Patent Application
20050166052
Electronic documents are routinely sent from one person to another via the Internet or over other networks. During transmission it is possible that an electronic document can be intercepted and altered, or become corrupted in transmission. In many instances an altered document can have significant consequences. For example, if a contract in the way of an electronic document were intercepted and altered to remove the word “not”, or to change a dollar value, it could have significant financial implications. It is therefore desirable to be able to verify the authenticity of an electronic document that is transmitted from a sender to a receiver by way of a network or other means.
A first embodiment the present invention provides for a method of generating an authentication key that can be used to authenticate an electronic document file representative of a document. The method includes providing the electronic document file as an initial digital file, and applying a predetermined halftoning process to the digital file to generate a digital halftone file of a plurality of discrete digital values. A predetermined mathematical process is then performed on the plurality of discrete digital values to thereby generate the authentication key.
Another embodiment of the present invention provides for a system to generate an authentication key to be used to authenticate an electronic document file representative of a document. The system includes a processor and a computer readable memory device which is readable by the processor. The computer readable memory device contains a series of computer executable steps configured to cause the processor to perform the following steps: retrieve a copy of the electronic document file as an initial digital file; apply a predetermined halftoning process to the initial digital file to generate a digital halftone file comprising a plurality of discrete digital values; perform a predetermined mathematical process on the plurality of discrete digital values to thereby generate the authentication key; and store a copy of the authentication key in the computer readable memory device.
These and other aspects and embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:
Non-limiting embodiments of the present invention provide for methods and apparatus for generating an authentication key for an electronic document file at a source of the electronic document file (such as a sender or creator of the electronic document file), and verifying the authenticity of an electronic document file by generating an authentication key for the electronic document file at a receiver location of the electronic document file. The receiver of the electronic document file can then compare the authentication key generated by the receiver at the receiver location to the authentication key generated at the source. If the two authentication keys match, then the authenticity of the electronic document file as received by the receiver is verified. As will be described more fully below, the authentication key can be generated using a halftoning process (i.e., using a halftoning algorithm).
Halftoning is a process that is used to convey gray scale information in printers which typically can print only black or white. Halftoning techniques are also used in color printers (discussed more fully below). Many halftone concepts and terms now used in electronic printing originated with the classic offset printing press. Printing presses can usually print areas of single intensity as they have only an ability to apply ink to a page or not apply ink to the page. This limited ability results in only two colors, i.e., that of the ink and that of the print media. By varying the size of printed dots, however, it is possible to give the impression of various shades of gray.
In electronic black and white printers, gray scales are accomplished by building a palette of grays that consists of clusters of black dots. A given cluster with more black dots is darker, while a cluster with less black dots is perceived as a lighter gray.
Halftone principles and procedures are applicable to color printers as well. In a color printer, the halftone technique is applied to each color plane (usually Cyan, Magenta, Yellow and blacK (CMYK)). Instead of generating only shades of gray, the printer provides mixtures of varying intensities of the four color planes. Layering of those variable intensity color planes enables the printing of a generally “full color” document.
In addition to halftoning for printing purposes, halftoning techniques can also be used in the display of an image, such as on a computer monitor.
Digital halftoning can thus be defined as a collection of techniques employed by various computer-controlled display and printing devices for converting continuous-tone images into binary information for displaying the image. The display or printed image is comprised of many individual picture elements, known as “pixels.” The computer generates data corresponding to the tone of the pixels to be displayed or printed. Hereafter, this data will be alternatively referred to as input tone values or tone value data.
The conversion and display of the tone value data is often referred to as rendering. As part of the rendering, the tone value data is associated with halftoning cells with which the display area is logically tiled. The pixels of those cells are colored (printed or displayed) in accord with the underlying halftoning technique. The halftoning techniques, or algorithms, can be generally broken-down into two classes.
One class of halftoning techniques comprises those algorithms that are relatively simple from a computational standpoint, thus providing good rendering speed. Exemplary of this first class of halftoning algorithms are those known as matrix-based, pattern, or ordered-dither algorithms.
Another class of halftoning algorithms includes those generally labeled as “error diffusion” halftoning algorithms. A popular version of an error diffusion halftoning algorithm is known as Floyd-Steinberg error diffusion. With this technique, the tone value of each pixel is examined (for colored output, the tone values include those of each colorant) and compared to a threshold value provided by the algorithm. If the incoming tone value exceeds the threshold, an output pixel is generated and the difference between the output and input values (error) is diffused among four neighboring pixels. For example, the pixel immediately to the right of the current pixel is assigned {fraction (7/16)} of the error (the error can be positive or negative), the pixel beneath that one is assigned {fraction (1/16)} of the error, the pixel beneath the current pixel is assigned {fraction (5/16)} of the error, and the pixel to the left of that one is assigned {fraction (3/16)} of the error. To further break-up geometric artifacts or patterns, some noise may be added to the error terms. The averaged value of the noise is 0, however, so that the image is not lightened or darkened as a result.
