MAC : Java Glossary

2008-07-21 by Roedy Green ©1996-2009 Canadian Mind Products
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MAC

Media Access Control. Huh? Every Ethernet LAN card has a unique 48-bit serial number, e.g. 00-0C-6E-27-4F-9B sometimes called its physical address. No other Ethernet and in the world has the same one unless they cheated. This physical address is usually usually just called the MAC, similar in function to the 32 bit IPv4 or 128-bit IPv6 IP addresses used on the Internet. Token Ring LAN cards don’t have a MAC. Though it is common to access the Internet via a small local Ethernet, some computers access the Internet via direct dialup and thus don’t necessarily have a MAC address.

The MAC is useful as a unique computer indentifier for software protection schemes. Intel’s Pentium class machines have a unique serial number burned into their silicon that can also serve that purpose. AMD’s do not.

In Java 1.6+ there is java.net.NetworkInterface. getHardwareAddress which will get you the hardware address of an adapter, usually the MAC. You need sufficient privilege to use it.

Here’s how to display a long MAC address in hex with the traditional dashes.

The code to extract the MAC in Windows in Java 1.5 or earlier is ugly, complicated, needs JNI and an extra iphlpapi library DLL not part of the normal Windows distribution. See this CodeGuru article. You can also find out what it is with the IPCONFIG utility.

MAC also stands for Message Authentication Codes. They are digital signatures used to verify that a piece of data originated with a given party and that it has not been tampered with. A MAC mechanism that is based on cryptographic hash functions is referred to as HMAC. HMAC can be used with any cryptographic hash function, e.g., MD5 or SHA-1, in combination with a secret shared key. How HMACs work is specified in RFC 2104. JCE has support for HMAC-MD5 and HMAC-SHA1.

The term Mac (not all caps) refers to Apple’s line of computers, the MacIntosh, deliberately spelled differently from the McIntosh apple tree species after which it was named and McIntosh the maker of high end stereo equipment, and presumably to avoid dealing with lawyers from that Scottish McFood company.

Learning More

Sun’s Javadoc on the getHardwareAddress method : available:

on the web at java.sun.com
in the current JDK 1.6.0_11 or in the old JDK 1.5.0_17 on your local Windows J: drive.

CC+ structures needed to access the MAC
CPU serial number
Ethernet
How To Determine the MAC
IP
JCE
LAN
MAC address: student project
MAC via ipconfig

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