fix UTCTimeField timezone

scapy/data.py

@@ -266,9 +266,8 @@
     PPI_BTLE: 'btle',
 }
 
-
-# On windows, epoch is 01/02/1970 at 00:00
-EPOCH = calendar.timegm((1970, 1, 2, 0, 0, 0, 3, 1, 0)) - 86400
+# See https://github.com/secdev/scapy/issues/4557
+EPOCH = calendar.timegm((1970, 1, 1, 0, 0, 0, 3, 1, 0))
 
 MTU = 0xffff  # a.k.a give me all you have
 

scapy/fields.py

@@ -3492,7 +3492,7 @@ def __init__(
 
 
 class UTCTimeField(Field[float, int]):
-    __slots__ = ["epoch", "delta", "strf",
+    __slots__ = ["epoch", "delta", "tz", "strf",
                  "use_msec", "use_micro", "use_nano", "custom_scaling"]
 
     def __init__(self,
@@ -3502,6 +3502,7 @@ def __init__(self,
                  use_micro=False,  # type: bool
                  use_nano=False,  # type: bool
                  epoch=None,  # type: Optional[Tuple[int, int, int, int, int, int, int, int, int]]  # noqa: E501
+                 tz=datetime.timezone.utc, # type: datetime.timezone
                  strf="%a, %d %b %Y %H:%M:%S %z",  # type: str
                  custom_scaling=None,  # type: Optional[int]
                  fmt="I"  # type: str
@@ -3511,6 +3512,7 @@ def __init__(self,
         mk_epoch = EPOCH if epoch is None else calendar.timegm(epoch)
         self.epoch = mk_epoch
         self.delta = mk_epoch - EPOCH
+        self.tz = tz
         self.strf = strf
         self.use_msec = use_msec
         self.use_micro = use_micro
@@ -3533,9 +3535,9 @@ def i2repr(self, pkt, x):
         # To make negative timestamps work on all plateforms (e.g. Windows),
         # we need a trick.
         t = (
-            datetime.datetime(1970, 1, 1) +
+            datetime.datetime(1970, 1, 1, tzinfo=datetime.timezone.utc) +
             datetime.timedelta(seconds=x)
-        ).strftime(self.strf)
+        ).astimezone(self.tz).strftime(self.strf)
         return "%s (%d)" % (t, int(x))
 
     def i2m(self, pkt, x):

test/fields.uts

@@ -377,15 +377,26 @@ class TestUTCTimeField(Packet):
             fmt="<Q",
             epoch=[1601, 1, 1, 0, 0, 0],
             custom_scaling=1e7,
+        ),
+        UTCTimeField(
+            "Time1",
+            None,
+            fmt="<Q",
+            epoch=[1601, 1, 1, 0, 0, 0],
+            tz=timezone(timedelta(seconds=14400)),
+            custom_scaling=1e7,
         )
     ]
 
 
 p = TestUTCTimeField(Time=0)
-assert p.sprintf("%Time%") == 'Mon, 01 Jan 1601 00:00:00  (-11644473600)'
+assert p.sprintf("%Time%") == 'Mon, 01 Jan 1601 00:00:00 +0000 (-11644473600)'
 
 p = TestUTCTimeField(Time=133587912345678900)
-assert p.sprintf("%Time%") == 'Sun, 28 Apr 2024 15:20:34  (1714317634)'
+assert p.sprintf("%Time%") == 'Sun, 28 Apr 2024 15:20:34 +0000 (1714317634)'
+
+p = TestUTCTimeField(Time1=133587912345678900)
+assert p.sprintf("%Time1%") == 'Sun, 28 Apr 2024 19:20:34 +0400 (1714317634)'
 
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