How to calculate the Info Hash of a torrent file?

Question

bittorrent

In the BitTorrent protocol, you need to know the Info Hash, but how do you calculate it?
Torrent file stores information in bencode format. Do I need to decrypt it and take only certain data from the Info dictionary? Or do you just need to take a piece of raw text from a file and hash it? If the second option, then from where and to where exactly?
Example torrent file:

d8:announce26:...(трекер).....4:infod6:len.....(хеш-суммы сегментов)....e9:publisher13:tracker.org13:publisher-url50:http://tracker.org/post/123e

What exactly needs to be hashed?