Abstract:
A communications link between a computer and a remote user is effected by a portable access unit which generates a nonrecurring access code which is a function of a password and a pseudorandomly generated number. The access code is transmitted and compared with an access code generated by a computer access controller. In addition to the access code, the pseudorandomly generated number provides an encryption key which is not transmitted but corresponds to a mating encryption key generated at the controller. The mating encryption keys are utilized to set up data transmission enciphering/deciphering networks successive links are established by incremented pseudorandomly generated access codes.

Description:
BACKGROUND OF THE INVENTION 
     1. Summary of the Invention 
     This invention relates generally to securing communication links between a computer and a remote terminal and more particularly to a system for accessing a computer and keying an encryption network for data transmission through pseudorandom number generation. 
     Society&#39;s multifaceted dependency upon computer systems has increased the possible effects of unauthorized computer access to untold levels. Computer networking, such as time sharing systems, has led to inherent security problems, since programs executed by such systems shared access and cooperated with each other. The capabilities of recent computer systems included not only the utilization of remote terminals but extensive resource sharing and batch processing of different projects. The use of such systems has necessarily increased the likelihood of deliberate or even accidental acquisition and/or alteration of data. 
     Computer systems have been subject to a variety of security risks ranging from misappropriation of confidential data through unauthorized use of computing time. Access controls have been used in virtually all time sharing and most other computer systems. Differences in the nature of the information being processed have given rise to various security measures and procedures commensurate with the value attached to such data and the consequences of unauthorized access and/or appropriation thereof. For example, the data processed in computer systems utilized for financial transactions has a substantial value due to the monetary losses which could be sustained as a result of system penetration. 
     A user has been traditionally identified by at least one of the following: 
     (a) through something he knew or had memorized, e.g. a password; 
     (b) through something he carried wih him, e.g. a card or badge; or 
     (c) through a personal physical characteristic, e.g. recognition by a guard. 
     Passwords have been widely employed to authenticate a remote terminal user. The use of passwords has been augmented by secondary security measures in many instances. For example, a typical consumer banking terminal accesses its computer by using a combination of a magnetically encoded card and the user&#39;s memorized password commonly referred to as a personal identification number. 
     While such systems might have been satisfactory from a cost/loss risk standpoint, they were subject to penetration with or without access to the individual user&#39;s card. Various password selection procedures and their susceptibility to penetration have been discussed in a U.S. Department of Commerce publication entitled The Use of Passwords for Controlled Access to Computer Resources, NBS Special Publication 500-9 dated May 1977. 
     In addition to penetration of the user&#39;s password, passwords themselves were ineffective, for example, against the penetration threat of between-lines entry and piggy-back infiltration. Unauthorized interception of communication links between the computer and a remote user has been a further security problem and resulted in obtaining not only the data transmitted but the user&#39;s password for subsequent access. 
     SUMMARY OF THE INVENTION 
     A remote computer is accessed by a nonrecurring access code generated as a function of a pseudorandom number and a user password. The access code is transmitted over telephone lines through the use of a digital signal to audio tone modem and decoded at the computer location. An access controller receives the decoded access code and compares it to an expected access code which has been congruently generated. Upon recognition of an equality between the controller generated access code and the transmitted access code, the controller grants access to the computer. The generated pseudorandom number can be divided into two segments, one of which is used to furnish the access code and the other an encryption key utilized for subsequent data transmission between the user and the computer or, in the alternative, two pseudorandom numbers are generated, one of which is utilized for access code generation and the other for the encryption key. 
     From the above compendium it will be appreciated that it is an object of the present invention to provide a remote accessing system of the general character described for establishing a communications link between a computer and a remote user which is not subject to the disadvantages aforementioned. 
     A further object of the present invention is to provide a remote accessing system of the general character described for establishing a communications link between a computer and a user employing an accessing password which is not transmitted over communications lines. 
     A further object of the present invention is to provide a remote accessing system of the general character described for establishing a communications link between a computer and a user which utilizes pseudorandom number generation to provide nonrecurring access codes. 
     Another object of the present invention is to provide a remote accessing system of the general character described for establishing communication links between a computer and a user which employs data encryption established in conjunction with a nonrecurring encryption key. 
     A further object of the present invention is to provide a remote accessing system of the general character described for establishing communications links between a computer and a user which utilizes pseudorandom number generation for the purpose of both accessing the computer and providing a data encryption key. 
     Another object of the present invention is to provide a remote accessing system of the general character described for establishing communications links between a computer and a user wherein interception of user-computer communications will not provide sufficient data for independently accessing the computer. 
