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fix(utils): use wider diff type for constant_time_equals #32

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Merged
LimiNode merged 1 commit into from
Sep 3, 2025
Merged

fix(utils): use wider diff type for constant_time_equals #32

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2 changes: 1 addition & 1 deletion hmac_utils.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@ namespace hmac {

bool constant_time_equals(const std::string &a, const std::string &b) {
size_t max_len = a.size() > b.size() ? a.size() : b.size();
unsigned char diff = static_cast<unsigned char>(a.size() ^ b.size());
unsigned int diff = (a.size() != b.size());
for (size_t i = 0; i < max_len; ++i) {
unsigned char ac = i < a.size() ? static_cast<unsigned char>(a[i]) : 0;
unsigned char bc = i < b.size() ? static_cast<unsigned char>(b[i]) : 0;
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8 changes: 8 additions & 0 deletions test_all.cpp
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Expand Up @@ -58,6 +58,14 @@ TEST(UtilsTest, ConstantTimeEqualsMismatch) {
EXPECT_FALSE(hmac::constant_time_equals("alpha", "alphabet"));
}

TEST(UtilsTest, ConstantTimeEqualsLengthMultiples256) {
std::string base(256, 'a');
std::string plus256 = base + std::string(256, '\0');
std::string plus512 = base + std::string(512, '\0');
EXPECT_FALSE(hmac::constant_time_equals(base, plus256));
EXPECT_FALSE(hmac::constant_time_equals(base, plus512));
}

TEST(HMACTest, SHA256) {
const std::string key = "12345";
const std::string input = "grape";
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