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// Copyright 2017 Guanhao Yin <sopium@mysterious.site>
// This file is part of WireGuard.rs.
// WireGuard.rs is free software: you can redistribute it and/or
// modify it under the terms of the GNU General Public License as
// published by the Free Software Foundation, either version 3 of the
// License, or (at your option) any later version.
// WireGuard.rs is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with WireGuard.rs. If not, see <https://www.gnu.org/licenses/>.
// This is RFC 6479.
use std::cmp::min;
// Power of 2.
const BITMAP_BITLEN: u64 = 2048;
const SIZE_OF_INTEGER: u64 = 32;
const BITMAP_LEN: usize = (BITMAP_BITLEN / SIZE_OF_INTEGER) as usize;
const BITMAP_INDEX_MASK: u64 = BITMAP_LEN as u64 - 1;
// REDUNDANT_BIT_SHIFTS = log2(SIZE_OF_INTEGER).
const REDUNDANT_BIT_SHIFTS: u64 = 5;
const BITMAP_LOC_MASK: u64 = SIZE_OF_INTEGER - 1;
/// Size of anti-replay window.
pub const WINDOW_SIZE: u64 = BITMAP_BITLEN - SIZE_OF_INTEGER;
pub struct AntiReplay {
last: u64,
bitmap: [u32; BITMAP_LEN],
}
impl Default for AntiReplay {
fn default() -> Self {
AntiReplay::new()
}
}
impl AntiReplay {
pub fn new() -> Self {
AntiReplay {
last: 0,
bitmap: [0; BITMAP_LEN],
}
}
/// Returns true if check is passed, i.e., not a replay or too old.
///
/// Unlike RFC 6479, zero is allowed.
pub fn check(&self, seq: u64) -> bool {
// Larger is always good.
if seq > self.last {
return true;
}
if self.last - seq > WINDOW_SIZE {
return false;
}
let bit_location = seq & BITMAP_LOC_MASK;
let index = (seq >> REDUNDANT_BIT_SHIFTS) & BITMAP_INDEX_MASK;
self.bitmap[index as usize] & (1 << bit_location) == 0
}
/// Should only be called if check returns true.
pub fn update(&mut self, seq: u64) {
debug_assert!(self.check(seq));
let index = seq >> REDUNDANT_BIT_SHIFTS;
if seq > self.last {
let index_cur = self.last >> REDUNDANT_BIT_SHIFTS;
let diff = min(index - index_cur, BITMAP_LEN as u64);
for i in 0..diff {
let real_index = (index_cur + i + 1) & BITMAP_INDEX_MASK;
self.bitmap[real_index as usize] = 0;
}
self.last = seq;
}
let index = index & BITMAP_INDEX_MASK;
let bit_location = seq & BITMAP_LOC_MASK;
self.bitmap[index as usize] |= 1 << bit_location;
}
pub fn check_and_update(&mut self, seq: u64) -> bool {
if self.check(seq) {
self.update(seq);
true
} else {
false
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn anti_replay() {
let mut ar = AntiReplay::new();
for i in 0..20000 {
assert!(ar.check_and_update(i));
}
for i in (0..20000).rev() {
assert!(!ar.check(i));
}
assert!(ar.check_and_update(65536));
for i in (65536 - WINDOW_SIZE)..65535 {
assert!(ar.check_and_update(i));
}
for i in (65536 - 10 * WINDOW_SIZE)..65535 {
assert!(!ar.check(i));
}
ar.check_and_update(66000);
for i in 65537..66000 {
assert!(ar.check_and_update(i));
}
for i in 65537..66000 {
assert!(!ar.check_and_update(i));
}
// Test max u64.
let next = u64::max_value();
assert!(ar.check_and_update(next));
assert!(!ar.check(next));
for i in (next - WINDOW_SIZE)..next {
assert!(ar.check_and_update(i));
}
for i in (next - 20 * WINDOW_SIZE)..next {
assert!(!ar.check(i));
}
}
}
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