X-Git-Url: https://git.openssl.org/gitweb/?p=openssl.git;a=blobdiff_plain;f=crypto%2Fdsa%2Fdsa_ossl.c;h=37c654d20ccd5cc5ce7b59a684d8b5dd78dbb260;hp=7304037947e5db01c0e80e66f7bf1efc75a44b5e;hb=3cdbea65b375bf00b31699c068c8404fe75c7d4c;hpb=57e7d3ce1546fc6026ffe3f1f243c54d0bb59d3e diff --git a/crypto/dsa/dsa_ossl.c b/crypto/dsa/dsa_ossl.c index 7304037947..37c654d20c 100644 --- a/crypto/dsa/dsa_ossl.c +++ b/crypto/dsa/dsa_ossl.c @@ -1,316 +1,428 @@ -/* crypto/dsa/dsa_ossl.c */ -/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com) - * All rights reserved. +/* + * Copyright 1995-2018 The OpenSSL Project Authors. 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.] + * Licensed under the Apache License 2.0 (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 */ -/* Original version from Steven Schoch */ - #include -#include "cryptlib.h" +#include "internal/cryptlib.h" +#include "internal/bn_int.h" #include -#include -#include +#include +#include "dsa_locl.h" #include -#include static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa); -static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, BIGNUM **rp); -static int dsa_do_verify(const unsigned char *dgst, int dgst_len, DSA_SIG *sig, - DSA *dsa); +static int dsa_sign_setup_no_digest(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, + BIGNUM **rp); +static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, + BIGNUM **rp, const unsigned char *dgst, int dlen); +static int dsa_do_verify(const unsigned char *dgst, int dgst_len, + DSA_SIG *sig, DSA *dsa); static int dsa_init(DSA *dsa); static int dsa_finish(DSA *dsa); -static int dsa_mod_exp(DSA *dsa, BIGNUM *rr, BIGNUM *a1, BIGNUM *p1, - BIGNUM *a2, BIGNUM *p2, BIGNUM *m, BN_CTX *ctx, - BN_MONT_CTX *in_mont); -static int dsa_bn_mod_exp(DSA *dsa, BIGNUM *r, BIGNUM *a, const BIGNUM *p, - const BIGNUM *m, BN_CTX *ctx, - BN_MONT_CTX *m_ctx); +static BIGNUM *dsa_mod_inverse_fermat(const BIGNUM *k, const BIGNUM *q, + BN_CTX *ctx); static DSA_METHOD openssl_dsa_meth = { -"OpenSSL DSA method", -dsa_do_sign, -dsa_sign_setup, -dsa_do_verify, -dsa_mod_exp, -dsa_bn_mod_exp, -dsa_init, -dsa_finish, -0, -NULL + "OpenSSL DSA method", + dsa_do_sign, + dsa_sign_setup_no_digest, + dsa_do_verify, + NULL, /* dsa_mod_exp, */ + NULL, /* dsa_bn_mod_exp, */ + dsa_init, + dsa_finish, + DSA_FLAG_FIPS_METHOD, + NULL, + NULL, + NULL }; +static const DSA_METHOD *default_DSA_method = &openssl_dsa_meth; + +void DSA_set_default_method(const DSA_METHOD *meth) +{ + default_DSA_method = meth; +} + +const DSA_METHOD *DSA_get_default_method(void) +{ + return default_DSA_method; +} + const DSA_METHOD *DSA_OpenSSL(void) { - return &openssl_dsa_meth; + return &openssl_dsa_meth; } static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa) - { - BIGNUM *kinv=NULL,*r=NULL,*s=NULL; - BIGNUM m; - BIGNUM xr; - BN_CTX *ctx=NULL; - int i,reason=ERR_R_BN_LIB; - DSA_SIG *ret=NULL; - - BN_init(&m); - BN_init(&xr); - s=BN_new(); - if (s == NULL) goto err; - - i=BN_num_bytes(dsa->q); /* should be 20 */ - if ((dlen > i) || (dlen > 50)) - { - reason=DSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE; - goto err; - } - - ctx=BN_CTX_new(); - if (ctx == NULL) goto err; - - if ((dsa->kinv == NULL) || (dsa->r == NULL)) - { - if (!DSA_sign_setup(dsa,ctx,&kinv,&r)) goto err; - } - else - { - kinv=dsa->kinv; - dsa->kinv=NULL; - r=dsa->r; - dsa->r=NULL; - } - - if (BN_bin2bn(dgst,dlen,&m) == NULL) goto err; - - /* Compute s = inv(k) (m + xr) mod q */ - if (!BN_mod_mul(&xr,dsa->priv_key,r,dsa->q,ctx)) goto err;/* s = xr */ - if (!BN_add(s, &xr, &m)) goto err; /* s = m + xr */ - if (BN_cmp(s,dsa->q) > 0) - BN_sub(s,s,dsa->q); - if (!BN_mod_mul(s,s,kinv,dsa->q,ctx)) goto err; - - ret=DSA_SIG_new(); - if (ret == NULL) goto err; - ret->r = r; - ret->s = s; - -err: - if (!ret) - { - DSAerr(DSA_F_DSA_DO_SIGN,reason); - BN_free(r); - BN_free(s); - } - if (ctx != NULL) BN_CTX_free(ctx); - BN_clear_free(&m); - BN_clear_free(&xr); - if (kinv != NULL) /* dsa->kinv is NULL now if we used it */ - BN_clear_free(kinv); - return(ret); - } - -static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, BIGNUM **rp) - { - BN_CTX *ctx; - BIGNUM k,*kinv=NULL,*r=NULL; - int ret=0; - - if (ctx_in == NULL) - { - if ((ctx=BN_CTX_new()) == NULL) goto err; - } - else - ctx=ctx_in; - - BN_init(&k); - if ((r=BN_new()) == NULL) goto err; - kinv=NULL; - - /* Get random k */ - if (!BN_rand_range(&k, BN_value_one(), dsa->q)) goto err; - - if ((dsa->method_mont_p == NULL) && (dsa->flags & DSA_FLAG_CACHE_MONT_P)) - { - if ((dsa->method_mont_p=(char *)BN_MONT_CTX_new()) != NULL) - if (!BN_MONT_CTX_set((BN_MONT_CTX *)dsa->method_mont_p, - dsa->p,ctx)) goto err; - } - - /* Compute r = (g^k mod p) mod q */ - if (!ENGINE_get_DSA(dsa->engine)->bn_mod_exp(dsa, r,dsa->g,&k,dsa->p,ctx, - (BN_MONT_CTX *)dsa->method_mont_p)) goto err; - if (!BN_mod(r,r,dsa->q,ctx)) goto err; - - /* Compute part of 's = inv(k) (m + xr) mod q' */ - if ((kinv=BN_mod_inverse(NULL,&k,dsa->q,ctx)) == NULL) goto err; - - if (*kinvp != NULL) BN_clear_free(*kinvp); - *kinvp=kinv; - kinv=NULL; - if (*rp != NULL) BN_clear_free(*rp); - *rp=r; - ret=1; -err: - if (!ret) - { - DSAerr(DSA_F_DSA_SIGN_SETUP,ERR_R_BN_LIB); - if (kinv != NULL) BN_clear_free(kinv); - if (r != NULL) BN_clear_free(r); - } - if (ctx_in == NULL) BN_CTX_free(ctx); - if (kinv != NULL) BN_clear_free(kinv); - BN_clear_free(&k); - return(ret); - } - -static int dsa_do_verify(const unsigned char *dgst, int dgst_len, DSA_SIG *sig, - DSA *dsa) - { - BN_CTX *ctx; - BIGNUM u1,u2,t1; - BN_MONT_CTX *mont=NULL; - int ret = -1; - - if ((ctx=BN_CTX_new()) == NULL) goto err; - BN_init(&u1); - BN_init(&u2); - BN_init(&t1); - - /* Calculate W = inv(S) mod Q - * save W in u2 */ - if ((BN_mod_inverse(&u2,sig->s,dsa->q,ctx)) == NULL) goto err; - - /* save M in u1 */ - if (BN_bin2bn(dgst,dgst_len,&u1) == NULL) goto err; - - /* u1 = M * w mod q */ - if (!BN_mod_mul(&u1,&u1,&u2,dsa->q,ctx)) goto err; - - /* u2 = r * w mod q */ - if (!BN_mod_mul(&u2,sig->r,&u2,dsa->q,ctx)) goto err; - - if ((dsa->method_mont_p == NULL) && (dsa->flags & DSA_FLAG_CACHE_MONT_P)) - { - if ((dsa->method_mont_p=(char *)BN_MONT_CTX_new()) != NULL) - if (!BN_MONT_CTX_set((BN_MONT_CTX *)dsa->method_mont_p, - dsa->p,ctx)) goto err; - } - mont=(BN_MONT_CTX *)dsa->method_mont_p; - -#if 0 - { - BIGNUM t2; - - BN_init(&t2); - /* v = ( g^u1 * y^u2 mod p ) mod q */ - /* let t1 = g ^ u1 mod p */ - if (!BN_mod_exp_mont(&t1,dsa->g,&u1,dsa->p,ctx,mont)) goto err; - /* let t2 = y ^ u2 mod p */ - if (!BN_mod_exp_mont(&t2,dsa->pub_key,&u2,dsa->p,ctx,mont)) goto err; - /* let u1 = t1 * t2 mod p */ - if (!BN_mod_mul(&u1,&t1,&t2,dsa->p,ctx)) goto err_bn; - BN_free(&t2); - } - /* let u1 = u1 mod q */ - if (!BN_mod(&u1,&u1,dsa->q,ctx)) goto err; -#else - { - if (!ENGINE_get_DSA(dsa->engine)->dsa_mod_exp(dsa, &t1,dsa->g,&u1,dsa->pub_key,&u2, - dsa->p,ctx,mont)) goto err; - /* BN_copy(&u1,&t1); */ - /* let u1 = u1 mod q */ - if (!BN_mod(&u1,&t1,dsa->q,ctx)) goto err; - } -#endif - /* V is now in u1. If the signature is correct, it will be - * equal to R. */ - ret=(BN_ucmp(&u1, sig->r) == 0); - - err: - if (ret != 1) DSAerr(DSA_F_DSA_DO_VERIFY,ERR_R_BN_LIB); - if (ctx != NULL) BN_CTX_free(ctx); - BN_free(&u1); - BN_free(&u2); - BN_free(&t1); - return(ret); - } +{ + BIGNUM *kinv = NULL; + BIGNUM *m, *blind, *blindm, *tmp; + BN_CTX *ctx = NULL; + int reason = ERR_R_BN_LIB; + DSA_SIG *ret = NULL; + int rv = 0; + + if (dsa->p == NULL || dsa->q == NULL || dsa->g == NULL) { + reason = DSA_R_MISSING_PARAMETERS; + goto err; + } + + ret = DSA_SIG_new(); + if (ret == NULL) + goto err; + ret->r = BN_new(); + ret->s = BN_new(); + if (ret->r == NULL || ret->s == NULL) + goto err; + + ctx = BN_CTX_new(); + if (ctx == NULL) + goto err; + m = BN_CTX_get(ctx); + blind = BN_CTX_get(ctx); + blindm = BN_CTX_get(ctx); + tmp = BN_CTX_get(ctx); + if (tmp == NULL) + goto err; + + redo: + if (!dsa_sign_setup(dsa, ctx, &kinv, &ret->r, dgst, dlen)) + goto err; + + if (dlen > BN_num_bytes(dsa->q)) + /* + * if the digest length is greater than the size of q use the + * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3, + * 4.2 + */ + dlen = BN_num_bytes(dsa->q); + if (BN_bin2bn(dgst, dlen, m) == NULL) + goto err; + + /* + * The normal signature calculation is: + * + * s := k^-1 * (m + r * priv_key) mod q + * + * We will blind this to protect against side channel attacks + * + * s := blind^-1 * k^-1 * (blind * m + blind * r * priv_key) mod q + */ + + /* Generate a blinding value */ + do { + if (!BN_priv_rand(blind, BN_num_bits(dsa->q) - 1, + BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY)) + 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 q */ + if (!BN_mod_mul(tmp, blind, dsa->priv_key, dsa->q, ctx)) + goto err; + if (!BN_mod_mul(tmp, tmp, ret->r, dsa->q, ctx)) + goto err; + + /* blindm := blind * m mod q */ + if (!BN_mod_mul(blindm, blind, m, dsa->q, ctx)) + goto err; + + /* s : = (blind * priv_key * r) + (blind * m) mod q */ + if (!BN_mod_add_quick(ret->s, tmp, blindm, dsa->q)) + goto err; + + /* s := s * k^-1 mod q */ + if (!BN_mod_mul(ret->s, ret->s, kinv, dsa->q, ctx)) + goto err; + + /* s:= s * blind^-1 mod q */ + if (BN_mod_inverse(blind, blind, dsa->q, ctx) == NULL) + goto err; + if (!BN_mod_mul(ret->s, ret->s, blind, dsa->q, ctx)) + goto err; + + /* + * Redo if r or s is zero as required by FIPS 186-3: this is very + * unlikely. + */ + if (BN_is_zero(ret->r) || BN_is_zero(ret->s)) + goto redo; + + rv = 1; + + err: + if (rv == 0) { + DSAerr(DSA_F_DSA_DO_SIGN, reason); + DSA_SIG_free(ret); + ret = NULL; + } + BN_CTX_free(ctx); + BN_clear_free(kinv); + return ret; +} -static int dsa_init(DSA *dsa) +static int dsa_sign_setup_no_digest(DSA *dsa, BN_CTX *ctx_in, + BIGNUM **kinvp, BIGNUM **rp) { - dsa->flags|=DSA_FLAG_CACHE_MONT_P; - return(1); + return dsa_sign_setup(dsa, ctx_in, kinvp, rp, NULL, 0); } -static int dsa_finish(DSA *dsa) +static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, + BIGNUM **kinvp, BIGNUM **rp, + const unsigned char *dgst, int dlen) +{ + BN_CTX *ctx = NULL; + BIGNUM *k, *kinv = NULL, *r = *rp; + BIGNUM *l; + int ret = 0; + int q_bits, q_words; + + if (!dsa->p || !dsa->q || !dsa->g) { + DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_MISSING_PARAMETERS); + return 0; + } + + k = BN_new(); + l = BN_new(); + if (k == NULL || l == NULL) + goto err; + + if (ctx_in == NULL) { + if ((ctx = BN_CTX_new()) == NULL) + goto err; + } else + ctx = ctx_in; + + /* Preallocate space */ + q_bits = BN_num_bits(dsa->q); + 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 */ + do { + if (dgst != NULL) { + /* + * We calculate k from SHA512(private_key + H(message) + random). + * This protects the private key from a weak PRNG. + */ + if (!BN_generate_dsa_nonce(k, dsa->q, dsa->priv_key, dgst, + dlen, ctx)) + goto err; + } else if (!BN_priv_rand_range(k, dsa->q)) + goto err; + } while (BN_is_zero(k)); + + BN_set_flags(k, BN_FLG_CONSTTIME); + BN_set_flags(l, BN_FLG_CONSTTIME); + + if (dsa->flags & DSA_FLAG_CACHE_MONT_P) { + if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p, + dsa->lock, dsa->p, ctx)) + goto err; + } + + /* Compute r = (g^k mod p) mod q */ + + /* + * We do not want timing information to leak the length of k, so we + * compute G^k using an equivalent scalar of fixed bit-length. + * + * We unconditionally perform both of these additions to prevent a + * small timing information leakage. We then choose the sum that is + * one bit longer than the modulus. + * + * 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(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)) + goto err; + } else { + if (!BN_mod_exp_mont(r, dsa->g, k, dsa->p, ctx, dsa->method_mont_p)) + goto err; + } + + if (!BN_mod(r, r, dsa->q, ctx)) + goto err; + + /* Compute part of 's = inv(k) (m + xr) mod q' */ + if ((kinv = dsa_mod_inverse_fermat(k, dsa->q, ctx)) == NULL) + goto err; + + BN_clear_free(*kinvp); + *kinvp = kinv; + kinv = NULL; + ret = 1; + err: + if (!ret) + DSAerr(DSA_F_DSA_SIGN_SETUP, ERR_R_BN_LIB); + if (ctx != ctx_in) + BN_CTX_free(ctx); + BN_clear_free(k); + BN_clear_free(l); + return ret; +} + +static int dsa_do_verify(const unsigned char *dgst, int dgst_len, + DSA_SIG *sig, DSA *dsa) { - if(dsa->method_mont_p) - BN_MONT_CTX_free((BN_MONT_CTX *)dsa->method_mont_p); - return(1); + BN_CTX *ctx; + BIGNUM *u1, *u2, *t1; + BN_MONT_CTX *mont = NULL; + const BIGNUM *r, *s; + int ret = -1, i; + if (!dsa->p || !dsa->q || !dsa->g) { + DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MISSING_PARAMETERS); + return -1; + } + + i = BN_num_bits(dsa->q); + /* fips 186-3 allows only different sizes for q */ + if (i != 160 && i != 224 && i != 256) { + DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_BAD_Q_VALUE); + return -1; + } + + if (BN_num_bits(dsa->p) > OPENSSL_DSA_MAX_MODULUS_BITS) { + DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MODULUS_TOO_LARGE); + return -1; + } + u1 = BN_new(); + u2 = BN_new(); + t1 = BN_new(); + ctx = BN_CTX_new(); + if (u1 == NULL || u2 == NULL || t1 == NULL || ctx == NULL) + goto err; + + DSA_SIG_get0(sig, &r, &s); + + if (BN_is_zero(r) || BN_is_negative(r) || + BN_ucmp(r, dsa->q) >= 0) { + ret = 0; + goto err; + } + if (BN_is_zero(s) || BN_is_negative(s) || + BN_ucmp(s, dsa->q) >= 0) { + ret = 0; + goto err; + } + + /* + * Calculate W = inv(S) mod Q save W in u2 + */ + if ((BN_mod_inverse(u2, s, dsa->q, ctx)) == NULL) + goto err; + + /* save M in u1 */ + if (dgst_len > (i >> 3)) + /* + * if the digest length is greater than the size of q use the + * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3, + * 4.2 + */ + dgst_len = (i >> 3); + if (BN_bin2bn(dgst, dgst_len, u1) == NULL) + goto err; + + /* u1 = M * w mod q */ + if (!BN_mod_mul(u1, u1, u2, dsa->q, ctx)) + goto err; + + /* u2 = r * w mod q */ + if (!BN_mod_mul(u2, r, u2, dsa->q, ctx)) + goto err; + + if (dsa->flags & DSA_FLAG_CACHE_MONT_P) { + mont = BN_MONT_CTX_set_locked(&dsa->method_mont_p, + dsa->lock, dsa->p, ctx); + if (!mont) + goto err; + } + + if (dsa->meth->dsa_mod_exp != NULL) { + if (!dsa->meth->dsa_mod_exp(dsa, t1, dsa->g, u1, dsa->pub_key, u2, + dsa->p, ctx, mont)) + goto err; + } else { + if (!BN_mod_exp2_mont(t1, dsa->g, u1, dsa->pub_key, u2, dsa->p, ctx, + mont)) + goto err; + } + + /* let u1 = u1 mod q */ + if (!BN_mod(u1, t1, dsa->q, ctx)) + goto err; + + /* + * V is now in u1. If the signature is correct, it will be equal to R. + */ + ret = (BN_ucmp(u1, r) == 0); + + err: + if (ret < 0) + DSAerr(DSA_F_DSA_DO_VERIFY, ERR_R_BN_LIB); + BN_CTX_free(ctx); + BN_free(u1); + BN_free(u2); + BN_free(t1); + return ret; } -static int dsa_mod_exp(DSA *dsa, BIGNUM *rr, BIGNUM *a1, BIGNUM *p1, - BIGNUM *a2, BIGNUM *p2, BIGNUM *m, BN_CTX *ctx, - BN_MONT_CTX *in_mont) +static int dsa_init(DSA *dsa) { - return BN_mod_exp2_mont(rr, a1, p1, a2, p2, m, ctx, in_mont); + dsa->flags |= DSA_FLAG_CACHE_MONT_P; + return 1; } - -static int dsa_bn_mod_exp(DSA *dsa, BIGNUM *r, BIGNUM *a, const BIGNUM *p, - const BIGNUM *m, BN_CTX *ctx, - BN_MONT_CTX *m_ctx) + +static int dsa_finish(DSA *dsa) +{ + BN_MONT_CTX_free(dsa->method_mont_p); + return 1; +} + +/* + * Compute the inverse of k modulo q. + * Since q is prime, Fermat's Little Theorem applies, which reduces this to + * mod-exp operation. Both the exponent and modulus are public information + * so a mod-exp that doesn't leak the base is sufficient. A newly allocated + * BIGNUM is returned which the caller must free. + */ +static BIGNUM *dsa_mod_inverse_fermat(const BIGNUM *k, const BIGNUM *q, + BN_CTX *ctx) { - return BN_mod_exp_mont(r, a, p, m, ctx, m_ctx); + BIGNUM *res = NULL; + BIGNUM *r, *e; + + if ((r = BN_new()) == NULL) + return NULL; + + BN_CTX_start(ctx); + if ((e = BN_CTX_get(ctx)) != NULL + && BN_set_word(r, 2) + && BN_sub(e, q, r) + && BN_mod_exp_mont(r, k, e, q, ctx, NULL)) + res = r; + else + BN_free(r); + BN_CTX_end(ctx); + return res; }