From 149fe5183f483d61a4d9c7559eda5256da9eaf72 Mon Sep 17 00:00:00 2001 From: tb Date: Mon, 16 Jul 2018 17:32:39 +0000 Subject: [PATCH] Recommit Billy Brumley's ECC constant time patch with a fix for sparc64 from Nicola Tuveri (who spotted the omission of ecp_nist.c from the PR). discussed with jsing tested by jsg --- lib/libcrypto/ec/ec2_smpl.c | 12 +- lib/libcrypto/ec/ec_lcl.h | 17 ++- lib/libcrypto/ec/ec_lib.c | 99 +++++++++----- lib/libcrypto/ec/ecp_mont.c | 5 +- lib/libcrypto/ec/ecp_nist.c | 5 +- lib/libcrypto/ec/ecp_smpl.c | 250 +++++++++++++++++++++++++++++++++++- 6 files changed, 341 insertions(+), 47 deletions(-) diff --git a/lib/libcrypto/ec/ec2_smpl.c b/lib/libcrypto/ec/ec2_smpl.c index 19a4250e415..1ca04194b31 100644 --- a/lib/libcrypto/ec/ec2_smpl.c +++ b/lib/libcrypto/ec/ec2_smpl.c @@ -1,4 +1,4 @@ -/* $OpenBSD: ec2_smpl.c,v 1.19 2018/07/15 16:27:39 tb Exp $ */ +/* $OpenBSD: ec2_smpl.c,v 1.20 2018/07/16 17:32:39 tb Exp $ */ /* ==================================================================== * Copyright 2002 Sun Microsystems, Inc. ALL RIGHTS RESERVED. * @@ -107,15 +107,11 @@ EC_GF2m_simple_method(void) .point_cmp = ec_GF2m_simple_cmp, .make_affine = ec_GF2m_simple_make_affine, .points_make_affine = ec_GF2m_simple_points_make_affine, - - /* - * the following three method functions are defined in - * ec2_mult.c - */ - .mul = ec_GF2m_simple_mul, + .mul_generator_ct = ec_GFp_simple_mul_generator_ct, + .mul_single_ct = ec_GFp_simple_mul_single_ct, + .mul_double_nonct = ec_GFp_simple_mul_double_nonct, .precompute_mult = ec_GF2m_precompute_mult, .have_precompute_mult = ec_GF2m_have_precompute_mult, - .field_mul = ec_GF2m_simple_field_mul, .field_sqr = ec_GF2m_simple_field_sqr, .field_div = ec_GF2m_simple_field_div, diff --git a/lib/libcrypto/ec/ec_lcl.h b/lib/libcrypto/ec/ec_lcl.h index bcfd817b703..e430b3f64d4 100644 --- a/lib/libcrypto/ec/ec_lcl.h +++ b/lib/libcrypto/ec/ec_lcl.h @@ -1,4 +1,4 @@ -/* $OpenBSD: ec_lcl.h,v 1.9 2018/07/15 05:38:48 jsg Exp $ */ +/* $OpenBSD: ec_lcl.h,v 1.10 2018/07/16 17:32:39 tb Exp $ */ /* * Originally written by Bodo Moeller for the OpenSSL project. */ @@ -160,10 +160,12 @@ struct ec_method_st { int (*make_affine)(const EC_GROUP *, EC_POINT *, BN_CTX *); int (*points_make_affine)(const EC_GROUP *, size_t num, EC_POINT *[], BN_CTX *); - /* used by EC_POINTs_mul, EC_POINT_mul, EC_POINT_precompute_mult, EC_POINT_have_precompute_mult - * (default implementations are used if the 'mul' pointer is 0): */ - int (*mul)(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar, - size_t num, const EC_POINT *points[], const BIGNUM *scalars[], BN_CTX *); + /* used by EC_POINTs_mul, EC_POINT_mul, EC_POINT_precompute_mult, EC_POINT_have_precompute_mult */ + int (*mul_generator_ct)(const EC_GROUP *, EC_POINT *r, const BIGNUM *scalar, BN_CTX *); + int (*mul_single_ct)(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar, + const EC_POINT *point, BN_CTX *); + int (*mul_double_nonct)(const EC_GROUP *group, EC_POINT *r, const BIGNUM *g_scalar, + const BIGNUM *p_scalar, const EC_POINT *point, BN_CTX *); int (*precompute_mult)(EC_GROUP *group, BN_CTX *); int (*have_precompute_mult)(const EC_GROUP *group); @@ -337,6 +339,11 @@ int ec_GFp_simple_make_affine(const EC_GROUP *, EC_POINT *, BN_CTX *); int ec_GFp_simple_points_make_affine(const EC_GROUP *, size_t num, EC_POINT *[], BN_CTX *); int ec_GFp_simple_field_mul(const EC_GROUP *, BIGNUM *r, const BIGNUM *a, const BIGNUM *b, BN_CTX *); int ec_GFp_simple_field_sqr(const EC_GROUP *, BIGNUM *r, const BIGNUM *a, BN_CTX *); +int ec_GFp_simple_mul_generator_ct(const EC_GROUP *, EC_POINT *r, const BIGNUM *scalar, BN_CTX *); +int ec_GFp_simple_mul_single_ct(const EC_GROUP *, EC_POINT *r, const BIGNUM *scalar, + const EC_POINT *point, BN_CTX *); +int ec_GFp_simple_mul_double_nonct(const EC_GROUP *, EC_POINT *r, const BIGNUM *g_scalar, + const BIGNUM *p_scalar, const EC_POINT *point, BN_CTX *); /* method functions in ecp_mont.c */ diff --git a/lib/libcrypto/ec/ec_lib.c b/lib/libcrypto/ec/ec_lib.c index 53d79f232c2..7e0ea017f99 100644 --- a/lib/libcrypto/ec/ec_lib.c +++ b/lib/libcrypto/ec/ec_lib.c @@ -1,4 +1,4 @@ -/* $OpenBSD: ec_lib.c,v 1.28 2018/07/15 16:27:39 tb Exp $ */ +/* $OpenBSD: ec_lib.c,v 1.29 2018/07/16 17:32:39 tb Exp $ */ /* * Originally written by Bodo Moeller for the OpenSSL project. */ @@ -1026,47 +1026,88 @@ EC_POINTs_make_affine(const EC_GROUP *group, size_t num, EC_POINT *points[], } -/* Functions for point multiplication. - * - * If group->meth->mul is 0, we use the wNAF-based implementations in ec_mult.c; - * otherwise we dispatch through methods. - */ - +/* Functions for point multiplication */ int EC_POINTs_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar, size_t num, const EC_POINT *points[], const BIGNUM *scalars[], BN_CTX *ctx) { - if (group->meth->mul == 0) - /* use default */ - return ec_wNAF_mul(group, r, scalar, num, points, scalars, ctx); - - return group->meth->mul(group, r, scalar, num, points, scalars, ctx); + /* + * The function pointers must be set, and only support num == 0 and + * num == 1. + */ + if (group->meth->mul_generator_ct == NULL || + group->meth->mul_single_ct == NULL || + group->meth->mul_double_nonct == NULL || + num > 1) { + ECerror(ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED); + return 0; + } + + /* Either bP or aG + bP, this is sane. */ + if (num == 1 && points != NULL && scalars != NULL) + return EC_POINT_mul(group, r, scalar, points[0], scalars[0], + ctx); + + /* aG, this is sane */ + if (scalar != NULL && points == NULL && scalars == NULL) + return EC_POINT_mul(group, r, scalar, NULL, NULL, ctx); + + /* anything else is an error */ + ECerror(ERR_R_EC_LIB); + return 0; } int EC_POINT_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *g_scalar, const EC_POINT *point, const BIGNUM *p_scalar, BN_CTX *ctx) { - /* just a convenient interface to EC_POINTs_mul() */ - - const EC_POINT *points[1]; - const BIGNUM *scalars[1]; - - points[0] = point; - scalars[0] = p_scalar; - - return EC_POINTs_mul(group, r, g_scalar, - (point != NULL && p_scalar != NULL), - points, scalars, ctx); + if (group->meth->mul_generator_ct == NULL || + group->meth->mul_single_ct == NULL || + group->meth->mul_double_nonct == NULL) { + ECerror(ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED); + return 0; + } + if (g_scalar != NULL && point == NULL && p_scalar == NULL) { + /* + * In this case we want to compute g_scalar * GeneratorPoint: + * this codepath is reached most prominently by (ephemeral) key + * generation of EC cryptosystems (i.e. ECDSA keygen and sign + * setup, ECDH keygen/first half), where the scalar is always + * secret. This is why we ignore if BN_FLG_CONSTTIME is actually + * set and we always call the constant time version. + */ + return group->meth->mul_generator_ct(group, r, g_scalar, ctx); + } + if (g_scalar == NULL && point != NULL && p_scalar != NULL) { + /* In this case we want to compute p_scalar * GenericPoint: + * this codepath is reached most prominently by the second half + * of ECDH, where the secret scalar is multiplied by the peer's + * public point. To protect the secret scalar, we ignore if + * BN_FLG_CONSTTIME is actually set and we always call the + * constant time version. + */ + return group->meth->mul_single_ct(group, r, p_scalar, point, + ctx); + } + if (g_scalar != NULL && point != NULL && p_scalar != NULL) { + /* + * In this case we want to compute + * g_scalar * GeneratorPoint + p_scalar * GenericPoint: + * this codepath is reached most prominently by ECDSA signature + * verification. So we call the non-ct version. + */ + return group->meth->mul_double_nonct(group, r, g_scalar, + p_scalar, point, ctx); + } + + /* Anything else is an error. */ + ECerror(ERR_R_EC_LIB); + return 0; } int EC_GROUP_precompute_mult(EC_GROUP * group, BN_CTX * ctx) { - if (group->meth->mul == 0) - /* use default */ - return ec_wNAF_precompute_mult(group, ctx); - if (group->meth->precompute_mult != 0) return group->meth->precompute_mult(group, ctx); else @@ -1076,10 +1117,6 @@ EC_GROUP_precompute_mult(EC_GROUP * group, BN_CTX * ctx) int EC_GROUP_have_precompute_mult(const EC_GROUP * group) { - if (group->meth->mul == 0) - /* use default */ - return ec_wNAF_have_precompute_mult(group); - if (group->meth->have_precompute_mult != 0) return group->meth->have_precompute_mult(group); else diff --git a/lib/libcrypto/ec/ecp_mont.c b/lib/libcrypto/ec/ecp_mont.c index 40c512a3570..ba4b9cad974 100644 --- a/lib/libcrypto/ec/ecp_mont.c +++ b/lib/libcrypto/ec/ecp_mont.c @@ -1,4 +1,4 @@ -/* $OpenBSD: ecp_mont.c,v 1.15 2018/07/15 16:27:39 tb Exp $ */ +/* $OpenBSD: ecp_mont.c,v 1.16 2018/07/16 17:32:39 tb Exp $ */ /* * Originally written by Bodo Moeller for the OpenSSL project. */ @@ -102,6 +102,9 @@ EC_GFp_mont_method(void) .point_cmp = ec_GFp_simple_cmp, .make_affine = ec_GFp_simple_make_affine, .points_make_affine = ec_GFp_simple_points_make_affine, + .mul_generator_ct = ec_GFp_simple_mul_generator_ct, + .mul_single_ct = ec_GFp_simple_mul_single_ct, + .mul_double_nonct = ec_GFp_simple_mul_double_nonct, .field_mul = ec_GFp_mont_field_mul, .field_sqr = ec_GFp_mont_field_sqr, .field_encode = ec_GFp_mont_field_encode, diff --git a/lib/libcrypto/ec/ecp_nist.c b/lib/libcrypto/ec/ecp_nist.c index 3e6005eebbd..6ae11708085 100644 --- a/lib/libcrypto/ec/ecp_nist.c +++ b/lib/libcrypto/ec/ecp_nist.c @@ -1,4 +1,4 @@ -/* $OpenBSD: ecp_nist.c,v 1.13 2018/07/15 16:27:39 tb Exp $ */ +/* $OpenBSD: ecp_nist.c,v 1.14 2018/07/16 17:32:39 tb Exp $ */ /* * Written by Nils Larsch for the OpenSSL project. */ @@ -103,6 +103,9 @@ EC_GFp_nist_method(void) .point_cmp = ec_GFp_simple_cmp, .make_affine = ec_GFp_simple_make_affine, .points_make_affine = ec_GFp_simple_points_make_affine, + .mul_generator_ct = ec_GFp_simple_mul_generator_ct, + .mul_single_ct = ec_GFp_simple_mul_single_ct, + .mul_double_nonct = ec_GFp_simple_mul_double_nonct, .field_mul = ec_GFp_nist_field_mul, .field_sqr = ec_GFp_nist_field_sqr }; diff --git a/lib/libcrypto/ec/ecp_smpl.c b/lib/libcrypto/ec/ecp_smpl.c index eabad4bd864..a25fd1df846 100644 --- a/lib/libcrypto/ec/ecp_smpl.c +++ b/lib/libcrypto/ec/ecp_smpl.c @@ -1,4 +1,4 @@ -/* $OpenBSD: ecp_smpl.c,v 1.21 2018/07/15 16:27:39 tb Exp $ */ +/* $OpenBSD: ecp_smpl.c,v 