X-Git-Url: https://git.openssl.org/gitweb/?p=openssl.git;a=blobdiff_plain;f=crypto%2Fbn%2Fbn_exp.c;h=88f2baf0e553cf6629644a9a415be643dd0f07c4;hp=c5e579c77cf457b2557fc0caa0ea25684b65779b;hb=72a7a7021fa8bc82a11bc08bac1b0241a92143d0;hpb=8fc8f486f7fa098c9fbb6a6ae399e3c6856e0d87 diff --git a/crypto/bn/bn_exp.c b/crypto/bn/bn_exp.c index c5e579c77c..88f2baf0e5 100644 --- a/crypto/bn/bn_exp.c +++ b/crypto/bn/bn_exp.c @@ -1,111 +1,10 @@ -/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com) - * All rights reserved. - * - * This package is an SSL implementation written - * by Eric Young (eay@cryptsoft.com). - * The implementation was written so as to conform with Netscapes SSL. - * - * This library is free for commercial and non-commercial use as long as - * the following conditions are aheared to. The following conditions - * apply to all code found in this distribution, be it the RC4, RSA, - * lhash, DES, etc., code; not just the SSL code. The SSL documentation - * included with this distribution is covered by the same copyright terms - * except that the holder is Tim Hudson (tjh@cryptsoft.com). - * - * Copyright remains Eric Young's, and as such any Copyright notices in - * the code are not to be removed. - * If this package is used in a product, Eric Young should be given attribution - * as the author of the parts of the library used. - * This can be in the form of a textual message at program startup or - * in documentation (online or textual) provided with the package. - * - * Redistribution and use in source and binary forms, with or without - * modification, are permitted provided that the following conditions - * are met: - * 1. Redistributions of source code must retain the copyright - * notice, this list of conditions and the following disclaimer. - * 2. Redistributions in binary form must reproduce the above copyright - * notice, this list of conditions and the following disclaimer in the - * documentation and/or other materials provided with the distribution. - * 3. All advertising materials mentioning features or use of this software - * must display the following acknowledgement: - * "This product includes cryptographic software written by - * Eric Young (eay@cryptsoft.com)" - * The word 'cryptographic' can be left out if the rouines from the library - * being used are not cryptographic related :-). - * 4. If you include any Windows specific code (or a derivative thereof) from - * the apps directory (application code) you must include an acknowledgement: - * "This product includes software written by Tim Hudson (tjh@cryptsoft.com)" - * - * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND - * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE - * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE - * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE - * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL - * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS - * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) - * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT - * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY - * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF - * SUCH DAMAGE. - * - * The licence and distribution terms for any publically available version or - * derivative of this code cannot be changed. i.e. this code cannot simply be - * copied and put under another distribution licence - * [including the GNU Public Licence.] - */ -/* ==================================================================== - * Copyright (c) 1998-2005 The OpenSSL Project. All rights reserved. - * - * Redistribution and use in source and binary forms, with or without - * modification, are permitted provided that the following conditions - * are met: - * - * 1. Redistributions of source code must retain the above copyright - * notice, this list of conditions and the following disclaimer. - * - * 2. Redistributions in binary form must reproduce the above copyright - * notice, this list of conditions and the following disclaimer in - * the documentation and/or other materials provided with the - * distribution. - * - * 