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Saflok: Fix datetime math helpers

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This commit is contained in:
Henry Gabryjelski
2025-11-17 01:27:32 -08:00
parent 1cfeb79003
commit 11eaa017d4
1 changed files with 120 additions and 67 deletions
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client/src/cmdhfsaflok.c
+120 -67
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@@ -39,6 +39,19 @@
// to many of the functions.
static const uint8_t days_in_month_lookup[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
static inline uint8_t get_days_in_month(uint16_t year, uint8_t month) {
assert(month >= 1 && month <= 12); // this uses 1-based indexing!
uint8_t days = days_in_month_lookup[month];
// Adjust for leap years
if ((month == 2u) &&
(year % 4u == 0u) &&
((year % 100u != 0u) || (year % 400u == 0u))
) {
days = 29u;
}
return days;
}
// TODO: consider separate structs for encrypted vs. decrypted
// for even greater type safety.
typedef struct _saflok_mfc_data_t {
@@ -51,18 +64,18 @@ typedef struct _saflok_mfc_key_t {
uint8_t key[6];
} saflok_mfc_key_t;
typedef struct _saflok_mfc_datetime_t {
uint16_t year;
uint8_t month;
uint8_t day;
uint8_t hour;
uint8_t minute;
uint16_t year; // full year, e.g., 2024
uint8_t month; // Month in range [1..12]
uint8_t day; // day of month, max range [1..31]
uint8_t hour; // hour of day, range [0..23]
uint8_t minute; // minute of hour, range [0..59]
} saflok_mfc_datetime_t;
typedef struct _saflok_mfc_datetime_offset_t {
uint8_t years;
uint8_t months;
uint8_t days;
uint8_t hours;
uint8_t minutes;
uint8_t years; // range [0..15]
uint8_t months; // range [0..11]
uint8_t days; // maximum range [0..31]
uint8_t hours; // range [0..23]
uint8_t minutes; // range [0..59]
} saflok_mfc_datetime_offset_t;
#define KEY_LENGTH sizeof(saflok_mfc_key_t)
@@ -429,7 +442,7 @@ static void insert_bits(saflok_mfc_data_t *data, size_t start_bit, size_t num_bi
#endif // getters for interval (expiration) components
#if 1 // Setting the interval date is based on the creation date.
static inline saflok_mfc_datetime_offset_t get_saflok_mfc_interval(
static saflok_mfc_datetime_offset_t get_saflok_mfc_interval(
const saflok_mfc_data_t *data
) {
saflok_mfc_datetime_offset_t offset = {
@@ -441,7 +454,7 @@ static void insert_bits(saflok_mfc_data_t *data, size_t start_bit, size_t num_bi
};
return offset;
}
static inline bool set_saflok_mfc_interval(
static bool set_saflok_mfc_interval(
saflok_mfc_data_t *data,
saflok_mfc_datetime_offset_t offset
) {
@@ -453,7 +466,7 @@ static void insert_bits(saflok_mfc_data_t *data, size_t start_bit, size_t num_bi
_set_saflok_mfc_interval_minutes_impl(data, offset.minutes);
return result;
}
static inline saflok_mfc_datetime_t add_offset(
static saflok_mfc_datetime_t add_offset(
const saflok_mfc_datetime_t *base,
const saflok_mfc_datetime_offset_t offset
) {
@@ -462,7 +475,7 @@ static void insert_bits(saflok_mfc_data_t *data, size_t start_bit, size_t num_bi
struct tm tm = {
.tm_year = base->year - 1900,
.tm_mon = base->month - 1,
.tm_mday = base->day,
.tm_mday = base->day - 1,
.tm_hour = base->hour,
.tm_min = base->minute,
.tm_sec = 30, // selecting midpoint to avoid leapseconds changing minute
@@ -474,67 +487,105 @@ static void insert_bits(saflok_mfc_data_t *data, size_t start_bit, size_t num_bi
tm.tm_mday += offset.days;
tm.tm_hour += offset.hours;
tm.tm_min += offset.minutes;
// normalize into EPOCH ... which allows out-of-bounds values
time_t fixed = timegm(&tm);
// convert EPOCH back into a tm structure
gmtime_r(&fixed, &tm);
// now deal with carrying overflows
if (tm.tm_min >= 60) {
tm.tm_hour ++;
tm.tm_min -= 60;
}
if (tm.tm_hour >= 24) {
tm.tm_mday ++;
tm.tm_hour -= 24;
}
// addition is easy...
