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Refactor and fix bn_mod_exp test
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The amount of copy-paste in this test led to a few bugs and it was hard to
spot them since things were done in random order. Use a different approach:
compute the result of a^b (mod m) according to BN_mod_exp_simple(), then
compare the results of all the other *_mod_exp* functions to that.

Reuse the test structure from bn_mod_exp_zero.c to loop over the list of
functions. This way we test more functions and don't forget to check some
crucial bits.
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tb committed Dec 3, 2022
1 parent 58884ff commit c1a3e64
Showing 1 changed file with 86 additions and 80 deletions.
166 changes: 86 additions & 80 deletions src/regress/lib/libcrypto/bn/bn_mod_exp.c
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
/* $OpenBSD: bn_mod_exp.c,v 1.7 2022/12/03 08:21:38 tb Exp $ */
/* $OpenBSD: bn_mod_exp.c,v 1.8 2022/12/03 09:37:02 tb Exp $ */
/* Copyright (C) 1995-1998 Eric Young ([email protected])
* All rights reserved.
*
Expand Down Expand Up @@ -67,14 +67,88 @@

#define NUM_BITS (BN_BITS*2)

#define INIT_MOD_EXP_FN(f) { .name = #f, .mod_exp_fn = (f), }
#define INIT_MOD_EXP_MONT_FN(f) { .name = #f, .mod_exp_mont_fn = (f), }

static const struct mod_exp_test {
const char *name;
int (*mod_exp_fn)(BIGNUM *,const BIGNUM *, const BIGNUM *,
const BIGNUM *, BN_CTX *);
int (*mod_exp_mont_fn)(BIGNUM *,const BIGNUM *, const BIGNUM *,
const BIGNUM *, BN_CTX *, BN_MONT_CTX *);
} mod_exp_fn[] = {
INIT_MOD_EXP_FN(BN_mod_exp),
INIT_MOD_EXP_FN(BN_mod_exp_ct),
INIT_MOD_EXP_FN(BN_mod_exp_nonct),
INIT_MOD_EXP_FN(BN_mod_exp_recp),
INIT_MOD_EXP_MONT_FN(BN_mod_exp_mont),
INIT_MOD_EXP_MONT_FN(BN_mod_exp_mont_ct),
INIT_MOD_EXP_MONT_FN(BN_mod_exp_mont_consttime),
INIT_MOD_EXP_MONT_FN(BN_mod_exp_mont_nonct),
};

#define N_MOD_EXP_FN (sizeof(mod_exp_fn) / sizeof(mod_exp_fn[0]))

static int
test_mod_exp(const BIGNUM *result_simple, const BIGNUM *a, const BIGNUM *b,
const BIGNUM *m, BN_CTX *ctx, const struct mod_exp_test *test)
{
BIGNUM *result;
int ret = 0;

BN_CTX_start(ctx);

if ((result = BN_CTX_get(ctx)) == NULL)
goto err;

if (test->mod_exp_fn != NULL) {
if (!test->mod_exp_fn(result, a, b, m, ctx)) {
fprintf(stderr, "%s problems\n", test->name);
ERR_print_errors_fp(stderr);
goto err;
}
} else {
if (!test->mod_exp_mont_fn(result, a, b, m, ctx, NULL)) {
fprintf(stderr, "%s problems\n", test->name);
ERR_print_errors_fp(stderr);
goto err;
}
}

if (BN_cmp(result_simple, result) != 0) {
printf("\nResults from BN_mod_exp_simple and %s differ\n",
test->name);

printf("a (%3d) = ", BN_num_bits(a));
BN_print_fp(stdout, a);
printf("\nb (%3d) = ", BN_num_bits(b));
BN_print_fp(stdout, b);
printf("\nm (%3d) = ", BN_num_bits(m));
BN_print_fp(stdout, m);
printf("\nsimple = ");
BN_print_fp(stdout, result_simple);
printf("\nresult = ");
BN_print_fp(stdout, result);
printf("\n");

goto err;
}

ret = 1;

err:
BN_CTX_end(ctx);

return ret;
}

int
main(int argc, char *argv[])
{
BIGNUM *r_mont, *r_mont_const, *r_recp, *r_simple;
BIGNUM *r_mont_ct, *r_mont_nonct, *a, *b, *m;
BIGNUM *result_simple, *a, *b, *m;
BN_CTX *ctx;
int c;
int i, ret;
int c, i;
size_t j;

