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use std::mem;
// Implementation of RFC 6479.
// https://tools.ietf.org/html/rfc6479
#[cfg(target_pointer_width = "64")]
type Word = u64;
#[cfg(target_pointer_width = "64")]
const REDUNDANT_BIT_SHIFTS: usize = 6;
#[cfg(target_pointer_width = "32")]
type Word = u32;
#[cfg(target_pointer_width = "32")]
const REDUNDANT_BIT_SHIFTS: usize = 5;
const SIZE_OF_WORD: usize = mem::size_of::<Word>() * 8;
const BITMAP_BITLEN: usize = 2048;
const BITMAP_LEN: usize = BITMAP_BITLEN / SIZE_OF_WORD;
const BITMAP_INDEX_MASK: u64 = BITMAP_LEN as u64 - 1;
const BITMAP_LOC_MASK: u64 = (SIZE_OF_WORD - 1) as u64;
const WINDOW_SIZE: u64 = (BITMAP_BITLEN - SIZE_OF_WORD) as u64;
pub struct AntiReplay {
bitmap: [Word; BITMAP_LEN],
last: u64,
}
impl Default for AntiReplay {
fn default() -> Self {
AntiReplay::new()
}
}
impl AntiReplay {
pub fn new() -> Self {
debug_assert_eq!(1 << REDUNDANT_BIT_SHIFTS, SIZE_OF_WORD);
debug_assert_eq!(BITMAP_BITLEN % SIZE_OF_WORD, 0);
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;
}
/// Checks and marks a sequence number in the replay filter
///
/// # Arguments
///
/// - seq: Sequence number check for replay and add to filter
///
/// # Returns
///
/// Ok(()) if sequence number is valid (not marked and not behind the moving window).
/// Err if the sequence number is invalid (already marked or "too old").
pub fn update(&mut self, seq: u64) -> bool {
if self.check(seq) {
self.update_store(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.update(i));
}
for i in (0..20000).rev() {
assert!(!ar.check(i));
}
assert!(ar.update(65536));
for i in (65536 - WINDOW_SIZE)..65535 {
assert!(ar.update(i));
}
for i in (65536 - 10 * WINDOW_SIZE)..65535 {
assert!(!ar.check(i));
}
assert!(ar.update(66000));
for i in 65537..66000 {
assert!(ar.update(i));
}
for i in 65537..66000 {
assert_eq!(ar.update(i), false);
}
// Test max u64.
let next = u64::max_value();
assert!(ar.update(next));
assert!(!ar.check(next));
for i in (next - WINDOW_SIZE)..next {
assert!(ar.update(i));
}
for i in (next - 20 * WINDOW_SIZE)..next {
assert!(!ar.check(i));
}
}
}
|
