The branch master has been updated via 99540ec79491f59ed8b46b4edf130e17dc907f52 (commit) via a9cfb8c2aa7254a4aa6a1716909e3f8cb78049b6 (commit) from 415c33563528667868c3c653a612e6fc8736fd79 (commit)
- Log ----------------------------------------------------------------- commit 99540ec79491f59ed8b46b4edf130e17dc907f52 Author: Pauli <paul.d...@oracle.com> Date: Fri Oct 26 10:54:58 2018 +1000 Timing vulnerability in ECDSA signature generation (CVE-2018-0735) Preallocate an extra limb for some of the big numbers to avoid a reallocation that can potentially provide a side channel. Reviewed-by: Bernd Edlinger <bernd.edlin...@hotmail.de> (Merged from https://github.com/openssl/openssl/pull/7486) commit a9cfb8c2aa7254a4aa6a1716909e3f8cb78049b6 Author: Pauli <paul.d...@oracle.com> Date: Wed Oct 24 07:42:46 2018 +1000 Timing vulnerability in DSA signature generation (CVE-2018-0734). Avoid a timing attack that leaks information via a side channel that triggers when a BN is resized. Increasing the size of the BNs prior to doing anything with them suppresses the attack. Thanks due to Samuel Weiser for finding and locating this. Reviewed-by: Bernd Edlinger <bernd.edlin...@hotmail.de> (Merged from https://github.com/openssl/openssl/pull/7486) ----------------------------------------------------------------------- Summary of changes: crypto/dsa/dsa_ossl.c | 28 +++++++++++++++------------- crypto/ec/ec_mult.c | 6 +++--- 2 files changed, 18 insertions(+), 16 deletions(-) diff --git a/crypto/dsa/dsa_ossl.c b/crypto/dsa/dsa_ossl.c index ca20811..2dd2d74 100644 --- a/crypto/dsa/dsa_ossl.c +++ b/crypto/dsa/dsa_ossl.c @@ -9,6 +9,7 @@ #include <stdio.h> #include "internal/cryptlib.h" +#include "internal/bn_int.h" #include <openssl/bn.h> #include <openssl/sha.h> #include "dsa_locl.h" @@ -180,9 +181,9 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, { BN_CTX *ctx = NULL; BIGNUM *k, *kinv = NULL, *r = *rp; - BIGNUM *l, *m; + BIGNUM *l; int ret = 0; - int q_bits; + int q_bits, q_words; if (!dsa->p || !dsa->q || !dsa->g) { DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_MISSING_PARAMETERS); @@ -191,8 +192,7 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, k = BN_new(); l = BN_new(); - m = BN_new(); - if (k == NULL || l == NULL || m == NULL) + if (k == NULL || l == NULL) goto err; if (ctx_in == NULL) { @@ -203,9 +203,9 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, /* Preallocate space */ q_bits = BN_num_bits(dsa->q); - if (!BN_set_bit(k, q_bits) - || !BN_set_bit(l, q_bits) - || !BN_set_bit(m, q_bits)) + q_words = bn_get_top(dsa->q); + if (!bn_wexpand(k, q_words + 2) + || !bn_wexpand(l, q_words + 2)) goto err; /* Get random k */ @@ -240,14 +240,17 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, * small timing information leakage. We then choose the sum that is * one bit longer than the modulus. * - * TODO: revisit the BN_copy aiming for a memory access agnostic - * conditional copy. + * There are some concerns about the efficacy of doing this. More + * specificly refer to the discussion starting with: + * https://github.com/openssl/openssl/pull/7486#discussion_r228323705 + * The fix is to rework BN so these gymnastics aren't required. */ if (!BN_add(l, k, dsa->q) - || !BN_add(m, l, dsa->q) - || !BN_copy(k, BN_num_bits(l) > q_bits ? l : m)) + || !BN_add(k, l, dsa->q)) goto err; + BN_consttime_swap(BN_is_bit_set(l, q_bits), k, l, q_words + 2); + if ((dsa)->meth->bn_mod_exp != NULL) { if (!dsa->meth->bn_mod_exp(dsa, r, dsa->g, k, dsa->p, ctx, dsa->method_mont_p)) @@ -260,7 +263,7 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, if (!BN_mod(r, r, dsa->q, ctx)) goto err; - /* Compute part of 's = inv(k) (m + xr) mod q' */ + /* Compute part of 's = inv(k) (m + xr) mod q' */ if ((kinv = dsa_mod_inverse_fermat(k, dsa->q, ctx)) == NULL) goto err; @@ -275,7 +278,6 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BN_CTX_free(ctx); BN_clear_free(k); BN_clear_free(l); - BN_clear_free(m); return ret; } diff --git a/crypto/ec/ec_mult.c b/crypto/ec/ec_mult.c index 7e1b365..0e0a5e1 100644 --- a/crypto/ec/ec_mult.c +++ b/crypto/ec/ec_mult.c @@ -206,8 +206,8 @@ int ec_scalar_mul_ladder(const EC_GROUP *group, EC_POINT *r, */ cardinality_bits = BN_num_bits(cardinality); group_top = bn_get_top(cardinality); - if ((bn_wexpand(k, group_top + 1) == NULL) - || (bn_wexpand(lambda, group_top + 1) == NULL)) { + if ((bn_wexpand(k, group_top + 2) == NULL) + || (bn_wexpand(lambda, group_top + 2) == NULL)) { ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_BN_LIB); goto err; } @@ -244,7 +244,7 @@ int ec_scalar_mul_ladder(const EC_GROUP *group, EC_POINT *r, * k := scalar + 2*cardinality */ kbit = BN_is_bit_set(lambda, cardinality_bits); - BN_consttime_swap(kbit, k, lambda, group_top + 1); + BN_consttime_swap(kbit, k, lambda, group_top + 2); group_top = bn_get_top(group->field); if ((bn_wexpand(s->X, group_top) == NULL) _____ openssl-commits mailing list To unsubscribe: https://mta.openssl.org/mailman/listinfo/openssl-commits