Abstract:
A media content printing method that includes storing encrypted media content data representing media content in a computing device, generating a file of print commands that include the encrypted media content data non-encrypted commands for printing the media content based on the encrypted media content data, and sending the file of print commands to an intermediate device that stores a cryptographic key. The method further includes sending the non-encrypted commands to a printing device, determining if the media content is authorized to be printed, and decrypting the encrypted media content data in the intermediate electronic device that corresponds to the authorized media content to produce decrypted media content data. The decrypted media content data is sent to the printing device for printing the media content based on the non-encrypted commands and the decrypted media content.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a system and method for printing images, and in particular to a system and method for securely printing an image that is securely stored in encrypted, digital form. 
     BACKGROUND OF THE INVENTION 
     There are a number of applications and systems where, for security and/or controls purposes, it is desirable to store valuable media contents, e.g., images, text and the like, in an encrypted, digital form. For example, access to copyrighted visual works, such as photographs or drawings, is often controlled by storing them in an encrypted digital form and permitting them to be decrypted and printed only with proper authorization. Another type of valuable image which must be protected and controlled is a postal indicium that is printed by a postage printing/metering system as evidence of postage. In addition, it is also often desirable to, with proper authorization, be able to print such images using a standard printer. The problem, however, is that in order to be properly printed, the images must first be successfully decrypted using an appropriate cryptographic key or keys, and once decrypted on the computer system on which they are stored, the images are accessible and therefore vulnerable to capture and improper use, such as unauthorized reprinting and/or modification. 
     SUMMARY OF THE INVENTION 
     The present invention alleviates the problems associated with the prior art and provides a method and system for securely printing media content, e.g., images, text and the like, such that the media content is not accessible on a computer system and therefore not vulnerable to capture and improper use. 
     According to the present invention, the media content is stored in a computer system only in encrypted form. When printing of the media content is desired, the computing device generates a file of print commands, preferably Printer Control Language (PCL) commands, which include the encrypted media content along with non-encrypted commands associated with printing the media content. The file of print commands is sent to a secure intermediate electronic device through a first USB channel and the intermediate electronic device is operatively coupled to a printing device through a second USB channel. 
     The intermediate electronic device sends the non-encrypted commands to the printing device through the second USB channel and determines whether printing the media content that corresponds to the encrypted media content is authorized. If printing of the media content is authorized, the intermediate electronic device decrypts the encrypted media content using a cryptographic key stored in the intermediate electronic device and sends the decrypted media content to the printing device for printing. Thus, the cryptographic key required to decrypt the media content is securely stored in the intermediate electronic device, making it difficult to obtain for improper use. Furthermore, the media content is never accessible on the computer system in decrypted form, and therefore is not vulnerable to being captured for improper use. 
     Therefore, it should now be apparent that the invention substantially achieves all the above aspects and advantages. Additional aspects and advantages of the invention will be set forth in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. Moreover, the aspects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description given below, serve to explain the principles of the invention. As shown throughout the drawings, like reference numerals designate like or corresponding parts. 
         FIG. 1  is a block diagram of a system for printing images according to one embodiment of the present invention; 
         FIG. 2  a block diagram of one particular embodiment of the inline pass-through device of the system of  FIG. 1 ; and 
         FIG. 3  is a flowchart illustrating a method of printing a document including an image using the system of  FIG. 1  according to one embodiment of the invention wherein the image is stored in an encrypted, digital form. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a block diagram of a system  2  for printing media content that is securely stored in an encrypted, digital form according to one embodiment of the present invention. As seen in  FIG. 1 , the system  2  includes a computing device  8 , which may be, without limitation, a PC or another suitable device, that is operatively coupled to a secure inline pass-through device  10 , described in greater detail below, through a first communications channel  12 , such as, without limitation, a USB channel. The inline pass-through device  10  is operatively coupled to a standard printer  14 , such as, without limitation, a standard ink-jet or laser printer, through a second communications channel  16 , such as, without limitation, a USB channel. Optionally, the inline pass-through device  10  and printer  14  could be incorporated into a single unit, or the inline pass-through device  10  could be implemented as software within a printing device. Optionally, the computing device  8  may be connected to a network  6 , such as, for example, the Internet or the like, which in turn is connected to a remote server  4 . The computing device  8  can communicate with the server  4 , via the network  6 , to conduct online transactions and the like. 
