Add hash customization traits

digest/src/core_api.rs

@@ -93,6 +93,12 @@ pub trait VariableOutputCore: UpdateCore + OutputSizeUser + BufferKindUser + Siz
     fn finalize_variable_core(&mut self, buffer: &mut Buffer<Self>, out: &mut Output<Self>);
 }
 
+/// Core trait for hash functions with customization string.
+pub trait CustomOutputCore {
+    /// Initialize hasher with customization string.
+    fn new(customization: &[u8]) -> Self;
+}
+
 /// Type which used for defining truncation side in the [`VariableOutputCore`]
 /// trait.
 #[derive(Copy, Clone, Debug)]

digest/src/core_api/wrapper.rs

@@ -2,8 +2,10 @@ use super::{
     AlgorithmName, Buffer, BufferKindUser, ExtendableOutputCore, FixedOutputCore, OutputSizeUser,
     Reset, UpdateCore, XofReaderCoreWrapper,
 };
+use crate::core_api::CustomOutputCore;
 use crate::{
-    ExtendableOutput, ExtendableOutputReset, FixedOutput, FixedOutputReset, HashMarker, Update,
+    CustomInit, ExtendableOutput, ExtendableOutputReset, FixedOutput, FixedOutputReset, HashMarker,
+    Update,
 };
 use block_buffer::BlockBuffer;
 use core::fmt;
@@ -184,6 +186,16 @@ where
     }
 }
 
+impl<T> CustomInit for CoreWrapper<T>
+where
+    T: BufferKindUser + CustomOutputCore,
+{
+    #[inline]
+    fn new_custom(customization: &[u8]) -> Self {
+        Self::from_core(T::new(customization))
+    }
+}
+
 #[cfg(feature = "oid")]
 #[cfg_attr(docsrs, doc(cfg(feature = "oid")))]
 impl<T> AssociatedOid for CoreWrapper<T>

digest/src/lib.rs

@@ -273,6 +273,12 @@ pub trait VariableOutputReset: VariableOutput + Reset {
     }
 }
 
+/// Trait for hash functions with customization string for domain separation.
+pub trait CustomInit {
+    /// Create new hasher instance with the given customization string.
+    fn new_custom(customization: &[u8]) -> Self;
+}
+
 /// The error type used in variable hash traits.
 #[derive(Clone, Copy, Debug, Default)]
 pub struct InvalidOutputSize;