Commit cf633fa0 authored by Emilia Kasper's avatar Emilia Kasper
Browse files

BN_mod_exp_mont_consttime: check for zero modulus. 



Don't dereference |d| when |top| is zero. Also test that various BIGNUM methods behave correctly on zero/even inputs.

Follow-up to b11980d7

Reviewed-by: default avatarRich Salz <rsalz@openssl.org>
parent 732a6b55

crypto/bn/bn_exp.c

+4 −3
Original line number Diff line number Diff line
@@ -662,12 +662,13 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, 
    bn_check_top(p);

    bn_check_top(m);



    top = m->top;



    if (!(m->d[0] & 1)) {

    if (!BN_is_odd(m)) {

        BNerr(BN_F_BN_MOD_EXP_MONT_CONSTTIME, BN_R_CALLED_WITH_EVEN_MODULUS);

        return (0);

    }



    top = m->top;



    bits = BN_num_bits(p);

    if (bits == 0) {

        ret = BN_one(rr);

crypto/bn/bntest.c

+52 −0
Original line number Diff line number Diff line
@@ -441,6 +441,14 @@ int test_div(BIO *bp, BN_CTX *ctx) 
    BN_init(&d);

    BN_init(&e);



    BN_one(&a);

    BN_zero(&b);



    if (BN_div(&d, &c, &a, &b, ctx)) {

        fprintf(stderr, "Division by zero succeeded!\n");

        return 0;

    }



    for (i = 0; i < num0 + num1; i++) {

        if (i < num1) {

            BN_bntest_rand(&a, 400, 0, 0);
@@ -781,6 +789,18 @@ int test_mont(BIO *bp, BN_CTX *ctx) 
    if (mont == NULL)

        return 0;



    BN_zero(&n);

    if (BN_MONT_CTX_set(mont, &n, ctx)) {

        fprintf(stderr, "BN_MONT_CTX_set succeeded for zero modulus!\n");

        return 0;

    }



    BN_set_word(&n, 16);

    if (BN_MONT_CTX_set(mont, &n, ctx)) {

        fprintf(stderr, "BN_MONT_CTX_set succeeded for even modulus!\n");

        return 0;

    }



    BN_bntest_rand(&a, 100, 0, 0);

    BN_bntest_rand(&b, 100, 0, 0);

    for (i = 0; i < num2; i++) {
@@ -887,6 +907,14 @@ int test_mod_mul(BIO *bp, BN_CTX *ctx) 
    d = BN_new();

    e = BN_new();



    BN_one(a);

    BN_one(b);

    BN_zero(c);

    if (BN_mod_mul(e, a, b, c, ctx)) {

        fprintf(stderr, "BN_mod_mul with zero modulus succeeded!\n");

        return 0;

    }



    for (j = 0; j < 3; j++) {

        BN_bntest_rand(c, 1024, 0, 0);

        for (i = 0; i < num0; i++) {
@@ -952,6 +980,14 @@ int test_mod_exp(BIO *bp, BN_CTX *ctx) 
    d = BN_new();

    e = BN_new();



    BN_one(a);

    BN_one(b);

    BN_zero(c);

    if (BN_mod_exp(d, a, b, c, ctx)) {

        fprintf(stderr, "BN_mod_exp with zero modulus succeeded!\n");

        return 0;

    }



    BN_bntest_rand(c, 30, 0, 1); /* must be odd for montgomery */

    for (i = 0; i < num2; i++) {

        BN_bntest_rand(a, 20 + i * 5, 0, 0);
@@ -999,6 +1035,22 @@ int test_mod_exp_mont_consttime(BIO *bp, BN_CTX *ctx) 
    d = BN_new();

    e = BN_new();



    BN_one(a);

    BN_one(b);

    BN_zero(c);

    if (BN_mod_exp_mont_consttime(d, a, b, c, ctx, NULL)) {

        fprintf(stderr, "BN_mod_exp_mont_consttime with zero modulus "

                "succeeded\n");

        return 0;

    }



    BN_set_word(c, 16);

    if (BN_mod_exp_mont_consttime(d, a, b, c, ctx, NULL)) {

        fprintf(stderr, "BN_mod_exp_mont_consttime with even modulus "

                "succeeded\n");

        return 0;

    }



    BN_bntest_rand(c, 30, 0, 1); /* must be odd for montgomery */

    for (i = 0; i < num2; i++) {

        BN_bntest_rand(a, 20 + i * 5, 0, 0);