Patent Publication Number: US-7908217-B2

Title: Method and system for optimizing throughput of mailing machines

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of prior application Ser. No. 10/246,040, filed Sep. 17, 2002, now U.S. Pat. No. 7,272,581, which claims the benefit of U.S. Provisional Application Ser. No. 60/363,790, filed on Mar. 12, 2002, the specifications of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention disclosed herein relates generally to mailing machines, and more particularly to a method and system for optimizing the throughput of a mailing machine. 
     BACKGROUND OF THE INVENTION 
     Mailing machines for printing postage indicia on envelopes and other forms of mail pieces have long been well known and have enjoyed considerable commercial success. There are many different types of mailing machines, ranging from relatively small units that handle only one mail piece at a time, to large, multi-functional units that can process hundreds of mail pieces per hour in a continuous stream operation. The larger mailing machines often include different modules that automate the processes of producing mail pieces, each of which performs a different task on the mail piece. The mail piece is conveyed downstream utilizing a transport mechanism, such as rollers or a belt, to each of the modules. Such modules could include, for example, a singulating module, i.e., separating a stack of mail pieces such that the mail pieces are conveyed one at a time along the transport path, a moistening/sealing module, i.e., wetting and closing the glued flap of an envelope, a weighing module, and a metering module, i.e., applying evidence of postage to the mail piece. The exact configuration of the mailing machine is, of course, particular to the needs of the user. 
     Typically, a control device, such as, for example, a microprocessor, performs user interface and controller functions for the mailing machine. Specifically, the control device provides all user interfaces, executes control of the mailing machine and print operations, calculates postage for debit based upon rate tables, provides the conduit for the Postal Security Device (PSD) to transfer postage indicia to the printer, operates with peripherals for accounting, printing and weighing, and conducts communications with a data center for postage funds refill, software download, rates download, and market-oriented data capture. The control device, in conjunction with an embedded PSD, provides the system meter that satisfies U.S. and international postal regulations regarding closed system information-based indicia postage meters. The United States Postal Service (USPS) initiated the Information-Based Indicia Program (IBIP) to enhance the security of postage metering by supporting new methods of applying postage to mail. The USPS has published draft specifications for the IBIP. The requirements for a closed system are defined in the “Performance Criteria for Information-Based Indicia and Security Architecture for Closed IBI Postage Metering System (PCIBI-C), dated Jan. 12, 1999. A closed system is a system whose basic components are dedicated to the production of information-based indicia and related functions, similar to an existing, traditional postage meter. A closed system, which may be a proprietary device used alone or in conjunction with other closely related, specialized equipment, includes the indicia print mechanism. 
     The PCIBI-C specification defines the requirements for the indicium to be applied to mail produced by closed systems. The indicium consists of a two-dimensional (2D) barcode and certain human-readable information. Some of the data included in the barcode includes, for example, the PSD manufacturer identification, PSD model identification, PSD serial number, values for the ascending and descending registers of the PSD, postage amount, and date of mailing. In addition, a digital signature is required to be created by the PSD for each mail piece and placed in the digital signature field of the barcode. Several types of digital signature algorithms are supported by the IBIP, including, for example, the Digital Signature Algorithm (DSA), the Rivest Shamir Adleman (RSA) Algorithm, and the Elliptic Curve Digital Signature Algorithm (ECDSA). 
     Thus, for each mail piece the PSD must generate the indicium once the relevant data needed for the indicium generation are passed into the PSD and compute the digital signature to be included in the indicium. The generation of the indicia and computation of the digital signature requires a predetermined amount of time. For smaller mailing machines that do not have high throughput, the time delay associated with such generation and computation does not limit the throughput, i.e., the calculations are performed quickly enough and therefore are not a limiting factor for the throughput. For larger mailing machines with higher throughputs, however, the speed of processing the mail pieces may be limited by the time required for the PSD to perform its calculations in generating the digital signature and the indicium. Accordingly, the throughput of the mailing machine is confined due to the calculating time required by the PSD. 
     Thus, there exists a need for a method and system that optimizes the throughput of a mailing machine by reducing the amount of time necessary for the PSD to generate the indicium and calculate the digital signature for each mail piece. 
     SUMMARY OF THE INVENTION 
     The present invention alleviates the problems associated with the prior art and provides a method and system that optimizes the throughput of a mailing machine by reducing the overall amount of time necessary for the PSD to generate the indicium and calculate the digital signature for each mail piece. 
