A DATA ENCRYPTION SYSTEM FOR INTERNET COMMUNICATION

Abstract: Two versions of a variable word length encryption method are discussed adapted for providing the means for long-term confidential transmission of printed characters, pictures, and voice dialogues over the telephone lines or the internet.

Description: A Data Encryption System for Internet Communication There is a general concensus that serious use of the internet potential for the needs of Commerce and Industry requires a 100% long-term effective system for protecting privacy of the interchanges. Several aspects apart from privacy would be important in making a choice of the technique. It would have to be suitable for all digital transmissions, irrespective of the coding employed. The same encryption system should be work- kable for lettered, audible or visual messages. Also, the tine of processing the data should preferably not add more than 80% to the time for transmitting the same data in the clear form. Furthermore, no time should be spent on looking up directories for keys or other procedure rules. The objectives of this patent application follow from what has just been said: o to create for owners of PC's certain supplementary components easily added with the result of replacing registered and high-priority mail transmissions by a less expensive and faster track. protected against breach of confidentiality. o to reduce the need for personal trustworthiness and to replace it by trustworthiness of the provisions of the system. o While the idea of "trusted third parties" is appropriate where Government interests are directly involved, the many contingencies that arise when applied to all communications would strain an already overburdened legal system. In contradistinction, the here proposed method would save trustworthy server stations from slipping into arbitrariness, favoritism and self-serving bureaucracy. At the same time it would open a clear route for observers at Goven- ment level to use their authority of sampling messages in the interest of crime prevention .and to do so even for longer periods if and when properly authorized and reasoned for in exposes open for public inspection within six years. This paper will outline the techn ica l p l atf orm for accomplishing the above sketched objectives, with the further provision that its service be available to everyone at a relatively low extra cost over and above the cost of using internet comπunication. The said 'technical platform' constitutes a system resting on two main pillars, namely (a) an algorithm which generates variable wordlength data scrambling (b) a hierarchic system of key distribution (e.g. a regulated method for ageing and then eliminating keys) In place of a lengthy explanation, we begin by referring to Figure 4 which illustrates the idea of variable word length text transformation. It will be clear that computerised scanning of the encrypted text will in this case have no prospect of providing any clue. Figure 5 shows a functional block diagram of the encryption/decryption hardware. In early implementations, a 16 bit shift register was used (block SR) with simple output to input connection. The encrypted output resulting from such an arrangement showed a certain periodicity if the clear text consisted of the binary representation of a single letter, for example the letter 'a' in unchanging repetition. This revealed the potential for a certain weakness of the method unless steps are taken to overcome this possible point of attack for a hacker. In present designs we use a 31 bit shift register as the basis for a pseudo random data generator wherein the periodicity is vastly (pattern recurrance only once every 2,14 billion different combinations) reduced. In addition, further measures .are t^Jcen to begin each message with an undefined length of meaningless text. That text is not delivered in clear by the algorithm. For the user it constitutes simply a few seconds waiting time added to the setting up time. One method of achieving this will be explained in conjunction with Figures 3,4 and 8. Returning to the description of Fig. 5, paralell outputs from the shift register .are connected to various logic elements under the heading U3GIC CONTROL. This comprises for example, a progr-ammable counter, several flip flops and bistables .and various gates. Some of the logic control elements are also exposed to inputs of the logic levels of the real data, both outgoing or incoming. These data are applied with a delay of one full clock pulse duration. This is done in the squares named 'bit delay' . The encrypted text on line 1 2 is derived from an OR gate into which alternately pass bit elements from the real data and from the Random data generator RDG, respectively a, by real data modified,output from said generator. Encrypted data received are descrambled by action of the Logic Control group, in a single AND gate. Figures 6 and 7 explain how it is possible to have 8 - 10 simultaneously valid keys and how they .are weighted in a number ageing process. Figure 8 shows a functional block diagram of an LSI chip such as would be capable of carrying out data encryption at a high clock rate suitable for any communication network and would provide added security over and .above the basic scheme of Figure 5. Detailed Discussion of the Drawings FIG. 1 shows two personal