3. All advertising materials mentioning features or use of this - * software must display the following acknowledgment: - * "This product includes software developed by the OpenSSL Project - * for use in the OpenSSL Toolkit. (http://www.openssl.org/)" - * - * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to - * endorse or promote products derived from this software without - * prior written permission. For written permission, please contact - * openssl-core@openssl.org. - * - * 5. Products derived from this software may not be called "OpenSSL" - * nor may "OpenSSL" appear in their names without prior written - * permission of the OpenSSL Project. - * - * 6. Redistributions of any form whatsoever must retain the following - * acknowledgment: - * "This product includes software developed by the OpenSSL Project - * for use in the OpenSSL Toolkit (http://www.openssl.org/)" - * - * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY - * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE - * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR - * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR - * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, - * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT - * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; - * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) - * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, - * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) - * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED - * OF THE POSSIBILITY OF SUCH DAMAGE. - * ==================================================================== - * - * This product includes cryptographic software written by Eric Young - * (eay@cryptsoft.com). This product includes software written by Tim - * Hudson (tjh@cryptsoft.com). +/* + * Copyright 1995-2019 The OpenSSL Project Authors. All Rights Reserved. * + * Licensed under the OpenSSL license (the "License"). You may not use + * this file except in compliance with the License. You can obtain a copy + * in the file LICENSE in the source distribution or at + * https://www.openssl.org/source/license.html */ #include "internal/cryptlib.h" @@ -144,17 +43,15 @@ int BN_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx) int i, bits, ret = 0; BIGNUM *v, *rr; - if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) { + if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0 + || BN_get_flags(a, BN_FLG_CONSTTIME) != 0) { /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */ BNerr(BN_F_BN_EXP, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED); - return -1; + return 0; } BN_CTX_start(ctx); - if ((r == a) || (r == p)) - rr = BN_CTX_get(ctx); - else - rr = r; + rr = ((r == a) || (r == p)) ? BN_CTX_get(ctx) : r; v = BN_CTX_get(ctx); if (rr == NULL || v == NULL) goto err; @@ -179,13 +76,14 @@ int BN_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx) goto err; } } - if (r != rr) - BN_copy(r, rr); + if (r != rr && BN_copy(r, rr) == NULL) + goto err; + ret = 1; err: BN_CTX_end(ctx); bn_check_top(r); - return (ret); + return ret; } int BN_mod_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m, @@ -198,7 +96,7 @@ int BN_mod_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m, bn_check_top(m); /*- - * For even modulus m = 2^k*m_odd, it might make sense to compute + * For even modulus m = 2^k*m_odd, it might make sense to compute * a^p mod m_odd and a^p mod 2^k separately (with Montgomery * exponentiation for the odd part), using appropriate exponent * reductions, and combine the results using the CRT. @@ -233,17 +131,12 @@ int BN_mod_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m, #define RECP_MUL_MOD #ifdef MONT_MUL_MOD - /* - * I have finally been able to take out this pre-condition of the top bit - * being set. It was caused by an error in BN_div with negatives. There - * was also another problem when for a^b%m a >= m. eay 07-May-97 - */ - /* if ((m->d[m->top-1]&BN_TBIT) && BN_is_odd(m)) */ - if (BN_is_odd(m)) { # ifdef MONT_EXP_WORD if (a->top == 1 && !a->neg - && (BN_get_flags(p, BN_FLG_CONSTTIME) == 