     In accordance with the present invention, the entire debit operation performed by the PSD is separated into three different sections: a pre-debit operation section, a perform debit operation section, and a complete debit operation section. In addition, the calculation of the digital signature can optionally be pre-computed, or alternatively, computed in stages, i.e., partial signature calculation. Utilizing this granularity, the cryptographic operations associated with generating the digital signature can be shifted between the three debit operations such that the execution time of the time critical portion of the debit operation (perform debit) can be optimized to meet the performance requirements of the mailing machine in which the PSD is deployed. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The above and other objects and advantages of the present invention will be apparent upon consideration of the following detailed description, taken in conjunction with accompanying drawings, in which like reference characters refer to like parts throughout, and in which: 
         FIG. 1  illustrates in block diagram form a portion of a mailing machine according to the present invention; 
         FIG. 2  illustrates in flow chart form the options for processing debit operations according to the present invention; 
         FIG. 3  illustrates a timing diagram for the processing of debit operations according to the present invention; 
         FIG. 4  illustrates in flow chart form an example for the processing of debit operations according to the present invention; 
         FIG. 5  illustrates in flow chart form another example for the processing of debit operations according to the present invention; and 
         FIG. 6  illustrates in flow chart form another example for the processing of debit operations according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PRESENT INVENTION 
     In describing the present invention, reference is made to the drawings, wherein there is seen in  FIG. 1  a portion of a mailing machine  10  according to the present invention. Mailing machine  10  includes a printer  16  adapted to print postage indicia on a mail piece. Printer  16  is coupled to processor  12 , which controls operation of the mailing machine  10 . Processor  12  is coupled to one or more input/output devices  18 , such as, for example, a keyboard and/or display unit for the input and output of various data and information. Processor  12  is further coupled to a PSD  14  the generates the indicium and calculates a digital signature included in the indicium. PSD  14  includes an ascending register (AR)  20  and a descending register (DR)  22  in which critical accounting data relevant to the operation of the mailing machine  10  is stored. It should be understood that PSD  14  may also include other types of registers as well. PSD  14  further includes a processor  24  that performs cryptographic operations necessary for generating the indicium for each mail piece and calculating the digital signature. The cryptographic operations to be performed by processor  24  could be stored in a memory (not shown) coupled to the processor  24 . The indicium, including the digital signature, is passed to the processor  12 , which then passes the assembled indicium to printer  16  for printing on a mail piece. Alternatively, processor  12  could perform some of the operations related to generation of the indicium that do not require secure cryptographic processing. 
     In accordance with the present invention, the operations performed by the PSD  14  in generating an indicium are separated into three different sections: a pre-debit operation section, a perform debit operation section, and a complete debit operation section. In the pre-debit section, the postage value, mailing date, and other data needed to produce the indicium are input into the PSD  14 . In the perform debit section, the registers  20 ,  22  of PSD  14  are updated based on the postage amount. Performance of this section is the most time critical, as once the registers  20 ,  22  have been updated, i.e., accounting for the postage has been completed, they can not be re-credited with the amount of postage if the indicium is not printed. Accordingly, if the perform debit operation has occurred and the indicium is not printed on a mail piece, the user risks losing the postage value. Thus, the perform debit operation is preferably not performed until the mail piece on which the indicium is to be printed has passed a “point of no return,” thereby providing some assurance that printing of the indicium will occur. In the complete debit operation, the data from registers  20 ,  22  is logged to redundant registers (not shown) in PSD  14 , along with other maintenance functions necessary for the PSD  14 . Further according to the present invention, the calculation of the digital signature may be completely pre-computed or alternatively, computed in stages, i.e., partial signature calculation. Utilizing this granularity, the cryptographic operations associated with generating the digital signature can be shifted between the three debit operations such that the execution time of the time critical portion of the debit operation (perform debit) can be optimized to meet the performance requirements of the mailing machine  10  in which the PSD  14  is deployed as will be further described below. 
     Referring now to  FIG. 2 , there is illustrated in flow chart form the processing for a general debit operation according to the present invention. In step  40 , initialization data is received by PSD  14 . Such initialization data includes, for example, postage value, submission date, and other relevant data necessary for the generation of the indicia and digital signature. In step  42 , the constant portion of the first signature is calculated by processor  24  of PSD  14 , or alternatively, the complete signature may be pre-computed in step  42 . A signature is computed by completing two calculations utilizing various parameters. For example, the DSA algorithm uses the following predetermined parameters known by the PSD  14 :
         p=a prime number between 512 and 1024 bits in length;   q=a 160 bit prime factor of (p−1);   g=h (p−1)/q  mod p, where h is any number less than p−1 such that h (p−1)/q  mod p&gt;1;   x=a number less than q (this is the private key);   y=g x  mod p (this is the public key).       