     The computing device  8  stores media content, e.g., images, text and the like, therein in an encrypted, digital form. In particular, the computing device  8  stores encrypted media content data for different media content. In this form, each of the media content is protected because if the data (encrypted) were to be used in a print operation, the resulting printed media content, e.g., image or text, would not resemble the actual original media content, but instead would be mottled in appearance. The encrypted media content data for an image may be, for example, an encrypted bit map. As will be appreciated, each encrypted media content may be created by encrypting the original media content using any suitable encryption algorithm (such as, without limitation, an appropriate symmetric encryption algorithm like the AES algorithm) and an associated key or keys (such as, without limitation, an appropriate symmetric encryption key). As will also be appreciated, the original media content may be obtained from the encrypted media content by decrypting the encrypted media content using the appropriate key or keys (e.g., the same symmetric encryption key). According to an aspect of the present invention and as described in greater detail below, media content data decryption is performed in a secure manner by the inline pass-through device  10 . 
       FIG. 2  is a block diagram of the inline pass-through device  10  according to one particular embodiment which, as described in greater detail herein, decrypts encrypted media content data so that the original media content can then be printed as part of a document. The inline pass-through device  10  includes an incoming communications port  18  for receiving commands (described in greater detail elsewhere herein) from the computing device  8  over the communications channel  12 . The incoming communications port  18  is operatively coupled to a processor  20 , such as, without limitation, a microprocessor, a microcontroller or some other suitable processing device. The processor  20  is operatively coupled to a secure key store  22 , e.g., memory device or the like, which stores one or more cryptographic keys which are used by the processor  20  to decrypt the encrypted media content data sent from the computing device  8 . As will be appreciated, the particular cryptographic keys that are stored in the key store  22  are the keys that are necessary to decrypt the encrypted media content data stored by the computing device  8  as described above. For example, the keys may be the same symmetric encryption key or keys used to generate the encrypted media content data, or alternatively, public key asymmetric cryptography may be employed. Key store  22  also includes a serial number which uniquely identifies the inline pass-through device  10  and a database of transactions. The database of transactions includes a counter that indicates the number of times media content has been successfully decrypted, based on a unique content identifier provided with the media content (as described further below). In addition, the processor  20  is operatively coupled to the outgoing communications port  24  which in turn is operatively coupled to the communications channel  16 . As described in greater detail elsewhere herein, the processor  20  is adapted to generate and send to the printer  14  commands for printing documents including the media content that is securely stored in the computing device  8  in encrypted, digital form. 
     The inline pass-through device  10  may be made secure using any of a number of known techniques for protecting the security of the keys stored therein. For example, one or more tamper prevention mechanisms may be employed in the inline pass-through device  10  to protect the device, and thus the keys stored therein, from an attacker. 
       FIG. 3  is a flowchart illustrating a method of printing a document including media content using the system  2  according to one embodiment of the invention. The method begins at step  50 , where the computing device  8  generates a file of print commands, preferably in the form of printer control language (PCL) commands, for printing a document that includes commands for printing identified media content that is stored by the computing device  8  in encrypted form. The identified media content may be either temporary, e.g., the result of an on-line transaction with the server  4  via network  6 , or persistent, e.g., downloaded and stored for future use. The encrypted media content is preferably received from a third party which is either an owner of the media content or a broker acting on behalf of the owner, e.g., a copyrighted image broker. For example, the media content may be a postage indicium that evidences payment of postage. The computing device  8  can request one or more indicium from the server  4 , which generates and encrypts the indicium and downloads it to the computing device  8  for printing. The encrypted content includes header information which contains instructions for processing the encrypted content and a body section which contains the encrypted identified media content. The instructions include the serial number of the device for which the content has been encrypted, a unique content identifier of the content and a counter indicating how many times the encrypted media content may be decrypted and printed. Preferably, this header information is implemented as a command or series of commands that would normally be ignored by a standard printer, e.g., a series of cursor movements which follow a path that return the cursor to its position prior to moving along the path, or command embedded in comments. The file of commands may optionally also include commands for printing other portions of a document along with the media content, such as other text or images. At step  52 , the computing device  8  sends the generated commands to the inline pass-through device  10  through the communications channel  12 . 
