GB2262418A

GB2262418A - Data transmission

Info

Publication number: GB2262418A
Application number: GB9122056A
Authority: GB
Inventors: Jennifer Mallows
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-10-17
Filing date: 1991-10-17
Publication date: 1993-06-16
Also published as: GB9122056D0

Abstract

A secure facsimile transmission system separates the transmission protocol (3) from data to be transmitted, encrypts the data only by a key code algorithm (5) known only to the sender and authorised receiver and transmits the encrypted transmission protocol together with the encrypted data (6). Thus, the data is received intelligibly by only an authorised receiver, whilst an unauthorised one receives unintelligible data, but of a length and number of sheets in accordance with the information sent. Thus an 'innocent' wrong recipient does not have the expense and inconvenience of a large number of sheets being outputted, as might happen if the transmission protocol were encrypted also. <IMAGE>

Description

DATA TRANSMISSION This invention relates to data transmission and in particular it relates to the transmission of data by means facsimile machines (telecopiers).

Facsimile machines are now commonly used to transmit data in the form of written data or pictures across telephone lines. A facsimile provides a efficient and usually error free method of transmitting this data and has the advantage over, for instance, telex that pictoral data an he transmitted almost instantly between any two parts of the world.

Any facsimile machine can communicate with any other facsimile machine in the worold, provided the two are both connected to the telephone network.

This can create a problem if a first facsimile machine inadvertently contacts a wrong machine ie not the one the sender wished to transmit data to. At the present time, if a wrong recipient were selected, that recipient would receive the message to be transmitted. This canm create embarrasement if that message is not intended to be viewed by that recipient and can also create severe security problems.

According to the present invention there is provided apparatus for secure transmission of facsimile messages, comprising means, for encrypting data, to be transmitted by facsimile, before transmission and means for decrypting the received data at a remote facsimile machine In tis way, if a message is inadvertently directed to a wrong machine, that machine will not include thje appropiate decryption and the message will not be decrypted. Garbage will result.

Preferably, the encrypting apparatus comprises means to separate transmission protocol information from the data, means for encrypting the data only, and means for transmitting the transmission protocol together with the encrypted data. The receiving apparatus may include means for noting and responding to the transmission protocol and means for decrypting only the data portion of the message.

The transmission protocol is preferably transmitted unchanged, in its correct temporal phase with respect to the information to be transmitted.

If the transmission protocol is not separated from the data before encryption, then a receiving facsimile machine, which is not intended to receive the message, will have no idea about the relevant transmissio^. protocol. Thus, it will not be able to set up line feeds, page feeds and so on ani may, in attempting to output the message to its paper roll, feed out many sheets of paper, all of which contain meaningless garbage. This can be very wasteful of paper and unfair to the wrongful recipient who may, through no fault of his, be receiving the unauthorised message, albeit in an unreadable form.Separating of the transmission protocol from the data, and transmitting the transmission protocol in an unmodified form, enables any receiving machine to at least set up its transmissions in accordance with the protocol. Thus, although it would not be able to decrypt the data, which would still be meaningless garbage, the line feed and page feeds, etc would still remain. If one page of information were transmitted, then only one page would be printed out by an unauthorised receiving machine, that page having the correct line feeds but having data which was meaningless and Essentially, the key code is applied to the encrypted part of the message in a particular manner. The key code is, of course, required to be known by both the sender and receiver.

Embodiments of the present invention will be described, b way of example only, with reference to the accompanying drawings, in which: Figure 1 shows, schematically, a line of data transmitted by a facsimile machine; Figure 2 shows the signal of Figure 1 when modified by an apparatus; and Figure 3 shows an decryption apparatus.

Facsimile comunication is determined by means of a method of coding known as the Huffman code. This determines the manner in which signals are transmitted along telephone lines between two machines. An important element of the transmission is the transmission protocol whcih, firstly, defines the hand shaking protocol which enable each machine to tell what type the other machine is and enables each machine appropiate. Secondly, the transmission protocol includes data such as page feeds, lines feeds, and so on which instruct the scanners and paper feeding mechanisms of the receiving machine when to move onto a new line and/or page.Other integers are resent in the transmission protocol as will be known to those skilled in the art. Figure 1 shows shcematically the information included in one line of transmission. As shown, at the beginning of the line is relevant transmission protocol T which induces, a+ least, a line feed and may also include page feeds cc. Following this, the data is transmitted. The data is shown in simple digital form in this example, but in practice systems such a frequency shift keying frequency or amplitude modulation are used.The digital data is used to modulate a carrier a frequency in knows manner. The data is shown schematically in the figure by D.

Figure 2 shows the line, in its digital form, before modulating a carrier frequency, when modified by the present invention. It is seen that the transmission protocol T remains unchanged and that the same relative point of the cycie or line, but that the transmission data DT representing image itself, is changed.

