--- /dev/null
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Support for verifying ML-DSA signatures
+ *
+ * Copyright 2025 Google LLC
+ */
+
+#include <crypto/mldsa.h>
+#include <crypto/sha3.h>
+#include <kunit/visibility.h>
+#include <linux/export.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/unaligned.h>
+
+#define Q 8380417 /* The prime q = 2^23 - 2^13 + 1 */
+#define QINV_MOD_2_32 58728449 /* Multiplicative inverse of q mod 2^32 */
+#define N 256 /* Number of components per ring element */
+#define D 13 /* Number of bits dropped from the public key vector t */
+#define RHO_LEN 32 /* Length of the public random seed in bytes */
+#define MAX_W1_ENCODED_LEN 192 /* Max encoded length of one element of w'_1 */
+
+/*
+ * The zetas array in Montgomery form, i.e. with extra factor of 2^32.
+ * Reference: FIPS 204 Section 7.5 "NTT and NTT^-1"
+ * Generated by the following Python code:
+ * q=8380417; [a%q - q*(a%q > q//2) for a in [1753**(int(f'{i:08b}'[::-1], 2)) << 32 for i in range(256)]]
+ */
+static const s32 zetas_times_2_32[N] = {
+ -4186625, 25847, -2608894, -518909, 237124, -777960, -876248,
+ 466468, 1826347, 2353451, -359251, -2091905, 3119733, -2884855,
+ 3111497, 2680103, 2725464, 1024112, -1079900, 3585928, -549488,
+ -1119584, 2619752, -2108549, -2118186, -3859737, -1399561, -3277672,
+ 1757237, -19422, 4010497, 280005, 2706023, 95776, 3077325,
+ 3530437, -1661693, -3592148, -2537516, 3915439, -3861115, -3043716,
+ 3574422, -2867647, 3539968, -300467, 2348700, -539299, -1699267,
+ -1643818, 3505694, -3821735, 3507263, -2140649, -1600420, 3699596,
+ 811944, 531354, 954230, 3881043, 3900724, -2556880, 2071892,
+ -2797779, -3930395, -1528703, -3677745, -3041255, -1452451, 3475950,
+ 2176455, -1585221, -1257611, 1939314, -4083598, -1000202, -3190144,
+ -3157330, -3632928, 126922, 3412210, -983419, 2147896, 2715295,
+ -2967645, -3693493, -411027, -2477047, -671102, -1228525, -22981,
+ -1308169, -381987, 1349076, 1852771, -1430430, -3343383, 264944,
+ 508951, 3097992, 44288, -1100098, 904516, 3958618, -3724342,
+ -8578, 1653064, -3249728, 2389356, -210977, 759969, -1316856,
+ 189548, -3553272, 3159746, -1851402, -2409325, -177440, 1315589,
+ 1341330, 1285669, -1584928, -812732, -1439742, -3019102, -3881060,
+ -3628969, 3839961, 2091667, 3407706, 2316500, 3817976, -3342478,
+ 2244091, -2446433, -3562462, 266997, 2434439, -1235728, 3513181,
+ -3520352, -3759364, -1197226, -3193378, 900702, 1859098, 909542,
+ 819034, 495491, -1613174, -43260, -522500, -655327, -3122442,
+ 2031748, 3207046, -3556995, -525098, -768622, -3595838, 342297,
+ 286988, -2437823, 4108315, 3437287, -3342277, 1735879, 203044,
+ 2842341, 2691481, -2590150, 1265009, 4055324, 1247620, 2486353,
+ 1595974, -3767016, 1250494, 2635921, -3548272, -2994039, 1869119,
+ 1903435, -1050970, -1333058, 1237275, -3318210, -1430225, -451100,
+ 1312455, 3306115, -1962642, -1279661, 1917081, -2546312, -1374803,
+ 1500165, 777191, 2235880, 3406031, -542412, -2831860, -1671176,
+ -1846953, -2584293, -3724270, 594136, -3776993, -2013608, 2432395,
+ 2454455, -164721, 1957272, 3369112, 185531, -1207385, -3183426,
+ 162844, 1616392, 3014001, 810149, 1652634, -3694233, -1799107,
+ -3038916, 3523897, 3866901, 269760, 2213111, -975884, 1717735,
