3.7 KiB
Steganographic
2016 05 12:
Now pads the remaining pixels with random data. Previously, the fact that the secret
file resided in only as many pixels as it needed meant there was a sudden decrease in
visual noise when the secret ended. Now there is noise throughout.
Your secret file should resemble random noise for this to be effective. Thus
encryption is recommended.
This does not change decoding, because the decoder only reads as many bytes as
needed.
2016 01 15:
Now supports variable "bitness", the number of bits per color channel to overwrite.
Previously, bitness was always 1, to maximize transparency.
Now, bitness can be 1-8 to favor transparency or information density.
Let's be honest, this was really just an excuse to make big Terminal headers out of hashmarks.
Requires pip install pillow
Hide files in images!
For each color channel of each pixel in an Image, modify the least significant bit to represent a bit of the Secret file.
This changes the RGB value of the pixel by a usually-imperceptible amount.
The first 32 bits (10.66 pixels) will be used to store the length of the Secret content in big endian.
Then, the Secret's extension is stored. A null byte indicates the end of the extension. This section is of variable length.
A file with no extension requires only that null byte. A file with an extension requires 1 additional byte per character.
Smallest image possible = 16 pixels with 48 bit secret: 32 for header; 8 for null extension; 8 for data.
Each Image pixel holds 3 Secret bits, so the Image must have at least ((secretbytes * (8 / 3)) + 14) pixels.
An Image can hold ((3 * (pixels - 14)) / 8) Secret bytes.
Usage:
> steganographic.py encode imagefilename.png secretfilename.ext bitness
> steganographic.py decode lacedimagename.png bitness
where bitness defaults to 1 in both cases.
Reference table for files with NO EXTENSION and bitness of 1. For each extension character, subtract 1 byte from secret size
pixels | example dimensions | Secret file size
100 | 10 x 10 | 32 bytes
400 | 20 x 20 | 144 bytes
2,500 | 50 x 50 | 932 bytes
10,000 | 100 x 100 | 3,744 bytes
40,000 | 200 x 200 | 14,994 bytes
25,000 | 500 x 500 | 93,744 bytes (91 kb)
1,000,000 | 1,000 x 1,000 | 374,994 bytes (366 kb)
4,000,000 | 2,000 x 2,000 | 1,499,994 bytes (1.43 mb)
25,000,000 | 5,000 x 5,000 | 9,374,994 bytes (8.94 mb)
100,000,000 | 10,000 x 10,000 | 37,499,994 bytes (35.7 mb)
pixels | example dimensions | Secret file size
100 | 10 x 10 | 32 bytes
697 | 25 x 28 (700) | 256 bytes
2,745 | 50 x 55 (2,750) | 1,024 bytes (1 kb)
21,860 | 142 x 154 (21,868) | 8,192 bytes (8 kb)
87,396 | 230 x 380 (87,400) | 32,768 bytes (32 kb)
349,540 | 463 x 755 (349,565) | 131,072 bytes (128 kb)
1,398,116 | 1146 x 1120 (1,398,120) | 524,288 bytes (512 kb)
2,796,217 | 1621 x 1725 (2,796,225) | 1,048,576 bytes (1 mb)
11,184,825 | 3500 x 3200 (11,200,000) | 4,194,304 bytes (4 mb)
44,739,257 | 6700 x 6700 (44,890,000) | 16,777,216 bytes (16 mb)
89,478,500 | 9500 x 9500 (90,250,000) | 33,554,432 bytes (32 mb)