     The 40-byte signature, comprising two portions r and s as defined below, is computed using the following additional parameters:
         k=a random number less than q (determined by processor  24  of PSD  14 );   m=the message to be signed; and   H(m)=the hash of the message to be signed.       

     The values for r and s of the signature are calculated as follows:
 
 r =( g   k  mod  p )mod  q   (1)
 
 s =( k   −1 *( H ( m )+ x*r ))mod  q   (2)
 
     Because the only variables in the signature data are the random number k, which is determined by processor  24 , the message m and the message hash H(m), the value of r in equation (1) above can be pre-computed in step  42 . In addition, in step  42  the values for k −1  and k −1 *x*r can also be computed, thus reducing the time required for calculation of the value of s in equation (2), or, alternatively, if the message is known, the value for s can be computed in step  42  as well, thereby pre-computing the complete signature. 
     In step  50  the registers  20 ,  22  of PSD  14  are adjusted, i.e., funds are debited from register  22  and register  20  is updated to reflect the postage amount. In step  52 , a Message Authentication Code (MAC) for the human readable data in the indicium is completed, thereby completing generation of the indicium. If the complete signature has not already been calculated, then in step  54 , the complete signature is calculated, i.e., the value of s is calculated using equation (2) above. Alternatively, instead of a MAC, the entire indicium data block, including the barcode data, the completed signature of the barcode data and the human readable data, can be over-signed with a second signature. In step  56 , the generated data, including the indicium and signature (and over-signature if used), is output to processor  12  of mailing machine  10 . 
     In step  58 , the processor  12  of mailing machine  10  performs postage meter processing, including, for example, formatting the data received from PSD  14  for printing, generating a bit map of the indicium (if necessary), and calculating an error correction code for the formatted data. In step  60 , the indicium, including the digital signature, is printed on a mail piece by printer  16  of mailing machine  10 . The processing then continues to step  80  to determine if a new indicium is to be generated for a next mail piece. 
     According to the present invention, while the postage meter processing in step  58  and printing of the indicium in step  60  are being performed, PSD  14  can optionally be performing functions for the next indicium to be generated. For example, in step  62 , processor  24  of PSD  14  can perform register housekeeping, i.e., data from registers  20 ,  22  is logged to redundant registers (not shown) in PSD  14 , along with other maintenance functions necessary for the PSD  14 . In step  64 , the constant portion of the next signature, i.e., the value for r, can be calculated using equation (1) above, or alternatively, the next complete signature can be pre-computed similarly as described with respect to step  42 . If the next complete signature is not pre-computed in step  64 , then in step  66  at least a portion of the variable portion of the next signature, i.e., the values for k −1  and k −1 *x*r, can be computed, thus reducing the time required for complete calculation of the value of s in equation (2) when that computation is performed. In step  68 , the MAC of the human readable data (or over-signature) for the next indicium is begun. The processing then continues to step  80  to determine if a new indicium is to be generated for a next mail piece. 
     In step  80 , it is determined if a new indicium is being generated. If no new indicium is being generated, then in step  82  the session ends. If in step  80  it is determined that a new indicium is being generated, then in step  84  it is determined if new initialization data is being entered, such as, for example, the weight of the next mail piece is different than the previous mail piece thereby altering the message m and correspondingly the hash of the message H(m), as well as the human readable data. If no new initialization data is being entered, then the processing returns to step  50  to begin the perform debit section utilizing the signature (or portions thereof) calculated in steps  64 - 68 . If in step  84  it is determined that new initialization data is being entered, then the processing returns to step  40  and the calculations previously performed in steps  64 - 68  may have to be recalculated in any one of steps  42 ,  52  and  54  (or any combination thereof) for the next indicium. In addition, it should be understood that calculation of the next signature could begin in the complete debit section of the previous indicium and be completed in the pre-debit section of the current indicium. Thus, the pre-debit section is necessary only if information provided to the PSD  14  has changed, such as, for example, the weight of the mail piece and accordingly the postage value, the submission date, or other necessary indicia data. 
