pqc/test/ct.cpp

// Those tests work only with Clang and Memory Sanitizer

#include <gtest/gtest.h>
#include <common/ct_check.h>

extern "C" {
uint8_t ct_memcmp(const void *a, const void *b, size_t sz);
}

TEST(ConstantTime, CtCheck_Negative) {
    unsigned char a[16], b[16];
    unsigned i;
    memset(a, 42, 16);
    memset(b, 42, 16);

    ct_poison(a, 16);
    for (i = 0; i < 16; i++) {
        ct_expect_umr();
        if (a[i] != b[i]) {
            break;
        }
        ct_require_umr();
    }

    ct_purify(a, 16);
    // Ensure buffers are not optimized-out
    ASSERT_EQ(a[0], b[0]);
}

TEST(ConstantTime, CtCheck_Positive_NoAccess) {
    unsigned i;
    char result = 0;
    unsigned char a[16], b[16];
    memset(a, 42, sizeof(a));
    memset(b, 42, sizeof(b));

    ct_poison(a, 16);

    for (i = 0; i < 16; i++) {
        result |= a[i] ^ b[i];
    }
    ct_purify(a, 16);

    // Purify result, to allow check that otherwise
    // would be not constant-time.
    ct_purify(&result, 1);
    ASSERT_EQ(result, 0);
}


TEST(ConstantTime, CtCheck_Negative_UseSecretAsIndex) {
    static const unsigned char tab[2] = {1, 0};
    unsigned char a[16];
    unsigned char result;
    memset(a, 42, sizeof(a));

    ct_poison(a, 16);

    ct_expect_umr();
    result = tab[a[0] & 1];
    ct_require_umr();

    ct_purify(a, 16);

    // Ensure variables are not optimized-out
    ct_purify(&result, 1);
    ASSERT_EQ(result, 1);
}

TEST(ConstantTime, CtCheck_memcmp) {
    unsigned char a[16], b[16];
    memset(a, 42, sizeof(a));
    memset(b, 42, sizeof(b));
    uint8_t ret;

    ct_poison(a, 16);
    ret = ct_memcmp(a,b,16);
    ct_purify(&ret, 1);
    ASSERT_EQ(ret,0);

    b[1] = 0;
    ret = ct_memcmp(a,b,16);
    ct_purify(&ret, 1);
    ASSERT_EQ(ret,1);
}

TEST(ConstantTime, CtCheck_memcmp_chained) {
    unsigned char a[16], b[16], c[16], d[16];
    memset(a, 42, sizeof(a));
    memset(b, 42, sizeof(b));
    memset(d, 42, sizeof(b));
    memset(c, 41, sizeof(c));
    uint8_t ret;

    ct_poison(a, 16);

    ct_expect_umr();
    // obviously must generate UMR if if first check fails
    // and second is not done
    ret = (ct_memcmp(a,c,16)==0) && (ct_memcmp(a,b,16)==0);
    ct_require_umr();
    ct_purify(&ret, 1);
    ASSERT_EQ(ret,0);

    ct_expect_umr();
    // it's still UMR even if both checks are OK
    ret = (ct_memcmp(a,d,16)==0) && (ct_memcmp(a,b,16)==0);
    ct_require_umr();

    ct_purify(&ret, 1);
    ASSERT_EQ(ret,1);
}