Yes - you need a key. You also need an attribute "type" with value "plain".
CSV importing is a general tool it is completely unaware of specifics for node kinds. If you import things you need to know what is needed and provide that information. So no - there is no automatic way to build a key. You need to provide one as part of the imported CSV data.
I tried adding some text(hoping it would hash it) in the import file as a key but the import process did not accept it. Does it have some parameters? Is it even possible to import a key via that csv import?
You cannot do any processing on the data - it will just take what is in the CSV file. If you include key in the list of attributes it will work fine - as far as tw_imp_csv in concerned there is nothing special about key.
A file of the form
name, key, type
GroupName, GroupKey, GroupType
tw_imp_csv --keys=key --kind=Group will create a Group node with attribute name (value GroupName), key (value GroupKey) and type (value GroupType).