A Message-ID should be globally unique. Currently mutt generates this ID
based on the current date and time, followed by ".G", followed by a letter
A to Z (A for the 1st and 27th email sent, Z for the 26th, etc.), followed
by the pid of the active mutt process, followed by "@" and the configured
fqdn.
This can lead to information being leaked as to an users email habits and
activities, which might be undesirable.
By replacing everything left of the "@" in the Message-ID with a Base64
encoded timestamp and 64 bits of randomness, we no longer include this
information.
---
sendlib.c | 26 ++++++++++++++++----------
1 file changed, 16 insertions(+), 10 deletions(-)
diff --git a/sendlib.c b/sendlib.c
index 77c14e8f..009f8971 100644
--- a/sendlib.c
+++ b/sendlib.c
@@ -80,8 +80,6 @@ const char B64Chars[64] = {
'8', '9', '+', '/'
};
-static char MsgIdPfx = 'A';
-
static void transform_to_7bit (BODY *a, FILE *fpin);
static void encode_quoted (FGETCONV * fc, FILE *fout, int istext)
@@ -2397,19 +2395,27 @@ const char *mutt_fqdn(short may_hide_host)
char *mutt_gen_msgid (void)
{
char buf[SHORT_STRING];
- time_t now;
- struct tm *tm;
+ time_t now = time (NULL);
+ u_int32_t randombits[2] = { mutt_random32(), mutt_random32() };
+ char localpart[12]; /* = 32 bit timestamp, plus 64 bit randomness */
+ unsigned char localpart_B64[16+1]; /* = Base64 encoded value of localpart
plus
+ terminating \0 */
const char *fqdn;
- now = time (NULL);
- tm = gmtime (&now);
+ /* Convert the four least significant bytes of our timestamp and put it in
+ localpart, with proper endianness (for humans) taken into account. */
+ for (int i = 0; i < 4; i++)
+ localpart[i] = (uint8_t) (now >> (3-i)*8u);
+
+ memcpy(&localpart[4], &randombits[0], 4);
+ memcpy(&localpart[8], &randombits[0], 4);
+
+ mutt_to_base64(localpart_B64, (unsigned char *) localpart, 12, 17);
+
if (!(fqdn = mutt_fqdn(0)))
fqdn = NONULL(Hostname);
- snprintf (buf, sizeof (buf), "<%d%02d%02d%02d%02d%02d.G%c%u@%s>",
- tm->tm_year + 1900, tm->tm_mon + 1, tm->tm_mday, tm->tm_hour,
- tm->tm_min, tm->tm_sec, MsgIdPfx, (unsigned int)getpid (), fqdn);
- MsgIdPfx = (MsgIdPfx == 'Z') ? 'A' : MsgIdPfx + 1;
+ snprintf (buf, sizeof (buf), "<%s@%s>", localpart_B64, fqdn);
return (safe_strdup (buf));
}
--
2.26.2
