for the purpose of illustrating the concepts presented in this embodiment of the present invention , the term “ software ” will refer to any computer data , program , instruction set , or any other computer - readable information that is stored in a computer readable medium or format . it will be typical of digital information that is delivered to a user for subsequent use in a computer system . other embodiments of the present invention may also address digitized documents , movies , music , books , magazines , voice presentations or any other material containing intellectual property that is protectable by copyright . embodiments can also address uses not involving copyrighted intellectual property but which still require protection from unauthorized copying or other reproduction . protection of software that is delivered to users for subsequent fair use has always been of significant importance to those who develop and own such intellectual property . copyright laws , developed before the advent of computers , do not always provide actual protection when illegally copied software is indistinguishable from its legal origins . the concept of copyright was developed in a time when the only recording medium was paper and the only method of copying a recorded document was by arduously producing another paper copy by hand . the invention of the printing press , typewriter , photography , audio recording devices , movie technology , xerography , video tape , computer memory and storage , and the internet , have each continued to erode the effectiveness of copyright laws . because digital media can be easily transmitted worldwide and recorded by use of the internet , copy protection laws are not sufficiently effective . producers of software have had to develop technical copy protection in the media itself . one means of protecting against illicit use and / or copying of software is by inserting restrictive coding into the digital data stream . since the digital data stream must be decoded by a processor in order to be usable as machine language instructions , commands can be inserted that disable copying , and possibly playback and execution . in order to properly respond to the instructions , the computer system must be enabled with a device that reads the coding correctly and most types of computers are constructed to do so . however , such protection can be bypassed by the determined wrongdoer . another , and very common , software protection scheme is encryption . in this method , software is encrypted using highly complex keys that make the unauthorized decryption effort much harder than seeking other means of “ cracking ” the machine code . encrypted software , however , must be decrypted in order to be used . typically , this decryption occurs at the point at which the software is read from its non - volatile storage site , usually a cd rom or hard drive , and the point at which it is read into ram to be readied for use . with the embodiment of the present invention discussed herein , a means by which the “ assault window ,” the stage in which decrypted software resides vulnerably in ram , can be reduced if not eliminated . the means is by decryption at a later stage in the process . the concepts underlying this embodiment of the present invention may best be understood by reference to the drawings . this discussion of this embodiment addresses the use and execution of software delivered to a legitimate user for subsequent execution on a computer system . other embodiments may address the same concepts of protection of other forms of digital material on systems other than computers . it must be borne in mind that the form of delivery , whether by cable , internet connection , direct satellite downlink , or in package form such as a magnetic tape or a compact disk ( cd ) or digital video disc ( dvd ), has no bearing on the concepts present in the discussion of this embodiment or any other . it is the protection of the intellectual property from wrongful reproduction that is important . this embodiment of the present invention addresses the use of a computer system as illustrated in fig1 . fig1 illustrates , in block diagram , a configuration of a typical computing device consistent with the methods disclosed in this embodiment of the present invention . computer system 100 comprises bus 110 which connects processor 101 , volatile ram 102 , non - volatile rom 103 and permanent data storage device 104 . also connected to the bus are display device 105 , usually a monitor ; alpha - numeric input device 106 , usually a keyboard ; cursor control 107 , sometimes implemented as a mouse ; and signal i / o device 108 . signal i / o device 108 can be implemented as a serial connection , an infrared transceiver , a parallel connection or some other device . fig2 a illustrates a typical operation of a computer system while executing software . software is delivered , 200 , to non - volatile storage 104 . note that the method of delivery is not important , whether by internet , intranet connection , disk or other medium . from non - volatile storage the software is loaded , 210 , to ram 102 as required . typically , whether the permanently stored software is encrypted or not , it is unencrypted software that resides in ram during execution . from ram , steps or other portions of the software are called into processor 101 &# 39 ; s instruction cache 201 as required by the software &# 39 ; s use . each software step executed must , at some point , be written into the instruction cache . an instruction cache typically includes multiple instruction registers . the process by which instructions are written to the instruction cache is illustrated in fig2 b . processor 101 issues an instruction fetch command to instruction cache 201 . if the demanded instruction is in cache , it is fed to the processor core . if it is not , a cache miss , the instruction is called from main memory 102 to the cache . fig3 illustrates the above operation as applied to encrypted software . encrypted software is delivered , 200 , and stored , 104 , in its encrypted state as discussed above . when called up for loading , encrypted software is decrypted , 215 , as it is read from permanent storage 104 and then written to ram 102 . the software then resides as required in ram in an unencrypted state . in that state in ram , the software is accessible to copying by sophisticated tools that can copy ram contents . fig4 illustrates an embodiment of the invention by which copying from ram can be prevented . after delivery and permanent storage as before , encrypted software is written , 220 , into ram 102 while still in its encrypted state . then , as required by software operation , steps or other portions of the software are decrypted , 215 , only as they are called into processor 101 &# 39 ; s instruction cache 201 , in accordance with the present invention . note that decryption 215 can be implemented as a hardware unit or as part of processor 101 &# 39 ; s instruction fetch command or other implementation . the contents of an instruction cache are continually changing . most operations of a processor alter the contents of the instruction cache , making it very difficult , if not impossible , to copy the cache contents . for this reason , decrypted portions of software that only exist in the instruction cache are extremely difficult to copy . furthermore , those decrypted portions of software resident in the instruction cache are not stored there in any sequential manner but as the processor and its execution of the software demand them . if a would - be copier were able to read and copy the instruction cache contents , those contents would be copied in a disjointed , non - sequential , arrangement that would be yet another nearly undecipherable puzzle . the illustrations in fig3 and 4 show decryption 215 as part of processor 101 . it is shown in this manner only for the sake of clarity of the concept . the implementation of decryption may take place in any manner consistent with this embodiment of the present invention , whether by a physical means within the processor , coding within the software and thus part of the program itself , or by any other means . fig5 illustrates , in flow diagram format , a process , 500 , of delivery , storage , decryption and use of software consistent with this embodiment of the present operation . delivery of software , 510 , occurs in any applicable manner , whether by network connection , packaged media or bundled in a purchased computer system . it typically remains resident in permanent storage 104 . when the encrypted software is loaded for execution , it is loaded to ram 102 at 520 in its encrypted state and remains in that state until execution calls for steps to be written to instruction cache 201 at 530 . when a step in the software is called to the instruction cache , if it is encrypted , 540 , it is decrypted , 550 , in the process of being written to the cache , 560 . from the instruction cache it is executed as required , 570 . note that , if the software is not in an encrypted state in ram , a selected software step does not pass through the decryption process and is written directly to the instruction cache . once no more steps in the software are required for execution , 580 , the process stops , 599 . note that , in the above described process , the physical implementation of each step in the process is not limited to any particular device . the decryption step , for example , may be performed by the involved processor or a dedicated device within the computer system . other steps in the process may also be performed by other means . a method to improve the security of delivered software has been described . the foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description . they are not intended to be exhaustive or to limit the invention to the precise forms disclosed , and obviously many modifications and variations are possible in light of the above teaching . the embodiments were chosen and described in order to best explain the principles of the invention and its practical application , to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated . it is intended that the scope of the invention be defined by the claims appended hereto and their equivalents .