1.22 2018/07/16 17:32:39 tb Exp $ */ /* Includes code written by Lenka Fibikova * for the OpenSSL project. * Includes code written by Bodo Moeller for the OpenSSL project. @@ -103,6 +103,9 @@ EC_GFp_simple_method(void) .point_cmp = ec_GFp_simple_cmp, .make_affine = ec_GFp_simple_make_affine, .points_make_affine = ec_GFp_simple_points_make_affine, + .mul_generator_ct = ec_GFp_simple_mul_generator_ct, + .mul_single_ct = ec_GFp_simple_mul_single_ct, + .mul_double_nonct = ec_GFp_simple_mul_double_nonct, .field_mul = ec_GFp_simple_field_mul, .field_sqr = ec_GFp_simple_field_sqr }; @@ -1409,3 +1412,248 @@ ec_GFp_simple_field_sqr(const EC_GROUP * group, BIGNUM * r, const BIGNUM * a, BN { return BN_mod_sqr(r, a, &group->field, ctx); } + +#define EC_POINT_BN_set_flags(P, flags) do { \ + BN_set_flags(&(P)->X, (flags)); \ + BN_set_flags(&(P)->Y, (flags)); \ + BN_set_flags(&(P)->Z, (flags)); \ +} while(0) + +#define EC_POINT_CSWAP(c, a, b, w, t) do { \ + if (!BN_swap_ct(c, &(a)->X, &(b)->X, w) || \ + !BN_swap_ct(c, &(a)->Y, &(b)->Y, w) || \ + !BN_swap_ct(c, &(a)->Z, &(b)->Z, w)) \ + goto err; \ + t = ((a)->Z_is_one ^ (b)->Z_is_one) & (c); \ + (a)->Z_is_one ^= (t); \ + (b)->Z_is_one ^= (t); \ +} while(0) + +/* + * This function computes (in constant time) a point multiplication over the + * EC group. + * + * At a high level, it is Montgomery ladder with conditional swaps. + * + * It performs either a fixed point multiplication + * (scalar * generator) + * when point is NULL, or a variable point multiplication + * (scalar * point) + * when point is not NULL. + * + * scalar should be in the range [0,n) otherwise all constant time bets are off. + * + * NB: This says nothing about EC_POINT_add and EC_POINT_dbl, + * which of course are not constant time themselves. + * + * The product is stored in r. + * + * Returns 1 on success, 0 otherwise. + */ +static int +ec_GFp_simple_mul_ct(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar, + const EC_POINT *point, BN_CTX *ctx) +{ + int i, cardinality_bits, group_top, kbit, pbit, Z_is_one; + EC_POINT *s = NULL; + BIGNUM *k = NULL; + BIGNUM *lambda = NULL; + BIGNUM *cardinality = NULL; + BN_CTX *new_ctx = NULL; + int ret = 0; + + if (ctx == NULL && (ctx = new_ctx = BN_CTX_new()) == NULL) + return 0; + + BN_CTX_start(ctx); + + if ((s = EC_POINT_new(group)) == NULL) + goto err; + + if (point == NULL) { + if (!EC_POINT_copy(s, group->generator)) + goto err; + } else { + if (!EC_POINT_copy(s, point)) + goto err; + } + + EC_POINT_BN_set_flags(s, BN_FLG_CONSTTIME); + + if ((cardinality = BN_CTX_get(ctx)) == NULL) + goto err; + if ((lambda = BN_CTX_get(ctx)) == NULL) + goto err; + if ((k = BN_CTX_get(ctx)) == NULL) + goto err; + if (!BN_mul(cardinality, &group->order, &group->cofactor, ctx)) + goto err; + + /* + * Group cardinalities are often on a word boundary. + * So when we pad the scalar, some timing diff might + * pop if it needs to be expanded due to carries. + * So expand ahead of time. + */ + cardinality_bits = BN_num_bits(cardinality); + group_top = cardinality->top; + if ((bn_wexpand(k, group_top + 1) == NULL) || + (bn_wexpand(lambda, group_top + 1) == NULL)) + goto err; + + if (!BN_copy(k, scalar)) + goto err; + + BN_set_flags(k, BN_FLG_CONSTTIME); + + if (BN_num_bits(k) > cardinality_bits || BN_is_negative(k)) { + /* + * This is an unusual input, and we don't guarantee + * constant-timeness + */ + if (!BN_nnmod(k, k, cardinality, ctx)) + goto