     Other objects of the invention in part will be obvious and in part will be pointed out hereinafter. 
     With these ends in view the invention finds embodiment in certain combinations of elements, arrangements of parts and series of steps by which the objects aforementioned and certain other objects are hereinafter attained, all as fully described with reference to the accompanying drawings and the scope of which is more particularly pointed out and indicated in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings in which is shown one of the various possible exemplary embodiments of the invention, 
     FIG. 1 is a schematized block diagram of a remote accessing system constructed in accordance with and embodying the invention and illustrating an access unit at a remote terminal establishing a communications link to a main computer; 
     FIG. 2 is a flow diagram illustrating an access controller routine for establishing access to the computer; and 
     FIG. 3 is a flow diagram illustrating a continuation of the controller routine originating in FIG. 2. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now in detail to the drawings, and specifically to FIG. 1 wherein a block diagram illustrating a typical communications channel linking a remote user with a computer is shown, the reference numeral 10 denotes generally a remote terminal from which a user communicates with a computer 12. In accordance with the present invention, a communications link 14 is established through the use of conventional data transmission facilities such as, for example, a telephone line or 
     The present invention prevents unauthorized access to the computer 12 through the use of a user assigned password which functions only in conjunction with a user assigned access unit 16. The access unit 16 is preferably lightweight and hand-carried and typically includes a microprocessor 18 such as MOS Technology 6502 programmed to generate a series of pseudorandom numbers in a reproducible fashion from an initial grouping of seed numbers. 
     The access unit 16 further includes a data encoder 20 for the purpose of encrypting data for transmission over the link 14 to render intercepted data communications unintelligible. The encoder 20 may comprise data encryption hardware compatible with the Data Encryptin Standard algorithm promulgated by the National Bureau of Standards. Among the devices presently available for data encryption utilizing the Data Encryption Standard algorithm are the Rockwell-Collins CR-100 Network Encryptor, the Hansco Data Processing-Federal 007 and the Motorola &#34;InfoGuard&#34; system. Use of the Data Encryption Standard algorithm is by way of example only, and any other encryption algorithms and encryptors such as the Datotek DH-26 security device can be employed. 
     In addition to the microprocessor 18 and the encoder 20, the access unit also includes an input/output device 22, typically comprising a keyboard and a transient display for indicating keyboard entries which, as will be described herein, comprise the user assigned password. 
     Preferably, an authorized user carries his access unit 16 to the remote terminal 10 and interconnects the access unit with remote terminal computer peripherals such as an input/output device 24 which may comprise a keyboard and/or CRT or TTY. Communication from the input/output device 24 to the computer 12 is first encrypted by the encoder 20 and then encoded into audiotones at a tone encoder/decoder modem 26 which may comprise, by way of example, a Bell System 103A Data Set. The tone encoded data is transmitted to the computer 12 via the communications link 14. 
     Pursuant to the invention, the microprocessor 18 is actuated to generate a chain of nonrecurring numbers from a group of seed numbers originally implanted. A typical processor sub-routine for repeatable pseudorandom number generation is disclosed in U.S. Pat. No. 3,792,446 issued Feb. 12, 1974 to McFiggins et al and assigned to the assignee of the present invention. It should be understood that such pseudorandom number generation sub-routine is exemplary of manifold random number generation algorithms which may be employed. 
     User password integrity is maintained in accordance with the present invention by not directly transmitting the password over the communications link 14. Further, pursuant to the instant invention, possession of the password without the access unit will not permit access to the computer, nor will possession of the access unit without the user&#39;s assigned password. 
     Generation of an acceptable access code signal by the access unit 16 entails the generation of a predicted pseudorandom number by the microprocessor 18 and modification of the pseudorandom number as a function of the password which is entered on the keyboard (input/output device 22). For example, the access code may comprise pseudorandomly generated numbers multiplied by the user&#39;s password which also comprises a number. The access code thus generated is fed to the modem 26 along with a constant access unit preface number for transmission via the communications link 14 to the computer 12. Interception of the access code transmission will not reveal the user&#39;s password but only the access unit preface number and the access code for the intercepted communication. As will be later described, such access code is not valid for subsequent communication links and cannot form the basis for deriving subsequent valid codes. 
     The tone encoded transmissions through the communications link 14 are received at a companion modem 28 for conversion to digital waveforms. Access to the main computer 12 is controlled by a controller unit 30 which monitors the communications link 14. The controller may comprise a minicomputer such as the Data General NOVA series or even a microprocessor such as the microprocessor used in conjunction with random number generation at the access unit. 