computers or communication work stations using a fixed secret key, or using a program permitting one of the stations to utilize the encryption key of the other. FIG. 2 illustrates a situation where the official key employed within an organisation is not normally used for the actual encryption/decryption of data. If for example station A represents the word processor in a secretarial pool of one company, and station B the processor office in another company. And the message sender has a small computer in his office p wishing to send a con ¬ fidential message to a particular person having a computer B , then the procedure would be as follows: (a) The secretary at A will type into the word processor A a statement from Mr. A^ in clear language and put it on disk. (b) Next, the secretary agrees with A_ to display on the window of A_ the text as written for approval or amendments. (c) When approved, A^ will contact the secretary at A over the phone to prepare internet connection with the comπunication of office at B. (d) When communication is established, the secretary rings Ap to report 'ready'. (e) The executive at Ap now types his private password ppw into his keyboard thereby transmitting it to work station A where the instruction code tells the conputer to deduct (or add) the password number, or a multiple thereof, from the encryption key of the organisation. (f) Once this is done a green light informs the secretary that the clear text derived from the disk is to be moved through the encryption algorithm and out into the internet. (g) The encrypted message is taken on disk at conputer unit B. It cannot be read by staff. (h) When executive B returns to his office, he will find a light signal indicating that he lias a personal message. .Accordingly, he will enter the agreed psss word ppw on his conputer keyboard together with the instruction of deducting it from the common general key. After that, the decrypted mes.sage will appear on the screen B . P It would be technically possible to provide the Managing Chief in each company with an automatic printout of all per.sonal messages, to enforce the sharing of confidential information. Since the encryption system here expounded is not primarily determined by mathematical conversions, and therefore all numbers are equally suitable, it would suffice if the executives concerned are told that they π st have a six-digit ppw. Knoledge of agreed pas-swords may therefore be limited to the parties themselves. FIG. 3 shows the structure of a Service Center SC for almost fully automatic connection service to clients wishing to send messages required to remain confidential. Fig.3 shows again a workstation A in one locality and another workstation in a remote locality but using the same equipment. The central server station consists of two sections (A & B) . These sections comprise channel switching section sw, switch control sections S A or LS β ? Two algorithmic sections virtually identically with those shown for exam- ple in Fig. 8; In each section is also a key register for storing a key K n and a random text data holding register D . Belcw is a corrputing section COMP, and below that a memory of past transactions, M. The computer unit COMP has a preferably direct link with a National Key Generator Center NKGC. Where a direct link is not available, a switched connection with NKGC will do because no clear data are passed through this link, (see also Fig. 6) The process prior to A sending a confidential message to B, can be reported in ten steps. (1) station A dials the local Service Center (SC) and immediately thereafter dials also the number of the desired receipient B. (2) Station A gets indication that connection is made (3) prompted by (2) , section A receives from station A the address code for identifying the key held at present by station A. (see address reg., fig.7) (4) section B of SC calls station B. (5) Station B responds by sending its address in clear (6) using the two address numbers from A and B, the SIlooks up from.a memory table similar to that of Fig. 7 the at the time valid secret key numbers. Section A of SC extracts the key nr. for station A, inserts it into the algorithm (algo) thereby encrypting K_by K_and sends it to station A for verification. - Section B of SC proceeds likewise with station B. (the table is stored in section COMP, and is periodically updated from the national key generator centre, see Fig. 6) . (7) A and B receive the encrypted keys K^' and 1C* respectively, decrypt them with their respective K, and K_ keys, and if any station cannot verify it sends to the respective section of SC a repeat request. If this also fails . a 'failed' signal in clear goes to both stations. (8) With both comparisons correct, the SC proceeds to obtain from its COMP section an alternative key number K c which section A encrypts with K A , and section B encrypts with K^, .and sends these numbers to stations A and B respectively where they are decrypted and entered into their key registers, substituting their earlier keys. (9) Stations A and B send out K c ' to the respective sections of SC where they .are compared to test equality. at this point both stations would be ready to communicate. The time lapse so far (after the initial dialling by station A) would be less than 4 seconds. To improve security further a further step is adding