Examples of halftoning algorithms are provided in U.S. Pat. No. 5,313,287 (“Imposed weight matrix error diffusion halftoning of image data”), U.S. Pat. No. 5,949,964 (“Method and apparatus for halftoning of images in a printer”), and U.S. Pat. No. 6,002,804 (“Tone dependent variable halftoning with adjustable algorithm selection”), all of which are assigned to the assignee of the present application.
Following halftoning of an initial digital file, such as an electronic document file, a digital halftone file is produced. The digital halftone file can then be used by a processor resident within an imaging device, typically with additional processing, to enable the imaging device to print a tangible copy of a document represented by the electronic document file. The digital halftone file is a bitmap file comprised of a plurality of discrete digital values, and as such is capable of being numerically processed to generate an authentication key according to the methods described further herein, in accordance with the present invention.
Typically, in a printing process, the halftoning algorithms are resident within a computer readable memory device (such as a random access memory, or RAM) resident within an imaging device. The term “imaging device” or “printing device”, as used herein, is intended to include, for example, stand-alone printers (such as ink jet printers, laser printers, etc.), photocopiers, and combination devices (known as “multi-function peripherals”). As indicated above, halftoning algorithms are frequently proprietary to the manufacturer of the imaging device. Further, since halftoning algorithms are typically embedded within a ROM device they are difficult for a user to access and thus reverse engineer. For this reason using the halftoning algorithm to generate an authentication key provides a fairly high degree of security since the halftoning algorithm used to generate the authentication key is not easily accessed.
As indicated above, embodiments of the present invention allow a first user (a “sender”) to generate an authentication key for an electronic document file by halftoning the electronic document file, and then using the resulting digital halftone file to generate the authentication key. The user can then transmit the electronic document file to a second user (a “receiver”) over a network. The sender can also transit the authentication key to the receiver (typically separately from transmission of the electronic document file). The receiver can then use the electronic document file to generate an authentication key (“receiver authentication key”) in the same manner as described above with respect to the sender. The receiver can then compare the authentication key received from the sender with the receiver authentication key. If the two keys match, it is highly probable that the electronic document file was not altered or corrupted between the time the sender generated the sender's authentication key and the time the receiver generated the receiver authentication key.
Since halftoning algorithms are frequently proprietary to the manufacturer of an associated imaging device, the digital halftone file generated by one make and model of an imaging device will typically be different than the digital halftone file generated by a different make and model of an imaging device. Since the authentication key is generated using the digital halftone file, authentication keys generated using different halftoning algorithms typically will not match. Accordingly, two users of methods and apparatus described further below will generally need to have access to the same halftoning algorithm, either by way of having essentially similar or identical imaging devices, of by having the halftoning algorithms accessible by other means (such as resident within a user computer).
Turning now to
The method next includes applying a predetermined halftoning process to the digital file to generate a digital halftone file comprising a plurality of discrete digital values. Thus, at step 103 the sender submits the initial digital file to a halftoning processor to generate the digital halftone file. For example, the user can transmit the electronic document file to an imaging device, such as an ink jet printer, and a processor resident within the printer can generate the digital halftone file as part of the normal printing process. As indicated above, exemplary halftoning processes include, without by way of limitation, error diffusion halftoning algorithms, matrix-based halftoning algorithms, pattern-based halftoning algorithms, and ordered-dither halftoning algorithms.
Once the digital halftone file is generated, then a predetermined mathematical process is performed on the plurality of discrete digital values (in the digital halftone file) to thereby generate the authentication key, as indicated at step 105 of the flowchart 100. As will be described in fuller detail below, the predetermined mathematical process can be part of an authentication key generation routine stored in a ROM device within the imaging device, and can take the form of a number of different mathematical algorithms (so long as the sender and the intended receiver of the electronic document file use the same algorithm). One example of a mathematical process that can be performed on the digital halftone file is a simple summation of the digital values representative of all of the halftoned pixels which make up the image. For example, in a four color printing process, each pixel will be represented by four 8-bit values. All of the 8-bit values can be added together, and the resulting sum is the authentication key. As this can be a rather large number, even when presented to a user in hexadecimal form, the mathematical process can further include truncating all but a predetermined number of final digits, for example, the last six digits. Another exemplary mathematical process that can be performed on the digital halftone file is a simple summation of the last binary number of the digital values representative of the halftoned pixels. This results in a much smaller final number, but can decrease the probability that any two different electronic document files (e.g., an original document file and an altered document file) will render different authentication keys.
