algos

Four short pages that explain what rsteg actually does to your bytes. Each one has an inline visualization — SVG or a tiny interactive form — so you can poke at the algorithm instead of just reading about it. Start with LSB linear if this is your first time with steganography; it's the baseline everything else builds on.

scheme BLSL / WLSL / PLSL

LSB linear

Sequential bit-flipping, the baseline. Sample bytes are walked in storage order; the n-th payload bit lands in the LSB of the n-th sample. Fast, simple, trivially detectable on a uniform cover.

scheme BLSP / WLSP / PLSP

LSB permuted

Same bit-flipping, but the walk order is a passphrase-seeded Fisher–Yates shuffle. Scatters the payload across the carrier so the first N samples no longer light up on chi-square.

framing — 32 bytes

PayloadHeader

Every rsteg stego file starts with a fixed 32-byte RSTG header: magic, version, flags, scheme fourcc, density, body length, CRC. The whole struct is bound into the AEAD tag when the payload is encrypted.

crypto — XCA1 / XChaCha20-Poly1305

AEAD envelope

Passphrase → Argon2id(64 MiB, t=3) → 32-byte key → XChaCha20-Poly1305 seal(plaintext, nonce, AAD=header). Tamper any header bit and the tag fails. Wrong passphrase looks identical to tampering, by design.

When to use which

All four schemes work on all three carrier formats rsteg supports (BMP, WAV, PNG); the fourcc's first letter selects the format. This table skips the format axis and compares just the walk-order / secrecy axis.

scheme	fourcc	walk order	detectable on naive steganalysis?	when to use
LSB linear	?LSL	sample 0, 1, 2, 3…	yes — chi-square on first N samples spikes as soon as N exceeds the payload length	teaching, non-adversarial transport, maximum speed
LSB permuted	?LSP	Fisher–Yates shuffle of `0..N` seeded by Argon2id(passphrase) low 64 bits	no — payload bits are spread uniformly, so no contiguous block is statistically distinguishable	default whenever a passphrase is supplied; pairs naturally with the AEAD envelope

The permuted seed is not the secret — the AEAD ciphertext is. The permutation exists as defense-in-depth: without it, detection of "something is hidden here" is trivial even when decryption is infeasible. The AEAD page explains why these are separate concerns.