0)) { + && (BN_get_flags(p, BN_FLG_CONSTTIME) == 0) + && (BN_get_flags(a, BN_FLG_CONSTTIME) == 0) + && (BN_get_flags(m, BN_FLG_CONSTTIME) == 0)) { BN_ULONG A = a->d[0]; ret = BN_mod_exp_mont_word(r, A, p, m, ctx, NULL); } else @@ -262,7 +155,7 @@ int BN_mod_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m, #endif bn_check_top(r); - return (ret); + return ret; } int BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, @@ -275,16 +168,18 @@ int BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, BIGNUM *val[TABLE_SIZE]; BN_RECP_CTX recp; - if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) { + if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0 + || BN_get_flags(a, BN_FLG_CONSTTIME) != 0 + || BN_get_flags(m, BN_FLG_CONSTTIME) != 0) { /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */ BNerr(BN_F_BN_MOD_EXP_RECP, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED); - return -1; + return 0; } bits = BN_num_bits(p); if (bits == 0) { - /* x**0 mod 1 is still zero. */ - if (BN_is_one(m)) { + /* x**0 mod 1, or x**0 mod -1 is still zero. */ + if (BN_abs_is_word(m, 1)) { ret = 1; BN_zero(r); } else { @@ -296,7 +191,7 @@ int BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, BN_CTX_start(ctx); aa = BN_CTX_get(ctx); val[0] = BN_CTX_get(ctx); - if (!aa || !val[0]) + if (val[0] == NULL) goto err; BN_RECP_CTX_init(&recp); @@ -395,7 +290,7 @@ int BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, BN_CTX_end(ctx); BN_RECP_CTX_free(&recp); bn_check_top(r); - return (ret); + return ret; } int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, @@ -409,7 +304,9 @@ int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, BIGNUM *val[TABLE_SIZE]; BN_MONT_CTX *mont = NULL; - if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) { + if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0 + || BN_get_flags(a, BN_FLG_CONSTTIME) != 0 + || BN_get_flags(m, BN_FLG_CONSTTIME) != 0) { return BN_mod_exp_mont_consttime(rr, a, p, m, ctx, in_mont); } @@ -419,12 +316,12 @@ int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, if (!BN_is_odd(m)) { BNerr(BN_F_BN_MOD_EXP_MONT, BN_R_CALLED_WITH_EVEN_MODULUS); - return (0); + return 0; } bits = BN_num_bits(p); if (bits == 0) { - /* x**0 mod 1 is still zero. */ - if (BN_is_one(m)) { + /* x**0 mod 1, or x**0 mod -1 is still zero. */ + if (BN_abs_is_word(m, 1)) { ret = 1; BN_zero(rr); } else { @@ -437,7 +334,7 @@ int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, d = BN_CTX_get(ctx); r = BN_CTX_get(ctx); val[0] = BN_CTX_get(ctx); - if (!d || !r || !val[0]) + if (val[0] == NULL) goto err; /* @@ -459,22 +356,17 @@ int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, aa = val[0]; } else aa = a; - if (BN_is_zero(aa)) { - BN_zero(rr); - ret = 1; - goto err; - } - if (!BN_to_montgomery(val[0], aa, mont, ctx)) + if (!bn_to_mont_fixed_top(val[0], aa, mont, ctx)) goto err; /* 1 */ window = BN_window_bits_for_exponent_size(bits); if (window > 1) { - if (!BN_mod_mul_montgomery(d, val[0], val[0], mont, ctx)) + if (!bn_mul_mont_fixed_top(d, val[0], val[0], mont, ctx)) goto err; /* 2 */ j = 1 << (window - 1); for (i = 1; i < j; i++) { if (((val[i] = BN_CTX_get(ctx)) == NULL) || - !BN_mod_mul_montgomery(val[i], val[i - 1], d, mont, ctx)) + !bn_mul_mont_fixed_top(val[i], val[i - 1], d, mont, ctx)) goto err; } } @@ -496,19 +388,15 @@ int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, for (i = 1; i < j; i++) r->d[i] = (~m->d[i]) & BN_MASK2; r->top = j; - /* - * Upper words will be zero if the corresponding words of 'm' were - * 0xfff[...], so decrement r->top accordingly. - */ - bn_correct_top(r); + r->flags |= BN_FLG_FIXED_TOP; } else #endif - if (!BN_to_montgomery(r, BN_value_one(), mont, ctx)) + if (!bn_to_mont_fixed_top(r, BN_value_one(), mont, ctx)) goto err; for (;;) { if (BN_is_bit_set(p, wstart) == 0) { if (!start) { - if (!BN_mod_mul_montgomery(r, r, r, mont, ctx)) + if (!bn_mul_mont_fixed_top(r, r, r, mont, ctx)) goto err; } if (wstart == 0) @@ -539,12 +427,12 @@ int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, /* add the 'bytes above' */ if (!start) for (i = 