diff options
Diffstat (limited to 'crypto/dsa')
| -rw-r--r-- | crypto/dsa/dsa_gen.c | 6 | ||||
| -rw-r--r-- | crypto/dsa/dsa_ossl.c | 61 |
2 files changed, 53 insertions, 14 deletions
diff --git a/crypto/dsa/dsa_gen.c b/crypto/dsa/dsa_gen.c index 46f4f01ee0e4..383d853b6d37 100644 --- a/crypto/dsa/dsa_gen.c +++ b/crypto/dsa/dsa_gen.c @@ -327,6 +327,12 @@ int dsa_builtin_paramgen2(DSA *ret, size_t L, size_t N, if (mctx == NULL) goto err; + /* make sure L > N, otherwise we'll get trapped in an infinite loop */ + if (L <= N) { + DSAerr(DSA_F_DSA_BUILTIN_PARAMGEN2, DSA_R_INVALID_PARAMETERS); + goto err; + } + if (evpmd == NULL) { if (N == 160) evpmd = EVP_sha1(); diff --git a/crypto/dsa/dsa_ossl.c b/crypto/dsa/dsa_ossl.c index ac1f65a51a75..7a0b0874c54e 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" @@ -23,6 +24,8 @@ 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", @@ -178,9 +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); @@ -189,8 +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) { @@ -201,9 +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 */ @@ -221,6 +223,7 @@ static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, } 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, @@ -238,14 +241,17 @@ 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)) @@ -258,8 +264,8 @@ 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' */ - if ((kinv = BN_mod_inverse(NULL, k, dsa->q, ctx)) == NULL) + /* 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); @@ -273,7 +279,6 @@ 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; } @@ -393,3 +398,31 @@ 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; +} |