     As illustrated in  FIG. 2 , the entire debit operation is separated into three different sections: the pre-debit operation including steps  40 - 42 , the perform debit operation including steps  50 - 56 , and the complete debit operation including steps  58 - 60 , and optionally in parallel steps  62 - 68 . The timing diagram illustrated in  FIG. 3  represents the debit scenario in a PSD  14  with timing requirements for a mail piece cycle of z milliseconds (ms). As illustrated, the timing cycle does not begin until the perform debit operation begins at t=0. The operations performed within the perform debit section (steps  50 - 56  of  FIG. 2 ) must be completed within a window of time t 1  (illustrated in  FIG. 3  as x ms) to allow the other components of mailing machine, such as, for example, processor  12  and printer  16 , to complete their necessary functions within the allotted time t 2  (illustrated in  FIG. 3  as y ms). As noted above, since the total mail piece cycle must not be more than z ms, the sum of x and y must not be greater than z. In accordance with the present invention, the time required for the calculation of the complete signature and MAC (or over-signature) can be significantly reduced by pre-calculating at least a portion of the signature and/or MAC (or over-signature) in the pre-debit section or in parallel with the complete debit section. Accordingly, the total time required for the most time critical part of the entire debit process, i.e., the perform debit operation (x ms in  FIG. 3 ), can be reduced, thereby reducing the total mail piece cycle time (z ms). By reducing the total mail piece cycle time, the throughput of mailing machine  10  in which PSD  14  is installed can be increased. 
     It should be understood that the debit section in which the processing for the cryptographic operations associated with calculating the digital signature is performed can be based on the desired throughput of the mailing machine  10  in which the PSD  14  is installed. Thus, not every step illustrated in  FIG. 2  may be present for a given application. For example,  FIG. 4  illustrates in flow chart form the processing performed by PSD  14  in a mailing machine  10  having a low throughput, thereby providing sufficient time for PSD  14  to generate the indicia and signature within the perform debit section.  FIG. 4  is similar to  FIG. 2 , except for the following. Since the mail piece cycle for the implementation illustrated in  FIG. 4  is of sufficient time to allow PSD  14  to generate the indicia and signature within the perform debit section, it will not be necessary to pre-compute or partially calculate the signature (steps  42 ,  64  and  66  of  FIG. 2 ) or to partially calculate the MAC (or over-signature) (step  68  of  FIG. 2 ). Thus, these steps are not necessary and the MAC for the human readable data (or over-signature) can be calculated completely in step  52 , and the complete signature calculated in step  54 , both within the allowed time frame of the perform debit section for this mail piece cycle. 
     For mailing machines requiring higher throughputs, there may not be sufficient time between each mail piece for PSD  14  to perform the debit and signature functions within the perform debit section. Accordingly, in the present invention, calculation of the complete signature can be moved outside of the perform debit section and performed either in the pre-debit section (step  42 ) or in parallel with the complete debit section (step  64 ). An example of this situation is illustrated in  FIG. 5 , which is similar to  FIG. 2  except for the following. In steps  142  and  164 , the full signature is pre-computed. Thus, it will not be necessary to complete the signature calculation (step  54  of  FIG. 2 ) or to begin the variable part of the next signature (step  66  of  FIG. 2 ). By pre-computing the complete signature, either in the pre-debit section or in the complete debit section in parallel with printing, the time required for the perform debit section can be reduced. By reducing the time required for the perform debit section, the mail piece cycle time can be reduced, thereby increasing the throughput of the mailing machine  10  in which the PSD  14  is installed. 
     In some mailing machines, the time required for printing the indicia (step  60  of  FIG. 2 ) may be insufficient to allow pre-computing of the complete signature in parallel with the printing operation. Accordingly, in the present invention, portions of the complete signature can be calculated in parallel with the printing operation. An example of this situation is illustrated in  FIG. 6 , which is similar to  FIG. 2  except for the following. In step  264 , only the constant portion of the next signature is calculated, and the complete signature calculation occurs in step  54  (or alternatively in step  42 ). In addition, after the first indicium has been printed, and a yes response is received in step  80  and step  84 , it will not be necessary to repeat the calculation of the constant portion in step  42 , after the initialization data is received in step  40 , as this will have already occurred previously in step  64 . By pre-computing a portion of the complete signature, either in the pre-debit section or in the complete debit section in parallel with printing, the time required for the perform debit section can be reduced. By reducing the time required for the perform debit section, the mail piece cycle time can be reduced, thereby increasing the throughput of the mailing machine  10  in which the PSD  14  is installed. 
     Thus, according to the present invention, the entire debit operation performed by the PSD is separated into three different sections: a pre-debit operation, a perform debit operation, and a complete debit operation. In addition, the calculation of the digital signature can optionally be pre-computed or, alternatively, computed in stages, i.e., partial signature calculation. Utilizing this granularity, the cryptographic operations associated with generating the digital signature can be shifted between the three debit operations such that the execution time of the time critical portion of the debit operation (perform debit) can be optimized to meet the performance requirements of the mailing machine in which the PSD is deployed. 
     It should be understood that while the present invention has been described with respect to use of the DSA algorithm for calculating signatures, the invention is not so limited and can be used with any type of algorithm utilized for cryptographic operations. 
     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.