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cast6: minor code tweaks (#392)
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@newpavlov
newpavlov authored Nov 22, 2023
1 parent afe1f90 commit f415d78
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3 changes: 1 addition & 2 deletions cast6/LICENSE-MIT
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Original file line number Diff line number Diff line change
@@ -1,5 +1,4 @@
Copyright (c) 2018-2019 Friedel Ziegelmayer
Copyright (c) 2018-2023 The RustCrypto Project Developers
Copyright (c) 2023 The RustCrypto Project Developers

Permission is hereby granted, free of charge, to any
person obtaining a copy of this software and associated
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103 changes: 43 additions & 60 deletions cast6/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -62,34 +62,20 @@ pub struct Cast6 {
}

impl Cast6 {
fn init_state() -> Cast6 {
Cast6 {
masking: [[0u32; 4]; 12],
rotate: [[0u8; 4]; 12],
}
}

/// Implements the key schedule according to RFC 2612 2.4.
/// https://tools.ietf.org/html/rfc2612#section-2.4
fn key_schedule(&mut self, key: &[u8]) {
let mut kappa = [
u32::from_be_bytes(key[0..4].try_into().unwrap()),
u32::from_be_bytes(key[4..8].try_into().unwrap()),
u32::from_be_bytes(key[8..12].try_into().unwrap()),
u32::from_be_bytes(key[12..16].try_into().unwrap()),
u32::from_be_bytes(key[16..20].try_into().unwrap()),
u32::from_be_bytes(key[20..24].try_into().unwrap()),
u32::from_be_bytes(key[24..28].try_into().unwrap()),
u32::from_be_bytes(key[28..32].try_into().unwrap()),
];

fn key_schedule(&mut self, key: &[u8; 32]) {
let mut kappa = to_u32s(key);
for i in 0..12 {
let m = &TM[(i * 16)..(i * 16 + 8)];
let r = &TR[((i % 2) * 16)..((i % 2) * 16 + 8)];
let m_idx = 16 * i;
let r_idx = 16 * (i % 2);

let m = &TM[m_idx..][..8];
let r = &TR[r_idx..][..8];
forward_octave(&mut kappa, m, r);

let m = &TM[(i * 16 + 8)..(i * 16 + 16)];
let r = &TR[((i % 2) * 16 + 8)..((i % 2) * 16 + 16)];
let m = &TM[m_idx + 8..][..8];
let r = &TR[r_idx + 8..][..8];
forward_octave(&mut kappa, m, r);

let [a, b, c, d, e, f, g, h] = kappa;
Expand Down Expand Up @@ -132,7 +118,7 @@ macro_rules! f3 {
}

#[inline]
fn forward_quad(beta: &mut [u32; 4], m: &[u32], r: &[u8]) {
fn forward_quad(beta: &mut [u32; 4], m: &[u32; 4], r: &[u8; 4]) {
// Let "BETA <- Qi(BETA)" be short-hand notation for the following:
// C = C ^ f1(D, Kr0_(i), Km0_(i))
// B = B ^ f2(C, Kr1_(i), Km1_(i))
Expand All @@ -147,7 +133,7 @@ fn forward_quad(beta: &mut [u32; 4], m: &[u32], r: &[u8]) {
}

#[inline]
fn reverse_quad(beta: &mut [u32; 4], m: &[u32], r: &[u8]) {
fn reverse_quad(beta: &mut [u32; 4], m: &[u32; 4], r: &[u8; 4]) {
// Let "BETA <- QBARi(BETA)" be short-hand notation for the
// following:
// D = D ^ f1(A, Kr3_(i), Km3_(i))
Expand Down Expand Up @@ -199,19 +185,18 @@ impl KeyInit for Cast6 {

fn new_from_slice(key: &[u8]) -> Result<Self, InvalidLength> {
// Available key sizes are 128, 160, 192, 224, and 256 bits.
if key.len() < 16 || key.len() > 32 || key.len() % 4 != 0 {
if ![16, 20, 24, 28, 32].contains(&key.len()) {
return Err(InvalidLength);
}
let mut cast6 = Cast6::init_state();

if key.len() < 32 {
// Pad keys that are less than 256 bits long.
let mut padded_key = [0u8; 32];
padded_key[..key.len()].copy_from_slice(key);
cast6.key_schedule(&padded_key[..]);
} else {
cast6.key_schedule(key);
}
let mut cast6 = Self {
masking: [[0u32; 4]; 12],
rotate: [[0u8; 4]; 12],
};

