--- uuid.c 2004/01/15 15:29:36 1.27
+++ uuid.c 2004/01/15 16:22:09 1.28
@@ -427,6 +427,65 @@
Unix UTC base time is January 1, 1970) */
#define UUID_TIMEOFFSET "01B21DD213814000"
+/*
+ * ATTENTION:
+ *
+ * In case no real/physical IEEE 802 address is available, both
+ * "draft-leach-uuids-guids-01" (section "4. Node IDs when no IEEE 802
+ * network card is available") and RFC 2518 (section "6.4.1 Node Field
+ * Generation Without the IEEE 802 Address") recommend (quoted from RFC
+ * 2518):
+ *
+ * "The ideal solution is to obtain a 47 bit cryptographic quality
+ * random number, and use it as the low 47 bits of the node ID, with the
+ * most significant bit of the first octet of the node ID set to 1. This
+ * bit is the unicast/multicast bit, which will never be set in IEEE 802
+ * addresses obtained from network cards; hence, there can never be a
+ * conflict between UUIDs generated by machines with and without network
+ * cards."
+ *
+ * This clearly explains what the intention is. Unfortunately, it
+ * explains it incorrectly how to achieve this. Because (see also
+ * http://www.iana.org/assignments/ethernet-numbers and "Understanding
+ * Physical Addresses" in "Ethernet -- The Definitive Guide", p.43) it
+ * is the "LEAST significant bit of the first octet of the node ID" in a
+ * memory representation of a 48-bit MAC address. The reason is that it
+ * is the MOST significant bit only in IEEE 802.3 _transmission order_
+ * of a MAC address. The memory order of an octet from a MAC address is
+ * always with the bits from left/MSB/bit-7 to right/LSB/bit-0!
+ *
+ * Unfortunately, even the reference code in
+ * "draft-leach-uuids-guids-01" incorrectly sets the multicast bit with
+ * an "OR 0x80" bit operation. This could be considered "standards
+ * compliant" (because the exact wording above is "with the most
+ * significant bit"), but from the remaining explanation it becomes 100%
+ * clear that the intention was different and the wording and code was
+ * incorrect because the authors were unaware of this difference in bit
+ * ordering between memory and wire transmission.
+ *
+ * So, OSSP uuid does it the intended/correct way and generates a real
+ * IEEE 802 multicast address, but with a compile-time option one can
+ * nevertheless enforce the generation of incorrect addresses according
+ * to the standards. For the decoding we always use the correct way, of
+ * course.
+ *
+ * Luckily, both DCE 1.1 and ISO/IEC 11578:1996 do not deal with the
+ * situation of not available IEEE 802 addresses at all and so have
+ * avoided to adopt this bug from the original draft and code ;-)
+ */
+
+/* encoding */
+#ifdef WITH_RFC2518
+#define IEEE_MAC_MCBIT_ENC BM_OCTET(1,0,0,0,0,0,0,0)
+#else
+#define IEEE_MAC_MCBIT_ENC BM_OCTET(0,0,0,0,0,0,0,1)
+#endif
+#define IEEE_MAC_LOBIT_ENC BM_OCTET(0,0,0,0,0,0,1,0)
+
+/* decoding */
+#define IEEE_MAC_MCBIT_DEC BM_OCTET(0,0,0,0,0,0,0,1)
+#define IEEE_MAC_LOBIT_DEC BM_OCTET(0,0,0,0,0,0,1,0)
+
/* INTERNAL: generate UUID version 1: time, clock and node based */
static uuid_rc_t uuid_generate_v1(uuid_t *uuid, unsigned int mode, va_list ap)
{
@@ -536,9 +595,10 @@
*/
if ((mode & UUID_MCASTRND) || (uuid->mac[0] & BM_OCTET(1,0,0,0,0,0,0,0))) {
- /* use random multi-cast MAC address */
+ /* generate random IEEE 802 local multicast MAC address */
prng_data(uuid->prng, (void *)&(uuid->obj.node), sizeof(uuid->obj.node));
- uuid->obj.node[0] |= BM_OCTET(1,0,0,0,0,0,0,0);
+ uuid->obj.node[0] |= IEEE_MAC_MCBIT_ENC;
+ uuid->obj.node[0] |= IEEE_MAC_LOBIT_ENC;
}
else {
/* use real regular MAC address */
@@ -784,14 +844,15 @@
str_rsprintf(str, " clock: %ld (usually random)\n", (unsigned long)tmp32);
/* decode node MAC address */
- str_rsprintf(str, " node: %02x:%02x:%02x:%02x:%02x:%02x (%s)\n",
+ str_rsprintf(str, " node: %02x:%02x:%02x:%02x:%02x:%02x (%s %s)\n",
(unsigned int)uuid->obj.node[0],
(unsigned int)uuid->obj.node[1],
(unsigned int)uuid->obj.node[2],
(unsigned int)uuid->obj.node[3],
(unsigned int)uuid->obj.node[4],
(unsigned int)uuid->obj.node[5],
- (uuid->obj.node[0] & 0x80 ? "random multicast" : "real unicast"));
+ (uuid->obj.node[0] & IEEE_MAC_LOBIT_DEC ? "local" : "global"),
+ (uuid->obj.node[0] & IEEE_MAC_MCBIT_DEC ? "multicast" : "unicast"));
}
else if (tmp16 == 3) {
/* decode version 3 */
|
