current format looks like this v1-sha256-128M-aa669dcefba57e01bd7ff0526a0001d2118f06adc8106d265b5743b0ee90084f
But there are already formats for hashed trees
(Till showed me a specific one, but I forgot)
problem: might not be compatible with hadoop fs
solution: replace ":" with "-", and maybe "-" with "--" (assuming "-" can be part of the URN in the first place)