Integrity of audio signals on a solid state recorder

The department Philips Key Modules (PKM), which is part of Philips Sound and Vision, builds the key modules of audio and video devices. One of the current projects is the Solid State Recorder (SSR). This is a device for storing audio on flash cards. One of the advantages of flash cards for the storage and reproduction of audio is the the absence of moving parts. This will extend the lifetime of such machines. MPEG is used for coding and decoding of the audio signal.

On uncompressed audio, it can be investigated if the data is manipulated after the original recording. This is done by analyzing the extreme high and low frequencies, which are not audible for the human ear. With MPEG data reduction, these frequencies are filtered out, which makes it impossible to verify the integrity of the data, using these classical methods.

This project is a study for the possibility of using cryptography for securing the integrity of the data on a temperresistant SSR. First a protocol is designed for signing the MPEG data with a digital signature algorithm. This protocol is implemented in assembly language on the Digital Signal Processor (a chip which is specialized for huge calculations) of the SSR. This code is highly optimized to meet the speed requirements.

Furthermore a computer program is written for the verification of the data. This DOS program will analyze the data and verify the signature. According to it's findings, it will generate a conclusion. Because of the modular structure, the program can easily be incorporated in a general SSR control program.

The project is done as a final project for the two year designers course "Mathematics for Industry" at the Eindhoven University of Technology (TUE). It was performed at Philips Natlab and PKM and supervised by ir. Peter Lenoir (Philips Natlab), ir. Guus van Eijck (PKM), and Henk van Tilborg (TUE).

A postscript version of the report can be downloaded from here (440 KB).
Jasper Cramwinckel <>