0; i < j; i++) { - if (!BN_mod_mul_montgomery(r, r, r, mont, ctx)) + if (!bn_mul_mont_fixed_top(r, r, r, mont, ctx)) goto err; } /* wvalue will be an odd number < 2^window */ - if (!BN_mod_mul_montgomery(r, r, val[wvalue >> 1], mont, ctx)) + if (!bn_mul_mont_fixed_top(r, r, val[wvalue >> 1], mont, ctx)) goto err; /* move the 'window' down further */ @@ -554,6 +442,11 @@ int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, if (wstart < 0) break; } + /* + * Done with zero-padded intermediate BIGNUMs. Final BN_from_montgomery + * removes padding [if any] and makes return value suitable for public + * API consumer. + */ #if defined(SPARC_T4_MONT) if (OPENSSL_sparcv9cap_P[0] & (SPARCV9_VIS3 | SPARCV9_PREFER_FPU)) { j = mont->N.top; /* borrow j */ @@ -573,10 +466,9 @@ int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, BN_MONT_CTX_free(mont); BN_CTX_end(ctx); bn_check_top(rr); - return (ret); + return ret; } -#if defined(SPARC_T4_MONT) static BN_ULONG bn_get_bits(const BIGNUM *a, int bitpos) { BN_ULONG ret = 0; @@ -595,7 +487,6 @@ static BN_ULONG bn_get_bits(const BIGNUM *a, int bitpos) return ret & BN_MASK2; } -#endif /* * BN_mod_exp_mont_consttime() stores the precomputed powers in a specific @@ -628,6 +519,14 @@ static int MOD_EXP_CTIME_COPY_FROM_PREBUF(BIGNUM *b, int top, { int i, j; int width = 1 << window; + /* + * We declare table 'volatile' in order to discourage compiler + * from reordering loads from the table. Concern is that if + * reordered in specific manner loads might give away the + * information we are trying to conceal. Some would argue that + * compiler can reorder them anyway, but it can as well be + * argued that doing so would be violation of standard... + */ volatile BN_ULONG *table = (volatile BN_ULONG *)buf; if (bn_wexpand(b, top) == NULL) @@ -672,7 +571,7 @@ static int MOD_EXP_CTIME_COPY_FROM_PREBUF(BIGNUM *b, int top, } b->top = top; - bn_correct_top(b); + b->flags |= BN_FLG_FIXED_TOP; return 1; } @@ -694,7 +593,7 @@ 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) { - int i, bits, ret = 0, window, wvalue; + int i, bits, ret = 0, window, wvalue, wmask, window0; int top; BN_MONT_CTX *mont = NULL; @@ -713,15 +612,19 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, if (!BN_is_odd(m)) { BNerr(BN_F_BN_MOD_EXP_MONT_CONSTTIME, BN_R_CALLED_WITH_EVEN_MODULUS); - return (0); + return 0; } top = m->top; - bits = BN_num_bits(p); + /* + * Use all bits stored in |p|, rather than |BN_num_bits|, so we do not leak + * whether the top bits are zero. + */ + bits = p->top * BN_BITS2; if (bits == 0) { - /* x**0 mod 1 is still zero. */ - if (BN_is_one(m)) { + /* x**0 mod 1, or x**0 mod -1 is still zero. */ + if (BN_abs_is_word(m, 1)) { ret = 1; BN_zero(rr); } else { @@ -745,6 +648,15 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, goto err; } + if (a->neg || BN_ucmp(a, m) >= 0) { + BIGNUM *reduced = BN_CTX_get(ctx); + if (reduced == NULL + || !BN_nnmod(reduced, a, m, ctx)) { + goto err; + } + a = reduced; + } + #ifdef RSAZ_ENABLED /* * If the size of the operands allow it, perform the optimized @@ -838,16 +750,11 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, tmp.top = top; } else #endif - if (!BN_to_montgomery(&tmp, BN_value_one(), mont, ctx)) + if (!bn_to_mont_fixed_top(&tmp, BN_value_one(), mont, ctx)) goto err; /* prepare a^1 in Montgomery domain */ - if (a->neg || BN_ucmp(a, m) >= 0) { - if (!BN_mod(&am, a, m, ctx)) - goto err; - if (!BN_to_montgomery(&am, &am, mont, ctx)) - goto err; - } else if (!BN_to_montgomery(&am, a, mont, ctx)) + if (!bn_to_mont_fixed_top(&am, a, mont, ctx)) goto err; #if defined(SPARC_T4_MONT) @@ -941,20 +848,27 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, top /= 2; bn_flip_t4(np, mont->N.d, top); - bits--; - for (wvalue = 0, i = bits % 5; i >= 0; i--, bits--) - wvalue = (wvalue << 1) + BN_is_bit_set(p, bits); + /* + * The exponent may not have a whole number of fixed-size windows. + * To simplify the main loop, the initial window has between 1 and + * full-window-size bits such that what remains is always a whole + * number of windows + */ + window0 = (bits - 1) % 