With respect to
At step 109 of the flowchart 100 the sender can transmit the electronic document file (in the form of the initial digital file) to the receiver (i.e., intended recipient) of the document. For example, the sender can send the electronic document file to the receiver as an attachment to an e-mail, or by placing the document file on a commonly accessible server. The electronic document can be sent to the receiver over a global network (e.g., the Internet), via a local or wide area network, or by other means for transmitting electronic document files from a first location (sender location) to a second location (receiver location).
It will also be appreciated that the method depicted in the flowchart does not require the transmission step 109. For example, as indicated earlier, following saving the authentication key at step 107, the “sender” can store the electronic document on a server or the like where access by third parties is possible. Thereafter, the “sender” can use the authentication key (as described further below) to verify that the document has not been altered.
At step 111 of the flowchart 100 the authentication key can be separately communicated to the receiver (i.e., separate from the electronic document file as transmitted to the receiver at step 109). For example, the sender can send the electronic document file and the authentication key to the receiver as attachments to separate e-mails. Alternately, for example, the sender can send the authentication key to the receiver by facsimile, or by voice message (as for example, via a telephone), by cellular phone text message, etc. Further, the electronic document file and the authentication key can be transmitted to the receiver together. Since, as described above, the authentication key is dependent on the halftoning algorithm used to generate the halftone digital file, and since a third party who may intercept the electronic document file will typically not know which halftoning algorithm was used to generate the authentication key, it is unlikely that a third party will be able to alter the electronic document file without affecting the authentication key generated by the receiver.
Turning now to
At step 123 of
After the receiver has generated the authentication key at step 127 (
It will be appreciated that the flowcharts 100, 120 of respective
Turning now to
The system 200 includes a processor and a computer readable memory device which is readable by the processor. As depicted in
While
The local user processor 202 can be, for example, a personal computer. Accordingly, the user processor 202 can be in signal communication with a user input device such as keyboard 204, and a display device such as monitor 206. The user processor 202 can be placed in signal communication with a network 256, such as the Internet, a LAN, or a WAN, for example, via a modem 208 and a network card 9not shown) resident within the user computer 202.
The system 200 can further include a secondary printer 252 (“Printer 2”). As will be described more fully below, Printer 1230 can be configured to perform authentication methods in accordance with embodiments of the present invention, while Printer 2252 can be incapable of performing authentication methods in accordance with embodiments of the present invention. More specifically, Printer 1230 can include the halftoning algorithm 246 used by both a sender and receiver of an electronic document in the authentication key generation process, as described above with respect to
The further details of
As depicted in
The printer RAM 236 can store the initial digital file (or portions thereof) received from the user processor in memory location 240, and can store the digital halftoned file of the initial digital file in memory location 242. The authentication key can be stored in printer RAM memory location 244.
The printer ROM 238 can include a halftoning routine and algorithm 246 which is configured to cause the printer processor 232 to produce a digital halftone image file from an initial image file. That is, the halftoning routine 246 can cause the printer processor 232 to retrieve a copy of the electronic document file from printer RAM 240, convert the initial digital document file 240 to a digital halftone file, and store the digital halftone file in printer RAM location 242.
The printer ROM 238 can further include an authentication key generation routine 248, which comprises a series of computer executable steps configured to cause the printer processor 232 to perform a predetermined mathematical process on the plurality of discrete digital values that make up the digital halftone file 242 to thereby generate the authentication key, and store a copy of the authentication key in the printer RAM memory location 244. The authentication key generation routine 248 can also contain additional executable steps to provide further options for the generation and transfer of the authentication key, as will be described more fully below.
The printer ROM 238 can further include printing routines 250 which are used to control the document printing components 254 during the imaging of sheet media, as well as to perform other control functions in the printer 230.
It will be appreciated that display 206 and user input device (keyboard) 204 can be in signal communication with the printer processor 232 rather than the user processor 202, and that the authentication routine 218 can be resident within printer ROM 238. Accordingly, the generation of the authentication key can be fully supported by an imaging device (printer 230) without requiring an external processor. For example, when user input device 204 is coupled to printer processor 232, a user can specify that a specific print job sent to the printer 230 is to include generation and printing of an authentication key.
