refactor xof

Author: newpavlov

ascon-xof128/Cargo.toml

@@ -10,7 +10,7 @@ repository = "https://github.com/RustCrypto/hashes"
 license = "Apache-2.0 OR MIT"
 keywords = ["hash", "ascon"]
 categories = ["cryptography", "no-std"]
-description = "Implementation of Ascon-XOF128"
+description = "Implementation of Ascon-XOF128 and Ascon-СXOF128"
 
 [dependencies]
 digest = "0.11"

ascon-xof128/README.md

@@ -7,7 +7,8 @@
 ![Rust Version][rustc-image]
 [![Project Chat][chat-image]][chat-link]
 
-Pure Rust implementation of the [Ascon-XOF128] extendable output function (XOF).
+Pure Rust implementation of the Ascon-XOF128 and Ascon-СXOF128 extendable output functions (XOF)
+specified in [NIST SP 800-232].
 
 ## Examples
 
@@ -23,7 +24,21 @@ xof.update(b"some bytes");
 let mut reader = xof.finalize_xof();
 let mut dst = [0u8; 5];
 reader.read(&mut dst);
-assert_eq!(dst, hex!("8c7dd114a0"));
+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 hex_literal::hex;
+
+let mut xof = AsconCxof128::new_customized(b"some customization string");
+xof.update(b"some bytes");
+let mut reader = xof.finalize_xof();
+let mut dst = [0u8; 5];
+reader.read(&mut dst);
+assert_eq!(dst, hex!("7824810FF7"));
 ```
 
 See the [`digest`] crate docs for additional examples.
@@ -58,5 +73,5 @@ dual licensed as above, without any additional terms or conditions.
 
 [//]: # (general links)
 
-[Ascon-XOF128]: https://doi.org/10.6028/NIST.SP.800-232.ipd
+[NIST SP 800-232]: https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-232.ipd.pdf
 [`digest`]: https://docs.rs/digest

ascon-xof128/src/block_api.rs

@@ -0,0 +1,13 @@
+use ascon::State;
+
+const XOF_IV: u64 = 0x0000_0800_00CC_0003;
+const CXOF_IV: u64 = 0x0000_0800_00CC_0004;
+
+pub(crate) const XOF_INIT_STATE: State = init_state(XOF_IV);
+pub(crate) const CXOF_INIT_STATE: State = init_state(CXOF_IV);
+
+const fn init_state(iv: u64) -> ascon::State {
+    let mut state = [iv, 0, 0, 0, 0];
+    ascon::permute12(&mut state);
+    state
+}