An Approach for Message Hiding using Substitution Techniques and Audio Hiding in Steganography

A crypto system can be used to encrypt messages sent between two communicating parties so that an eavesdropper who overhears the encrypted messages will not be able to decode them. The paper mainly concentrates on the method in which the substitution technique of steganography can been used to hide data in a 24-bit bitmap file. Popular audio hiding techniques based on methods of steganography is also discussed here.

💡 Research Summary

The paper presents two complementary steganographic approaches: a substitution‑based method for embedding arbitrary secret data into 24‑bit bitmap (BMP) images, and audio hiding techniques that exploit the weaknesses of the human auditory system.

Image hiding (LSB substitution).
The cover medium is a 24‑bit BMP file. Each secret byte is split into three parts: the two most‑significant bits (bits 7‑6) are placed into the two least‑significant bits of the red channel, the next three bits (bits 5‑3) into the three LSBs of the green channel, and the remaining three bits (bits 2‑0) into the three LSBs of the blue channel. Thus one pixel carries one secret byte. To avoid clustering, the algorithm computes a fixed pixel spacing:

pixel_spacing = (cover_file_size – header_offset) /
                (sizeof(RGB) * secret_file_size)

and embeds data only at pixels separated by this interval. The secret file’s length and its original extension are stored in the BMP header, allowing the receiver to reconstruct the exact file after extraction.

Decryption reverses the process: it reads the length and extension from the header, creates an empty file with the same extension, then walks through the stego‑image using the same pixel spacing, extracts the LSBs (2 from red, 3 from green, 3 from blue), recombines them into a byte, and writes it to the output file.

The authors provide a complete C implementation, using simple bit‑masking (&, |) and shift operations (>>, <<). The code handles header parsing, pixel‑spacing calculation, and the actual embedding/extraction loops.

Audio hiding.
Two classic audio steganography schemes are described:

1. Phase coding. The original audio signal is transmitted first. A delayed version of the same signal is then transmitted with a subtle phase shift that encodes the secret data. The receiver, having both signals, computes the relative phase difference to retrieve the hidden bits. This method preserves the relative phase among segments, making the distortion imperceptible.

2. Echo hiding. An echo—an attenuated, delayed copy of the original signal—is added to the cover audio:

s(t) = f(t) + f(t – Δt)

where Δt is the echo delay that carries the hidden information. Extraction can be performed by correlation (detecting the null‑point where the original and echo cancel) or by XORing the original and delayed signals followed by a T‑flip‑flop to recover the binary data. The paper illustrates both approaches with block diagrams.

Discussion and limitations.
The authors argue that the choice of technique depends on application requirements such as robustness, payload capacity, and perceptibility. They note that cryptography can be layered on top of steganography but must not reveal the existence of hidden data. However, the paper lacks quantitative security analysis: no experiments are reported on resistance to statistical attacks (e.g., chi‑square, RS analysis) or on payload‑distortion trade‑offs (e.g., PSNR for images, SNR for audio). The audio section remains theoretical; no implementation code or experimental results are provided, and the applicability to modern compressed formats (MP3, AAC) is not addressed.

Contribution.
Despite these gaps, the paper offers a clear, beginner‑friendly description of LSB image steganography with a complete source code example, and it concisely surveys two fundamental audio hiding methods. It serves as an educational resource for readers new to steganography, illustrating how simple bit‑level manipulations can embed arbitrary files in images and how phase or echo manipulation can conceal data in audio signals.