Belt-Wblock implementation (#362)

Author: makavity

Cargo.lock

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## 0.1.2 (2023-04-15)
+### Added
+- `belt_wblock_enc`, `belt_wblock_dec`, and `to_u32` functions ([#362])
+
+[#362]: https://github.com/RustCrypto/block-ciphers/pull/362
+
 ## 0.1.1 (2022-09-23)
 ### Added
 - `belt_block_raw` function and `cipher` crate feature (enabled by default) ([#333])

belt-block/CHANGELOG.md

@@ -1,6 +1,6 @@
 [package]
 name = "belt-block"
-version = "0.1.1"
+version = "0.1.2"
 description = "belt-block block cipher implementation"
 authors = ["RustCrypto Developers"]
 license = "MIT OR Apache-2.0"

belt-block/Cargo.toml

@@ -1,4 +1,4 @@
-use crate::{belt_block_raw, g13, g21, g5, key_idx};
+use crate::{belt_block_raw, from_u32, g13, g21, g5, key_idx, to_u32};
 use cipher::consts::{U16, U32};
 use cipher::{inout::InOut, AlgorithmName, Block, BlockCipher, Key, KeyInit, KeySizeUser};
 use core::{fmt, mem::swap, num::Wrapping};
@@ -17,34 +17,25 @@ impl BeltBlock {
     /// Encryption as described in section 6.1.3
     #[inline]
     fn encrypt(&self, mut block: InOut<'_, '_, Block<Self>>) {
-        let block_in = block.get_in();
         // Steps 1 and 4
-        let x = [
-            get_u32(block_in, 0),
-            get_u32(block_in, 1),
-            get_u32(block_in, 2),
-            get_u32(block_in, 3),
-        ];
-
+        let x = to_u32(block.get_in());
         let y = belt_block_raw(x, &self.key);
 
         let block_out = block.get_out();
         // 6) Y ← b ‖ d ‖ a ‖ c
-        for i in 0..4 {
-            set_u32(block_out, &y, i);
-        }
+        *block_out = from_u32(&y).into();
     }
 
     /// Decryption as described in section 6.1.4
     #[inline]
     fn decrypt(&self, mut block: InOut<'_, '_, Block<Self>>) {
         let key = &self.key;
-        let block_in = block.get_in();
+        let block_in: [u32; 4] = to_u32(block.get_in());
         // Steps 1 and 4
-        let mut a = Wrapping(get_u32(block_in, 0));
-        let mut b = Wrapping(get_u32(block_in, 1));
-        let mut c = Wrapping(get_u32(block_in, 2));
-        let mut d = Wrapping(get_u32(block_in, 3));
+        let mut a = Wrapping(block_in[0]);
+        let mut b = Wrapping(block_in[1]);
+        let mut c = Wrapping(block_in[2]);
+        let mut d = Wrapping(block_in[3]);
 
         // Step 5
         for i in (1..9).rev() {
@@ -77,9 +68,7 @@ impl BeltBlock {
         let block_out = block.get_out();
         // 6) 𝑋 ← c ‖ a ‖ d ‖ b
         let x = [c.0, a.0, d.0, b.0];
-        for i in 0..4 {
-            set_u32(block_out, &x, i);
-        }
+        *block_out = from_u32(&x).into();
     }
 }
 
@@ -91,18 +80,7 @@ impl KeySizeUser for BeltBlock {
 
 impl KeyInit for BeltBlock {
     fn new(key: &Key<Self>) -> Self {
-        Self {
-            key: [
-                get_u32(key, 0),
-                get_u32(key, 1),
-                get_u32(key, 2),
-                get_u32(key, 3),
-                get_u32(key, 4),
-                get_u32(key, 5),
-                get_u32(key, 6),
-                get_u32(key, 7),
-            ],
-        }
+        Self { key: to_u32(key) }
     }
 }
 
