r5steg

Encrypted text in text steganography program using zero width space characters. It hides and encrypts a message in between plain text using zero-width characters which are invisible in most browsers and interfaces.

Installation

Make sure you meet all the requirements, if not install them with pip

Clone the repository and navigate to it's directory:

git clone https://github.com/byru55o/r5steg.git && cd r5steg

Install it with GNU make:
```
sudo make install
```
or to uninstall: sudo make uninstall

Usage

Execute the program: r5steg or, if you didn't install: ./r5steg.py or python3 r5steg.py
To encrypt and hide a message: select option [1], enter message to hide, enter the plain text you want to show and the password for the encryption. The resulting string, which is copied to the clipboard contains your secret message which you can decrypt using option [2].
To decrypt and unhide a message in between plain text: select option [2], enter the message and the password.

Configuration

It is possible to change some options such as encryption (some of you may prefer to disable it, for a shorter/lighter hidden message) or colours (you can either disable or modify them). The configuration file is located in ~/.config/r5steg/config.ini. I suggest copying the provided example_config.ini with this command:

mkdir -p ~/.config/r5steg && cp example_config.ini ~/.config/r5steg/config.ini

More options are going to be added in the future: choosing binary (or other bases) or changing the zero-width characters in the config file are some examples from the top of my head!

Requirements

Python 3 (3.10.8 was used but should work with any)
pyperclip for auto copy-to-clipboard.
readline for input usability.
binascii for ASCII character support when encoding.
pycryptodome for encryption.
scrypt for key derivation.
gettext for the translations.
configparser for configuration files.
pathlib for better path-handling.

How does it work?

First of all, the message is encrypted:

AES in GCM mode:

The key is derived using the password and salt
The IV or nonce is randomized on each encryption and stored alongside the cipher text

Using the key and the initial vector, the plain text becomes cipher text. The salt is not transferred with the ciphertext, so it has to be a fixed value (I used random bytes). That's why, for optimal security, it should be changed and stored safely, because it has to remain the same value encrypting and decrypting.

To change the salt:

Find the salt variable at the beginning of the code:

salt = b'\xdc\xebh\x132\x7f\x8cD\xb1U\x1bI\xfa\x1d/i'

Replace its value with 16 different random bytes (e.g., using urandom function):

python3
>>> import os
>>> os.urandom(16)
b'\xfaFp6\x0e[\x9e\x9dKM\x80^O\x99\x92\xf9'

After the encryption, the message looks like this: f6989326b5198f881e634da623f1af5e2a632540.
The first 32 hex. characters represent the initial vector used, the rest represent the ciphertext, which weights the same as the secret message. This hex code is later hidden using the following zero width unicode characters:

Characters used:

Unicode code point	UTF-8 (in literal)	Name	hex to replace
U+2060	\xe2\x81\xa0	WORD JOINER	0
U+200B	\xe2\x80\x8b	ZERO WIDTH SPACE	1
U+200D	\xe2\x80\x8d	ZERO WIDTH JOINER	2
U+200E	\xe2\x80\x8e	LEFT-TO-RIGHT MARK	3
U+200F	\xe2\x80\x8f	RIGHT-TO-LEFT MARK	4
U+200C	\xe2\x80\x8c	ZERO WIDTH NON-JOINER	5
U+2061	\xe2\x81\xa1	FUNCTION APPLICATION	6
U+180E	\xe1\xa0\x8e	MONGOLIAN VOWEL SEPARATOR	7
U+202A	\xe2\x80\xaa	LEFT-TO-RIGHT EMBEDDING	8
U+202C	\xe2\x80\xac	POP DIRECTIONAL FORMATTING	9
U+202D	\xe2\x80\xad	LEFT-TO-RIGHT OVERRIDE	a
U+2062	\xe2\x81\xa2	INVISIBLE TIMES	b
U+2063	\xe2\x81\xa3	INVISIBLE SEPARATOR	c
U+2064	\xe2\x81\xa4	INVISIBLE PLUS	d
U+2065	\xe2\x81\xa5	Undefined	e
U+2066	\xe2\x81\xa6	LEFT-TO-RIGHT ISOLATE	f
U+FEFF	\xef\xbb\xbf	ZERO WIDTH NO-BREAK SPACE	[*]for wrapping

The last one in the table, is the wrapper character, it's added at the beginning and at the end of the current hidden hex code.

Once the steganography is completed, the invisible characters are inserted in between the plain text and everything is copied to the clipboard.

The message can now be transferred securely without anyone to notice and, even if they notice, it still cannot be decrypted without the password and salt!

For the decryption:

The reversed process is applied, with the difference that it manages multiple messages at once, if they exist. However, take in mind the same password and salt will be used for every message. In case of failure the program will prompt the error for every message individually.

Feedback

I'm up to any kind of feedback, questions, feature requests, etc.
Just write an email!