Browse WireGuard specs (12 of 38)
Proofs / WireGuard / Replay protection
rp_limit
Every nonce at or above REJECT_AFTER_MESSAGES (2^64 - 8130) is rejected.
- spec
- 19 lines of C
- with its headers
- 59 lines
- status
- Proved
- 12 of 38
On this page
The spec
The spec is the C program harness/rp_limit.c, 19 lines, shown whole as it is in the repository at 3c1fc13. It includes harness/wg_laws.h (40 lines). Its first comment states the property in full, with every bound.
// Law rp_limit: For a new key's replay window (zero, as keypair_create makes it), after any sequence of any number of
// any nonces given to counter_validate, every nonce at or above REJECT_AFTER_MESSAGES (2^64 - 8130) is rejected.
#include "wg_laws.h"
int main(void) {
// Choose the inputs: any nonces, then any nonce from REJECT_AFTER_MESSAGES to 2^64 - 1
struct noise_replay_counter window;
new_counter(&window);
while (nondet_u8() != 0)
(void) wg_counter_validate(&window, any_u64());
u64 n = REJECT_AFTER + upto(U64_MAX - REJECT_AFTER);
// Check. WireGuard paper, 6.2: "After Reject-After-Messages transport data messages ... WireGuard will refuse
// to send or receive any more transport data messages using the current secure session"; the paper's table
// gives 2^64 - 2^13 - 1, the kernel's messages.h "REJECT_AFTER_MESSAGES = U64_MAX - COUNTER_WINDOW_SIZE - 1"
// (63 more); selftest/counter.c, tests 25, 27, 30, 31.
bool accepted = wg_counter_validate(&window, n);
gp_assert(accepted == 0);
return 0;
}harness/wg_laws.h, 40 lines
// wg_laws.h: trivial helpers shared by the WireGuard laws (each law includes it once). No models, no algorithms.
#include "quickproof.h"
#include "noise.h"
#include <crypto/blake2s.h>
#include <crypto/chacha.h>
#include <crypto/poly1305.h>
#include <crypto/chacha20poly1305.h>
bool wg_counter_validate(struct noise_replay_counter *counter, u64 nonce); // receive.c's counter_validate (S19)
#define REJECT_AFTER (U64_MAX - COUNTER_WINDOW_SIZE - 1) // messages.h: REJECT_AFTER_MESSAGES, 2^64 - 8130
static size_t upto(size_t max) { // any value from 0 to max
size_t value = nondet_size();
return value < max ? value : max;
}
static u64 any_u64(void) { // any 64-bit value
u64 high = nondet_u32();
return high << 32 | nondet_u32();
}
static u8 *any_bytes(size_t n) { // a new object of n arbitrary bytes (NULL if malloc fails)
u8 *bytes = malloc(n);
if (bytes != NULL && n != 0)
nondet_bytes(bytes, n);
return bytes;
}
static u8 *copy_of(const u8 *source, size_t n) { // a new object holding source[0..n-1]
u8 *copy = malloc(n);
for (size_t i = 0; copy != NULL && i < n; i++)
copy[i] = source[i];
return copy;
}
static int bytes_eq(const u8 *a, const u8 *b, size_t n) { // a[0..n-1] == b[0..n-1]
for (size_t i = 0; i < n; i++)
if (a[i] != b[i])
return 0;
return 1;
}
static void new_counter(struct noise_replay_counter *c) { // a new key's replay counter: zero (keypair_create)
c->counter = 0;
for (size_t i = 0; i < COUNTER_BITS_TOTAL / BITS_PER_LONG; i++)
c->backtrack[i] = 0;
}The theorem
QuickProof generated this statement from the spec, in src/contracts/rp_limit.v:
Theorem rp_limit : harness_safe whole_prog.src/contracts/laws.v states it on the spec's own program, whole_prog (the spec linked with the code under test), with its proof:
Theorem rp_limit : harness_safe WgNoise.contracts.rp_limit.whole_prog.
Proof. exact (proj1 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 WgNoise.contracts.suite.suite)))))))))))))))))). Qed.Read as a statement about runs, it says that no run of the program has undefined behaviour or a failing check, for every value the spec can draw. That reading rests on VST's adequacy theorem, which is not yet instantiated in Rocq (formerly Coq) for QuickProof's environment.
The C files (units) its program links
patch/counter_validate.c
What it leaves out
- What the first comment of the spec excludes, and its bounds.
- Like every spec of this proof: runs of more than one thread (the locks and RCU are those of one thread), termination (a run that never returns is not a counterexample), and binaries built by a compiler (the theorem is about the code as CompCert defines C for 64-bit x86).
- The kernel around the code is a shim of plain C for one thread, and the code carries rewrites of idioms that VST cannot handle. Both are tested against the kernel's code, not proved.
The summary page says what the proof as a whole covers.
How it was proved
AI agents wrote the proof, and Rocq checks it. qp verify passes on this repository: this statement is the one generated from the spec at the contract commit, and its proof uses only Rocq's standard axioms and VST's abstract malloc library.