syndrome-trellis-codes

Implementation of Syndrome-Trellis Codes, a widely used embedding method in adaptive steganography.
Proposed in Minimizing Additive Distortion in Steganography using Syndrome-Trellis Codes.

It's recommended to compile with the following CPU instructions enabled:

RUSTFLAGS="-C target-feature=+avx2,+fma,+bmi1"

Enabling these instructions has shown a significant performance increase.

Examples

use syndrome_trellis_codes::{HHat, embed, extract};

// `x` is usually an array of the least significant bits of image pixels
let x = [1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1];
// Cost map `rho`: how "expensive" it is to modify each bit
// High costs (like 10.0) mark "wet" bits that shouldn't be touched
// They are usually called "wet pixels" because image steganography is the most common
let rho = [
    0.2, 10.0, 10.0, 0.5, 10.0, 10.0, 0.2, 0.2, 0.2, 5.0, 0.2, 5.0, 5.0, 0.2, 5.0,
];
// Our secret message
let m = [1, 1, 0];

let h_hat = HHat::from_dims(7, 5).unwrap();

let (y, distortion) = embed(&x, &rho, &m, h_hat).unwrap();
// y = [1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1]
//                                    ^ this bit was changed
// distortion = 0.2

let m_extracted = extract(&y, h_hat);
assert_eq!(m.to_vec(), m_extracted);