How Gifshuffle Works
4 days ago
- #data-encoding
- #GIF
- #steganography
- Steganography involves hiding messages in mediums like digital audio, images, or pseudo-English text.
- Effective steganography uses redundant data (e.g., raw audio/images) but struggles with compressed formats like JPEG/MPEG.
- gifshuffle conceals messages by altering the color order in GIF color maps, which doesn't affect image display.
- The program has two modes: message concealment and extraction, reversing the process for retrieval.
- gifshuffle uses Huffman compression optimized for English text, achieving 25-40% compression for short messages.
- For longer or non-text messages, external compression is recommended for better ratios.
- Built-in encryption uses ICE (64-bit block cipher) in 1-bit CFB mode for security, adjusting key length based on password.
- CFB mode uses an initialization vector (IV) derived from the key, encrypting bits via XOR and shifting.
- Card ordering analogy: n cards can store log2(n!) bits; GIF color maps (up to 256 entries) store ~1683 bits.
- Message extraction reverses concealment: color map order constructs a binary number, decrypted/uncompressed to output.