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Letter Shift Steganography

Hide secret messages by subtly shifting letters in cover text images

📄 Letter Shift Image Steganography

This method hides data by shifting letters in cover text images by 1 pixel in one of eight directions, encoding 3 bits per character. The output is a rectangular PNG image that looks like normal text but contains hidden information via pixel-level letter shifts.

🔓 Extract Hidden Message from Image

Upload a PNG image produced by the letter shift steganography encoder to reveal the hidden message.

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About Letter Shift Steganography

How It Works

This technique hides secret data by shifting each letter in the cover text image by 1 pixel in one of eight possible directions. Each direction encodes 3 bits (one of 8 values), allowing data to be embedded at a rate of 3 bits per cover character.

The resulting image looks like a normal text rectangle, but the subtle pixel shifts encode the secret message.

Encoding Process

  1. Convert the secret message to binary (8 bits per character).
  2. Split the binary into chunks of 3 bits.
  3. Map each 3-bit chunk to an offset direction (one of eight 1-pixel shifts).
  4. Replace each cover text letter’s position with the corresponding offset letter image.
  5. Generate the output PNG image containing the stego text.

Decoding Process

The decoder extracts each letter tile from the PNG image, computes a hash for each tile, and matches it to a precomputed hash table to recover the offset direction, then converts offsets back to 3-bit chunks, reconstructing the secret message in binary and finally ASCII text.

Requirements & Limitations

  • PNG format: Input and output images must be lossless PNGs to preserve exact pixel shifts.
  • Cover text: Limited to ASCII characters with max 50 characters per line.
  • Capacity: 3 bits encoded per cover text letter.
  • Letter images: Must be pre-generated using the setup script.
  • Hashing: Exact hash or perceptual hash matching used to detect shifts.

Advantages

  • Subtle and hard to detect by casual observation.
  • Maintains readable and visually consistent text images.
  • Robust to minor pixel variations if perceptual hashes are used.

Security Considerations

  • Not encryption: Only hides data existence, doesn't protect data confidentiality.
  • Requires careful handling: Re-saving or compressing the PNG can break hidden data.
  • Depends on exact images: The letter images used for encoding must match those for decoding.
  • Detectability: Statistical analysis can potentially reveal patterns.

Use Cases

  • Covert communication by hiding data in readable text images.
  • Artistic projects where text images conceal secret information.
  • Educational tools to learn about steganography and image hashing.
  • Data obfuscation in digital documents.