to use appropriately sized customization strings.
+/// Implementation of the [`TryCustomizedInit`] trait for this type returns
+/// [`InvalidCustomizationError`] for longer customization strings.
 #[derive(Clone, Debug)]
 pub struct AsconCxof128 {
     state: State,
     cursor: SpongeCursor<8>,
 }
 
-impl CustomizedInit for AsconCxof128 {
+impl TryCustomizedInit for AsconCxof128 {
+    type Error = InvalidCustomizationError;
     #[inline]
-    fn new_customized(customization: &[u8]) -> Self {
-        // We assume that in practice customization strings are always smaller than 2^61 bytes.
+    fn try_new_customized(customization: &[u8]) -> Result<Self, InvalidCustomizationError> {
+        if customization.len() > MAX_CUSTOMIZATION_LEN {
+            return Err(InvalidCustomizationError);
+        }
+
         let bit_len = 8 * customization.len();
         let mut state = CXOF_INIT_STATE;
 
-        state[0] ^= u64::try_from(bit_len).expect("`usize` always fits into `u64` in practice");
+        state[0] ^= u64::try_from(bit_len).expect("`bit_len` can not be greater than 2048");
 
         ascon::permute12(&mut state);
 
@@ -53,7 +62,7 @@ impl CustomizedInit for AsconCxof128 {
         ascon::permute12(&mut state);
 
         let cursor = Default::default();
-        Self { state, cursor }
+        Ok(Self { state, cursor })
     }
 }
 
@@ -141,3 +150,18 @@ impl Drop for AsconCxof128 {
 
 #[cfg(feature = "zeroize")]
 impl digest::zeroize::ZeroizeOnDrop for AsconCxof128 {}
+
+/// Invalid Ascon-CXOF128 customization string error.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct InvalidCustomizationError;
+
+impl fmt::Display for InvalidCustomizationError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(
+            "Invalid Ascon-CXOF128 customization string. \
+            The length of the customization string shall be at most 256 bytes.",
+        )
+    }
+}
+
+impl core::error::Error for InvalidCustomizationError {}

ascon-xof128/src/lib.rs

@@ -8,7 +8,7 @@
 #![warn(missing_docs, unreachable_pub)]
 #![forbid(unsafe_code)]
 
-pub use digest::{self, CustomizedInit, ExtendableOutput, Update, XofReader};
+pub use digest::{self, ExtendableOutput, TryCustomizedInit, Update, XofReader};
 
 mod consts;
 mod cxof;

ascon-xof128/tests/mod.rs

@@ -1,7 +1,7 @@
 use ascon_xof128::{AsconCxof128, AsconXof128};
 use core::fmt::Debug;
 use digest::{
-    CustomizedInit, ExtendableOutput, Update,
+    ExtendableOutput, TryCustomizedInit, Update,
     common::hazmat::SerializableState,
     dev::{feed_rand_16mib, xof_reset_test},
 };
@@ -59,7 +59,7 @@ fn ascon_xof128_rand() {
 
 #[test]
 fn ascon_cxof128_rand() {
-    let mut h = AsconCxof128::new_customized(b"randomized cxof test");
+    let mut h = AsconCxof128::try_new_customized(b"randomized cxof test").unwrap();
     h.update(b"hello");
     feed_rand_16mib(&mut h);
 
@@ -90,14 +90,16 @@ struct CxofTestVector {
 }
 
 /// Customized XOF test.
-fn cxof_reset_test<D: ExtendableOutput + CustomizedInit + Debug + Clone>(
+fn cxof_reset_test<D: ExtendableOutput + TryCustomizedInit + Debug + Clone>(
     &CxofTestVector {
         customization,
         input,
         output,
     }: &CxofTestVector,
 ) -> Result<(), &'static str> {
-    let mut hasher = D::new_customized(customization);
+    let Ok(mut hasher) = D::try_new_customized(customization) else {
+        return Err("initialization error");
+    };
     let mut buf = [0u8; 1024];
     let buf = &mut buf[..output.len()];
     // Test that it works when accepting the message all at once
@@ -110,7 +112,9 @@ fn cxof_reset_test<D: ExtendableOutput + CustomizedInit + Debug + Clone>(
 
     // Test that it works when accepting the message in chunks
     for n in 1..core::cmp::min(17, input.len()) {
-        let mut hasher = D::new_customized(customization);
+        let Ok(mut hasher) = D::try_new_customized(customization) else {
+            return Err("initialization error");
+        };
         for chunk in input.chunks(n) {
             hasher.update(chunk);
         }