From 07272b05b04836a762b4baa874958af51d513844 Mon Sep 17 00:00:00 2001 From: Tomas Mraz Date: Wed, 15 Jan 2025 18:27:02 +0100 Subject: [PATCH] Fix timing side-channel in ECDSA signature computation There is a timing signal of around 300 nanoseconds when the top word of the inverted ECDSA nonce value is zero. This can happen with significant probability only for some of the supported elliptic curves. In particular the NIST P-521 curve is affected. To be able to measure this leak, the attacker process must either be located in the same physical computer or must have a very fast network connection with low latency. Attacks on ECDSA nonce are also known as Minerva attack. Fixes CVE-2024-13176 Reviewed-by: Tim Hudson Reviewed-by: Neil Horman Reviewed-by: Paul Dale (Merged from https://github.com/openssl/openssl/pull/26429) (cherry picked from commit 63c40a66c5dc287485705d06122d3a6e74a6a203) --- crypto/bn/bn_exp.c | 21 +++++++++++++++------ crypto/ec/ec_lib.c | 7 ++++--- include/crypto/bn.h | 3 +++ 3 files changed, 22 insertions(+), 9 deletions(-) Index: openssl-3.2.3/crypto/bn/bn_exp.c =================================================================== --- openssl-3.2.3.orig/crypto/bn/bn_exp.c +++ openssl-3.2.3/crypto/bn/bn_exp.c @@ -606,7 +606,7 @@ static int MOD_EXP_CTIME_COPY_FROM_PREBU * out by Colin Percival, * http://www.daemonology.net/hyperthreading-considered-harmful/) */ -int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, +int bn_mod_exp_mont_fixed_top(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *in_mont) { @@ -623,10 +623,6 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr unsigned int t4 = 0; #endif - bn_check_top(a); - bn_check_top(p); - bn_check_top(m); - if (!BN_is_odd(m)) { ERR_raise(ERR_LIB_BN, BN_R_CALLED_WITH_EVEN_MODULUS); return 0; @@ -1146,7 +1142,7 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr goto err; } else #endif - if (!BN_from_montgomery(rr, &tmp, mont, ctx)) + if (!bn_from_mont_fixed_top(rr, &tmp, mont, ctx)) goto err; ret = 1; err: @@ -1160,6 +1156,19 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr return ret; } +int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, + const BIGNUM *m, BN_CTX *ctx, + BN_MONT_CTX *in_mont) +{ + bn_check_top(a); + bn_check_top(p); + bn_check_top(m); + if (!bn_mod_exp_mont_fixed_top(rr, a, p, m, ctx, in_mont)) + return 0; + bn_correct_top(rr); + return 1; +} + int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p, const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *in_mont) { Index: openssl-3.2.3/crypto/ec/ec_lib.c =================================================================== --- openssl-3.2.3.orig/crypto/ec/ec_lib.c +++ openssl-3.2.3/crypto/ec/ec_lib.c @@ -21,6 +21,7 @@ #include #include #include "crypto/ec.h" +#include "crypto/bn.h" #include "internal/nelem.h" #include "ec_local.h" @@ -1265,10 +1266,10 @@ static int ec_field_inverse_mod_ord(cons if (!BN_sub(e, group->order, e)) goto err; /*- - * Exponent e is public. - * No need for scatter-gather or BN_FLG_CONSTTIME. + * Although the exponent is public we want the result to be + * fixed top. */ - if (!BN_mod_exp_mont(r, x, e, group->order, ctx, group->mont_data)) + if (!bn_mod_exp_mont_fixed_top(r, x, e, group->order, ctx, group->mont_data)) goto err; ret = 1; Index: openssl-3.2.3/include/crypto/bn.h =================================================================== --- openssl-3.2.3.orig/include/crypto/bn.h +++ openssl-3.2.3/include/crypto/bn.h @@ -73,6 +73,9 @@ int bn_set_words(BIGNUM *a, const BN_ULO */ int bn_mul_mont_fixed_top(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, BN_MONT_CTX *mont, BN_CTX *ctx); +int bn_mod_exp_mont_fixed_top(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, + const BIGNUM *m, BN_CTX *ctx, + BN_MONT_CTX *in_mont); int bn_to_mont_fixed_top(BIGNUM *r, const BIGNUM *a, BN_MONT_CTX *mont, BN_CTX *ctx); int bn_from_mont_fixed_top(BIGNUM *r, const BIGNUM *a, BN_MONT_CTX *mont,