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Use subtle::ConstantTimeEq for MAC and key comparisons #479

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1 change: 1 addition & 0 deletions Cargo.lock
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1 change: 1 addition & 0 deletions boringtun/Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,7 @@ tracing-subscriber = { version = "0.3", features = ["fmt"], optional = true }
ip_network = "0.4.1"
ip_network_table = "0.2.0"
ring = "0.17"
subtle = "2.6"
x25519-dalek = { version = "2.0.1", features = [
"reusable_secrets",
"static_secrets",
Expand Down
16 changes: 11 additions & 5 deletions boringtun/src/noise/handshake.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,7 @@ use rand_core::OsRng;
use ring::aead::{Aad, LessSafeKey, Nonce, UnboundKey, CHACHA20_POLY1305};
use std::convert::TryInto;
use std::time::{Duration, SystemTime};
use subtle::ConstantTimeEq;

#[cfg(feature = "mock-instant")]
use mock_instant::Instant;
Expand Down Expand Up @@ -521,11 +522,16 @@ impl Handshake {
&hash,
)?;

ring::constant_time::verify_slices_are_equal(
self.params.peer_static_public.as_bytes(),
&peer_static_public_decrypted,
)
.map_err(|_| WireGuardError::WrongKey)?;
if self
.params
.peer_static_public
.as_bytes()
.ct_eq(&peer_static_public_decrypted)
.unwrap_u8()
!= 1
{
return Err(WireGuardError::WrongKey);
}

// initiator.hash = HASH(initiator.hash || msg.encrypted_static)
hash = b2s_hash(&hash, packet.encrypted_static);
Expand Down
9 changes: 5 additions & 4 deletions boringtun/src/noise/rate_limiter.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@ use aead::{AeadInPlace, KeyInit};
use chacha20poly1305::{Key, XChaCha20Poly1305};
use parking_lot::Mutex;
use rand_core::{OsRng, RngCore};
use ring::constant_time::verify_slices_are_equal;
use subtle::ConstantTimeEq;

const COOKIE_REFRESH: u64 = 128; // Use 128 and not 120 so the compiler can optimize out the division
const COOKIE_SIZE: usize = 16;
Expand Down Expand Up @@ -166,8 +166,9 @@ impl RateLimiter {
let (mac1, mac2) = macs.split_at(16);

let computed_mac1 = b2s_keyed_mac_16(&self.mac1_key, msg);
verify_slices_are_equal(&computed_mac1[..16], mac1)
.map_err(|_| TunnResult::Err(WireGuardError::InvalidMac))?;
if computed_mac1[..16].ct_eq(mac1).unwrap_u8() != 1 {
return Err(TunnResult::Err(WireGuardError::InvalidMac));
}

if self.is_under_load() {
let addr = match src_addr {
Expand All @@ -179,7 +180,7 @@ impl RateLimiter {
let cookie = self.current_cookie(addr);
let computed_mac2 = b2s_keyed_mac_16_2(&cookie, msg, mac1);

if verify_slices_are_equal(&computed_mac2[..16], mac2).is_err() {
if computed_mac2[..16].ct_eq(mac2).unwrap_u8() != 1 {
let cookie_packet = self
.format_cookie_reply(sender_idx, cookie, mac1, dst)
.map_err(TunnResult::Err)?;
Expand Down