@@ -133,13 +111,3 @@ cipher::impl_simple_block_encdec!(
         cipher.decrypt(block);
     }
 );
-
-#[inline(always)]
-fn get_u32(block: &[u8], i: usize) -> u32 {
-    u32::from_le_bytes(block[4 * i..][..4].try_into().unwrap())
-}
-
-#[inline(always)]
-fn set_u32(block: &mut [u8], val: &[u32; 4], i: usize) {
-    block[4 * i..][..4].copy_from_slice(&val[i].to_le_bytes());
-}

belt-block/src/cipher_impl.rs

@@ -99,3 +99,103 @@ pub fn belt_block_raw(x: [u32; 4], key: &[u32; 8]) -> [u32; 4] {
     // Step 6
     [b.0, d.0, a.0, c.0]
 }
+
+const BLOCK_SIZE: usize = 16;
+type Block = [u8; BLOCK_SIZE];
+
+/// Wide block encryption as described in section 6.2.3 of the standard.
+///
+/// Returns [`InvalidLengthError`] if `data` is smaller than 32 bytes.
+#[inline]
+pub fn belt_wblock_enc(data: &mut [u8], key: &[u32; 8]) -> Result<(), InvalidLengthError> {
+    if data.len() < 2 * BLOCK_SIZE {
+        return Err(InvalidLengthError);
+    }
+
+    let len = data.len();
+    let n = (len + BLOCK_SIZE - 1) / BLOCK_SIZE;
+    for i in 1..(2 * n + 1) {
+        let s = data[..len - 1]
+            .chunks_exact(BLOCK_SIZE)
+            .fold(Block::default(), xor);
+
+        data.copy_within(BLOCK_SIZE.., 0);
+        let (tail1, tail2) = data[len - 2 * BLOCK_SIZE..].split_at_mut(BLOCK_SIZE);
+        tail2.copy_from_slice(&s);
+
+        let s = belt_block_raw(to_u32(&s), key);
+        xor_set(tail1, &from_u32::<16>(&s));
+        xor_set(tail1, &i.to_le_bytes());
+    }
+
+    Ok(())
+}
+
+/// Wide block decryption as described in section 6.2.4 of the standard.
+///
+/// Returns [`InvalidLengthError`] if `data` is smaller than 32 bytes.
+#[inline]
+pub fn belt_wblock_dec(data: &mut [u8], key: &[u32; 8]) -> Result<(), InvalidLengthError> {
+    if data.len() < 2 * BLOCK_SIZE {
+        return Err(InvalidLengthError);
+    }
+
+    let len = data.len();
+    let n = (len + BLOCK_SIZE - 1) / BLOCK_SIZE;
+    for i in (1..(2 * n + 1)).rev() {
+        let tail_pos = len - BLOCK_SIZE;
+        let s = Block::try_from(&data[tail_pos..]).unwrap();
+        data.copy_within(..tail_pos, BLOCK_SIZE);
+
+        let s_enc = belt_block_raw(to_u32(&s), key);
+        xor_set(&mut data[tail_pos..], &from_u32::<16>(&s_enc));
+        xor_set(&mut data[tail_pos..], &i.to_le_bytes());
+
+        let r1 = data[..len - 1]
+            .chunks_exact(BLOCK_SIZE)
+            .skip(1)
+            .fold(s, xor);
+        data[..BLOCK_SIZE].copy_from_slice(&r1);
+    }
+    Ok(())
+}
+
+/// Error used when data smaller than 32 bytes is passed to the `belt-wblock` functions.
+#[derive(Debug, Copy, Clone)]
+pub struct InvalidLengthError;
+
+/// Helper function for transforming BelT keys and blocks from a byte array
+/// to an array of `u32`s.
+///
+/// # Panics
+/// If length of `src` is not equal to `4 * N`.
+#[inline(always)]
+pub fn to_u32<const N: usize>(src: &[u8]) -> [u32; N] {
+    assert_eq!(src.len(), 4 * N);
+    let mut res = [0u32; N];
+    res.iter_mut()
+        .zip(src.chunks_exact(4))
+        .for_each(|(dst, src)| *dst = u32::from_le_bytes(src.try_into().unwrap()));
+    res
+}
+
+#[inline(always)]
+fn from_u32<const N: usize>(src: &[u32]) -> [u8; N] {
+    assert_eq!(N, 4 * src.len());
+    let mut res = [0u8; N];
+    res.chunks_exact_mut(4)
+        .zip(src.iter())
+        .for_each(|(dst, src)| dst.copy_from_slice(&src.to_le_bytes()));
+    res
+}
+
+#[inline(always)]
+fn xor_set(block: &mut [u8], val: &[u8]) {
+    block.iter_mut().zip(val.iter()).for_each(|(a, b)| *a ^= b);
+}
+
+#[inline(always)]
+fn xor(mut block: Block, val: &[u8]) -> Block {
+    block.iter_mut().zip(val.iter()).for_each(|(a, b)| *a ^= b);
+    block
+}

