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/* SPDX-License-Identifier: GPL-2.0
*
* Copyright (C) 2017-2018 WireGuard LLC. All Rights Reserved.
*/
use failure::Error;
// This is RFC 6479.
// 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 {
bitmap: [u32; BITMAP_LEN],
last: u64,
}
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.
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.
fn update_store(&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 = index - index_cur;
if diff >= BITMAP_LEN as u64 {
self.bitmap = [0; BITMAP_LEN];
} else {
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 update(&mut self, seq: u64) -> Result<(), Error> {
if self.check(seq) {
self.update_store(seq);
Ok(())
} else {
bail!("replayed nonce")
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn anti_replay() {
let mut ar = AntiReplay::new();
for i in 0..20000 {
ar.update(i).unwrap();
}
for i in (0..20000).rev() {
assert!(!ar.check(i));
}
ar.update(65536).unwrap();
for i in (65536 - WINDOW_SIZE)..65535 {
ar.update(i).unwrap();
}
for i in (65536 - 10 * WINDOW_SIZE)..65535 {
assert!(!ar.check(i));
}
ar.update(66000).unwrap();
for i in 65537..66000 {
ar.update(i).unwrap();
}
for i in 65537..66000 {
assert!(ar.update(i).is_err());
}
// Test max u64.
let next = u64::max_value();
ar.update(next).unwrap();
assert!(!ar.check(next));
for i in (next - WINDOW_SIZE)..next {
ar.update(i).unwrap();
}
for i in (next - 20 * WINDOW_SIZE)..next {
assert!(!ar.check(i));
}
}
#[bench]
fn bench_anti_replay_sequential(b: &mut ::test::Bencher) {
let mut ar = AntiReplay::new();
let mut seq = 0;
b.iter(|| {
ar.update(seq).unwrap();
seq += 1;
});
}
#[bench]
fn bench_anti_replay_old(b: &mut ::test::Bencher) {
let mut ar = AntiReplay::new();
ar.update(12345).unwrap();
ar.update(11234).unwrap();
b.iter(|| {
assert!(ar.update(11234).is_err());
});
}
#[bench]
fn bench_anti_replay_large_skip(b: &mut ::test::Bencher) {
let mut ar = AntiReplay::new();
let mut seq = 0;
b.iter(|| {
ar.update(seq).unwrap();
seq += 30000;
});
}
}
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