+ 472078, -426683, 1723600, -1803090, 1910376, -1667432, -1104333,
+ -260646, -3833893, -2939036, -2235985, -420899, -2286327, 183443,
+ -976891, 1612842, -3545687, -554416, 3919660, -48306, -1362209,
+ 3937738, 1400424, -846154, 1976782
+};
+
+/* Reference: FIPS 204 Section 4 "Parameter Sets" */
+static const struct mldsa_parameter_set {
+ u8 k; /* num rows in the matrix A */
+ u8 l; /* num columns in the matrix A */
+ u8 ctilde_len; /* length of commitment hash ctilde in bytes; lambda/4 */
+ u8 omega; /* max num of 1's in the hint vector h */
+ u8 tau; /* num of +-1's in challenge c */
+ u8 beta; /* tau times eta */
+ u16 pk_len; /* length of public keys in bytes */
+ u16 sig_len; /* length of signatures in bytes */
+ s32 gamma1; /* coefficient range of y */
+} mldsa_parameter_sets[] = {
+ [MLDSA44] = {
+ .k = 4,
+ .l = 4,
+ .ctilde_len = 32,
+ .omega = 80,
+ .tau = 39,
+ .beta = 78,
+ .pk_len = MLDSA44_PUBLIC_KEY_SIZE,
+ .sig_len = MLDSA44_SIGNATURE_SIZE,
+ .gamma1 = 1 << 17,
+ },
+ [MLDSA65] = {
+ .k = 6,
+ .l = 5,
+ .ctilde_len = 48,
+ .omega = 55,
+ .tau = 49,
+ .beta = 196,
+ .pk_len = MLDSA65_PUBLIC_KEY_SIZE,
+ .sig_len = MLDSA65_SIGNATURE_SIZE,
+ .gamma1 = 1 << 19,
+ },
+ [MLDSA87] = {
+ .k = 8,
+ .l = 7,
+ .ctilde_len = 64,
+ .omega = 75,
+ .tau = 60,
+ .beta = 120,
+ .pk_len = MLDSA87_PUBLIC_KEY_SIZE,
+ .sig_len = MLDSA87_SIGNATURE_SIZE,
+ .gamma1 = 1 << 19,
+ },
+};
+
+/*
+ * An element of the ring R_q (normal form) or the ring T_q (NTT form). It
+ * consists of N integers mod q: either the polynomial coefficients of the R_q
+ * element or the components of the T_q element. In either case, whether they
+ * are fully reduced to [0, q - 1] varies in the different parts of the code.
+ */
+struct mldsa_ring_elem {
+ s32 x[N];
+};
+
+struct mldsa_verification_workspace {
+ /* SHAKE context for computing c, mu, and ctildeprime */
+ struct shake_ctx shake;
+ /* The fields in this union are used in their order of declaration. */
+ union {
+ /* The hash of the public key */
+ u8 tr[64];
+ /* The message representative mu */
+ u8 mu[64];
+ /* Temporary space for rej_ntt_poly() */
+ u8 block[SHAKE128_BLOCK_SIZE + 1];
+ /* Encoded element of w'_1 */
+ u8 w1_encoded[MAX_W1_ENCODED_LEN];
+ /* The commitment hash. Real length is params->ctilde_len */
+ u8 ctildeprime[64];
+ };
+ /* SHAKE context for generating elements of the matrix A */
+ struct shake_ctx a_shake;
+ /*
+ * An element of the matrix A generated from the public seed, or an
+ * element of the vector t_1 decoded from the public key and pre-scaled
+ * by 2^d. Both are in NTT form. To reduce memory usage, we generate
+ * or decode these elements only as needed.
+ */
+ union {
+ struct mldsa_ring_elem a;
+ struct mldsa_ring_elem t1_scaled;
+ };
+ /* The challenge c, generated from ctilde */
+ struct mldsa_ring_elem c;
+ /* A temporary element used during calculations */
+ struct mldsa_ring_elem tmp;
+
+ /* The following fields are variable-length: */
+
+ /* The signer's response vector */
+ struct mldsa_ring_elem z[/* l */];
+
+ /* The signer's hint vector */
+ /* u8 h[k * N]; */
+};
+
+/*
+ * Compute a * b * 2^-32 mod q. a * b must be in the range [-2^31 * q, 2^31 * q
+ * - 1] before reduction. The return value is in the range [-q + 1, q - 1].