belt-block/src/lib.rs

@@ -1,42 +1,33 @@
+//! Example vectors from STB 34.101.31 (2020):
+//! http://apmi.bsu.by/assets/files/std/belt-spec371.pdf
+use belt_block::{belt_block_raw, belt_wblock_dec, belt_wblock_enc, to_u32};
 #[cfg(feature = "cipher")]
-use belt_block::BeltBlock;
-#[cfg(feature = "cipher")]
-use cipher::{BlockDecrypt, BlockEncrypt, KeyInit};
+use belt_block::{
+    cipher::{BlockDecrypt, BlockEncrypt, KeyInit},
+    BeltBlock,
+};
 use hex_literal::hex;
 
-fn get_u32(block: &[u8], i: usize) -> u32 {
-    u32::from_le_bytes(block[4 * i..][..4].try_into().unwrap())
-}
-
-/// Example vectors from STB 34.101.31 (2020):
-/// http://apmi.bsu.by/assets/files/std/belt-spec371.pdf
 #[test]
 fn belt_block() {
     // Table A.1
-    let key1 = hex!("E9DEE72C 8F0C0FA6 2DDB49F4 6F739647 06075316 ED247A37 39CBA383 03A98BF6");
+    let key1 = hex!(
+        "E9DEE72C 8F0C0FA6 2DDB49F4 6F739647"
+        "06075316 ED247A37 39CBA383 03A98BF6"
+    );
     let pt1 = hex!("B194BAC8 0A08F53B 366D008E 584A5DE4");
     let ct1 = hex!("69CCA1C9 3557C9E3 D66BC3E0 FA88FA6E");
     // Table A.2
-    let key2 = hex!("92BD9B1C E5D14101 5445FBC9 5E4D0EF2 682080AA 227D642F 2687F934 90405511");
+    let key2 = hex!(
+        "92BD9B1C E5D14101 5445FBC9 5E4D0EF2"
+        "682080AA 227D642F 2687F934 90405511"
+    );
     let pt2 = hex!("0DC53006 00CAB840 B38448E5 E993F421");
     let ct2 = hex!("E12BDC1A E28257EC 703FCCF0 95EE8DF1");
 
     for (key, pt, ct) in [(key1, pt1, ct1), (key2, pt2, ct2)] {
-        let mut k = [0u32; 8];
-        for i in 0..8 {
-            k[i] = get_u32(&key, i);
-        }
-        let mut x = [0u32; 4];
-        for i in 0..4 {
-            x[i] = get_u32(&pt, i);
-        }
-        let mut y = [0u32; 4];
-        for i in 0..4 {
-            y[i] = get_u32(&ct, i);
-        }
-
-        let res = belt_block::belt_block_raw(x, &k);
-        assert_eq!(res, y);
+        let res = belt_block_raw(to_u32(&pt), &to_u32(&key));
+        assert_eq!(res, to_u32(&ct));
 