a few seconds to the setting up procedure: (10) The Computer Resource Unit COMP supplies to the operative sections a random number called D where it is entered into a register connected for generating through re-circulation a fairly large pseudo random passed number. This number is continually -" "' through t±a algo sections is of SC,and the output/sent to stations A and B where they are decrypted and continually passed through a comparator register being- only a few bits (5 - 12) long. Paralell outputs from this register are continually compared with ■ . -. a. similar number of selected paralell bit out uts from the larger, in the opposite sense rotating, key register. Whenever all the bit positions of the static bit comparator are at the strobing moment equal, a pulse is released both in the stations A and B and in the Server Center SC internally which stops the D bit generator and esta- '..Dlishes in the switching sections sw a direct connection between A .and B. It should be noted that the true time distance in terms of real data clock pulses could not be " determined by a hacker and therefore no conclusion be drawn as to the number structure of the initial key in the key register of the algorithm. This is because the variable word length encryption applies also to the D data stream transmission. Figure 4 illustrates the nature of an encrypted message consisting as it does of an initial phase of random data the length of which cannot be externally detected, and a transmission phase consisting of a quasi-random mixture of real data bits and random bits - all in a single undivided string of bits giving no clue where one word begins or ends. There is thus no reference points against which an analyst might be able to study the bit sequences. Figure 5 h.as already been adequately dealt with on page 2 FIGURE 6 explains the role of the N K G C (national key generator center) . In that Center the Kn numbers with their address allocations, and also the D numbers are generated and the protocol for the transfer of these numbers to head offices of various kind is observed. The management of the Center would be limited to determining the optimum rate at which updates for new numbers should be made. This would be set responsive to the performance of the system as a whole as reported by supervisors. Performance reports from head offices such as Bk (banks) or TR (transport organisations) or SC's (service centers for confidential communications) would be studied by supervisors and appropriate responses formulated. Management would have no access to actual key numbers. When a station mal-performs, its encryption module is detached and sent to the factory,and replaced by a factory-new one. It is here suggested that both systeπwise and with respect to the encryption module IC, the here explained confidential message system may.be..used..-also in bank transaction as also in remotely issued travel passes and routing instructions. FIGURE 7. This table surveys the position changes of a number which ranges from a nascent phase to an active, semi-active, and finally abandoned phase. The numbers are classified in terms of age. The active number range comprises in this example five ageing positions, and so does the semi-active range of numbers. If each column segment represents the time span of, say, one week, it would take ten weeks for a number to travel from the nascent region through the active and semi-active region, in order to exit into the for normal use ineccessable abandoned region. Once an address is allocated to a number, the two numbers remain associated during their migration through said regions. Both active and semi-active numbers are valid numbers, and are therefore accepted by terminals and server stations for commencing a communication. However, either right at the beginning or after completion of the communication event, an older active number is substituted by a younger one, or any semi-active number is substituted by any number from the active region. If an internet station, or an IC card - ttirough non-useage over a longer period of time - has in its encryption algorithm a number which at the time of re-use belongs to an abandoned number, it would be necessary to make contact with certain supervisory organs which have at their disposal access to a central register which keeps a record of numbers abandoned in the past. Such organs would be allowed to make also additional checks before they override the absence of a valid key number .and bring the station or card up to date again. FIGURE 8 This shows an example for the LSI chip circuit block diagram. A chip of this type would be needed in an extension card for insertion one in/of the the slots for extension functions, such as .are common in personal computers. *the following are the main features of the Chip: The four clock phases needed to operate the circuit may be either on chi generated or supplied by the Computer (as fig. 8 indicates). The chip would also be used in the Service Center SC.There is a STORED KEY VERIFICATION AND KEY EXCHANGE MODULE (1). This group has four input lines " (ROP, CK2, En . ' and password .) and ^wo output lines , ..In connection with internet operation there may be at least one more input from outside the chip, when namely the output EN has to be delayed because of delays,in getting a connection completed