+ *
+ * To reduce mod q efficiently, this uses Montgomery reduction with R=2^32.
+ * That's where the factor of 2^-32 comes from. The caller must include a
+ * factor of 2^32 at some point to compensate for that.
+ *
+ * To keep the input and output ranges very close to symmetric, this
+ * specifically does a "signed" Montgomery reduction. That is, when computing
+ * d = c * q^-1 mod 2^32, this chooses a representative in [S32_MIN, S32_MAX]
+ * rather than [0, U32_MAX], i.e. s32 rather than u32. This matters in the
+ * wider multiplication d * Q when d keeps its value via sign extension.
+ *
+ * Reference: FIPS 204 Appendix A "Montgomery Multiplication". But, it doesn't
+ * explain it properly: it has an off-by-one error in the upper end of the input
+ * range, it doesn't clarify that the signed version should be used, and it
+ * gives an unnecessarily large output range. A better citation is perhaps the
+ * Dilithium reference code, which functionally matches the below code and
+ * merely has the (benign) off-by-one error in its documentation.
+ */
+static inline s32 Zq_mult(s32 a, s32 b)
+{
+ /* Compute the unreduced product c. */
+ s64 c = (s64)a * b;
+
+ /*
+ * Compute d = c * q^-1 mod 2^32. Generate a signed result, as
+ * explained above, but do the actual multiplication using an unsigned
+ * type to avoid signed integer overflow which is undefined behavior.
+ */
+ s32 d = (u32)c * QINV_MOD_2_32;
+
+ /*
+ * Compute e = c - d * q. This makes the low 32 bits zero, since
+ * c - (c * q^-1) * q mod 2^32
+ * = c - c * (q^-1 * q) mod 2^32
+ * = c - c * 1 mod 2^32
+ * = c - c mod 2^32
+ * = 0 mod 2^32
+ */
+ s64 e = c - (s64)d * Q;
+
+ /* Finally, return e * 2^-32. */
+ return e >> 32;
+}
+
+/*
+ * Convert @w to its number-theoretically-transformed representation in-place.
+ * Reference: FIPS 204 Algorithm 41, NTT
+ *
+ * To prevent intermediate overflows, all input coefficients must have absolute
+ * value < q. All output components have absolute value < 9*q.
+ */
+static void ntt(struct mldsa_ring_elem *w)
+{
+ int m = 0; /* index in zetas_times_2_32 */
+
+ for (int len = 128; len >= 1; len /= 2) {
+ for (int start = 0; start < 256; start += 2 * len) {
+ const s32 z = zetas_times_2_32[++m];
+
+ for (int j = start; j < start + len; j++) {
+ s32 t = Zq_mult(z, w->x[j + len]);
+
+ w->x[j + len] = w->x[j] - t;
+ w->x[j] += t;
+ }
+ }
+ }
+}
+
+/*
+ * Convert @w from its number-theoretically-transformed representation in-place.
+ * Reference: FIPS 204 Algorithm 42, NTT^-1
+ *
+ * This also multiplies the coefficients by 2^32, undoing an extra factor of
+ * 2^-32 introduced earlier, and reduces the coefficients to [0, q - 1].
+ */
+static void invntt_and_mul_2_32(struct mldsa_ring_elem *w)
+{
+ int m = 256; /* index in zetas_times_2_32 */
+
+ /* Prevent intermediate overflows. */
+ for (int j = 0; j < 256; j++)
+ w->x[j] %= Q;
+
+ for (int len = 1; len < 256; len *= 2) {
+ for (int start = 0; start < 256; start += 2 * len) {
+ const s32 z = -zetas_times_2_32[--m];
+
+ for (int j = start; j < start + len; j++) {
+ s32 t = w->x[j];
+
+ w->x[j] = t + w->x[j + len];
+ w->x[j + len] = Zq_mult(z, t - w->x[j + len]);
+ }
+ }
+ }
+ /*
+ * Multiply by 2^32 * 256^-1. 2^32 cancels the factor of 2^-32 from
+ * earlier Montgomery multiplications. 256^-1 is for NTT^-1. This
+ * itself uses Montgomery multiplication, so *another* 2^32 is needed.
+ * Thus the actual multiplicand is 2^32 * 2^32 * 256^-1 mod q = 41978.
+ *
+ * Finally, also reduce from [-q + 1, q - 1] to [0, q - 1].