     It should be appreciated that the controller 30 is programmed with a congruent random number generation algorithm and initial seed numbers compatible with those assigned to all authorized access units. Further, the controller 30 may be set up such that the initial access code generated by each authorized access unit and its associated assigned password is stored in a self-contained memory for ready reference. 
     Referring now to the flow diagram of FIGS. 2 and 3 where the accessing sub-routine of the controller unit 30 is depicted, it will be appreciated that after answering an incoming telephone signal, the controller receives, through the modem 28, the unit preface number followed by the transmitted access code as shown at an input block 32. 
     As shown in a decision block 34, inquiry is made for verification of the incoming access unit preface number with access unit preface numbers stored in the controller memory to determine whether the attempt to gain computer access is being made through the use of a validly assigned access unit 16 which has not been reported to be in the possession of anyone other than its authorized user. If the access unit preface number is not valid or if the preface number has been generated by a unit reported as stolen or missing, the program exits the decision block 34 on a branch 36 and the controller 30 logs the security violation and terminates the telephone link 14. 
     Upon acknowledgment of an incoming signal from a valid access unit, the program exits the decision block 34 on a branch 38 and the controller retrieves the expected access code to be received from such access unit from a memory and compares the expected access code with the code received over the communications link as depicted in a further decision block 40. 
     In order to prevent access code discrepancies due to signal interference from terminating a valid access attempt, the controller 30 will permit a valid access unit to transmit its access code a predetermined number of times. If the transmitted access code does not match the access code assigned to that unit number and stored in the controller memory, the program exits on a branch 42, the access code attempt is logged and the controller determines how many attempts have been made to transmit the access code as shown in a decision block 44. If there have been less than the allotted number of attempts, a message is returned to indicate that the transmitted access code has been rejected and is to be retransmitted and the program reverts to the input block 32. After the allotted number of attempts has been reached, the program exits the decision block 44 on a branch 46 to break the communications link 14. 
     Upon receiving a transmitted access code which coincides with the stored access code anticipated, the program exits the decision block 40 on a branch 48 and the controller 30 thereafter sends a message to the access unit microprocessor 18 indicating acceptance of the access code such that the microprocessor will generate the next sequential pseudorandom number upon subsequent actuation rather than repeat its last pseudorandom number. 
     The controller 30 then searches its nonvolatile memory and retrieves a stored encryption key for the assigned access unit 16. The encryption key can comprise either a segment of a single random number generation or a separate random number as generated by both the access unit microprocessor 18 and the controller 30. The encryption key retrieved by the controller 30 is used to key an encoder/decoder 50 associated with the controller. It should be appreciated that the encryption key is not transmitted over the communications link 14 and is independently generated at both the access unit 16 and the controller 30 on opposite ends of the link 14. Thus, anyone intercepting and recording the data transmission over the link 14 will not obtain the encryption key used to set up the enciphering/deciphering network. 
     As shown in a block 52 of FIG. 3, the controller 30 thereafter generates the next expected access code for the access unit 16 through the pseudorandom number generation algorithm with seed numbers which have been generated, e.g. as described in U.S. Pat. No. 3,792,446, and modifies the pseudorandom number by the password. Additionally generated is the successive encryption key which may comprise a segment of the random number. The controller 30 thereafter replaces the previous access code and encryption keys for the access unit 16 in its nonvolatile memory. 
     The program thereafter exits the block 52 and advises the computer 12 of the access unit preface number, as shown in a block 54, and connects a data path from the remote terminal 10 to the computer 12 through the encoder 50 and a computer access switch 56. 
     At the termination of the communication between the input/output device 24 at the terminal 10 and the computer 12, the controller logs the communication with reference to the access unit preface number, the time and the data and thereafter disconnects the communications link 14. 
     It should be appreciated that the controller 30 may readily be adapted to simultaneously control a plurality of communication links 14 established by various access units. Further, in lieu of generating the access code and encryption key in advance, the controller may generate these numbers during accessing procedure. Similarly, the access unit microprocessor 18 may generate its pseudorandom number upon each actuation or generate the numbers once and store them in a memory for recall when an access code is to be generated. 
     The access unit 16, upon actuation, will generate its next sequential pseudorandom number modified by whatever password is attempted. If the user is not authorized, he will not know that the access code generated will not grant access unless an attempt is made to gain access. Such attempts are logged by the controller 30, and security personnel will be alerted upon the occurrence of any unusual pattern of access attempts by any given access unit as identified by its preface number. 
     Thus, it will be seen that there is provided a computer accessing system which achieves the various objects of the invention and is well suited to meet the conditions of practical usage.