Application for a Secure Fax System

Abstract

Fax is an important means to transfer official documents even today because of its features like instant acknowledgement and legal recognition; giving it an edge over Internet facilities like e-mail. Some problems still persist today. One is that sending text only data by fax is expensive.

This project document describes a system for compression and encryption of fax documents and error recovery over the channel. The document to be faxed, which may contain text, pictures, charts, and other graphic images, is first converted into a portable bitmap. Bitmap compression thus used reduces the size of the document. This portable bitmap is further compressed by applying JBIG compression technique which is highly suitable for fax documents. The compressed file is then encrypted using the fast Salsa20 routine using the private key. The encrypted file is then converted into portable grayscale format for printing. The file is now sent via the fax machine as any other normal document, but without disclosing its contents to anyone other than the intended recipient. The fax machine at the receiving end is able to recover the errors introduced during transmission, using an error correcting code (specifically LDPC), ensuring correct reception of file. The received data is decoded, producing the encrypted file which is unintelligible. This is then converted to portable grayscale format, printed and scanned and given to decryption device, which performs decryption using the private key. Finally, decompression is performed and the original document is recovered as a portable bitmap. This document is now displayed or converted to any suitable format for printing.

This project solves the problem of achieving secure, loss less, and efficient transmission of data by facsimile (where a direct computer network is not available).