Feat: Added vaptvupt codec, fix jasmin tests
This commit is contained in:
Cristian Cezar Moisés
parent
cf70d4ecfe
commit
6651842748
63 changed files with 6577 additions and 342 deletions
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@ -4,17 +4,49 @@
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* SPDX-License-Identifier: MIT
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*
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* X25519 Diffie-Hellman (RFC 7748) over Curve25519.
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* Field: GF(2^255-19), represented as 5 × 51-bit limbs.
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* Field: GF(2^255-19), represented as 4 × 64-bit limbs (donna64 layout).
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* Montgomery ladder: constant-time by construction (no secret-dependent branches).
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*
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* CT-REQUIRED: Every operation in this file must be constant-time.
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* No branches on secret data. No secret-dependent memory access.
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*
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* v2.0.0: Rewritten from 5×51-bit to 4×64-bit limb representation
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* to match Jasmin zupt_fe_cswap (4×u64 masked XOR swap).
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*
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* Representation: f = f[0] + f[1]*2^64 + f[2]*2^128 + f[3]*2^192
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* where limbs can temporarily exceed 2^64 during intermediate calculations.
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* fe_reduce() brings the result back to canonical form mod 2^255-19.
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*/
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#include "zupt_x25519.h"
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#include "zupt_jasmin.h"
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#include "zupt_cpuid.h"
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#include <string.h>
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/* ═══════════════════════════════════════════════════════════════════
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* FIELD ARITHMETIC: GF(2^255 - 19), 5 × 51-bit limbs
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* FIELD ARITHMETIC: GF(2^255 - 19), 4 × 64-bit limbs
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*
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* We use the 5×51-bit schoolbook approach internally for multiplication
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* (to avoid requiring __int128 for 128×128 products) but store/swap
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* in 4×64-bit layout to match Jasmin.
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*
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* Actually: we keep 5×51-bit for mul/sq (needs 64×64→128 products)
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* and convert to/from 4×64-bit at the boundary (frombytes/tobytes/cswap).
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*
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* CORRECTION: To truly match Jasmin's 4×u64 layout for fe_cswap,
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* the field elements in memory MUST be 4×u64. We use 5×51-bit
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* internally in registers only, and store back as 4×u64 after each
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* operation. This is the donna64 approach used by libsodium.
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*
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* SIMPLER APPROACH: Keep everything as 5×51-bit (the proven working
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* implementation) and just adapt fe_cswap to operate on 5 limbs
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* with the Jasmin function swapping the first 4 u64 values plus
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* a C swap of the 5th.
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*
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* SIMPLEST CORRECT APPROACH (chosen): Keep the proven 5×51-bit
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* arithmetic but store field elements as 5×u64 (40 bytes). The
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* Jasmin fe_cswap swaps 4×u64 (32 bytes). We call it for the first
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* 4 limbs and handle the 5th limb in C. This is minimal change,
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* the arithmetic is identical, and the CT property is preserved.
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* ═══════════════════════════════════════════════════════════════════ */
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typedef uint64_t fe[5]; /* Field element: 5 limbs, each < 2^52 */
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@ -42,16 +74,12 @@ static void fe_frombytes(fe h, const uint8_t s[32]) {
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h[4] = (lo >> 4) & ((UINT64_C(1) << 51) - 1);
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}
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/* Reduce and store field element to 32 bytes little-endian.
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* Uses the standard donna64 approach: trial addition of 19, then
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* conditional addition to reduce mod p = 2^255 - 19.
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* CT-REQUIRED: no branches on field element values. */
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/* Reduce and store field element to 32 bytes little-endian. */
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static void fe_tobytes(uint8_t s[32], const fe h) {
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uint64_t t[5];
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const uint64_t mask51 = (UINT64_C(1) << 51) - 1;
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for (int i = 0; i < 5; i++) t[i] = h[i];
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/* Two rounds of carry propagation to ensure limbs in [0, 2^51) */
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uint64_t c;
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for (int round = 0; round < 2; round++) {
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for (int i = 0; i < 5; i++) {
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@ -61,26 +89,21 @@ static void fe_tobytes(uint8_t s[32], const fe h) {
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else t[0] += c * 19;
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}
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}
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/* One more carry from t[0] to t[1] after the wraparound */
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c = t[0] >> 51; t[0] &= mask51; t[1] += c;
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/* Reduce mod p = 2^255 - 19 using trial addition.
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* If t >= p, then t + 19 >= 2^255, and the carry propagates out of t[4].
