brunnerh / hacknet-decypher

Automatically decrypts .dec files from the game Hacknet.

hacknet-decypher

Automatically decrypts .dec files from the game Hacknet.

The basic algorithm can be found in the game in the form of C# code. This application uses that algorithm and brute-forces the decryption, so no password is needed.

Tools like onlineocr.net can be used to more easily get the encrypted text out of the game. (Then again, the unencrypted file contents are stored in plain XML files in the game data directories, so none of this is really necessary.)

.dec File Format

These files are broken into two lines of data, the first stores the headers, the second the content.

The header looks like this:

#DEC_ENC::<message>::<link>::<"ENCODED">[::<file-extension>]

Header	Description
message	A subject/title line.
link	IP address of machine on which message was encrypted.
"ENCODED"	The text literal "ENCODED". Used to verify that the entered password is correct.
file-extention	Optional file extension of the decoded document

All of the above headers except the "ENCODED" literal are encrypted using a hard-coded seed. The code used for both the "ENCODED" header and the content are derived from the user-provided password.

That header makes a known-plaintext brute-force attack trivial.