+ */
+ for (int j = 0; j < 256; j++) {
+ w->x[j] = Zq_mult(w->x[j], 41978);
+ w->x[j] += (w->x[j] >> 31) & Q;
+ }
+}
+
+/*
+ * Decode an element of t_1, i.e. the high d bits of t = A*s_1 + s_2.
+ * Reference: FIPS 204 Algorithm 23, pkDecode.
+ * Also multiply it by 2^d and convert it to NTT form.
+ */
+static const u8 *decode_t1_elem(struct mldsa_ring_elem *out,
+ const u8 *t1_encoded)
+{
+ for (int j = 0; j < N; j += 4, t1_encoded += 5) {
+ u32 v = get_unaligned_le32(t1_encoded);
+
+ out->x[j + 0] = ((v >> 0) & 0x3ff) << D;
+ out->x[j + 1] = ((v >> 10) & 0x3ff) << D;
+ out->x[j + 2] = ((v >> 20) & 0x3ff) << D;
+ out->x[j + 3] = ((v >> 30) | (t1_encoded[4] << 2)) << D;
+ static_assert(0x3ff << D < Q); /* All coefficients < q. */
+ }
+ ntt(out);
+ return t1_encoded; /* Return updated pointer. */
+}
+
+/*
+ * Decode the signer's response vector 'z' from the signature.
+ * Reference: FIPS 204 Algorithm 27, sigDecode.
+ *
+ * This also validates that the coefficients of z are in range, corresponding
+ * the infinity norm check at the end of Algorithm 8, ML-DSA.Verify_internal.
+ *
+ * Finally, this also converts z to NTT form.
+ */
+static bool decode_z(struct mldsa_ring_elem z[/* l */], int l, s32 gamma1,
+ int beta, const u8 **sig_ptr)
+{
+ const u8 *sig = *sig_ptr;
+
+ for (int i = 0; i < l; i++) {
+ if (l == 4) { /* ML-DSA-44? */
+ /* 18-bit coefficients: decode 4 from 9 bytes. */
+ for (int j = 0; j < N; j += 4, sig += 9) {
+ u64 v = get_unaligned_le64(sig);
+
+ z[i].x[j + 0] = (v >> 0) & 0x3ffff;
+ z[i].x[j + 1] = (v >> 18) & 0x3ffff;
+ z[i].x[j + 2] = (v >> 36) & 0x3ffff;
+ z[i].x[j + 3] = (v >> 54) | (sig[8] << 10);
+ }
+ } else {
+ /* 20-bit coefficients: decode 4 from 10 bytes. */
+ for (int j = 0; j < N; j += 4, sig += 10) {
+ u64 v = get_unaligned_le64(sig);
+
+ z[i].x[j + 0] = (v >> 0) & 0xfffff;
+ z[i].x[j + 1] = (v >> 20) & 0xfffff;
+ z[i].x[j + 2] = (v >> 40) & 0xfffff;
+ z[i].x[j + 3] =
+ (v >> 60) |
+ (get_unaligned_le16(&sig[8]) << 4);
+ }
+ }
+ for (int j = 0; j < N; j++) {
+ z[i].x[j] = gamma1 - z[i].x[j];
+ if (z[i].x[j] <= -(gamma1 - beta) ||
+ z[i].x[j] >= gamma1 - beta)
+ return false;
+ }
+ ntt(&z[i]);
+ }
+ *sig_ptr = sig; /* Return updated pointer. */
+ return true;
+}
+
+/*
+ * Decode the signer's hint vector 'h' from the signature.
+ * Reference: FIPS 204 Algorithm 21, HintBitUnpack
+ *
+ * Note that there are several ways in which the hint vector can be malformed.
