the present invention in some embodiments is used in the exemplary system 10 depicted in fig1 in which each element is largely conventional . in a first embodiment , host 14 is , e . g ., a computer server platform such as a server in a drm ( digital rights management ) system for distribution and protection of copyrighted digital content . in a second embodiment , host 14 is e . g . a desktop or laptop computer , smart phone , audio / video player or other end user computing apparatus . host 14 is coupled to a communications link 16 such as the internet in the first embodiment , but which could be another type of communication network , wired or wireless including ethernet , cellular telephone , etc . in the second embodiment , the communications link is a more local type wired or wireless link such as a usb ( universal serial bus ), fire wire , or internal computer bus . in both embodiments , also coupled to link 16 are one or more ( client ) devices 20 , 22 , . . . , 26 which are e . g . in the first embodiment consumer electronic devices , other types of computing devices , smart phones , etc ., here respectively designated device 1 , device 2 , . . . , device i . in the second embodiment , devices 20 , 22 , . . . , 26 are e . g . computer or consumer electronic device accessories or components or peripherals such as a computer display screen , a computer optical or hard disc drive , a usb key , or other electronic device which is internal or external to the host and communicates therewith . in this second embodiment , in addition to the security aspect , the present method has the commercial and reliability advantages of allowing only authenticated ( qualified ) devices to be coupled to or installed in the host , preventing interoperability problems . at the time of manufacturing ( or initialization ) of these third - party devices , the organization or person operating or manufacturing the host 14 conventionally establishes a master array or set of n batches d bi of random data , and m random fixed - size cryptographic keys d aki . this master array is stored in memory located in or associated with the host and remains there for the lifetime of the host . as new third - party devices such as 20 , 22 , 26 come to life ( e . g ., are manufactured or initialized ), identifier id ( identification number ) pairs ( d bid , d akid ) are assigned uniquely to each of these device models and the corresponding data d b and key d ak are distributed to the device manufacturer by the system implementer ( who typically also maintains or manufactures the host ) for inclusion ( e . g ., storage in memory ) into each device . a given device model ( instance or unit ), therefore , stores only one of the many data batches and one of the many keys known by the host . as the host is updated by the implementer , should the authentication of particular devices be revoked for the purposes of this authentication , the revoked identifier pairs are conventionally recorded at the host as being revoked . the following authentication process then takes place at arbitrary times during the life of each third - party device , at the prerogative of the host . for this process , it is assumed that each device has stored in it a data batch d b , of size ( length ) designated d bsz and the associated data batch identifier designated d bid and a fixed - size authentication key d ak and the associated key identifier designated d akid as earlier assigned by the host implementer to the manufacturer of the device and as installed into memory in the device as explained above . the key length is , e . g ., conventionally about 20 bytes but this ( like the other numerical parameters described here ) is not limiting . furthermore , the process assumes that each such device i can perform a mac computation such as a keyed hash computation ( e . g ., the well known hmac - sha1 function as defined in rfc 2104 or other keyed hash functions , of which many are known ) using the data batches and keys or alternatively a keyed cipher - based mac computation . hmac stands for hash message authentication code ( a keyed hash function ). the present mac computation is typically done by an appropriately programmed processor or dedicated logic circuitry resident in the device as explained in further detail below . the notation hmac ( k , d ) below indicates the hmac computation of generic data d using generic key k . more generally , the authentication may use any message authentication code process , including a cipher based mac . the authentication process , as depicted with time running along the vertical axis in fig2 for the host and device , includes : 1 . the host ( which is a computing apparatus as explained above ) generates a fixed - size random number as an authentication nonce h an . ( a nonce in cryptography is a random number used once to avoid a replay attack by making each exchange unique .) the nonce is , e . g ., of about the same length as the intended hash digest such as about 20 bytes . 2 . the host also generates a random offset value designated h do and a random length value designated h dl such that h do + h dl is less than or equal to the total size ( e . g ., in bits or bytes ) d bsz of the data batch d b held by the device . these “ random ” number generations may be performed conventionally , for instance by conventional pseudo random number generator software executed by a processor in the host . 