deny-sh 1.0.0

Deniable encryption — AES-256 with plausible deniability via control files

deny-sh — Python SDK

Deniable encryption for Python. Same algorithm as the TypeScript reference implementation. Ciphertext is byte-for-byte compatible across SDKs.

Install

pip install deny-sh

Quick Start

from deny_sh import encrypt, decrypt, generate_deniable_control

# Encrypt a secret message
ciphertext, control = encrypt(b"seed phrase: abandon ability ...", "pw1", "pw2")

# Decrypt with the real control data
message = decrypt(ciphertext, "pw1", "pw2", control)
# b"seed phrase: abandon ability ..."

# Generate deniable control data — same ciphertext decrypts to a decoy
fake_control = generate_deniable_control(ciphertext, "pw1", "pw2", b"nothing here")
decoy = decrypt(ciphertext, "pw1", "pw2", fake_control)
# b"nothing here"

How It Works

1. Dual-password key derivation — SHA-256(pw1) || SHA-256(pw2) → scrypt → AES-256 key
2. XOR deniability layer — plaintext is XOR'd with control data before encryption
3. AES-256-CTR encryption — standard authenticated encryption
4. Length prefix inside encrypted zone — no metadata leaks the real message size

The control data is what makes it deniable. Different control data + same ciphertext + same passwords = different plaintext. Both the real and fake control data look like random bytes — there's no way to tell which is "real".

API

encrypt(plaintext, password1, password2, control_data=None)

Encrypt plaintext with dual passwords and optional control data.

• plaintext (bytes) — data to encrypt
• password1 (str) — first password
• password2 (str) — second password
• control_data (bytes | None) — control file data; auto-generated if None

Returns (ciphertext: bytes, control_data: bytes).

decrypt(ciphertext, password1, password2, control_data)

Decrypt ciphertext with dual passwords and control data.

Returns bytes — the decrypted plaintext.

generate_deniable_control(ciphertext, password1, password2, desired_plaintext)

Generate new control data that makes existing ciphertext decrypt to a different message.

Returns bytes — new control data.

generate_control_data(size)

Generate cryptographically secure random control data.

Returns bytes.

derive_key(password1, password2, salt)

Derive the AES-256 key from two passwords and a salt. Exposed for cross-implementation testing.

Returns bytes (32 bytes).

Algorithm Compatibility

The ciphertext format is identical across all deny-sh SDKs:

salt (32 bytes) | iv (16 bytes) | AES-256-CTR(key, payload XOR control_data)

Where payload = length_prefix (4 bytes LE) + plaintext.

KDF parameters: scrypt(N=16384, r=8, p=1, dklen=32).

A file encrypted with the Python SDK can be decrypted with the TypeScript SDK, and vice versa.

Dependencies

• pycryptodome — AES-256-CTR encryption
• hashlib (stdlib) — SHA-256 and scrypt KDF
• os (stdlib) — urandom for secure random bytes

License

AGPL-3.0. Commercial licenses available.