err; + } + + if (!BN_add(lambda, k, cardinality)) + goto err; + BN_set_flags(lambda, BN_FLG_CONSTTIME); + if (!BN_add(k, lambda, cardinality)) + goto err; + /* + * lambda := scalar + cardinality + * k := scalar + 2*cardinality + */ + kbit = BN_is_bit_set(lambda, cardinality_bits); + if (!BN_swap_ct(kbit, k, lambda, group_top + 1)) + goto err; + + group_top = group->field.top; + if ((bn_wexpand(&s->X, group_top) == NULL) || + (bn_wexpand(&s->Y, group_top) == NULL) || + (bn_wexpand(&s->Z, group_top) == NULL) || + (bn_wexpand(&r->X, group_top) == NULL) || + (bn_wexpand(&r->Y, group_top) == NULL) || + (bn_wexpand(&r->Z, group_top) == NULL)) + goto err; + + /* top bit is a 1, in a fixed pos */ + if (!EC_POINT_copy(r, s)) + goto err; + + EC_POINT_BN_set_flags(r, BN_FLG_CONSTTIME); + + if (!EC_POINT_dbl(group, s, s, ctx)) + goto err; + + pbit = 0; + + /* + * The ladder step, with branches, is + * + * k[i] == 0: S = add(R, S), R = dbl(R) + * k[i] == 1: R = add(S, R), S = dbl(S) + * + * Swapping R, S conditionally on k[i] leaves you with state + * + * k[i] == 0: T, U = R, S + * k[i] == 1: T, U = S, R + * + * Then perform the ECC ops. + * + * U = add(T, U) + * T = dbl(T) + * + * Which leaves you with state + * + * k[i] == 0: U = add(R, S), T = dbl(R) + * k[i] == 1: U = add(S, R), T = dbl(S) + * + * Swapping T, U conditionally on k[i] leaves you with state + * + * k[i] == 0: R, S = T, U + * k[i] == 1: R, S = U, T + * + * Which leaves you with state + * + * k[i] == 0: S = add(R, S), R = dbl(R) + * k[i] == 1: R = add(S, R), S = dbl(S) + * + * So we get the same logic, but instead of a branch it's a + * conditional swap, followed by ECC ops, then another conditional swap. + * + * Optimization: The end of iteration i and start of i-1 looks like + * + * ... + * CSWAP(k[i], R, S) + * ECC + * CSWAP(k[i], R, S) + * (next iteration) + * CSWAP(k[i-1], R, S) + * ECC + * CSWAP(k[i-1], R, S) + * ... + * + * So instead of two contiguous swaps, you can merge the condition + * bits and do a single swap. + * + * k[i] k[i-1] Outcome + * 0 0 No Swap + * 0 1 Swap + * 1 0 Swap + * 1 1 No Swap + * + * This is XOR. pbit tracks the previous bit of k. + */ + + for (i = cardinality_bits - 1; i >= 0; i--) { + kbit = BN_is_bit_set(k, i) ^ pbit; + EC_POINT_CSWAP(kbit, r, s, group_top, Z_is_one); + if (!EC_POINT_add(group, s, r, s, ctx)) + goto err; + if (!EC_POINT_dbl(group, r, r, ctx)) + goto err; + /* + * pbit logic merges this cswap with that of the + * next iteration + */ + pbit ^= kbit; + } + /* one final cswap to move the right value into r */ + EC_POINT_CSWAP(pbit, r, s, group_top, Z_is_one); + + ret = 1; + + err: + EC_POINT_free(s); + if (ctx != NULL) + BN_CTX_end(ctx); + BN_CTX_free(new_ctx); + + return ret; +} + +#undef EC_POINT_BN_set_flags +#undef EC_POINT_CSWAP + +int +ec_GFp_simple_mul_generator_ct(const EC_GROUP *group, EC_POINT *r, + const BIGNUM *scalar, BN_CTX *ctx) +{ + return ec_GFp_simple_mul_ct(group, r, scalar, NULL, ctx); +} + +int +ec_GFp_simple_mul_single_ct(const EC_GROUP *group, EC_POINT *r, + const BIGNUM *scalar, const EC_POINT *point, BN_CTX *ctx) +{ + return ec_GFp_simple_mul_ct(group, r, scalar, point, ctx); +} + +int +ec_GFp_simple_mul_double_nonct(const EC_GROUP *group, EC_POINT *r, + const BIGNUM *g_scalar, const BIGNUM *p_scalar, const EC_POINT *point, + BN_CTX *ctx) +{ + return ec_wNAF_mul(group, r, g_scalar, 1, &point, &p_scalar, ctx); +} -- 2.20.1