dbl/
lib.rs

1//! Double operation in Galois Field (GF)
2#![no_std]
3#![doc(
4    html_logo_url = "https://raw.githubusercontent.com/RustCrypto/media/6ee8e381/logo.svg",
5    html_favicon_url = "https://raw.githubusercontent.com/RustCrypto/media/6ee8e381/logo.svg",
6    html_root_url = "https://docs.rs/dbl/0.3.2"
7)]
8#![forbid(unsafe_code)]
9
10extern crate generic_array;
11
12use generic_array::typenum::{U16, U32, U8};
13use generic_array::GenericArray;
14
15use core::convert::TryInto;
16
17const C64: u64 = 0b1_1011;
18const C128: u64 = 0b1000_0111;
19const C256: u64 = 0b100_0010_0101;
20
21/// Double and inverse double over GF(2^n).
22///
23/// This trait is implemented for 64, 128 and 256 bit block sizes. Big-endian
24/// order is used.
25pub trait Dbl {
26    /// Double block. (alternatively: multiply block by x)
27    ///
28    /// If most significant bit of the block equals to zero will return
29    /// `block<<1`, otherwise `(block<<1)^C`, where `C` is the non-leading
30    /// coefficients of the lexicographically first irreducible degree-b binary
31    /// polynomial with the minimal number of ones.
32    fn dbl(self) -> Self;
33
34    /// Reverse double block. (alternatively: divbide block by x)
35    ///
36    /// If least significant bit of the block equals to zero will return
37    /// `block>>1`, otherwise `(block>>1)^(1<<n)^(C>>1)`
38    fn inv_dbl(self) -> Self;
39}
40
41impl Dbl for GenericArray<u8, U8> {
42    #[inline]
43    fn dbl(self) -> Self {
44        let mut val = u64::from_be_bytes(self.into());
45
46        let a = val >> 63;
47        val <<= 1;
48        val ^= a * C64;
49
50        val.to_be_bytes().into()
51    }
52
53    #[inline]
54    fn inv_dbl(self) -> Self {
55        let mut val = u64::from_be_bytes(self.into());
56
57        let a = val & 1;
58        val >>= 1;
59        val ^= a * ((1 << 63) ^ (C64 >> 1));
60
61        val.to_be_bytes().into()
62    }
63}
64
65impl Dbl for GenericArray<u8, U16> {
66    #[inline]
67    fn dbl(self) -> Self {
68        let mut val = [
69            u64::from_be_bytes(self[..8].try_into().unwrap()),
70            u64::from_be_bytes(self[8..].try_into().unwrap()),
71        ];
72
73        let b = val[1] >> 63;
74        let a = val[0] >> 63;
75
76        val[0] <<= 1;
77        val[0] ^= b;
78        val[1] <<= 1;
79        val[1] ^= a * C128;
80
81        let mut res = Self::default();
82        res[..8].copy_from_slice(&val[0].to_be_bytes());
83        res[8..].copy_from_slice(&val[1].to_be_bytes());
84        res
85    }
86
87    #[inline]
88    fn inv_dbl(self) -> Self {
89        let mut val = [
90            u64::from_be_bytes(self[..8].try_into().unwrap()),
91            u64::from_be_bytes(self[8..].try_into().unwrap()),
92        ];
93
94        let a = (val[0] & 1) << 63;
95        let b = val[1] & 1;
96
97        val[0] >>= 1;
98        val[1] >>= 1;
99        val[1] ^= a;
100        val[0] ^= b * (1 << 63);
101        val[1] ^= b * (C128 >> 1);
102
103        let mut res = Self::default();
104        res[..8].copy_from_slice(&val[0].to_be_bytes());
105        res[8..].copy_from_slice(&val[1].to_be_bytes());
106        res
107    }
108}
109
110impl Dbl for GenericArray<u8, U32> {
111    #[inline]
112    fn dbl(self) -> Self {
113        let mut val = [
114            u64::from_be_bytes(self[0..8].try_into().unwrap()),
115            u64::from_be_bytes(self[8..16].try_into().unwrap()),
116            u64::from_be_bytes(self[16..24].try_into().unwrap()),
117            u64::from_be_bytes(self[24..32].try_into().unwrap()),
118        ];
119
120        let a = val[0] >> 63;
121        let b = val[1] >> 63;
122        let c = val[2] >> 63;
123        let d = val[3] >> 63;
124
125        val[0] <<= 1;
126        val[0] ^= b;
127        val[1] <<= 1;
128        val[1] ^= c;
129        val[2] <<= 1;
130        val[2] ^= d;
131        val[3] <<= 1;
132        val[3] ^= a * C256;
133
134        let mut res = Self::default();
135        res[0..8].copy_from_slice(&val[0].to_be_bytes());
136        res[8..16].copy_from_slice(&val[1].to_be_bytes());
137        res[16..24].copy_from_slice(&val[2].to_be_bytes());
138        res[24..32].copy_from_slice(&val[3].to_be_bytes());
139        res
140    }
141
142    #[inline]
143    fn inv_dbl(self) -> Self {
144        let mut val = [
145            u64::from_be_bytes(self[0..8].try_into().unwrap()),
146            u64::from_be_bytes(self[8..16].try_into().unwrap()),
147            u64::from_be_bytes(self[16..24].try_into().unwrap()),
148            u64::from_be_bytes(self[24..32].try_into().unwrap()),
149        ];
150
151        let a = (val[0] & 1) << 63;
152        let b = (val[1] & 1) << 63;
153        let c = (val[2] & 1) << 63;
154        let d = val[3] & 1;
155
156        val[0] >>= 1;
157        val[1] >>= 1;
158        val[2] >>= 1;
159        val[3] >>= 1;
160        val[1] ^= a;
161        val[2] ^= b;
162        val[3] ^= c;
163
164        val[0] ^= d * (1 << 63);
165        val[3] ^= d * (C256 >> 1);
166
167        let mut res = Self::default();
168        res[0..8].copy_from_slice(&val[0].to_be_bytes());
169        res[8..16].copy_from_slice(&val[1].to_be_bytes());
170        res[16..24].copy_from_slice(&val[2].to_be_bytes());
171        res[24..32].copy_from_slice(&val[3].to_be_bytes());
172        res
173    }
174}
dbl/lib.rs

dbl/
lib.rs