Figure 3 shows one apparatus for a achieving the encryption. An image, which is shown as lines of script on a sheet of paper is scanned in conventional fashion by a digital scanner 2. The scanning may be done in real time, or lIne by line or page by page, or example, as desired. Th digitised information from the scanner is fed to a transmission protocol separator 3 which is arranged to separate out all the transmisson protocol data. This may be done using timing methods, delays, etc. The separated trarim ssion protocol data may then be stored or fed to a suitable delay means 4 whilst the data which remains is applied to a encrytion apparatus 5. There, it is suitably encrypted before being transmitted. Prior to transmission the transmission protocol is reapplied, in its correct position, by means of the delay function or timers on the store, for example, and the message is then transmitted over telephone lines 6 to a receiving machine.

At the receiving machine, which is provided with a decryption apparatus having the same code as the encryption apparatus, the transmission protocol data is first separated, the encrypted data is then decrypted, and the separated transmission protocol used to set up the receiving machines transmission protocol, from which the message can be received correctly and printed by the receiving machine.

If, by an error or by calculation, the message is received by an unauthorised machine, then this machine will still recognise the transmission protocol but will be able to make no sense oQ the data itself. Thus, if one page of data is transmitted then one page will be printed by the receiving machine although this page will be meaningless to the reaper. Similarly, to or more paghes will produce an equivalent number of received pages.

The encryption unit 5 may be arranged to include an encryption key, which is known only to the users of the respective sending and receiving facsimile machines. In one embodiment, this key can be up to fifty two characters long. Encryption methods, per se, are known in the art, but in one method, each character may be stoired in turn in a look up table and each character in turn acts upon each received binary digit of the data. Thus the first digit in the message 1, is acted upon by the first digit of the keycode. The operation may be an addition, subtraction, multiplication or any other suitable operater in one particular embodiment. It is preferable that only unique result is the outcome of each operation, to avoid ambiguity t the eceiving end.After the first key code character has actet upon the first binary digit, and the second character has acted upon the second digit, if a t character cone is used, for example, then the third digit will eb acted upon by first character again ant so on. It will be appreciated that many other encryption methods could be used.

Each facsimile machine in a network would preferably be provided with both encryption and decryption apparatus. Authorised facsimile machines will of course be provided with the same key code.

For additional security, this key code may be changed periodically, such as daily or weekly. This may be done in an agreed, planned, manner which may be pseudo random or may be agreed periodically as appropriate. Different levels of authorisation may be included in the system, so that each machine includes a plurality of different key codes. Thus, a first machine, which could be a master machine, may be allowed to communicate with all other machines by using their own individual key code. Other machines may only be allowed to communicate with the master itself and not with th each other or in certain redefined sub networks. Alternatively, only certain types of infor:nation may be allowed to be received by certain machines, the transmission protocol determining whether a receiving machine is authorised to receive any particular message.

For some types of encryption/decryption systems, the key codes at the receiver and sender may not necessarily be identical, but could complementary so that, for example, one is the inverse of the other.

Claims

1. Apparatus for secure transmission of facsimile messages, comprising means for encrypting data, to be transmitted by facsimile, before transmission and means for decrypting the received data at a remote facsimile machine.

2. Apparatus as claimed in Claim 1, wherein the encrypting apparatus comprises means to separate transmission protocol information from the data, means for encrypting the data only, and means for transmitting the transmission protocol together with the encrypted data.

3. Apparatus as claimed in Claim 2, wherein the receiving apparatus includes means for noting and responding to the transmission protocol and means for decrypting only the data portion of the message.

4. Apparatus as claimed in Claim 2 or Claim 3, wherein the transmission protocol is transmitted unchanged, in its correct temporal phase with respect to the information to be transmitted.

5. Apparatus as claimed in any one of Claims 2 to 4, wherein line feeds and/or page feeds are transmitted unchanged.

6. Apparatus as claimed in any of Claims 2 to 5, wherein the means for separating and/or reinstating the transmission protocol comprises timing means.

7. Apparatus as claimed in any of Claims 2 to 5, wherein the means for separating and/or reinstating the transmission protocol comprises a delay means.

8. Apparatus as claimed in any one the preceding claims, wherein the encryption and decryption means are adapted to act upon data in accordance with a key code known at both the transmitting and receiving ends.

9. Apparatus as claimed in Claim 6, wherein the key code is variable.

10. Apparatus for transmitting facsimile messages, including means to separate the transmission protocol from the data, encryption means adapted to encrypt data only, by a specific algorithm such that the data when received is only intelligible if acted upon by a specific identical or complementary algorithm, and means for transmitting the transmission protocol and the encrypted data.

11. Apparatus for receiving facsimile messages from a remote apparatus as claimed in Claim 10, which receiving apparatus comprises means for receiving the transmission protocol and the encrypted data, means for decrypting the encrypted data using an identical or complementary algorithm to that of the transmitter, and means for outputting or displaying the data.

12. Facsimile apparatus substantially as hereinbefore described with reference to, and as illustrated by, the accompanying drawings.