3 . the host sends ( via communications link 16 to which it is conventionally coupled in fig1 the nonce h an , the data offset h do and the data length h dl ( which collectively are the data batch selection parameters ) generated in steps 1 and 2 to the device . these particular selection parameters are only exemplary . 4 . the host sends ( via the communications link 16 ) a request to the device to return the computed authentication hash digest value d ah . ( steps 3 and 4 may be combined into one transmission or reversed in order .) 5 . the device ( also a computing device , see above ) computes , e . g ., the mac digest value d ah = hmac ( d ak , ∥ d b [ h do . . . h dl + h dl − 1 ]), that is , the predetermined hmac or keyed cipher mac function as keyed by the device key d ak , of the data , where the data is the concatenation of the host nonce h an and the subset of the data batch d b specified as being offset h do and of length h dl in data batch d b . 6 . the device sends to the host via the communications link the computed authentication digest value d ah computed in step 5 , with its batch identifier which is d bid and its key identifier which is d akid ( which together are the id pair ). 7 . the host verifies whether the received id pair ( b did , d akid ) has been revoked . if so , the host elects to sever communication with the device immediately and the process stops . an error message may be sent to the device by the host at this point . 8 . if there is no revocation , then using the received batch identifier d bid and key identifier d akid , the host using that received id pair looks up the associated data batch b d and key d ak in its storage and using them and the earlier generated selection parameters h an , h do , h al independently computes the equivalent mac digest d ah . note that the data batches do not need each to be stored as a separate entry in the host . instead the data batches may overlap in the host memory to economize on host memory , and looked up using an addressing scheme with offsets or other conventional addressing techniques . the host then conventionally compares this computed mac digest d ah to the authentication value d ah received from the device . if the verification of step 8 fails ( no match of the two digests ), the host determines that the device is not an authenticated device and severs its communication with the device ( e . g ., sends an error message or just stops communications ). but as long as this authentication exchange is completed successfully ( the two digests do match ), the host has no reason to distrust that the particular device is authenticated and may continue to communicate with it , in other words the authentication is successful . fig3 a shows in a block diagram relevant portions of exemplary device 20 . non - relevant portions of the device ( those not involved in the authentication process ) are conventional and not shown , for ease of illustration . device 20 includes a conventional access port which is adapted to couple to the external communications link 16 . incoming data or requests are sent to storage ( memory such as ram ) 32 or conventional processor 40 as shown . ( the processor may be the main processor for the device which also performs other functions , or may be a processor or circuit dedicated to the authentication task .) also provided is storage 34 ( e . g ., rom ) which holds the factory installed data , key and id pair as shown . also provided is storage 38 ( e . g ., rom ) storing code ( computer software ) such as the mac computation software 40 (“ mac function ”) to be executed by processor 40 . the output of the mac function 44 is stored in storage ( e . g ., ram ) 48 also coupled to port 30 . an example of host 14 is depicted in similar block diagram form in fig3 b , with many similar elements . port 31 supports two way communications to link 16 . incoming data ( the digest and id pair from the device ) is stored in memory ( e . g ., ram ) 33 . processor ( or equivalent ) 41 executes code provided from code memory 39 to do the prng calculation in prng 43 and the mac computation in calculator 45 . memory 35 ( ram or rom ) stores the id pairs and associated data batches and keys . comparator 47 in processor 41 verifies both the key pairs and the incoming device digests as explained above . verifier 49 then severs communications or not . note that the comparator and verifier also me in the form of software executed by the processor . both are conventional functions . fig4 shows further conventional detail of the fig3 a device ( or the fig3 b host ) in one embodiment . fig4 illustrates a typical and conventional computing system 60 that may be employed to implement processing functionality in embodiments of the invention . computing systems of this type may also be used in a computer host ( server ) or user ( client ) computer or other computing device or peripheral or accessory or component as described above , for example . those skilled in the relevant art will also recognize how to implement embodiments of the invention using other computer systems or architectures . computing system 60 may represent , for example , a desktop , laptop or notebook computer , hand - held computing device ( personal digital assistant ( pda ), cell phone , consumer electronic device , palmtop , etc . ), mainframe , server , client , or any other type of special or general purpose