If I understand this correctly, I think the requirement is to translate a base64 encoded string to a hex string in blocks of 8 bytes (16 hex digits). If so, od -t x8 -An
, after the base64 decoding will get you there:
$ echo -n "7WkoOEfwfTTioxG6CatHBw==" | base64 -d | od -t x8 -An
347df047382869ed 0747ab09ba11a3e2
$