         #[cfg(feature = "cipher")]
         {
@@ -49,3 +40,87 @@ fn belt_block() {
         }
     }
 }
+
+#[test]
+fn belt_wblock() {
+    // Table A.6
+    let k1 = hex!(
+        "E9DEE72C 8F0C0FA6 2DDB49F4 6F739647"
+        "06075316 ED247A37 39CBA383 03A98BF6"
+    );
+    let x1 = hex!(
+        "B194BAC8 0A08F53B 366D008E 584A5DE4"
+        "8504FA9D 1BB6C7AC 252E72C2 02FDCE0D"
+        "5BE3D612 17B96181 FE6786AD 716B890B"
+    );
+    let y1 = hex!(
+        "49A38EE1 08D6C742 E52B774F 00A6EF98"
+        "B106CBD1 3EA4FB06 80323051 BC04DF76"
+        "E487B055 C69BCF54 1176169F 1DC9F6C8"
+    );
+    let x2 = hex!(
+        "B194BAC8 0A08F53B 366D008E 584A5DE4"
+        "8504FA9D 1BB6C7AC 252E72C2 02FDCE0D"
+        "5BE3D612 17B96181 FE6786AD 716B89"
+    );
+    let y2 = hex!(
+        "F08EF22D CAA06C81 FB127219 74221CA7"
+        "AB82C628 56FCF2F9 FCA006E0 19A28F16"
+        "E5821A51 F5735946 25DBAB8F 6A5C94"
+    );
+
+    // Table A.7
+    let k2 = hex!(
+        "92BD9B1C E5D14101 5445FBC9 5E4D0EF2"
+        "682080AA 227D642F 2687F934 90405511"
+    );
+    let y3 = hex!(
+        "E12BDC1A E28257EC 703FCCF0 95EE8DF1"
+        "C1AB7638 9FE678CA F7C6F860 D5BB9C4F"
+        "F33C657B 637C306A DD4EA779 9EB23D31"
+    );
+    let x3 = hex!(
+        "92632EE0 C21AD9E0 9A39343E 5C07DAA4"
+        "889B03F2 E6847EB1 52EC99F7 A4D9F154"
+        "B5EF68D8 E4A39E56 7153DE13 D72254EE"
+    );
+    let x4 = hex!(
+        "DF3F8822 30BAAFFC 92F05660 32117231"
+        "0E3CB218 2681EF43 102E6717 5E177BD7"
+        "5E93E4E8"
+    );
+    let y4 = hex!(
+        "E12BDC1A E28257EC 703FCCF0 95EE8DF1"
+        "C1AB7638 9FE678CA F7C6F860 D5BB9C4F"
+        "F33C657B"
+    );
+
+    let tests = [
+        (k1, &x1[..], &y1[..]),
+        (k1, &x2[..], &y2[..]),
+        (k2, &x3[..], &y3[..]),
+        (k2, &x4[..], &y4[..]),
+    ];
+    for (key, x, y) in tests {
+        let k = to_u32(&key);
+        let mut t = x.to_vec();
+        belt_wblock_enc(&mut t, &k).unwrap();
+        assert_eq!(t, y);
+        belt_wblock_dec(&mut t, &k).unwrap();
+        assert_eq!(t, x)
+    }
+
+    // synthetic round-trip tests
+    let k = to_u32(&k1);
+    let x: Vec<u8> = (0u8..255).collect();
+    for i in 32..x.len() {
+        let mut t = x[..i].to_vec();
+        for _ in 0..16 {
+            belt_wblock_enc(&mut t, &k).unwrap();
+        }
+        for _ in 0..16 {
+            belt_wblock_dec(&mut t, &k).unwrap();
+        }
+        assert_eq!(t, x[..i]);
+    }
+}