+ */
+static bool decode_hint_vector(u8 h[/* k * N */], int k, int omega, const u8 *y)
+{
+ int index = 0;
+
+ memset(h, 0, k * N);
+ for (int i = 0; i < k; i++) {
+ int count = y[omega + i]; /* num 1's in elems 0 through i */
+ int prev = -1;
+
+ /* Cumulative count mustn't decrease or exceed omega. */
+ if (count < index || count > omega)
+ return false;
+ for (; index < count; index++) {
+ if (prev >= y[index]) /* Coefficients out of order? */
+ return false;
+ prev = y[index];
+ h[i * N + y[index]] = 1;
+ }
+ }
+ return mem_is_zero(&y[index], omega - index);
+}
+
+/*
+ * Expand @seed into an element of R_q @c with coefficients in {-1, 0, 1},
+ * exactly @tau of them nonzero. Reference: FIPS 204 Algorithm 29, SampleInBall
+ */
+static void sample_in_ball(struct mldsa_ring_elem *c, const u8 *seed,
+ size_t seed_len, int tau, struct shake_ctx *shake)
+{
+ u64 signs;
+ u8 j;
+
+ shake256_init(shake);
+ shake_update(shake, seed, seed_len);
+ shake_squeeze(shake, (u8 *)&signs, sizeof(signs));
+ le64_to_cpus(&signs);
+ *c = (struct mldsa_ring_elem){};
+ for (int i = N - tau; i < N; i++, signs >>= 1) {
+ do {
+ shake_squeeze(shake, &j, 1);
+ } while (j > i);
+ c->x[i] = c->x[j];
+ c->x[j] = 1 - 2 * (s32)(signs & 1);
+ }
+}
+
+/*
+ * Expand the public seed @rho and @row_and_column into an element of T_q @out.
+ * Reference: FIPS 204 Algorithm 30, RejNTTPoly
+ *
+ * @shake and @block are temporary space used by the expansion. @block has
+ * space for one SHAKE128 block, plus an extra byte to allow reading a u32 from
+ * the final 3-byte group without reading out-of-bounds.
+ */
+static void rej_ntt_poly(struct mldsa_ring_elem *out, const u8 rho[RHO_LEN],
+ __le16 row_and_column, struct shake_ctx *shake,
+ u8 block[SHAKE128_BLOCK_SIZE + 1])
+{
+ shake128_init(shake);
+ shake_update(shake, rho, RHO_LEN);
+ shake_update(shake, (u8 *)&row_and_column, sizeof(row_and_column));
+ for (int i = 0; i < N;) {
+ shake_squeeze(shake, block, SHAKE128_BLOCK_SIZE);
+ block[SHAKE128_BLOCK_SIZE] = 0; /* for KMSAN */
+ static_assert(SHAKE128_BLOCK_SIZE % 3 == 0);
+ for (int j = 0; j < SHAKE128_BLOCK_SIZE && i < N; j += 3) {
+ u32 x = get_unaligned_le32(&block[j]) & 0x7fffff;
+
+ if (x < Q) /* Ignore values >= q. */
+ out->x[i++] = x;
+ }
+ }
+}
+
+/*
+ * Return the HighBits of r adjusted according to hint h
+ * Reference: FIPS 204 Algorithm 40, UseHint
+ *
+ * This is needed because of the public key compression in ML-DSA.
+ *
+ * h is either 0 or 1, r is in [0, q - 1], and gamma2 is either (q - 1) / 88 or
+ * (q - 1) / 32. Except when invoked via the unit test interface, gamma2 is a
+ * compile-time constant, so compilers will optimize the code accordingly.
+ */
+static __always_inline s32 use_hint(u8 h, s32 r, const s32 gamma2)
+{
+ const s32 m = (Q - 1) / (2 * gamma2); /* 44 or 16, compile-time const */
+ s32 r1;
+
+ /*
+ * Handle the special case where r - (r mod+- (2 * gamma2)) == q - 1,
+ * i.e. r >= q - gamma2. This is also exactly where the computation of
+ * r1 below would produce 'm' and would need a correction.
+ */
+ if (r >= Q - gamma2)
+ return h == 0 ? 0 : m - 1;
+
+ /*
+ * Compute the (non-hint-adjusted) HighBits r1 as:
+ *
+ * r1 = (r - (r mod+- (2 * gamma2))) / (2 * gamma2)
+ * = floor((r + gamma2 - 1) / (2 * gamma2))
+ *
+ * Note that when '2 * gamma2' is a compile-time constant, compilers
+ * optimize the division to a reciprocal multiplication and shift.
+ */
+ r1 = (u32)(r + gamma2 - 1) / (2 * gamma2);
+
+ /*
+ * Return the HighBits r1:
+ * + 0 if the hint is 0;
+ * + 1 (mod m) if the hint is 1 and the LowBits are positive;
+ * - 1 (mod m) if the hint is 1 and the LowBits are negative or 0.
