Byte order in AES-CMAC test code
Keys for AES are not numbers; they are defined as bits / octets (or bytes). They therefore do not have a &quot;least significant octet&quot;, they just consist of octets. So the same order from lowest index (left) to highest index (right) is being used.
As common the bits are indexed from right to left though; this is probably due to humans having some trouble converting hexadecimal digits otherwise. It just shows that humans are terrible at thinking in little endian.
The exact ordering is specified in the AES specification as mentioned by fgrieu int he comments.