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Use constant-time comparison for MAC and hash verification #27

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3deceb7
Replace sprintf with snprintf in refclock_ripencc logging
kodareef5 Mar 23, 2026
036355e
Use constant-time comparison for MAC and hash verification
kodareef5 Mar 23, 2026
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12 changes: 10 additions & 2 deletions ntpd/ntp_leapsec.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1141,8 +1141,16 @@ leapsec_validate(
return LSVALID_NOHASH;
if (0 == hlseen)
return LSVALID_BADFORMAT;
if (0 != memcmp(&rdig, &ldig, sizeof(sha1_digest)))
return LSVALID_BADHASH;
{
volatile unsigned char diff = 0;
const unsigned char *a = (const unsigned char *)&rdig;
const unsigned char *b = (const unsigned char *)&ldig;
size_t i;
for (i = 0; i < sizeof(sha1_digest); i++)
diff |= a[i] ^ b[i];
if (diff != 0)
return LSVALID_BADHASH;
}
return LSVALID_GOODHASH;
}

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8 changes: 4 additions & 4 deletions ntpd/refclock_ripencc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1507,7 +1507,7 @@ parse0x8FAD(
utcflags = buf[19];


sprintf(logbuf, "U1 %d.%d.%d %02d:%02d:%02d %d %02x",
snprintf(logbuf, sizeof(logbuf), "U1 %d.%d.%d %02d:%02d:%02d %d %02x",
day, month, year, hour, minute, second, trackstat, utcflags);

#ifdef DEBUG_NCC
Expand Down Expand Up @@ -1674,7 +1674,7 @@ parse0x8F0B(
}


sprintf(logbuf, "C1 %02d%02d%04d %02d%02d%02d %d %7.0f %.1f %.0f %.1f %d %02d%09.6f %c %02d%09.6f %c %.0f %d %d %d %d %d %d %d %d",
snprintf(logbuf, sizeof(logbuf), "C1 %02d%02d%04d %02d%02d%02d %d %7.0f %.1f %.0f %.1f %d %02d%09.6f %c %02d%09.6f %c %.0f %d %d %d %d %d %d %d %d",
day, month, year, hour, minute, second, mode, bias, biasunc,
rate, rateunc, utcoff, lat_deg, lat_min, north_south, lon_deg,
lon_min, east_west, alt, sv[0], sv[1], sv[2], sv[3], sv[4],
Expand Down Expand Up @@ -1750,7 +1750,7 @@ parse0x4F(
dn = bGetShort (&buf[22]);
dt_lsf = bGetShort (&buf[24]);

sprintf(logbuf, "L1 %d %d %d %g %g %g %d %d %d",
snprintf(logbuf, sizeof(logbuf), "L1 %d %d %d %g %g %g %d %d %d",
dt_lsf - dt_ls, dt_ls, dt_lsf, a0, a1, tot, wn_t, wn_lsf, dn);

#ifdef DEBUG_NCC
Expand Down Expand Up @@ -1802,7 +1802,7 @@ parse0x5C(
elevation = bGetSingle(&buf[12]) * R2D;
azinuth = bGetSingle(&buf[16]) * R2D;

sprintf(logbuf, "S1 %02d %d %d %02x %4.1f %5.1f %4.1f",
snprintf(logbuf, sizeof(logbuf), "S1 %02d %d %d %02x %4.1f %5.1f %4.1f",
prn, channel, aqflag, ephstat, snr, azinuth, elevation);

#ifdef DEBUG_NCC
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15 changes: 10 additions & 5 deletions sntp/crypto.c
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Original file line number Diff line number Diff line change
Expand Up @@ -174,11 +174,16 @@ auth_md5(

pkt_ptr += pkt_len + sizeof(keyid_t);

/* isc_tsmemcmp will be better when its easy to link with. sntp
* is a 1-shot program, so snooping for timing attacks is
* Harder.
*/
return mac_len == len && !memcmp(dbuf, pkt_ptr, mac_len);
/* Use constant-time comparison for MAC verification. */
if (mac_len != len)
return 0;
{
volatile unsigned char diff = 0;
size_t i;
for (i = 0; i < mac_len; i++)
diff |= dbuf[i] ^ pkt_ptr[i];
return (diff == 0);
}
}

static int
Expand Down