     At step  54 , the inline pass-through device  10  begins processing the commands received from computing device  8 . At step  56 , a determination is made in the inline pass-through device  10  as to whether or not the current command being processed includes encrypted media content. Any commands that do not include encrypted media content are sent to the printer  14  via communication channel  16  at step  62 . It should be noted that this determining step allows standard print files that do not include encrypted media content to be sent to the printer through the inline pass-through device  10  without alteration. 
     If, at step  56 , it is determined that the command includes encrypted media content, a determination is made at step  58  whether printing of the encrypted media content is authorized. The determination is based upon the header information included in the encrypted contents and the database of transactions stored in the inline pass-through device  10 . The encrypted content is authorized for printing only if the serial number in the content matches the device serial number and the content identifier in the header has not been previously decrypted more than the counter in the header. The latter is determined by comparing the counter in the header with the successful decryption counter for the unique content identifier stored in the database of transactions. For example, the header for a postage indicium would include a serial number of the inline pass-through device  10 , a unique identifier for the postage indicium and a counter with a value of one, indicating that the indicium should be printed only a single time. Thus, in this example, the step  58  determination would include a determination as to whether the identified encrypted media content has been previously printed. Alternatively, in other embodiments, each stored encrypted media content is able to be successfully printed a predetermined number of times (i.e., limited reprints of a copyrighted image). Thus, in those embodiments, the inline pass-through device  10  keeps track of the number of times that each stored encrypted media content has been printed in the decryption counter of key store  22 , based on the unique identifier for each encrypted media content, and the step  58  determination would include a determination as to whether the identified encrypted media content has already been printed the maximum number of times. If at step  58  it is determined that the encrypted media content is authorized for printing, the encrypted media content is decrypted at step  60  and then sent to the printer  14  via communication channel  16  at step  62 . If, at step  58 , it is determined that the encrypted media content is not authorized to be printed, the encrypted media content is sent directly to the printer  14  via communication channel  16  at step  62  without decrypting. Sending the encrypted media content directly to the printer results in the printing of random content, e.g. a mottled image, rather than the original unencrypted media content. 
     Following step  62 , the inline pass-through device determines if there are more commands to process. If more commands have been received, processing continues at step  56 . It should be noted that these additional commands could include encrypted and/or unencrypted content If there are no more further commands to process (e.g., if an end of file command is received), processing terminates at step  66 . 
     Thus, in the system  2  and using the method of  FIG. 3 , encrypted media content, e.g., an identified image or text, that is securely stored in an encrypted fashion is able to be securely printed by a standard printer by decrypting encrypted media content data for printing the media content inline so that the decrypted media content data is never present on the computing device  8 . In addition, as the cryptographic key or keys used to decrypt the encrypted media content data are protected in the inline pass-through device  10 , the presence of the printed original media content in a document proves that the inline pass-through device  10  was used to print the original media content. 
     As a further level of security, the encrypted media content data may be digitally signed by the computing device  8  with a private key that is a pair to a public key stored in the key store  22  of the inline pass-through device  10 . Alternatively, a message authentication code (MAC) based upon symmetric key cryptography may be used. In this embodiment, the processor  20  of the inline pass-through device  10  will proceed to decrypt the encrypted media content data as described in step  58  and cause the media content to be printed as described in step  60  to  64  only if the processor  20  is able to verify the digital signature of the encrypted media content data using the stored public key or the MAC using the symmetric key. 
     While the above description was provided with respect to printed content, e.g., images or text, the present invention is not so limited and can be utilized with other types of media content as well. For example, the media content could also include audio or video files that are being sent to an audio or video device for playback. Thus, the printer  14  of  FIG. 1  would be replaced by an audio device or video device, depending on the application. Portions of the audio or video file could be encrypted, which require the inline pass-through device  10  to decrypt. If the inline pass-through device  10  is not provided, or if the content is not properly decrypted by the inline pass-through device  10 , the result would be audio or video that while intelligible, would have lower fidelity or noisy outputs. Such an application might be useful for previewing audio or video prior to purchase. 
     While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, deletions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as limited by the foregoing description but is only limited by the scope of the appended claims.