hi, i'm answering in english, but if you speak german please continue in german then since this forum is a german speaking one.

Guest thegreatonech

I've got a hash. every key has a hexadecimal value with two signs like "fe" or "05" or "f4".

so, this description tells me you have a hash with values like "fe" or "05".
you don't mention the keys, so I assume that they don't matter.

Quote

I have to put two of this hexs together to a hex with four signs like "fe05". (The first with the second, the third with the forth...)

problem at this point: you are talking about first, second and so forth. what is the first and the second? all we have until now is a hash. there is no order in a hash.
what do you want to do? how is first and second defined? please give example input and output, so maybe we can at least guess from that.