// Pad keys that are less than 256 bits long.
let mut padded_key = [0u8; 32];
padded_key[..key.len()].copy_from_slice(key);
cast6.key_schedule(&padded_key);
Ok(cast6)
}
}
Expand Down Expand Up @@ -250,13 +235,7 @@ cipher::impl_simple_block_encdec!(
// Let BETA = (ABCD) be a 128-bit block where A, B, C and D are each
// 32 bits in length.
// BETA = 128bits of plaintext.
let b = block.get_in();
let mut beta = [
u32::from_be_bytes(b[0..4].try_into().unwrap()),
u32::from_be_bytes(b[4..8].try_into().unwrap()),
u32::from_be_bytes(b[8..12].try_into().unwrap()),
u32::from_be_bytes(b[12..16].try_into().unwrap()),
];
let mut beta = to_u32s(block.get_in());

// for (i=0; i<6; i++)
// BETA <- Qi(BETA)
Expand All @@ -277,23 +256,13 @@ cipher::impl_simple_block_encdec!(
reverse_quad(&mut beta, &masking[11], &rotate[11]);

// 128bits of ciphertext = BETA
let block = block.get_out();
block[0..4].copy_from_slice(&beta[0].to_be_bytes());
block[4..8].copy_from_slice(&beta[1].to_be_bytes());
block[8..12].copy_from_slice(&beta[2].to_be_bytes());
block[12..16].copy_from_slice(&beta[3].to_be_bytes());
*block.get_out() = to_u8s::<16>(&beta).into();
}
decrypt: {
let masking = &cipher.masking;
let rotate = &cipher.rotate;

let b = block.get_in();
let mut beta = [
u32::from_be_bytes(b[0..4].try_into().unwrap()),
u32::from_be_bytes(b[4..8].try_into().unwrap()),
u32::from_be_bytes(b[8..12].try_into().unwrap()),
u32::from_be_bytes(b[12..16].try_into().unwrap()),
];
let mut beta = to_u32s(block.get_in());

forward_quad(&mut beta, &masking[11], &rotate[11]);
forward_quad(&mut beta, &masking[10], &rotate[10]);
Expand All @@ -309,10 +278,24 @@ cipher::impl_simple_block_encdec!(
reverse_quad(&mut beta, &masking[1], &rotate[1]);
reverse_quad(&mut beta, &masking[0], &rotate[0]);

let block = block.get_out();
block[0..4].copy_from_slice(&beta[0].to_be_bytes());
block[4..8].copy_from_slice(&beta[1].to_be_bytes());
block[8..12].copy_from_slice(&beta[2].to_be_bytes());
block[12..16].copy_from_slice(&beta[3].to_be_bytes());
*block.get_out() = to_u8s::<16>(&beta).into();
}
);

fn to_u32s<const N: usize>(src: &[u8]) -> [u32; N] {
assert_eq!(src.len(), 4 * N);
let mut res = [0u32; N];
for (chunk, dst) in src.chunks_exact(4).zip(res.iter_mut()) {
*dst = u32::from_be_bytes(chunk.try_into().unwrap());
}
res
}

fn to_u8s<const N: usize>(src: &[u32]) -> [u8; N] {
assert_eq!(4 * src.len(), N);
let mut res = [0u8; N];
for (dst_chunk, src) in res.chunks_exact_mut(4).zip(src.iter()) {
dst_chunk.copy_from_slice(&src.to_be_bytes());
}
res
}
10 changes: 5 additions & 5 deletions cast6/tests/mod.rs
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
use cast6::Cast6;
use cipher::{generic_array::GenericArray, BlockDecrypt, BlockEncrypt, KeyInit};
use cipher::{Block, BlockDecrypt, BlockEncrypt, KeyInit};
use hex_literal::hex;

/// Test vectors from RFC 2612 Appendix A
Expand All @@ -9,10 +9,10 @@ fn rfc2144_a() {
let key128 = hex!("2342bb9efa38542c0af75647f29f615d");
let key192 = hex!("2342bb9efa38542cbed0ac83940ac298bac77a7717942863");
let key256 = hex!("2342bb9efa38542cbed0ac83940ac2988d7c47ce264908461cc1b5137ae6b604");
let ct128 = GenericArray::from(hex!("c842a08972b43d20836c91d1b7530f6b"));
let ct192 = GenericArray::from(hex!("1b386c0210dcadcbdd0e41aa08a7a7e8"));
let ct256 = GenericArray::from(hex!("4f6a2038286897b9c9870136553317fa"));
let pt = GenericArray::default();
let ct128 = hex!("c842a08972b43d20836c91d1b7530f6b").into();
let ct192 = hex!("1b386c0210dcadcbdd0e41aa08a7a7e8").into();
let ct256 = hex!("4f6a2038286897b9c9870136553317fa").into();
let pt = Block::<Cast6>::default();

let mut buf = pt;

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