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added time stamp handling functions

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This commit is contained in:
Logan007 2020-07-23 01:55:02 +05:45
parent 252ce9779a
commit 36eb807fca
1 changed files with 65 additions and 2 deletions
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67
src/n2n.c
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@ -25,6 +25,9 @@
#define PURGE_REGISTRATION_FREQUENCY 30
#define REGISTRATION_TIMEOUT 60
#define TIME_STAMP_FRAME 0x0000001000000000LL /* clocks of different computers are allowed +/- 16 seconds to be off */
#define TIME_STAMP_JITTER 0x0000000027100000LL /* we allow a packet to arrive 160 ms (== 0x27100 us) before another */
static const uint8_t broadcast_addr[6] = { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF };
static const uint8_t multicast_addr[6] = { 0x01, 0x00, 0x5E, 0x00, 0x00, 0x00 }; /* First 3 bytes are meaningful */
static const uint8_t ipv6_multicast_addr[6] = { 0x33, 0x33, 0x00, 0x00, 0x00, 0x00 }; /* First 2 bytes are meaningful */
@ -380,8 +383,8 @@ int sock_equal(const n2n_sock_t * a,
/* *********************************************** */
#if defined(WIN32) && !defined(__GNUC__)
static int gettimeofday(struct timeval *tp, void *tzp)
{
// REVISIT during the years 2035...2038
int gettimeofday(struct timeval *tp, void *tzp) {
time_t clock;
struct tm tm;
SYSTEMTIME wtm;
@ -399,3 +402,63 @@ static int gettimeofday(struct timeval *tp, void *tzp)
return (0);
}
#endif
// returns a time stamp for use with replay protection
// REVISIT during the years 2035...2038
uint64_t time_stamp (void) {
struct timeval tod;
uint64_t micro_seconds;
gettimeofday (&tod, NULL);
/* We will (roughly) calculate the microseconds since 1970 leftbound into the return value.
The leading 32 bits are used for tv_sec. The following 20 bits (sufficent as microseconds
fraction never exceeds 1,000,000,) encode the value tv_usec. The remaining lowest 12 bits
are kept random for use in IV */
micro_seconds = n2n_rand();
micro_seconds = ( (((uint64_t)(tod.tv_sec) << 32) + (tod.tv_usec << 12))
| (micro_seconds >> 52) );
// more exact but more costly due to the multiplication:
// micro_seconds = (tod.tv_sec * 1000000 + tod.tv_usec) << 12) | ...
return (micro_seconds);
}
// checks if a provided time stamp is consistent with current time and previously valid time stamps
// returns the time stamp to store as "last valid time stamp" or zero in case of invalid time stamp
// uses branchless sign extensio tricks inspired by https://www.chessprogramming.org/Avoiding_Branches
// and also https://hbfs.wordpress.com/2008/08/05/branchless-equivalents-of-simple-functions
// REVISIT during the years 2035...2038
uint64_t time_stamp_verify (uint64_t stamp, uint64_t previous_stamp) {
int64_t diff; // do not change this to unsigned for keeping the following code work
// is it higher than previous time stamp (including allowed deviation of TIME_STAMP_JITTER)?
diff = stamp - previous_stamp + TIME_STAMP_JITTER;
if(diff > 0) {
// is it around current time (+/- allowed deviation TIME_STAMP_FRAME)?
diff = stamp - time_stamp();
// branchless abs()
diff = (diff + (diff >> 63)) ^ (diff >> 63);
if(diff < TIME_STAMP_FRAME) {
// for not allowing to exploit the allowed TIME_STAMP_JITTER to "turn the clock backwards",
// return the higher value making use of branchless max()
diff = stamp - previous_stamp;
diff = stamp - (diff & (diff >> 63));
return ((uint64_t)diff);
} else {
traceEvent(TRACE_DEBUG, "time_stamp_verify found a timestamp out of allowed frame.");
return (0);
}
} else {
traceEvent(TRACE_DEBUG, "time_stamp_verify found a timestamp too old / older than previous.");
return (0);
}
}