+ *
+ * r1 is in (and remains in) [0, m - 1]. Note that when 'm' is a
+ * compile-time constant, compilers optimize the '% m' accordingly.
+ */
+ if (h == 0)
+ return r1;
+ if (r > r1 * (2 * gamma2))
+ return (u32)(r1 + 1) % m;
+ return (u32)(r1 + m - 1) % m;
+}
+
+static __always_inline void use_hint_elem(struct mldsa_ring_elem *w,
+ const u8 h[N], const s32 gamma2)
+{
+ for (int j = 0; j < N; j++)
+ w->x[j] = use_hint(h[j], w->x[j], gamma2);
+}
+
+#if IS_ENABLED(CONFIG_CRYPTO_LIB_MLDSA_KUNIT_TEST)
+/* Allow the __always_inline function use_hint() to be unit-tested. */
+s32 mldsa_use_hint(u8 h, s32 r, s32 gamma2)
+{
+ return use_hint(h, r, gamma2);
+}
+EXPORT_SYMBOL_IF_KUNIT(mldsa_use_hint);
+#endif
+
+/*
+ * Encode one element of the commitment vector w'_1 into a byte string.
+ * Reference: FIPS 204 Algorithm 28, w1Encode.
+ * Return the number of bytes used: 192 for ML-DSA-44 and 128 for the others.
+ */
+static size_t encode_w1(u8 out[MAX_W1_ENCODED_LEN],
+ const struct mldsa_ring_elem *w1, int k)
+{
+ size_t pos = 0;
+
+ static_assert(N * 6 / 8 == MAX_W1_ENCODED_LEN);
+ if (k == 4) { /* ML-DSA-44? */
+ /* 6 bits per coefficient. Pack 4 at a time. */
+ for (int j = 0; j < N; j += 4) {
+ u32 v = (w1->x[j + 0] << 0) | (w1->x[j + 1] << 6) |
+ (w1->x[j + 2] << 12) | (w1->x[j + 3] << 18);
+ out[pos++] = v >> 0;
+ out[pos++] = v >> 8;
+ out[pos++] = v >> 16;
+ }
+ } else {
+ /* 4 bits per coefficient. Pack 2 at a time. */
+ for (int j = 0; j < N; j += 2)
+ out[pos++] = w1->x[j] | (w1->x[j + 1] << 4);
+ }
+ return pos;
+}
+
+/* Reference: FIPS 204 Section 6.3 "ML-DSA Verifying (Internal)" */
+int mldsa_verify(enum mldsa_alg alg, const u8 *sig, size_t sig_len,
+ const u8 *msg, size_t msg_len, const u8 *pk, size_t pk_len)
+{
+ const struct mldsa_parameter_set *params = &mldsa_parameter_sets[alg];
+ const int k = params->k, l = params->l;
+ /* For now this just does pure ML-DSA with an empty context string. */
+ static const u8 msg_prefix[2] = { /* dom_sep= */ 0, /* ctx_len= */ 0 };
+ const u8 *ctilde; /* The signer's commitment hash */
+ const u8 *t1_encoded = &pk[RHO_LEN]; /* Next encoded element of t_1 */
+ u8 *h; /* The signer's hint vector, length k * N */
+ size_t w1_enc_len;
+
+ /* Validate the public key and signature lengths. */
+ if (pk_len != params->pk_len || sig_len != params->sig_len)
+ return -EBADMSG;
+
+ /*
+ * Allocate the workspace, including variable-length fields. Its size
+ * depends only on the ML-DSA parameter set, not the other inputs.
+ *
+ * For freeing it, use kfree_sensitive() rather than kfree(). This is
+ * mainly to comply with FIPS 204 Section 3.6.3 "Intermediate Values".
+ * In reality it's a bit gratuitous, as this is a public key operation.