or for whatever other reason. When the electric level at EN changes this indicates that verification and key exchange are satisfactorily completed, and, with everything else being ready the next phase can begin. - The ROP input to module 1 resets all internal bistables and occurs when power is switched on or shortly afterwards. The d-input is con - nected to the incoming signal line to enable the address reference for the encryption key held, to be read out . This last mentioned detail is not shown worked out in figure 8. In practice, the circuit must satisfy the condition that external communication of keys must take place only in the encrypted form. The input CK2 provides the proper clock phase for the key exchange functions. The output K transfers to block 2 the new key before commencing the encryption and decryption functions. All encrypted incoming line signals are decrypted by- gate 16, * The pseudo random key generator rotates t^q fihiffr rTiffTT 9 + h every CK3 clock pulse. The programmable counter 4 is advanced with every CK3 clock pulse. The bistable 23 is reset with every CK2 clock pulse. The programmable counter , after producing a carry output is loaded with the paralell output from the key generator at the time, that is between CK3 and the following CK2. The incoming or outgoing real data bits also have an effect on the constellation of the logic interconnections, block 3 in that the consecutive data bits are fed with the delay of one complete clock cycle to block 3.From this arrangement it follows that discovery of the clear text is not possible without the prior knowledge of the clear text, irøking discovery superfluous. Text generated in the P C is connected to a buffer register,* or perhaps two such registers, via the terminal d The buffer fills until a signal F (full) is fed back to the conputer. As the buffer clearSdue to passing on data to gate 14, the buffer register is filled up again from an overflow register in the conputer itself. The job of the pseudo random data generator, block 11, is to provide meaningless data bits to be fed to outlet 'd' via the gates 12 and 13 when c " is high. The gate 14 admits data from the buffer 17 only when c is high. As the istable outputs c and c " are dependent on the rest of the algorithm, a quasi random mixture of real and fake data is produced at the d output when in the sending phase. When in the receiving phase, the scrambled mixture of real and random data bits is descrambled by gate 16. The remaining real data in the gate 16 output .are channeled in the very beginning before the .actual message transmission to gate 21 and to the d input to block 1 during the initial key checking and exchanging phase. The output from 21 feeds into a short shif register 7 which has paralell outputs for each of the bits it holds. These are applied to a static comparator 8 and compared bit by bit with an equal number of outputs from the register of block 2. As both the registers are shifted on the rising edge of CK3 but in opposite directions this has the effect of scanning and testing the registers .as to the chance of hitting a seven bit (or 5-bit, etc.) combination where all the input bit comparisons are successful causing an output pulse by the strobing clock CK4 on AND gate 9 to trigger bistable 10. As the gate of 16b is enabled by Q , with the disappearance of this high level the flow of encrypted nonsense data stops. A very similar arrangement in the Service Center SC also causes the flow of these data to stop and to connect the station A (Fig. 3)with station B directly via switch elements sw. From now on, encrypted data are ecuύngful text from A to B. Station B will from that moment on channel data received at d (Fig. 8) through gates 16 and 16a to the output interface d. on the PCB whose adge contactors are plugged into the appropriate sockets inside the P C. When the workstation PC sends, .an output SE is generated which disables the gate 16a. The computer can also generate a signal along chip input pwl (p.assword line) to modify the encryption key as explained.in connection with the comment on Figure 2. Finally, the question should be addressed whether the present encryption system permits the communicating parties to engage in a dialogue. The answer is yes, lH»or messages may be sent in both directions/without pause and there is no limit to the length of the message or of the dialogue. Because of the nature of the encryptotion method which defies any form of systematic factoring of the encrypted text, it is unlikely that a freelance hacker can be a threat to the described system in spite of the fact that the interchnages between the Client Conputer (CC) and the Server Station (SSt) contain one element, the address information, in the clear. In a slightly better position are the expert engineers of the server stations which may have an insight into the precise iTioment when within the encrypted data flow various addresses are offered. In a very general way one may admit the possibility of a problem that may then arise.An alternative scheme would permit also the address code to be sent only in the encrypted form. According to our proposal, the Client Computers of a local region would hat e a special relationship with the Internet Secure Server station of that same region (SSt) . The Client Conputer (CC, Fig. 9) would when