ERR_load_BN_strings();

Expand All @@ -83,24 +157,14 @@ main(int argc, char *argv[])

BN_CTX_start(ctx);

if ((r_mont = BN_CTX_get(ctx)) == NULL)
goto err;
if ((r_mont_const = BN_CTX_get(ctx)) == NULL)
goto err;
if ((r_mont_ct = BN_CTX_get(ctx)) == NULL)
goto err;
if ((r_mont_nonct = BN_CTX_get(ctx)) == NULL)
goto err;
if ((r_recp = BN_CTX_get(ctx)) == NULL)
goto err;
if ((r_simple = BN_CTX_get(ctx)) == NULL)
goto err;
if ((a = BN_CTX_get(ctx)) == NULL)
goto err;
if ((b = BN_CTX_get(ctx)) == NULL)
goto err;
if ((m = BN_CTX_get(ctx)) == NULL)
goto err;
if ((result_simple = BN_CTX_get(ctx)) == NULL)
goto err;

for (i = 0; i < 200; i++) {
c = (arc4random() % BN_BITS) - BN_BITS2;
Expand All @@ -120,74 +184,16 @@ main(int argc, char *argv[])
if (!BN_mod(b, b, m, ctx))
goto err;

ret = BN_mod_exp_mont(r_mont, a, b, m, ctx, NULL);
if (ret <= 0) {
printf("BN_mod_exp_mont() problems\n");
goto err;
}

ret = BN_mod_exp_mont_ct(r_mont_ct, a, b, m, ctx, NULL);
if (ret <= 0) {
printf("BN_mod_exp_mont_ct() problems\n");
goto err;
}

ret = BN_mod_exp_mont_nonct(r_mont_nonct, a, b, m, ctx, NULL);
if (ret <= 0) {
printf("BN_mod_exp_mont_nonct() problems\n");
goto err;
}

ret = BN_mod_exp_recp(r_recp, a, b, m, ctx);
if (ret <= 0) {
printf("BN_mod_exp_recp() problems\n");
goto err;
}

ret = BN_mod_exp_simple(r_simple, a, b, m, ctx);
if (ret <= 0) {
if ((BN_mod_exp_simple(result_simple, a, b, m, ctx)) <= 0) {
printf("BN_mod_exp_simple() problems\n");
goto err;
}

ret = BN_mod_exp_mont_consttime(r_mont_const, a, b, m, ctx, NULL);
if (ret <= 0) {
printf("BN_mod_exp_mont_consttime() problems\n");
goto err;
}
for (j = 0; j < N_MOD_EXP_FN; j++) {
const struct mod_exp_test *test = &mod_exp_fn[j];

if (BN_cmp(r_simple, r_mont) != 0 ||
BN_cmp(r_simple, r_mont_const) ||
BN_cmp(r_simple, r_recp) != 0 ||
BN_cmp(r_simple, r_mont_ct) != 0 ||
BN_cmp(r_simple, r_mont_nonct) != 0) {
if (BN_cmp(r_simple, r_mont) != 0)
printf("\nsimple and mont results differ\n");
if (BN_cmp(r_simple, r_mont_const) != 0)
printf("\nsimple and mont const time results differ\n");
if (BN_cmp(r_simple, r_recp) != 0)
printf("\nsimple and recp results differ\n");
if (BN_cmp(r_simple, r_mont_ct) != 0)
printf("\nsimple and mont results differ\n");
if (BN_cmp(r_simple, r_mont_nonct) != 0)
printf("\nsimple and mont_nonct results differ\n");

printf("a (%3d) = ", BN_num_bits(a));
BN_print_fp(stdout, a);
printf("\nb (%3d) = ", BN_num_bits(b));
BN_print_fp(stdout, b);
printf("\nm (%3d) = ", BN_num_bits(m));
BN_print_fp(stdout, m);
printf("\nsimple =");
BN_print_fp(stdout, r_simple);
printf("\nrecp =");
BN_print_fp(stdout, r_recp);
printf("\nmont =");
BN_print_fp(stdout, r_mont);
printf("\nmont_ct =");
BN_print_fp(stdout, r_mont_const);
printf("\n");
exit(1);
if (!test_mod_exp(result_simple, a, b, m, ctx, test))
goto err;
}
}

Expand Down

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