5 + 1; + wmask = (1 << window0) - 1; + bits -= window0; + wvalue = bn_get_bits(p, bits) & wmask; bn_gather5_t4(tmp.d, top, powerbuf, wvalue); /* * Scan the exponent one window at a time starting from the most * significant bits. */ - while (bits >= 0) { + while (bits > 0) { if (bits < stride) - stride = bits + 1; + stride = bits; bits -= stride; - wvalue = bn_get_bits(p, bits + 1); + wvalue = bn_get_bits(p, bits); if ((*pwr5_worker) (tmp.d, np, n0, powerbuf, wvalue, stride)) continue; @@ -1062,32 +976,36 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, bn_scatter5(tmp.d, top, powerbuf, i); } # endif - bits--; - for (wvalue = 0, i = bits % 5; i >= 0; i--, bits--) - wvalue = (wvalue << 1) + BN_is_bit_set(p, bits); + /* + * The exponent may not have a whole number of fixed-size windows. + * To simplify the main loop, the initial window has between 1 and + * full-window-size bits such that what remains is always a whole + * number of windows + */ + window0 = (bits - 1) % 5 + 1; + wmask = (1 << window0) - 1; + bits -= window0; + wvalue = bn_get_bits(p, bits) & wmask; bn_gather5(tmp.d, top, powerbuf, wvalue); /* * Scan the exponent one window at a time starting from the most * significant bits. */ - if (top & 7) - while (bits >= 0) { - for (wvalue = 0, i = 0; i < 5; i++, bits--) - wvalue = (wvalue << 1) + BN_is_bit_set(p, bits); - + if (top & 7) { + while (bits > 0) { bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top); bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top); bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top); bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top); bn_mul_mont(tmp.d, tmp.d, tmp.d, np, n0, top); bn_mul_mont_gather5(tmp.d, tmp.d, powerbuf, np, n0, top, - wvalue); + bn_get_bits5(p->d, bits -= 5)); + } } else { - while (bits >= 0) { - wvalue = bn_get_bits5(p->d, bits - 4); - bits -= 5; - bn_power5(tmp.d, tmp.d, powerbuf, np, n0, top, wvalue); + while (bits > 0) { + bn_power5(tmp.d, tmp.d, powerbuf, np, n0, top, + bn_get_bits5(p->d, bits -= 5)); } } @@ -1114,14 +1032,14 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, * performance advantage of sqr over mul). */ if (window > 1) { - if (!BN_mod_mul_montgomery(&tmp, &am, &am, mont, ctx)) + if (!bn_mul_mont_fixed_top(&tmp, &am, &am, mont, ctx)) goto err; if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&tmp, top, powerbuf, 2, window)) goto err; for (i = 3; i < numPowers; i++) { /* Calculate a^i = a^(i-1) * a */ - if (!BN_mod_mul_montgomery(&tmp, &am, &tmp, mont, ctx)) + if (!bn_mul_mont_fixed_top(&tmp, &am, &tmp, mont, ctx)) goto err; if (!MOD_EXP_CTIME_COPY_TO_PREBUF(&tmp, top, powerbuf, i, window)) @@ -1129,27 +1047,44 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, } } - bits--; - for (wvalue = 0, i = bits % window; i >= 0; i--, bits--) - wvalue = (wvalue << 1) + BN_is_bit_set(p, bits); + /* + * The exponent may not have a whole number of fixed-size windows. + * To simplify the main loop, the initial window has between 1 and + * full-window-size bits such that what remains is always a whole + * number of windows + */ + window0 = (bits - 1) % window + 1; + wmask = (1 << window0) - 1; + bits -= window0; + wvalue = bn_get_bits(p, bits) & wmask; if (!MOD_EXP_CTIME_COPY_FROM_PREBUF(&tmp, top, powerbuf, wvalue, window)) goto err; + wmask = (1 << window) - 1; /* * Scan the exponent one window at a time starting from the most * significant bits. */ - while (bits >= 0) { - wvalue = 0; /* The 'value' of the window */ + while (bits > 0) { - /* Scan the window, squaring the result as we go */ - for (i = 0; i < window; i++, bits--) { - if (!BN_mod_mul_montgomery(&tmp, &tmp, &tmp, mont, ctx)) + /* Square the result window-size times */ + for (i = 0; i < window; i++) + if (!bn_mul_mont_fixed_top(&tmp, &tmp, &tmp, mont, ctx)) goto err; - wvalue = (wvalue << 1) + BN_is_bit_set(p, bits); - } + /* + * Get a window's worth of bits from the exponent + * This avoids calling BN_is_bit_set for each bit, which + * is not only slower but also makes each bit vulnerable to + * EM (and likely other) side-channel attacks like One&Done + * (for details