123 lines
4.6 KiB
Diff
123 lines
4.6 KiB
Diff
From 4b1cb94a734a7d4ec363ac0a215a25c181e11f65 Mon Sep 17 00:00:00 2001
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From: Tomas Mraz <tomas@openssl.org>
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Date: Wed, 15 Jan 2025 18:27:02 +0100
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Subject: [PATCH] Fix timing side-channel in ECDSA signature computation
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There is a timing signal of around 300 nanoseconds when the top word of
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the inverted ECDSA nonce value is zero. This can happen with significant
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probability only for some of the supported elliptic curves. In particular
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the NIST P-521 curve is affected. To be able to measure this leak, the
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attacker process must either be located in the same physical computer or
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must have a very fast network connection with low latency.
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Attacks on ECDSA nonce are also known as Minerva attack.
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Fixes CVE-2024-13176
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Reviewed-by: Tim Hudson <tjh@openssl.org>
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Reviewed-by: Neil Horman <nhorman@openssl.org>
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Reviewed-by: Paul Dale <ppzgs1@gmail.com>
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(Merged from https://github.com/openssl/openssl/pull/26429)
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(cherry picked from commit 63c40a66c5dc287485705d06122d3a6e74a6a203)
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(cherry picked from commit 392dcb336405a0c94486aa6655057f59fd3a0902)
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---
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crypto/bn/bn_exp.c | 21 +++++++++++++++------
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crypto/ec/ec_lib.c | 7 ++++---
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include/crypto/bn.h | 3 +++
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3 files changed, 22 insertions(+), 9 deletions(-)
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diff --git a/crypto/bn/bn_exp.c b/crypto/bn/bn_exp.c
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index b876edbfac36e..af52e2ced6914 100644
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--- a/crypto/bn/bn_exp.c
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+++ b/crypto/bn/bn_exp.c
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@@ -606,7 +606,7 @@ static int MOD_EXP_CTIME_COPY_FROM_PREBUF(BIGNUM *b, int top,
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* out by Colin Percival,
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* http://www.daemonology.net/hyperthreading-considered-harmful/)
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*/
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-int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
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+int bn_mod_exp_mont_fixed_top(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
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const BIGNUM *m, BN_CTX *ctx,
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BN_MONT_CTX *in_mont)
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{
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@@ -623,10 +623,6 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
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unsigned int t4 = 0;
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#endif
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- bn_check_top(a);
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- bn_check_top(p);
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- bn_check_top(m);
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-
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if (!BN_is_odd(m)) {
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ERR_raise(ERR_LIB_BN, BN_R_CALLED_WITH_EVEN_MODULUS);
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return 0;
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@@ -1146,7 +1142,7 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
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goto err;
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} else
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#endif
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- if (!BN_from_montgomery(rr, &tmp, mont, ctx))
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+ if (!bn_from_mont_fixed_top(rr, &tmp, mont, ctx))
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goto err;
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ret = 1;
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err:
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@@ -1160,6 +1156,19 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
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return ret;
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}
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+int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
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+ const BIGNUM *m, BN_CTX *ctx,
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+ BN_MONT_CTX *in_mont)
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+{
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+ bn_check_top(a);
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+ bn_check_top(p);
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+ bn_check_top(m);
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+ if (!bn_mod_exp_mont_fixed_top(rr, a, p, m, ctx, in_mont))
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+ return 0;
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+ bn_correct_top(rr);
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+ return 1;
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+}
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+
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int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p,
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const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *in_mont)
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{
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diff --git a/crypto/ec/ec_lib.c b/crypto/ec/ec_lib.c
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index c92b4dcb0ac45..a79fbb98cf6fa 100644
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--- a/crypto/ec/ec_lib.c
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+++ b/crypto/ec/ec_lib.c
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@@ -21,6 +21,7 @@
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#include <openssl/opensslv.h>
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#include <openssl/param_build.h>
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#include "crypto/ec.h"
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+#include "crypto/bn.h"
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#include "internal/nelem.h"
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#include "ec_local.h"
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@@ -1261,10 +1262,10 @@ static int ec_field_inverse_mod_ord(const EC_GROUP *group, BIGNUM *r,
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if (!BN_sub(e, group->order, e))
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goto err;
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/*-
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- * Exponent e is public.
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- * No need for scatter-gather or BN_FLG_CONSTTIME.
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+ * Although the exponent is public we want the result to be
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+ * fixed top.
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*/
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- if (!BN_mod_exp_mont(r, x, e, group->order, ctx, group->mont_data))
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+ if (!bn_mod_exp_mont_fixed_top(r, x, e, group->order, ctx, group->mont_data))
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goto err;
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ret = 1;
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diff --git a/include/crypto/bn.h b/include/crypto/bn.h
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index 302f031c2ff1d..499e1d10efab0 100644
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--- a/include/crypto/bn.h
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+++ b/include/crypto/bn.h
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@@ -73,6 +73,9 @@ int bn_set_words(BIGNUM *a, const BN_ULONG *words, int num_words);
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*/
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int bn_mul_mont_fixed_top(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
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BN_MONT_CTX *mont, BN_CTX *ctx);
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+int bn_mod_exp_mont_fixed_top(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
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+ const BIGNUM *m, BN_CTX *ctx,
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+ BN_MONT_CTX *in_mont);
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int bn_to_mont_fixed_top(BIGNUM *r, const BIGNUM *a, BN_MONT_CTX *mont,
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BN_CTX *ctx);
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int bn_from_mont_fixed_top(BIGNUM *r, const BIGNUM *a, BN_MONT_CTX *mont,
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