Issue #19940: ssl.cert_time_to_seconds() now interprets the given time string in the UTC timezone (as specified in RFC 5280), not the local timezone.

Patch by Akira.

Lib/ssl.py

@@ -879,12 +879,34 @@ def wrap_socket(sock, keyfile=None, certfile=None,
 # some utility functions
 
 def cert_time_to_seconds(cert_time):
-    """Takes a date-time string in standard ASN1_print form
-    ("MON DAY 24HOUR:MINUTE:SEC YEAR TIMEZONE") and return
-    a Python time value in seconds past the epoch."""
+    """Return the time in seconds since the Epoch, given the timestring
+    representing the "notBefore" or "notAfter" date from a certificate
+    in ``"%b %d %H:%M:%S %Y %Z"`` strptime format (C locale).
 
-    import time
-    return time.mktime(time.strptime(cert_time, "%b %d %H:%M:%S %Y GMT"))
+    "notBefore" or "notAfter" dates must use UTC (RFC 5280).
+
+    Month is one of: Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
+    UTC should be specified as GMT (see ASN1_TIME_print())
+    """
+    from time import strptime
+    from calendar import timegm
+
+    months = (
+        "Jan","Feb","Mar","Apr","May","Jun",
+        "Jul","Aug","Sep","Oct","Nov","Dec"
+    )
+    time_format = ' %d %H:%M:%S %Y GMT' # NOTE: no month, fixed GMT
+    try:
+        month_number = months.index(cert_time[:3].title()) + 1
+    except ValueError:
+        raise ValueError('time data %r does not match '
+                         'format "%%b%s"' % (cert_time, time_format))
+    else:
+        # found valid month
+        tt = strptime(cert_time[3:], time_format)
+        # return an integer, the previous mktime()-based implementation
+        # returned a float (fractional seconds are always zero here).
+        return timegm((tt[0], month_number) + tt[2:6])
 
 PEM_HEADER = "-----BEGIN CERTIFICATE-----"
 PEM_FOOTER = "-----END CERTIFICATE-----"