CentOS - Jul 2016 - How to convert /etc/machine-id into a default-duid for IPv6 static DHCP?

Hi,

The use-case is deploying C7 VMs with a pre-set machine-id and 
default-duid based on the machine-id to facilitate static DHCP with 
IPv6. The default-duid is found in dhclient6-<value>-eth0.lease and IPv6 
DHCP uses default-duid like IPv4 DHCP uses MAC addresses for static DHCP.

How does one convert /etc/machine-id to a default-duid (in bash)?

1) /etc/machine-id -> DUID:

<read RFC6355 and try to grasp the NetworkManager code at [0] & [1]>

Use sha256 hash of machine-id, use first 128 bits, add colons and 
prepend 00:04:

$ MACHINE_ID_SHA256=`cat /etc/machine_id | sha256sum | cut -c1-32`
$ TMPID=$(sed -e 's/.\{2\}/&:/g;s/.$//'
<<<$MACHINE_ID_SHA256)
$ DUID=00:04:`echo $TMPID`

Correct?

2) convert $DUID to a default-duid. Example value of default-duid can be 
found in /var/lib/NetworkManager/dhclient6-<string>-eth0.lease.
Will stick the pre-set default-duid in /etc/dhclient6.leases so it gets 
picked up by NM once the VM is deployed and started.

So going from e.g.
/etc/machine-id 52d8c0f2a04a462a9c9ac1a906446d85
to
duid 00:04:a6:89:54:e8:bf:e2:13:71:82:3d:ea:33:4d:a5:2f:75
to
default-duid ???

example:
default-duid 
"\000\004%\011\324\251\274\334\001c\304\366\275\314\220\357\255(";

So how does one create the default-duid from the duid? The default-duid 
seems escaped octal with some chars here and there. The NetworkManager 
code at [2] that does the duid->default-duid conversion is above my pay 
grade. Anyone know how do this conversion preferably in bash?

TIA,
Patrick

[0] 
https://cgit.freedesktop.org/NetworkManager/NetworkManager/tree/src/nm-core-utils.c#n2658

[1] 
https://cgit.freedesktop.org/NetworkManager/NetworkManager/tree/src/dhcp-manager/nm-dhcp-client.c#n439

[2] 
https://cgit.freedesktop.org/NetworkManager/NetworkManager/tree/src/dhcp-manager/nm-dhcp-dhclient-utils.c#n356