+ */
+ struct mldsa_verification_workspace *ws __free(kfree_sensitive) =
+ kmalloc(sizeof(*ws) + (l * sizeof(ws->z[0])) + (k * N),
+ GFP_KERNEL);
+ if (!ws)
+ return -ENOMEM;
+ h = (u8 *)&ws->z[l];
+
+ /* Decode the signature. Reference: FIPS 204 Algorithm 27, sigDecode */
+ ctilde = sig;
+ sig += params->ctilde_len;
+ if (!decode_z(ws->z, l, params->gamma1, params->beta, &sig))
+ return -EBADMSG;
+ if (!decode_hint_vector(h, k, params->omega, sig))
+ return -EBADMSG;
+
+ /* Recreate the challenge c from the signer's commitment hash. */
+ sample_in_ball(&ws->c, ctilde, params->ctilde_len, params->tau,
+ &ws->shake);
+ ntt(&ws->c);
+
+ /* Compute the message representative mu. */
+ shake256(pk, pk_len, ws->tr, sizeof(ws->tr));
+ shake256_init(&ws->shake);
+ shake_update(&ws->shake, ws->tr, sizeof(ws->tr));
+ shake_update(&ws->shake, msg_prefix, sizeof(msg_prefix));
+ shake_update(&ws->shake, msg, msg_len);
+ shake_squeeze(&ws->shake, ws->mu, sizeof(ws->mu));
+
+ /* Start computing ctildeprime = H(mu || w1Encode(w'_1)). */
+ shake256_init(&ws->shake);
+ shake_update(&ws->shake, ws->mu, sizeof(ws->mu));
+
+ /*
+ * Compute the commitment w'_1 from A, z, c, t_1, and h.
+ *
+ * The computation is the same for each of the k rows. Just do each row
+ * before moving on to the next, resulting in only one loop over k.
+ */
+ for (int i = 0; i < k; i++) {
+ /*
+ * tmp = NTT(A) * NTT(z) * 2^-32
+ * To reduce memory use, generate each element of NTT(A)
+ * on-demand. Note that each element is used only once.
+ */
+ ws->tmp = (struct mldsa_ring_elem){};
+ for (int j = 0; j < l; j++) {
+ rej_ntt_poly(&ws->a, pk /* rho is first field of pk */,
+ cpu_to_le16((i << 8) | j), &ws->a_shake,
+ ws->block);
+ for (int n = 0; n < N; n++)
+ ws->tmp.x[n] +=
+ Zq_mult(ws->a.x[n], ws->z[j].x[n]);
+ }
+ /* All components of tmp now have abs value < l*q. */
+
+ /* Decode the next element of t_1. */
+ t1_encoded = decode_t1_elem(&ws->t1_scaled, t1_encoded);
+
+ /*
+ * tmp -= NTT(c) * NTT(t_1 * 2^d) * 2^-32
+ *
+ * Taking a conservative bound for the output of ntt(), the
+ * multiplicands can have absolute value up to 9*q. That
+ * corresponds to a product with absolute value 81*q^2. That is
+ * within the limits of Zq_mult() which needs < ~256*q^2.
+ */
+ for (int j = 0; j < N; j++)
+ ws->tmp.x[j] -= Zq_mult(ws->c.x[j], ws->t1_scaled.x[j]);
+ /* All components of tmp now have abs value < (l+1)*q. */
+
+ /* tmp = w'_Approx = NTT^-1(tmp) * 2^32 */
+ invntt_and_mul_2_32(&ws->tmp);
+ /* All coefficients of tmp are now in [0, q - 1]. */
+
+ /*
+ * tmp = w'_1 = UseHint(h, w'_Approx)
+ * For efficiency, set gamma2 to a compile-time constant.
+ */
+ if (k == 4)
+ use_hint_elem(&ws->tmp, &h[i * N], (Q - 1) / 88);
+ else
+ use_hint_elem(&ws->tmp, &h[i * N], (Q - 1) / 32);
+
+ /* Encode and hash the next element of w'_1. */
+ w1_enc_len = encode_w1(ws->w1_encoded, &ws->tmp, k);
+ shake_update(&ws->shake, ws->w1_encoded, w1_enc_len);
+ }
+
+ /* Finish computing ctildeprime. */
+ shake_squeeze(&ws->shake, ws->ctildeprime, params->ctilde_len);
+
+ /* Verify that ctilde == ctildeprime. */
+ if (memcmp(ws->ctildeprime, ctilde, params->ctilde_len) != 0)
+ return -EKEYREJECTED;
+ /* ||z||_infinity < gamma1 - beta was already checked in decode_z(). */
+ return 0;
+}
+EXPORT_SYMBOL_GPL(mldsa_verify);
+
+MODULE_DESCRIPTION("ML-DSA signature verification");
+MODULE_LICENSE("GPL");
projects / thirdparty / kernel / linux.git / commitdiff