uint8_t days_in_month = get_days_in_month(tm.tm_year + 1900, tm.tm_mon + 1);
if (tm.tm_mday >= days_in_month) {
tm.tm_mon ++;
tm.tm_mday -= days_in_month;
}
if (tm.tm_mon >= 12) {
tm.tm_year ++;
tm.tm_mon -= 12;
}
// and finally convert back into saflok_mfc_datetime_t
saflok_mfc_datetime_t result = {
.year = tm.tm_year + 1900,
.month = tm.tm_mon + 1,
.day = tm.tm_mday,
.day = tm.tm_mday + 1,
.hour = tm.tm_hour,
.minute = tm.tm_min
};
return result;
}
static inline saflok_mfc_datetime_offset_t get_datetime_offset(
static saflok_mfc_datetime_offset_t get_datetime_offset(
const saflok_mfc_datetime_t *start,
const saflok_mfc_datetime_t *end
) {
// convert both to `struct tm`
struct tm tm_start = {
.tm_year = start->year - 1900,
.tm_mon = start->month - 1,
.tm_mday = start->day,
.tm_hour = start->hour,
.tm_min = start->minute,
.tm_sec = 30, // selecting midpoint to avoid leapseconds changing minute
.tm_isdst = 0, // UTC has no DST
};
struct tm tm_end = {
.tm_year = end->year - 1900,
.tm_mon = end->month - 1,
.tm_mday = end->day,
.tm_hour = end->hour,
.tm_min = end->minute,
.tm_sec = 30, // selecting midpoint to avoid leapseconds changing minute
.tm_isdst = 0, // UTC has no DST
};
// convert both to EPOCH
time_t epoch_start = timegm(&tm_start);
time_t epoch_end = timegm(&tm_end);
// subtract the epoch values to get delta in seconds
if (epoch_end < epoch_start) {
PrintAndLogEx(ERR, _RED_("ERROR:") " end date is before start date\n");
saflok_mfc_datetime_offset_t zero_offset = {0};
return zero_offset;
enum logLevel MYDBG = WARNING;
saflok_mfc_datetime_offset_t result = {0};
if (!is_saflok_mfc_datetime_valid(start)) {
PrintAndLogEx(ERR, _RED_("ERROR:") " start date is invalid\n");
return result;
}
time_t delta = epoch_end - epoch_start;
// convert delta seconds back into `struct tm`
struct tm result_tm = {0};
gmtime_r(&delta, &result_tm);
saflok_mfc_datetime_offset_t result = {
.years = result_tm.tm_year,
.months = result_tm.tm_mon,
.days = result_tm.tm_mday,
.hours = result_tm.tm_hour,
.minutes = result_tm.tm_min
if (!is_saflok_mfc_datetime_valid(end)) {
PrintAndLogEx(ERR, _RED_("ERROR:") " end date is invalid\n");
return result;
}
PrintAndLogEx(MYDBG, "Calculating offset from %04u-%02u-%02uT%02u:%02u to %04u-%02u-%02uT%02u:%02u\n",
start->year, start->month, start->day, start->hour, start->minute,
end->year, end->month, end->day, end->hour, end->minute
);
// use `struct tm`, which uses signed integers for each part
// and thus allows simpler checks for borrowing
struct tm diff = {
.tm_year = end->year - start->year,
.tm_mon = end->month - start->month,
.tm_mday = end->day - start->day,
.tm_hour = end->hour - start->hour,
.tm_min = end->minute - start->minute,
};
PrintAndLogEx(MYDBG, "Initial diff: %d years, %d months, %d days, %d hours, %d minutes\n",
diff.tm_year, diff.tm_mon, diff.tm_mday, diff.tm_hour, diff.tm_min
);
if (diff.tm_min < 0) {
diff.tm_min += 60;
diff.tm_hour -= 1;
}
if (diff.tm_hour < 0) {
diff.tm_hour += 24;
diff.tm_mday -= 1;
}
if (diff.tm_mday < 0) {
// determine days in previous month
uint16_t tgt_year = end->year - (end->month == 1 ? 1 : 0);
uint8_t tgt_month = (end->month == 1 ? 12 : (end->month - 1));
uint8_t days_in_prev_month = get_days_in_month(tgt_year, tgt_month);
PrintAndLogEx(MYDBG, "Borrowing days from month %02u of year %04u which has %02u days\n",
tgt_month, tgt_year, days_in_prev_month
);
// borrow from previous month
diff.tm_mon -= 1;
diff.tm_mday += days_in_prev_month;
}
if (diff.tm_mon < 0) {