One exemplary use of the system 200 to generate a document authentication key will now be described. However, it will be appreciated that a number of different variations of the use of the system 200 are possible, all within the spirit of the present invention. In the following example it will be assumed that a user wishes to print a document and also generate and print an authentication key for the document. Accordingly, a user accesses an electronic document file 214 via user processor 202 and keyboard 204. The user can then use the authentication routine 218 to indicate that the document represented by the electronic document file 214 is to be printed as a tangible copy, and that an authentication key is to be generated for the document file and also printed with the document, either as a separate page or on the printed document itself. A print job, bearing the electronic document file and the authentication key instructions, is then transmitted to the printer 230. The printer processor 232 stores the electronic document file in printer RAM 240. The printer processor 232 then calls the halftoning routine 246, which renders the initial digital file 240 as a digital halftoned file, which is then stored in printer memory 242. Thereafter, acting on the authentication key instruction included with the print job, the printer processor 232 calls the authentication key generation routine 248. The authentication key generation routine 248 performs the predetermined mathematical process (discussed above) on the discrete digital values which comprise the digital halftone file 242, to thereby generate the authentication key. The printer processor 232 then saves the authentication key in printer memory location 244, and proceeds with printing the halftoned file 242 and the authentication key 244 using printing routines 250. At this point the user can then transmit the document file 214 to a receiver using the modem 208, and can communicate the authentication key to the receiver by any of the means discussed above (telephone, facsimile, e-mail, etc.).
In one variation, rather than printing the authentication key, the printer processor 232 can transmit the authentication key 244 to the user processor 202, and the authentication key can be stored in memory 220. The user can then display the authentication key on the display 206.
As a further example of the use of the system 200, a receiver of an electronic document file can use the system 200 to authenticate the document file. Thus, following from the example just described of how a user (sender) can generate an authentication key for an original document file, the receiver has received both the electronic document file and the authentication key from the sender. The receiver stores the electronic document file in RAM location 214. It is assumed that the receiver has also received the authentication key generated by the sender, and has recorded the sender authentication key (as, for example by writing the authentication key on paper, or saving an e-mail containing the sender authentication key). The receiver then proceeds to generate a receiver authentication key using the electronic document file 214 in essentially the same manner as the sender generated the sender authentication key in the example described above. That is, the electronic document file 214 is rendered as a digital halftone image file by printer processor 232, and a receiver authentication key is generated using the halftone image file. The receiver can then compare the authentication key received from the sender to the authentication key generated by the receiver. If the two keys match, then the receiver's copy of the electronic document file is authenticated. However, if the two keys do not match, then the authenticity of the receiver's copy of the electronic document file is not verified.
As discussed earlier, methods and apparatus described herein generally require that the same halftoning algorithm be used to generate the digital halftone file at the “sender” and “receiver” locations. Likewise, the “sender” and “receiver” generally need to apply the same mathematical process on the digital halftone file to generate the final authentication key. Accordingly, methods and apparatus described herein are particularly useful in an enterprise environment such as a “home office/field office” arrangement. For example, the field office can send the home office a proposed sales contract in the form of an electronic document file via a network connection (e.g., via the Internet), and the home office may wish to authenticate the electronic document file to ensure that it has not been altered during transmission. Since the home office and field office are typically related entities, it is easy to coordinate having printers at each location that include the appropriate halftoning algorithms and authentication key generating routines to allow electronic document authentication, as described herein, to be performed between the two locations. For example, a particular make and model of a printing device can be specified in a corporate setting as the printing device to be used for electronic document authentication processes, thus establishing a common halftoning algorithm to be used. Further, the manufacturer of a selected printing device can be consulted to determine a serial number range of a particular make and model of a printing device to ensure that all such printing devices used for electronic document authentication use the same halftoning algorithm. In certain instances, if a manufacturer has upgraded a particular make and model of a printing device with a new or modified halftoning algorithm, then printers to be used in an enterprise environment for electronic document file authentication can be provided with new firmware (the new or revised halftoning algorithm on a semiconductor, for example) so that all printing devices to be used for authentication purposes have the same halftoning algorithm.
The sender side 310 (
The receiver side 350 of the system 300 includes a receiver computer 352 configured to receive the electronic document file from the sender side 310 as a receiver initial digital file. It will be appreciated that the receiver computer 352 can be configured the same as the sender computer 312 and the user computer 202 (of
It will be appreciated that the sender side 310 and the receiver side 350 of the system 300 depicted in
While the above invention has been described in language more or less specific as to structural and methodical features, it is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.
