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SUSE:SLE-12-SP2:GA
compat-openssl098.27677
0001-Add-blinding-to-an-ECDSA-signature.patch
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File 0001-Add-blinding-to-an-ECDSA-signature.patch of Package compat-openssl098.27677
From 949ff36623eafc3523a9f91784992965018ffb05 Mon Sep 17 00:00:00 2001 From: Matt Caswell <matt@openssl.org> Date: Fri, 25 May 2018 12:10:13 +0100 Subject: [PATCH] Add blinding to an ECDSA signature Keegan Ryan (NCC Group) has demonstrated a side channel attack on an ECDSA signature operation. During signing the signer calculates: s:= k^-1 * (m + r * priv_key) mod order The addition operation above provides a sufficient signal for a flush+reload attack to derive the private key given sufficient signature operations. As a mitigation (based on a suggestion from Keegan) we add blinding to the operation so that: s := k^-1 * blind^-1 (blind * m + blind * r * priv_key) mod order Since this attack is a localhost side channel only no CVE is assigned. Reviewed-by: Rich Salz <rsalz@openssl.org> --- CHANGES | 4 ++ crypto/ecdsa/ecdsatest.c | 9 ++++- crypto/ecdsa/ecs_ossl.c | 82 ++++++++++++++++++++++++++++++++-------- 3 files changed, 79 insertions(+), 16 deletions(-) Index: openssl-0.9.8j/crypto/ecdsa/ecdsatest.c =================================================================== --- openssl-0.9.8j.orig/crypto/ecdsa/ecdsatest.c 2018-08-13 12:22:52.525216069 +0200 +++ openssl-0.9.8j/crypto/ecdsa/ecdsatest.c 2018-08-13 12:24:05.001676253 +0200 @@ -137,7 +137,7 @@ int restore_rand(void) return 1; } -static int fbytes_counter = 0; +static int fbytes_counter = 0, use_fake = 0; static const char *numbers[8] = { "651056770906015076056810763456358567190100156695615665659", "6140507067065001063065065565667405560006161556565665656654", @@ -157,6 +157,11 @@ int fbytes(unsigned char *buf, int num) int ret; BIGNUM *tmp = NULL; + if (use_fake == 0) + return old_rand->bytes(buf, num); + + use_fake = 0; + if (fbytes_counter >= 8) return 0; tmp = BN_new(); @@ -200,11 +205,13 @@ int x9_62_test_internal(BIO *out, int ni /* create the key */ if ((key = EC_KEY_new_by_curve_name(nid)) == NULL) goto x962_int_err; + use_fake = 1; if (!EC_KEY_generate_key(key)) goto x962_int_err; BIO_printf(out, "."); (void)BIO_flush(out); /* create the signature */ + use_fake = 1; signature = ECDSA_do_sign(digest, 20, key); if (signature == NULL) goto x962_int_err; Index: openssl-0.9.8j/crypto/ecdsa/ecs_ossl.c =================================================================== --- openssl-0.9.8j.orig/crypto/ecdsa/ecs_ossl.c 2018-08-13 12:23:01.033270090 +0200 +++ openssl-0.9.8j/crypto/ecdsa/ecs_ossl.c 2018-08-13 12:40:21.767908367 +0200 @@ -225,6 +225,7 @@ static ECDSA_SIG *ecdsa_do_sign(const un { int ok = 0; BIGNUM *kinv=NULL, *s, *m=NULL,*tmp=NULL,*order=NULL; + BIGNUM *blind = NULL, *blindm = NULL; const BIGNUM *ckinv; BN_CTX *ctx = NULL; const EC_GROUP *group; @@ -250,9 +251,19 @@ static ECDSA_SIG *ecdsa_do_sign(const un } s = ret->s; - if ((ctx = BN_CTX_new()) == NULL || (order = BN_new()) == NULL || - (tmp = BN_new()) == NULL || (m = BN_new()) == NULL) - { + ctx = BN_CTX_new(); + if (ctx == NULL) { + ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_MALLOC_FAILURE); + goto err; + } + + BN_CTX_start(ctx); + order = BN_CTX_get(ctx); + tmp = BN_CTX_get(ctx); + m = BN_CTX_get(ctx); + blind = BN_CTX_get(ctx); + blindm = BN_CTX_get(ctx); + if (blindm == NULL) { ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_MALLOC_FAILURE); goto err; } @@ -303,18 +314,59 @@ static ECDSA_SIG *ecdsa_do_sign(const un } } - if (!BN_mod_mul(tmp, priv_key, ret->r, order, ctx)) - { + /* + * The normal signature calculation is: + * + * s := k^-1 * (m + r * priv_key) mod order + * + * We will blind this to protect against side channel attacks + * + * s := blind^-1 * k^-1 * (blind * m + blind * r * priv_key) mod order + */ + + /* Generate a blinding value */ + do { + if (!BN_rand(blind, BN_num_bits(order) - 1, -1, 0)) + goto err; + } while (BN_is_zero(blind)); + BN_set_flags(blind, BN_FLG_CONSTTIME); + BN_set_flags(blindm, BN_FLG_CONSTTIME); + BN_set_flags(tmp, BN_FLG_CONSTTIME); + + /* tmp := blind * priv_key * r mod order */ + if (!BN_mod_mul(tmp, blind, priv_key, order, ctx)) { + ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_BN_LIB); + goto err; + } + if (!BN_mod_mul(tmp, tmp, ret->r, order, ctx)) { + ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_BN_LIB); + goto err; + } + + /* blindm := blind * m mod order */ + if (!BN_mod_mul(blindm, blind, m, order, ctx)) { + ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_BN_LIB); + goto err; + } + + /* s : = (blind * priv_key * r) + (blind * m) mod order */ + if (!BN_mod_add_quick(s, tmp, blindm, order)) { + ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_BN_LIB); + goto err; + } + + /* s := s * k^-1 mod order */ + if (!BN_mod_mul(s, s, ckinv, order, ctx)) { ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_BN_LIB); goto err; } - if (!BN_mod_add_quick(s, tmp, m, order)) - { + /* s:= s * blind^-1 mod order */ + if (BN_mod_inverse(blind, blind, order, ctx) == NULL) { ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_BN_LIB); goto err; } - if (!BN_mod_mul(s, s, ckinv, order, ctx)) - { + /* s := s * k^-1 mod order */ + if (!BN_mod_mul(s, s, blind, order, ctx)) { ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_BN_LIB); goto err; } @@ -341,15 +393,11 @@ err: ECDSA_SIG_free(ret); ret = NULL; } - if (ctx) + if (ctx != NULL) { + BN_CTX_end(ctx); BN_CTX_free(ctx); - if (m) - BN_clear_free(m); - if (tmp) - BN_clear_free(tmp); - if (order) - BN_free(order); - if (kinv) + } + if (kinv != NULL) BN_clear_free(kinv); return ret; }
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