/* * 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 <stdio.h> #include "internal/cryptlib.h" #include "crypto/bn.h" #include <openssl/bn.h> #include <openssl/sha.h> #include "dsa_local.h" #include <openssl/asn1.h> static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, 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 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_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; } static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa) { 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; } if (dsa->priv_key == NULL) { reason = DSA_R_MISSING_PRIVATE_KEY; 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_sign_setup_no_digest(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, BIGNUM **rp) { return dsa_sign_setup(dsa, ctx_in, kinvp, rp, NULL, 0); } 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; } /* Reject obviously invalid parameters */ if (BN_is_zero(dsa->p) || BN_is_zero(dsa->q) || BN_is_zero(dsa->g)) { DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_INVALID_PARAMETERS); return 0; } if (dsa->priv_key == NULL) { DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_MISSING_PRIVATE_KEY); 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 * specifically 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) { 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_init(DSA *dsa) { dsa->flags |= DSA_FLAG_CACHE_MONT_P; return 1; } 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) { 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; }