CHK: Content Hash Keys
All files within Freenet are identified and requested by a key, in a similar way that normal websites are identified by a domain name. You don't really need to know the technical details to use Freenet; tools such as jSite will sort it all out for you.
Content Hash Keys are for files that aren't going to change. For example: mp3 files. They look something like this:
CHK@SVbD9~HM5nzf3AX4yFCBc-A4dhNUF5DPJZLL5NX5Brs,bA7qLNJR7IXRKn6uS5PAySjIM6azPFvK~18kSi6bbNQ,AAEA--8
These are created by making a hash of the file. This is like a fingerprint of the file: it is generally a lot smaller than the file itself. It should not be possible for two different files to have the same CHK; a CHK uniquely identifies a file (assuming that SHA-256 is not broken!).
This hash is used as an index to the file, in a similar way to the address, or URL, or a standard website. The CHK key is generated automatically, so it won't look as user-friendly as a domain name. For user-friendly keys, have a look at SSK pages.
Example
This example will add a small text file to Freenet using the Content Hash Key to identify it. We will use the basic telnet interface to Freenet for illustrative purposes but you can use a more featured site creator like jSite.
At the command line, type the following to access Freenet's command line interface:
telnet localhost 2323
You should be presented with a list of options. Type the following and then press Enter:
put:this is a test
after a short while (be patient, it could take a minute or two) it will return this:
URI: freenet:CHK@SVbD9~HM5nzf3AX4yFCBc-A4dhNUF5DPJZLL5NX5Brs,bA7qLNJR7IXRKn6uS5PAySjIM6azPFvK~18kSi6bbNQ,AAEA--8
This random-looking string is the Content Hash Key (CHK) of the line of text this is a test, and is telling you the address that other people can use to access this file in Freenet. You can see that it consists of three segments, separated by commas:
- The first part, SVbD9~HM5nzf3AX4yFCBc-A4dhNUF5DPJZLL5NX5Brs, is the actual hash of the file.
- The second part, bA7qLNJR7IXRKn6uS5PAySjIM6azPFvK~18kSi6bbNQ, is the decryption key that unlocks the file (which is stored encrypted).
- The third part, AAEA--8, is something to do with settings such as cryptographical algorithms used.
To exit from the telnet interface, press Ctrl-] and press Enter, then type quit and press Enter.
To verify your file exists in Freenet, open a web browser and go to:
http://localhost:8888/CHK@SVbD9~HM5nzf3AX4yFCBc-A4dhNUF5DPJZLL5NX5Brs,bA7qLNJR7IXRKn6uS5PAySjIM6azPFvK~18kSi6bbNQ,AAEA--8
You may get a warning come up at first, but just tell the browser to open it as a plain text page. If all goes well, you should see the text you have just inserted to Freenet.