contacting the Server send to it its ID number. his number serves as an address in the Serve station's memory bank which would contain the very same data as the Client station, namely a chip serial nr. and / or the date of inauguration of the client chip (from an unalterable ROM) . the last entered encryption Key nr. The last entered Preamble Delay nr. D and in place of a revolving address code, an annual sequential entry serial nr. Based on this information, the calling station may immediately begin with sending its own data in encrypted form which me, Server station would place into a comparator register, and if all these data are correct will automatically issue a new key number and preamble random delay number and the next sequential nr., in encrypted form using the old key, and the corresponding^clear data are then placed into the memory of the Client Conputer station. Its operator is requested to dial the distant station to which message material is to be sent. The dial number would pass through the encryption algorithm and therefor does not allow a third party to know which company or person will be connected. The first part of the dial code will call up the distant Server station (for example BBZ) and the number part will call up the particula CC, say 1500. When the latter responds, it sends its own ID number to the distant local Server station, and a similar comparison process as described above, is initiated. If this verifies that the correct CC station has been contacted, the new key (K _) given to the calling station is now also given to the called station. After this is verified, this is made known to the calling station, and a display invites its operator to proceed sending the intended material (text, drawings, voiced comment, etc) . The just described alternative logistics for a variable word length data transmission system, would blend well into telephone and internet based communication infra structures. It is feasible that just one further step in this direction could be made by integrating the envisaged function of secure Server Stations with the location of telephone branch Exchanges (as indicated in Figure 10) , This would be economical - n installation costs,and could work fully automatically in the environment of an automatic switching system. This does not exclude the computerized electronic equipment being housed in a separate reinforced building. It would suffice to have that building in close vicinity to the said telephone Exchange station.

Claims: C L A I M S 1. An encryption and automatic key renewal system for confidential E-Mail comprising at least one E-mail station or internet computer linked to a communication system a national center for the generation of random keys for the use of said stations, means for the scrambling or encrypting of data in said stations, means for the periodic renewal of keys controling said scrambling means and local server centers which store and update the said random keys generated in said national center, WHEREIN said keys shortly before they are delivered from the said Center become associated with one of a limited number of address codes, and WHEREIN the number of the week within a year or some other flag data are attached to said address code that vd.ll readily permit the evaluation of the age of said key at any time .and to classify its age relative to the age of other keys in use at a given time, and WHEREIN FURTHER a server station when issuing the youngest number to ah internet station will delete the -oldest number from its current list of valid key numbers and utilise the former address code of that abandoned key for associating it with the youngest key (Fig. 7) . 2. An encryption and automatic key renewal system for confidential E-mail as in CLAIM 1 WHEREIN the procedure for recognising the legitimacy of a Server Station by a calling E-mail station is as follows: (a) sending to the server station the address code attached to its own encryption key (b) the address must assist the server station in obtaining the calling station's encryption key (c) The Server station equipment encrypts that key number by itself (d) the Server station sends th encrypted key to the E-mail station (e) the E-mail station decrjcpts using its cwn key and places the result into a comparator register (f) If the compared numbers are equal, the E-mail equipment informs the Server sttaion accordingly (FIG. 7) . 3. An encryption and automatic key renewal system for confidential E-mail as in Claim 2, WHEREIN in the case of receiving the OK signal the Server sta-Lon is programmed to obtain from its computer section (COMP) an alternative key number (K ) from the current valid list of key numbers, and to encrypt that new number with the key of the calling station, and wherein the latter is programmed upon receipt of the encrypted new key to decrypt sigad number and to place it into its key register in substitution of the number it had before. 