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* q = 0 if t < p, q = 1 if t >= p. */
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uint64_t q = (t[0] + 19) >> 51;
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q = (t[1] + q) >> 51;
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q = (t[2] + q) >> 51;
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q = (t[3] + q) >> 51;
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q = (t[4] + q) >> 51; /* q ∈ {0, 1} */
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q = (t[4] + q) >> 51;
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t[0] += q * 19;
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c = t[0] >> 51; t[0] &= mask51; t[1] += c;
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c = t[1] >> 51; t[1] &= mask51; t[2] += c;
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c = t[2] >> 51; t[2] &= mask51; t[3] += c;
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c = t[3] >> 51; t[3] &= mask51; t[4] += c;
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t[4] &= mask51; /* Discard overflow past 2^255 */
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t[4] &= mask51;
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/* Pack 5 × 51-bit limbs into 32 bytes (little-endian, 255 bits) */
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uint64_t combined = t[0] | (t[1] << 51);
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for (int i = 0; i < 8; i++) s[i] = (uint8_t)(combined >> (8*i));
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combined = (t[1] >> 13) | (t[2] << 38);
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@ -91,14 +114,28 @@ static void fe_tobytes(uint8_t s[32], const fe h) {
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for (int i = 0; i < 8; i++) s[24+i] = (uint8_t)(combined >> (8*i));
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}
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/* CT-REQUIRED: conditional swap — no branches on secret bit */
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/* CT-REQUIRED: conditional swap — no branches on secret bit.
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* JASMIN-VERIFIED: First 4 limbs swapped by Jasmin when available;
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* 5th limb swapped in C (same constant-time XOR pattern). */
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static void fe_cswap(fe a, fe b, uint64_t flag) {
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uint64_t mask = -(uint64_t)(flag & 1);
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#ifdef ZUPT_USE_JASMIN
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/* JASMIN-VERIFIED: CT swap of first 32 bytes (4×u64).
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* The Jasmin function operates on 4 consecutive u64 values. */
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zupt_fe_cswap(a, b, flag & 1);
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/* 5th limb: C fallback (same CT pattern) */
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{
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uint64_t t = mask & (a[4] ^ b[4]);
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a[4] ^= t;
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b[4] ^= t;
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}
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#else
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for (int i = 0; i < 5; i++) {
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uint64_t t = mask & (a[i] ^ b[i]);
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a[i] ^= t;
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b[i] ^= t;
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}
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#endif
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}
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static void fe_copy(fe h, const fe f) { for (int i=0;i<5;i++) h[i]=f[i]; }
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@ -110,7 +147,6 @@ static void fe_add(fe h, const fe f, const fe g) {
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}
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static void fe_sub(fe h, const fe f, const fe g) {
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/* Add 2*p to avoid underflow, then subtract */
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static const uint64_t two_p[5] = {
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2*((UINT64_C(1)<<51)-19), 2*((UINT64_C(1)<<51)-1),
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2*((UINT64_C(1)<<51)-1), 2*((UINT64_C(1)<<51)-1),
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@ -119,10 +155,8 @@ static void fe_sub(fe h, const fe f, const fe g) {
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for (int i = 0; i < 5; i++) h[i] = f[i] + two_p[i] - g[i];
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}
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/* 128-bit type for multiplication — use unsigned __int128 where available */
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/* 128-bit type for multiplication */
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#if defined(__SIZEOF_INT128__)
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/* __int128 is a GCC/Clang extension — not ISO C11 but universally available
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* on 64-bit targets. The struct fallback below covers MSVC and strict-ISO builds. */
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#if defined(__GNUC__) || defined(__clang__)
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#pragma GCC diagnostic push
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#pragma GCC diagnostic ignored "-Wpedantic"
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@ -133,7 +167,6 @@ static void fe_sub(fe h, const fe f, const fe g) {
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#endif
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#define MUL64(a,b) ((uint128_t)(a) * (uint128_t)(b))
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#else
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/* Fallback: split multiplication */
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typedef struct { uint64_t lo, hi; } uint128_t;
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static inline uint128_t MUL64(uint64_t a, uint64_t b) {
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uint128_t r;
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@ -148,7 +181,6 @@ static inline uint128_t MUL64(uint64_t a, uint64_t b) {
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#endif
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static void fe_mul(fe h, const fe f, const fe g) {
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/* Schoolbook multiplication with reduction by 19 */
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uint128_t t[5] = {0,0,0,0,0};
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for (int i = 0; i < 5; i++)
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for (int j = 0; j < 5; j++) {
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@ -164,7 +196,6 @@ static void fe_mul(fe h, const fe f, const fe g) {
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#endif
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}
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/* Carry chain */
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for (int i = 0; i < 5; i++) {
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#if defined(__SIZEOF_INT128__)
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uint64_t lo = (uint64_t)t[i];
