Velody 2—Resilient High-Capacity MIDI Steganography for Organ and Harpsichord Music

Eric Järpe,Mattias Weckstén

doi:10.3390/app11010039

Abstract

A new method for musical steganography for the MIDI format is presented. The MIDI standard is a user-friendly music technology protocol that is frequently deployed by composers of different levels of ambition. There is to the author’s knowledge no fully implemented and rigorously specified, publicly available method for MIDI steganography. The goal of this study, however, is to investigate how a novel MIDI steganography algorithm can be implemented by manipulation of the velocity attribute subject to restrictions of capacity and security. Many of today’s MIDI steganography methods—less rigorously described in the literature—fail to be resilient to steganalysis. Traces (such as artefacts in the MIDI code which would not occur by the mere generation of MIDI music: MIDI file size inflation, radical changes in mean absolute error or peak signal-to-noise ratio of certain kinds of MIDI events or even audible effects in the stego MIDI file) that could catch the eye of a scrutinizing steganalyst are side-effects of many current methods described in the literature. This steganalysis resilience is an imperative property of the steganography method. However, by restricting the carrier MIDI files to classical organ and harpsichord pieces, the problem of velocities following the mood of the music can be avoided. The proposed method, called Velody 2, is found to be on par with or better than the cutting edge alternative methods regarding capacity and inflation while still possessing a better resilience against steganalysis. An audibility test was conducted to check that there are no signs of audible traces in the stego MIDI files.

Highlights

Steganography provides means for hiding information, not just making it intelligible by encrypting it
The method purposed in this paper is to develop a balanced picture of what aspects are more important in MIDI steganography and put the suggested method for MIDI steganography, Velody 2, into its scientific context among alternative methods
The results are divided into those regarding security aspects, mainly steganalysis resilience aspects such as whether there are no audible revealing footprints of the steganography and other changes which may catch the attention of an alert steganalyst, and capacity aspects, such as embedding capacity, the number of bits per event and file-size change rate, following the definitions by Liu and Wu [7]

Summary

Introduction

Steganography provides means for hiding information, not just making it intelligible by encrypting it. In effect, adding an encryption step can greatly improve security aspects of the message exchange—the content of the communication is secret but even the very existence that any kind of communication took place is unknown. This is an additional property that can be crucial in some circumstances where the occurrence of encrypted messages can draw attention from the authorities. Since the percentage of users of steganography is unknown to a much larger extent than is the case for e.g., cryptography, it is harder to motivate its relevance [2] This is the reason why there are few reports on the numbers of use of such methods. This does not mean that methods of steganography are not used

Methods

Results

Conclusion