stegcrypt

Quick Start

Install via jcli

jcli install stegcrypt

Single carrier

# Hide a file inside one PNG
stegcrypt embed --carrier photo.png --secret notes.txt --out stego.png

# Recover it
stegcrypt extract --in stego.png --out notes.txt

K-of-N threshold split

# Distribute a file across 5 carriers; any 3 of them can reconstruct
stegcrypt embed-split --shares 5 --threshold 3 \
    --carrier a.png --carrier b.png --carrier c.png \
    --carrier d.png --carrier e.png \
    --secret vault.tar.gz --out-dir shares

# Recipient with any 3 of the 5 stego files:
stegcrypt gather --out vault.tar.gz shares/share-00.png shares/share-02.png shares/share-04.png

Defensive use — statistical detection

# Run chi-square + sample-pair tests on a suspect file
stegcrypt detect --in suspect.png

What it does

stegcrypt hides a secret inside one or more carrier files. Encryption is authenticated (any tampering surfaces as a clean failure, not garbage output), and the K-of-N threshold mode means an attacker needs both the password and at least K of N carriers to recover anything.

• Carriers: PNG / BMP (LSB in RGBA pixels) and 16-bit PCM WAV (LSB in audio samples). JPEG is deferred to v1.1 (DCT embedding is a separate engine).
• Cipher: AES-256-GCM (default; hardware-accelerated on modern CPUs) or ChaCha20-Poly1305 via --cipher chacha. Both are AEAD — authenticated and tamper-evident.
• Key derivation: Argon2id with 64 MiB memory cost. Memory-hard, GPU-resistant. The OWASP-recommended KDF for password-protected data.
• Position shuffle: a password-derived ChaCha20 RNG picks non-sequential LSB target positions. Naive "scan the LSB plane" tools find nothing.
• K-of-N split: Shamir's Secret Sharing on the data key (information-theoretically secure) + Reed-Solomon erasure-coded ciphertext. Lose up to N-K carriers and still recover. Each share is itself password-wrapped.
• Self-describing header: the recipient needs only the password — salt, nonce, and KDF parameters travel inside the carrier.
• Detection module: chi-square + sample-pair statistical tests for triage. NOT a guaranteed detector (modern stego evades both), but catches naive LSB embedding.

Subcommands

Security notes

• Passwords are read from --password-file, STEGCRYPT_PASSWORD, or an interactive prompt — never from the command line, because the ps table and shell history both leak literal arguments.
• The Shamir share each carrier holds is itself encrypted under a password-derived key, so capturing K stego files without the password reveals nothing.
• Reed-Solomon parity provides resilience, not confidentiality. The AEAD layer above it is what protects the secret.
• Default settings (LSB 1 bit, shuffle on) produce images that survive naive LSB-plane visualisation and pass chi-square at default thresholds. Higher --lsb-bits trades visibility for capacity.
• Use independent carriers for threshold splits (different photos, not N copies of the same one). Otherwise a steganalyst comparing them detects the structure.
• The chi-square / sample-pair detectors are intentionally conservative — they catch naive LSB embedding but won't see modern stego or stegcrypt's own shuffled output at low utilisation. They are a triage signal, not a verdict.