see "One&Done: A Single-Decryption EM-Based + * Attack on OpenSSL's Constant-Time Blinded RSA" by M. Alam, + * H. Khan, M. Dey, N. Sinha, R. Callan, A. Zajic, and + * M. Prvulovic, in USENIX Security'18) + */ + bits -= window; + wvalue = bn_get_bits(p, bits) & wmask; /* * Fetch the appropriate pre-computed value from the pre-buf */ @@ -1158,12 +1093,16 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, goto err; /* Multiply the result into the intermediate result */ - if (!BN_mod_mul_montgomery(&tmp, &tmp, &am, mont, ctx)) + if (!bn_mul_mont_fixed_top(&tmp, &tmp, &am, mont, ctx)) goto err; } } - /* Convert the final result from montgomery to standard format */ + /* + * Done with zero-padded intermediate BIGNUMs. Final BN_from_montgomery + * removes padding [if any] and makes return value suitable for public + * API consumer. + */ #if defined(SPARC_T4_MONT) if (OPENSSL_sparcv9cap_P[0] & (SPARCV9_VIS3 | SPARCV9_PREFER_FPU)) { am.d[0] = 1; /* borrow am */ @@ -1184,7 +1123,7 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, OPENSSL_free(powerbufFree); } BN_CTX_end(ctx); - return (ret); + return ret; } int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p, @@ -1194,7 +1133,7 @@ int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p, int b, bits, ret = 0; int r_is_one; BN_ULONG w, next_w; - BIGNUM *d, *r, *t; + BIGNUM *r, *t; BIGNUM *swap_tmp; #define BN_MOD_MUL_WORD(r, w, m) \ (BN_mul_word(r, (w)) && \ @@ -1213,10 +1152,11 @@ int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p, #define BN_TO_MONTGOMERY_WORD(r, w, mont) \ (BN_set_word(r, (w)) && BN_to_montgomery(r, r, (mont), ctx)) - if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) { + if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0 + || BN_get_flags(m, BN_FLG_CONSTTIME) != 0) { /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */ BNerr(BN_F_BN_MOD_EXP_MONT_WORD, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED); - return -1; + return 0; } bn_check_top(p); @@ -1224,15 +1164,15 @@ int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p, if (!BN_is_odd(m)) { BNerr(BN_F_BN_MOD_EXP_MONT_WORD, BN_R_CALLED_WITH_EVEN_MODULUS); - return (0); + return 0; } if (m->top == 1) a %= m->d[0]; /* make sure that 'a' is reduced */ bits = BN_num_bits(p); if (bits == 0) { - /* x**0 mod 1 is still zero. */ - if (BN_is_one(m)) { + /* x**0 mod 1, or x**0 mod -1 is still zero. */ + if (BN_abs_is_word(m, 1)) { ret = 1; BN_zero(rr); } else { @@ -1247,10 +1187,9 @@ int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p, } BN_CTX_start(ctx); - d = BN_CTX_get(ctx); r = BN_CTX_get(ctx); t = BN_CTX_get(ctx); - if (d == NULL || r == NULL || t == NULL) + if (t == NULL) goto err; if (in_mont != NULL) @@ -1331,7 +1270,7 @@ int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p, BN_MONT_CTX_free(mont); BN_CTX_end(ctx); bn_check_top(rr); - return (ret); + return ret; } /* The old fallback, simple version :-) */ @@ -1344,16 +1283,18 @@ int BN_mod_exp_simple(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, /* Table of variables obtained from 'ctx' */ BIGNUM *val[TABLE_SIZE]; - if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0) { + if (BN_get_flags(p, BN_FLG_CONSTTIME) != 0 + || BN_get_flags(a, BN_FLG_CONSTTIME) != 0 + || BN_get_flags(m, BN_FLG_CONSTTIME) != 0) { /* BN_FLG_CONSTTIME only supported by BN_mod_exp_mont() */ BNerr(BN_F_BN_MOD_EXP_SIMPLE, ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED); - return -1; + return 0; } bits = BN_num_bits(p); - if (bits == 0) { - /* x**0 mod 1 is still zero. */ - if (BN_is_one(m)) { + if (bits == 0) { + /* x**0 mod 1, or x**0 mod -1 is still zero. */ + if (BN_abs_is_word(m, 1)) { ret = 1; BN_zero(r); } else { @@ -1365,7 +1306,7 @@ int BN_mod_exp_simple(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, BN_CTX_start(ctx); d = BN_CTX_get(ctx); val[0] = BN_CTX_get(ctx); - if (!d || !val[0]) + if (val[0] == NULL) goto err; if (!BN_nnmod(val[0], a, m, ctx)) @@ -1450,5 +1391,5 @@ int BN_mod_exp_simple(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, err: BN_CTX_end(ctx); bn_check_top(r); - return (ret); + return ret; }