diff.tm_mon += 12;
diff.tm_year -= 1;
}
result.years = diff.tm_year;
result.months = diff.tm_mon;
result.days = diff.tm_mday;
result.hours = diff.tm_hour;
result.minutes = diff.tm_min;
PrintAndLogEx(MYDBG, "Final offset: %d years, %d months, %d days, %d hours, %d minutes\n",
result.years, result.months, result.days, result.hours, result.minutes
);
return result;
}
static inline saflok_mfc_datetime_t get_saflok_mfc_card_expiration_datetime(
static saflok_mfc_datetime_t get_saflok_mfc_card_expiration_datetime(
const saflok_mfc_data_t *data
) {
saflok_mfc_datetime_t creation_date = get_saflok_mfc_card_creation_datetime(data);
@@ -542,7 +593,7 @@ static void insert_bits(saflok_mfc_data_t *data, size_t start_bit, size_t num_bi
saflok_mfc_datetime_t expiration = add_offset(&creation_date, offset);
return expiration;
}
static inline bool set_saflok_mfc_card_expiration_datetime(
static bool set_saflok_mfc_card_expiration_datetime(
saflok_mfc_data_t *data,
const saflok_mfc_datetime_t * expiration
) {
@@ -743,17 +794,17 @@ static uint32_t extract_bits(const saflok_mfc_data_t *data, size_t start_bit, si
static const size_t total_available_bits = ARRAYLEN(data->raw) * 8;
if (start_bit >= total_available_bits) {
// Out of bounds access
assert(!"extract_bits: Out of bounds access (start_bit)");
PrintAndLogEx(ERR, "extract_bits: out of bounds access (start_bit=%zu, total_available_bits=%zu)\n", start_bit, total_available_bits);
return 0;
}
if (num_bits > 32) {
// Exceeds maximum supported bit extraction
assert(!"extract_bits: num_bits exceeds 32");
PrintAndLogEx(ERR, "extract_bits: out of bounds access (num_bits=%zu, max=32)\n", num_bits);
return 0;
}
if (total_available_bits - start_bit < num_bits) {
// Out of bounds access
assert(!"extract_bits: Out of bounds access (num_bits)");
PrintAndLogEx(ERR, "extract_bits: out of bounds access (start_bit=%zu + num_bits=%zu > total_available_bits=%zu)\n", start_bit, num_bits, total_available_bits);
return 0;
}
@@ -772,22 +823,22 @@ static void insert_bits(saflok_mfc_data_t *data, size_t start_bit, size_t num_bi
static const size_t total_available_bits = ARRAYLEN(data->raw) * 8;
if (start_bit >= total_available_bits) {
// Out of bounds access
assert(!"insert_bits: Out of bounds access (start_bit)");
PrintAndLogEx(ERR, "insert_bits: out of bounds access (start_bit=%zu, total_available_bits=%zu)\n", start_bit, total_available_bits);
return;
}
if (num_bits > 32) {
// Exceeds maximum supported bit extraction
assert(!"insert_bits: num_bits exceeds 32");
PrintAndLogEx(ERR, "insert_bits: num_bits exceeds 32\n", num_bits);
return;
}
if (total_available_bits - start_bit < num_bits) {
// Out of bounds access
assert(!"insert_bits: Out of bounds access (num_bits)");
PrintAndLogEx(ERR, "insert_bits: out of bounds access (start_bit=%zu + num_bits=%zu > total_available_bits=%zu)\n", start_bit, num_bits, total_available_bits);
return;
}
if ((num_bits < 32) && ((value >> num_bits) != 0)) {
// Value exceeds the size of the specified bit field
assert(!"insert_bits: value exceeds bit field size");
PrintAndLogEx(ERR, "insert_bits: value exceeds bit field size (value=%u (0x%08x), num_bits=%zu)\n", value, value, num_bits);
return;
}
@@ -1408,6 +1459,8 @@ saflok_mfc_datetime_offset_t get_datetime_offset
saflok_mfc_datetime_t get_saflok_mfc_card_expiration_datetime
bool set_saflok_mfc_card_expiration_datetime
*/
saflok_mfc_data_t test_data = {0};
(void)get_saflok_mfc_card_expiration_datetime(&test_data);