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From 932ea29845da1ae350d9c056cb2cb0379a66d642 Mon Sep 17 00:00:00 2001
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From: Daiki Ueno <dueno@redhat.com>
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Date: Tue, 30 Mar 2021 09:22:47 +0200
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Subject: [PATCH] Port upstream hardening of EC scaler multiplication
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Some internal functions used in point multiplications are known to
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misbehave if the scaler is out-of-range. This performs canonical
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reduction on scalers, before point multiplication.
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Signed-off-by: Daiki Ueno <dueno@redhat.com>
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---
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ecc-ecdsa-sign.c | 7 +++++--
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ecc-ecdsa-verify.c | 14 ++++++++++++--
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eddsa-hash.c | 9 +++++++--
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3 files changed, 24 insertions(+), 6 deletions(-)
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diff --git a/ecc-ecdsa-sign.c b/ecc-ecdsa-sign.c
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index 3b9e9cc1..45062528 100644
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--- a/ecc-ecdsa-sign.c
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+++ b/ecc-ecdsa-sign.c
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@@ -62,6 +62,8 @@ ecc_ecdsa_sign (const struct ecc_curve *ecc,
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mp_limb_t *rp, mp_limb_t *sp,
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mp_limb_t *scratch)
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{
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+ mp_limb_t cy;
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+
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#define P scratch
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#define kinv scratch /* Needs 5*ecc->p.size for computation */
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#define hp (scratch + ecc->p.size) /* NOTE: ecc->p.size + 1 limbs! */
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@@ -91,8 +93,9 @@ ecc_ecdsa_sign (const struct ecc_curve *ecc,
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ecc_modq_mul (ecc, tp, zp, rp);
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ecc_modq_add (ecc, hp, hp, tp);
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ecc_modq_mul (ecc, tp, hp, kinv);
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-
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- mpn_copyi (sp, tp, ecc->p.size);
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+ /* Ensure canonical reduction. */
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+ cy = mpn_sub_n (sp, tp, ecc->q.m, ecc->q.size);
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+ cnd_copy (cy, sp, tp, ecc->q.size);
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#undef P
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#undef hp
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#undef kinv
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diff --git a/ecc-ecdsa-verify.c b/ecc-ecdsa-verify.c
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index d7f5b684..6b8acb07 100644
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--- a/ecc-ecdsa-verify.c
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+++ b/ecc-ecdsa-verify.c
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@@ -75,6 +75,8 @@ ecc_ecdsa_verify (const struct ecc_curve *ecc,
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const mp_limb_t *rp, const mp_limb_t *sp,
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mp_limb_t *scratch)
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{
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+ mp_limb_t cy;
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+
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/* Procedure, according to RFC 6090, "KT-I". q denotes the group
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order.
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@@ -98,6 +100,7 @@ ecc_ecdsa_verify (const struct ecc_curve *ecc,
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#define P1 (scratch + 4*ecc->p.size)
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#define sinv (scratch)
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#define hp (scratch + ecc->p.size)
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+#define tp (scratch + 4*ecc->p.size)
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if (! (ecdsa_in_range (ecc, rp)
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&& ecdsa_in_range (ecc, sp)))
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@@ -112,10 +115,16 @@ ecc_ecdsa_verify (const struct ecc_curve *ecc,
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/* u1 = h / s, P1 = u1 * G */
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ecc_hash (&ecc->q, hp, length, digest);
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- ecc_modq_mul (ecc, u1, hp, sinv);
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+ ecc_modq_mul (ecc, tp, hp, sinv);
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+ /* Ensure canonical reduction. */
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+ cy = mpn_sub_n (u1, tp, ecc->q.m, ecc->q.size);
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+ cnd_copy (cy, u1, tp, ecc->q.size);
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/* u2 = r / s, P2 = u2 * Y */
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- ecc_modq_mul (ecc, u2, rp, sinv);
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+ ecc_modq_mul (ecc, hp, rp, sinv);
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+ /* Ensure canonical reduction. */
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+ cy = mpn_sub_n (u2, hp, ecc->q.m, ecc->q.size);
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+ cnd_copy (cy, u2, hp, ecc->q.size);
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/* Total storage: 5*ecc->p.size + ecc->mul_itch */
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ecc->mul (ecc, P2, u2, pp, u2 + ecc->p.size);
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@@ -154,4 +163,5 @@ ecc_ecdsa_verify (const struct ecc_curve *ecc,
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#undef u2
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#undef hp
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#undef u1
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+#undef tp
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}
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diff --git a/eddsa-hash.c b/eddsa-hash.c
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index 4fb79f1b..53c6fc49 100644
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--- a/eddsa-hash.c
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+++ b/eddsa-hash.c
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@@ -45,7 +45,12 @@ void
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_eddsa_hash (const struct ecc_modulo *m,
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mp_limb_t *rp, const uint8_t *digest)
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{
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+ mp_limb_t cy;
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+
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size_t nbytes = 1 + m->bit_size / 8;
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- mpn_set_base256_le (rp, 2*m->size, digest, 2*nbytes);
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- m->mod (m, rp);
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+ mpn_set_base256_le (rp + m->size, 2*m->size, digest, 2*nbytes);
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+ m->mod (m, rp + m->size);
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+ /* Ensure canonical reduction. */
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+ cy = mpn_sub_n (rp, rp + m->size, m->m, m->size);
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+ cnd_copy (cy, rp, rp + m->size, m->size);
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}
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--
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2.30.2
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