Module stego 

Steganographic encoding and decoding pipelines.

This module provides two embedding modes:

• Ghost (ghost_encode / ghost_decode): Stealth mode using J-UNIWARD cost function and Syndrome-Trellis Coding (STC) to minimize statistical detectability. Best for images that will not be recompressed.

• Armor (armor_encode / armor_decode): Robustness mode using STDM (Spread Transform Dither Modulation) with Reed-Solomon error correction to survive JPEG recompression. Trades capacity for survivability.

Both modes share the same payload frame format, encryption (AES-256-GCM-SIV), and key derivation (Argon2id two-tier). The smart_decode function auto-detects which mode was used.

Re-exports

pub use error::StegoError;

pub use armor::pipeline::armor_encode;

pub use armor::pipeline::armor_encode_with_quality;

pub use armor::pipeline::armor_decode;

pub use armor::pipeline::DecodeQuality;

pub use armor::pipeline::ArmorCapacityInfo;

pub use armor::pipeline::armor_capacity_info;

pub use armor::capacity::estimate_armor_capacity as armor_capacity;

pub use payload::PayloadData;

pub use payload::FileEntry;

pub use payload::compressed_payload_size;

Modules

armor

Armor mode: robust steganography resistant to JPEG recompression.

capacity

Ghost mode capacity estimation.

cost

Embedding cost functions for steganographic coding.

crypto

Cryptographic primitives for payload encryption.

error

Error types for the steganography pipeline.

frame

Payload frame construction and parsing.

optimizer

Cover image preprocessing optimizer for steganographic embedding.

payload

Payload serialization, compression, and file embedding.

permute

Media-agnostic coefficient position permutation.

progress

Global decode progress tracking.

quality

Encode quality scoring: Stealth (Ghost) and Robustness (Armor).

shadow

Shadow messages: Y-channel direct LSB embedding + RS ECC (headerless brute-force).

shadow_layer

Media-agnostic shadow-layer primitives.

side_info

Side information for SI-UNIWARD (Side-Informed UNIWARD).

stc

Syndrome-Trellis Coding (STC) for minimal-distortion embedding.

Structs

EncodeQuality

Encode quality result returned alongside stego bytes.

OptimizerConfig

Configuration for the cover image optimizer.

ShadowLayer

Shadow layer descriptor for encoding.

Enums

OptimizerMode

Which optimization pipeline to run.

Constants

ARMOR_TARGET_DIMENSION

Target pixel dimension (longest side) for Armor/Fortress pre-resize. Images larger than this are downsampled by the frontend before encoding in Armor mode, so that the 8×8 block grid survives platform recompression (e.g. WhatsApp resizes to ~1600px on the longest side).

GHOST_DECODE_STEPS

Total number of progress steps reported by ghost_decode.

GHOST_ENCODE_STEPS

Total number of progress steps reported by Ghost encode.

GHOST_ENCODE_WITH_SHADOWS_STEPS

Progress steps for Ghost encode with shadows.

MAX_DIMENSION

Maximum pixel dimension (width or height) for encode. Images exceeding this are downsampled by the frontend before reaching Rust.

MAX_PIXELS

Maximum total pixel count for encode (width × height). 200 MP covers all current cameras including flagship 200 MP sensors. Memory-optimized: strip-based UNIWARD (~170 MB/strip), compact positions (8 bytes each), segmented STC Viterbi. Total ~1 GB for 200 MP.

MIN_ENCODE_DIMENSION

Minimum pixel dimension (width or height) for encode. Images below this are rejected with an error message.

Functions

estimate_shadow_capacity

Estimate shadow layer capacity for a JPEG image.

ghost_capacity

Estimate Ghost mode capacity (standard J-UNIWARD).

ghost_capacity_si

Estimate Ghost mode capacity with SI-UNIWARD (“Deep Cover”).

ghost_capacity_with_shadows

Estimate Ghost primary capacity accounting for shadow position overhead.

ghost_decode

Decode a payload from a stego JPEG using Ghost mode.

ghost_encode

Encode a text message into a cover JPEG using Ghost mode.

ghost_encode_si

Encode using Ghost mode with side information (SI-UNIWARD / “Deep Cover”).

ghost_encode_si_with_files

Encode with side information and file attachments.

ghost_encode_si_with_files_quality

Encode with SI-UNIWARD + files and return the encode quality score.

ghost_encode_si_with_quality

Encode with SI-UNIWARD and return the encode quality score.

ghost_encode_si_with_shadows

Encode with Ghost SI-UNIWARD plus shadow messages.

ghost_encode_si_with_shadows_quality

Encode with SI-UNIWARD + shadows and return the encode quality score.

ghost_encode_with_files

Encode a text message with file attachments into a cover JPEG using Ghost mode.

ghost_encode_with_files_quality

Encode with Ghost mode + files and return the encode quality score.

ghost_encode_with_quality

Encode with Ghost mode and return the encode quality score.

ghost_encode_with_shadows

Encode with Ghost mode plus shadow messages for plausible deniability.

ghost_encode_with_shadows_quality

Encode with Ghost mode + shadows and return the encode quality score.

ghost_shadow_decode

Decode a shadow message from a stego JPEG.

optimize_cover

Optimize raw RGB pixels for steganographic embedding.

shadow_capacity

Compute shadow capacity in plaintext bytes from Y nzAC count.

smart_decode

Unified decode: auto-detects Ghost or Armor mode from the embedded frame.

validate_encode_dimensions

Validate image dimensions for encoding.