computing device such as a peripheral or accessory or component as explained above as may be desirable or appropriate for a given application or environment . computing system 60 can include one or more processors , such as a processor 64 ( equivalent to processor 40 in fig3 a ). processor 64 can be implemented using a general or special purpose processing engine such as , for example , a microprocessor , microcontroller or other control logic . in this example , processor 64 is connected to a bus 62 or other communications medium . note that in some embodiments the present process is carried out in whole or in part by “ hardware ” ( dedicated circuitry ) which is equivalent to the above described software embodiments . computing system 60 can also include a main memory 68 ( equivalent to memories 32 , 48 in fig3 a ), such as random access memory ( ram or read only memory ( rom )) or other dynamic memory , for storing information and instructions to be executed by processor 64 . main memory 68 also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by processor 64 . computing system 60 may likewise include a read only memory ( rom ) or other static storage ( equivalent to memories 34 , 38 in fig3 a ) device coupled to bus 62 for storing static information and instructions for processor 64 . computing system 60 may also include information storage system 70 , which may include , for example , a media drive 72 and a removable storage interface 80 . the media drive 72 may include a drive or other mechanism to support fixed or removable storage media , such as flash memory , a hard disk drive , a floppy disk drive , a magnetic tape drive , an optical disk drive , a compact disk ( cd ) or digital versatile disk ( dvd ) drive ( r or rw ), or other removable or fixed media drive . storage media 78 may include , for example , a hard disk , floppy disk , magnetic tape , optical disk , cd or dvd , or other fixed or removable medium that is read by and written to by media drive 72 . as these examples illustrate , the storage media 78 may include a computer - readable storage medium having stored therein particular computer software or data . in alternative embodiments , information storage system 70 may include other similar components for allowing computer programs or other instructions or data to be loaded into computing system 60 . such components may include , for example , a removable storage unit 82 and an interface 80 , such as a program cartridge and cartridge interface , a removable memory ( for example , a flash memory or other removable memory module ) and memory slot , and other removable storage units 82 and interfaces 80 that allow software and data to be transferred from the removable storage unit 78 to computing system 60 . computing system 60 can also include a communications interface 84 ( equivalent to port 30 in fig3 a ). communications interface 84 can be used to allow software and data to be transferred between computing system 60 and external devices . examples of communications interface 84 can include a modem , a network interface ( such as an ethernet or other network interface card ( nic )), a communications port ( such as for example , a usb port ), a pcmcia slot and card , etc . software and data transferred via communications interface 84 are in the form of signals which can be electronic , electromagnetic , optical or other signals capable of being received by communications interface 84 . these signals are provided to communications interface 84 via a channel 88 . this channel 88 may carry signals and may be implemented using a wireless medium , wire or cable , fiber optics , or other communications medium . some examples of a channel include a phone line , a cellular phone link , an rf link , a network interface , a local or wide area network , and other communications channels . in this disclosure , the terms “ computer program product ,” “ computer - readable medium ” and the like may be used generally to refer to media such as , for example , memory 68 , storage device 78 , or storage unit 82 . these and other forms of computer - readable media may store one or more instructions for use by processor 64 , to cause the processor to perform specified operations . such instructions , generally referred to as “ computer program code ” ( which may be grouped in the form of computer programs or other groupings ), when executed , enable the computing system 60 to perform functions of embodiments of the invention . note that the code may directly cause the processor to perform specified operations , be compiled to do so , and / or be combined with other software , hardware , and / or firmware elements ( e . g ., libraries for performing standard functions ) to do so . in an embodiment where the elements are implemented using software , the software may be stored in a computer - readable medium and loaded into computing system 60 using , for example , removable storage drive 74 , drive 72 or communications interface 84 . the control logic ( in this example , software instructions or computer program code ), when executed by the processor 64 , causes the processor 64 to perform the functions of embodiments of the invention as described herein . this disclosure is illustrative and not limiting . further modifications will be apparent to these skilled in the art in light of this disclosure and are intended to fall within the scope of the appended claims .