Sometimes, and in some select situations, I want to share a screenshot or some terminal output that contains MAC addresses. But for privacy reasons, I do not want to reveal the actual MAC addresses. Why? Because they’re unique identifiers (unless intentionally changed).

If the output only contained one or two physical addresses, I could manually mask them. But I wanted to explore another way to solve this problem. So, I wrote a Python module that pseudo randomizes MAC addresses for me.

So not to confuse myself, or others that may see the output, with what is the actual MAC vs randomized, I use the locally administered address (LAA) format. This means tje randomized MAC addresses from my module can be identified as such.

locally administered addresses

To differentiate MAC addresses, as stated above, the module creates Locally Administered Addresses (LAA).

The LAA is distinguished by setting the second least significant bit (LSB) of the addresses first octet. If the second LSB is set to 1, the address is administered locally.

For example, the first octet of d6:70:b6:a2:b8:8a contains d6 (2 hex digits). The binary representation of the first octect is 11010110. Where bits 7-4 = 1101 or hex digit d, and then bits 3-0 = 0110 or hex digit 6.

The second LSB is 1. It’s bit 1 in the table below (the value two from the far right).

b7	b6	b5	b4	b3	b2	b1	b0
1	1	0	1	0	1	1	0
MSB							LSB

So this represents a unicast LAA. Here’s how we know it’s unicast:

b0 values:

0: unicast
1: multicast

b1 values:

0: globally unique (OUI enforced)
1: locally administered

LAA identifiers

Here are other possible values that identify unicast LAA addresses:

LSB 0010 = 02:00:00:00:00:00
LSB 0110 = 06:00:00:00:00:00
LSB 1010 = 0a:00:00:00:00:00
LSB 1110 = 0e:00:00:00:00:00

Note: 0 in the MAC address examples above could be any hexadecimal digit.

formats

The module supports a few common MAC address formats and can output using any of these:

FF-FF-FF-FF-FF-FF
FF.FF.FF.FF.FF.FF
FFFF.FFFF.FFFF

One caveat is the way I implemented formatting. It requires you to tell the module what format you want. It needs to know what format for output. For example providing something like 00-00-00-00-00-00 to the module would return something like 00-00-00-c7-11-fc.

This is clunky, and could be improved. Let me know how you think it could be better.

installation

I put the module on PyPi so that it can be installed using pip:

pip install randmac

example usage

>>> from randmac import RandMac
>>> RandMac("00-00-00-00-00-00")
'00-00-00-c7-11-fc'
>>> RandMac("00:00:00:00:00:00", True)
'ba:ac:5f:09:fc:bb'
>>> RandMac("0000.0000.0000", True)
'fe84.857f.900f'

$ python3 randmac.py 00:00:00:00:00:00
00:00:00:fc:e1:5b
$ python3 randmac.py 00:00:00:00:00:00 -f
2a:81:b0:e7:1d:08

links

you can find it at these locations on the Internet:

feedback

I’d love to hear any constructive feedback or suggestions on how to improve this project.