4. An encryption and automatic key renewal system for confidential E-mail as in Claim 3, WHEREIN the Server station (SC) ,Fig. 3, also acts as an (A ) Switchboard for connecting a calling station/to a requested receiving station (B) , and WHEREIN the Server station consists of a twin structure which is equipped with two sets of encryption algorithm (algo) , two sets of switching controls, (LSA and LSB) , and two sets of buffer memories (K ) for holding key number, address codes and other relevant flags as supplied by the conputer section COMP. 5. An encryption and automatic key renewal system for confidential E-mail as in any preceding Claim WHEREIN the said twin sections of the said Server Center equipment (SC) also contains a pseudo-random generator register (D ) in order to generate quasi-data inputs of equal length simultaneously transmitted and encrypted by the said K number to the communicating stations (A,B) in order thereby to shift the starting conditions in the algorithms of the E-mail units for the real text (see Fig. 4) to an undetectable point. 6. An encryption and automatic key renewal system for confidential E-mail as in claims 1 - 5 wherein the algorithms used for the encrypting process produce . word-bit configurations consisting of more than 8 bits and less than 16 bits per word transmitted , and the bit number per word is continually changing. 7. An encryption and automatic key renewal system for confidential E-Mail as in CLAIM 5, WHEREIN the precise point in time for switching the communicating stations from the said initial meaningless random information (being received but not in its decrypted form outputted) is functionally defined by comparing the data flew in two registers, namely register 2 with that of register 7 whereby the data shift is prompted by the same clock phase (CK3) but occurs in opposite directions. 8. An encryption and automatic key renewal system for confidential E-Mail as in any of the preceding claims, WHEREIN the main circuit groups of the integrated algorithm circuit (FIG. 8) comprises (a) a stored key verification and key exchange module (1) (b) a Pseudo Random Key Generator (2) (c) a system of logic circuit elements and interconnections between them (d) a programmable counter (4) (e) an open-ended shift register with paralell bit outputs (7) (f) a pseudorandom Data Generator (11) for supplying surplus data bits (g) a one clock-pulse delay circuit which delays real data bits (incoming and outgoing in affecting the state machine or algorithm status (h) a serial buffer system 17 for accepting work station data and to pass them to the algorithm in accordance with the instant state of the algorithm. 9. An encryption and automatic renewal system for confidential E- ^l as in Claim 8, wherein the said circuit block (1) also contains mathematical processing means, for example for adding or deducting a P.ass Word from the operative Key number in the key register of said module. 10. An encryption and automatic key renewal system for confidential E-M.ail as in any of the aforegoing claims, and / or as shown and described in the accompanying drawings and the Specification. 11. An encryption and automatic encryption key renewal system for confidential E-Mail wherein the output of the said pseudo-random data generator is mixed with the bit levels of other outputs of the encryption circuit or with the clear bit levels of the data flow so as to diffuse any pattern such as may be recognised in the expanded data words. 12. An encryption and automatic key renewal system for confidential E-Mail w h e r e i n the basic functionality of the said algorithm circuit is continually influenced and modified (a) by the paralell bit outputs of a revolving encryption key register and (b) by the clear bits of the data inputted to the algorithm circuit for encryption or outputted from the algorithm circuit after decryption. 13. An encryption and automatic key renewal system for confidential E-Mail essentially as characterised in Claim 1 wherein the functionality of the encryption process is broadly determined by an, partly in special hardware executed, algorithm and embodied in a microelectronic chip and wherein this functionality is not rigidly predetermined but continually influenced and modified (a) by the paralell bit outputs of a revolving encryption key register, and (b) by some but not all the clear bits of the data inputted to the said algorithm circuit for encryption or outputted from the said algorithm circuit after decryption. 14. An encryption and automatic key renewal system for confidential E-Mail as characterised in Claim 13 wherein the functionality of the said microelectronic chip circuit is further influenced and modified (c) by the configuration of a password entered by an operator at the sending and receiving stations in order to ensure that the transmitted text, picture, or voice mail is faithfully reproduced only for those persons who are intended to know it. 15. An encryption and automatic key renewal system for confidential E-Mail as in Claim 13 w h e r e i n the in hardware represented portion of the encryption algorithm also contains memory into which can be written only once, namely when a specific E-Mail station is inaugurated and associated with a definite inauguration date, a definite serial number, and a definite name and a definite Server Station (SSt) , and w h e r e i n the said Client Conputer (CC) details are also held in memory by the local Server Station (SSt) at an address numvber which is numerically identical with the ID of the CC concerned.

Inventors: HALPERN JOHN WOLFGANG, HALPERN, JOHN, WOLFGANG
Applicants: HALPERN JOHN WOLFGANG, HALPERN, JOHN, WOLFGANG
Application year: 1998
Main classification: H04K
IPC codes: H04L9, H04L12, H04L29