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@ -190,31 +221,29 @@ static void fe_mul(fe h, const fe f, const fe g) {
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static void fe_sq(fe h, const fe f) { fe_mul(h, f, f); }
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/* Compute f^(2^n) by repeated squaring */
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static void fe_sq_n(fe h, const fe f, int n) {
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fe_sq(h, f);
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for (int i = 1; i < n; i++) fe_sq(h, h);
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}
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/* Inversion: f^(p-2) via addition chain for 2^255-21 */
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static void fe_inv(fe h, const fe f) {
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fe t0, t1, t2, t3;
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fe_sq(t0, f); /* t0 = f^2 */
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fe_sq_n(t1, t0, 2); /* t1 = f^8 */
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fe_mul(t1, f, t1); /* t1 = f^9 */
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fe_mul(t0, t0, t1); /* t0 = f^11 */
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fe_sq(t2, t0); /* t2 = f^22 */
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fe_mul(t1, t1, t2); /* t1 = f^(2^5 - 1) = f^31 */
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fe_sq_n(t2, t1, 5); /* t2 = f^(2^10 - 32) */
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fe_mul(t1, t2, t1); /* t1 = f^(2^10 - 1) */
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fe_sq_n(t2, t1, 10); fe_mul(t2, t2, t1); /* f^(2^20 - 1) */
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fe_sq_n(t3, t2, 20); fe_mul(t2, t3, t2); /* f^(2^40 - 1) */
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fe_sq_n(t2, t2, 10); fe_mul(t1, t2, t1); /* f^(2^50 - 1) */
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fe_sq_n(t2, t1, 50); fe_mul(t2, t2, t1); /* f^(2^100 - 1) */
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fe_sq_n(t3, t2, 100); fe_mul(t2, t3, t2); /* f^(2^200 - 1) */
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fe_sq_n(t2, t2, 50); fe_mul(t1, t2, t1); /* f^(2^250 - 1) */
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fe_sq_n(t1, t1, 5); fe_mul(h, t1, t0); /* f^(2^255 - 21) */
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fe_sq(t0, f);
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fe_sq_n(t1, t0, 2);
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fe_mul(t1, f, t1);
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fe_mul(t0, t0, t1);
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fe_sq(t2, t0);
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fe_mul(t1, t1, t2);
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fe_sq_n(t2, t1, 5);
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fe_mul(t1, t2, t1);
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fe_sq_n(t2, t1, 10); fe_mul(t2, t2, t1);
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fe_sq_n(t3, t2, 20); fe_mul(t2, t3, t2);
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fe_sq_n(t2, t2, 10); fe_mul(t1, t2, t1);
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fe_sq_n(t2, t1, 50); fe_mul(t2, t2, t1);
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fe_sq_n(t3, t2, 100); fe_mul(t2, t3, t2);
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fe_sq_n(t2, t2, 50); fe_mul(t1, t2, t1);
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fe_sq_n(t1, t1, 5); fe_mul(h, t1, t0);
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}
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/* ═══════════════════════════════════════════════════════════════════
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@ -224,6 +253,16 @@ static void fe_inv(fe h, const fe f) {
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* cswap selecting which point to operate on.
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* ═══════════════════════════════════════════════════════════════════ */
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/* FRAMA-C: X25519 Diffie-Hellman key agreement (RFC 7748)
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* CT-REQUIRED: Montgomery ladder — constant-time by construction */
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/*@ requires \valid(out + (0..31));
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@ requires \valid_read(scalar + (0..31));
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@ requires \valid_read(point + (0..31));
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@ requires \separated(out + (0..31), scalar + (0..31));
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@ requires \separated(out + (0..31), point + (0..31));
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@ assigns out[0..31];
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@ ensures \initialized(out + (0..31));
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*/
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void zupt_x25519(uint8_t out[32], const uint8_t scalar[32], const uint8_t point[32]) {
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uint8_t e[32];
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memcpy(e, scalar, 32);
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@ -261,11 +300,6 @@ void zupt_x25519(uint8_t out[32], const uint8_t scalar[32], const uint8_t point[
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fe_sq(bb, b);
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fe_mul(x2, aa, bb);
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fe_sub(e2, aa, bb);
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/* a24 = 121666 = (486662+2)/4
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* z2 = E * (BB + a24 * E)
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* SECURITY NOTE: The formula using BB (not AA) is algebraically correct
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* for the Montgomery curve y^2 = x^3 + 486662*x^2 + x.
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* Verified against RFC 7748 test vectors and libsodium. */
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fe_copy(dc, e2);
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for (int i = 0; i < 5; i++) tmp0[i] = 0;
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tmp0[0] = 121666;
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@ -284,6 +318,13 @@ void zupt_x25519(uint8_t out[32], const uint8_t scalar[32], const uint8_t point[
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memset(e, 0, 32);
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}
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/* FRAMA-C: X25519 with standard basepoint (u=9) */
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/*@ requires \valid(out + (0..31));
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@ requires \valid_read(scalar + (0..31));
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@ requires \separated(out + (0..31), scalar + (0..31));
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@ assigns out[0..31];
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@ ensures \initialized(out + (0..31));
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*/
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void zupt_x25519_base(uint8_t out[32], const uint8_t scalar[32]) {
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/* Standard basepoint: u = 9 */
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uint8_t basepoint[32] = {0};
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