openssl-encrypt has non-cryptographic PRNG used for steganography pixel selection

Summary

The generate_pseudorandom_sequence() function in openssl_encrypt/plugins/steganography/core/utils.py at lines 89-91 uses Python's random module (Mersenne Twister) for steganographic pixel/sample selection.

Affected Code

random.seed(seed)
sequence = random.sample(range(max_value), min(length, max_value))
return sequence

Additionally, the steganography password is stored as a plain Python string (not SecureBytes) and only 8 bytes (64 bits) of the SHA-256 hash are used for the seed, reducing effective security to 64 bits.

Impact

The Mersenne Twister's state can be recovered from approximately 624 outputs. An attacker who knows or guesses the password can predict the PRNG sequence and determine exactly which pixels contain hidden data, potentially extracting the hidden data without the password.

Recommended Fix

• Use HMAC-DRBG or secrets module for cryptographically secure pixel selection
• Use full 32-byte SHA-256 output as seed material
• Store the password in SecureBytes instead of a plain string

Fix

Fixed in commit 09e96e0 on branch releases/1.4.x — replaced random.seed(hash(password)) with HMAC-SHA256 based CSPRNG (Fisher-Yates shuffle) and numpy Generator with HMAC-derived seeds across all steganography format modules.