Franking system

This invention relates to a method of franking postal items by which postal authorities are enabled to account for charges relating to the handling of mail items and to obtain payment for such charges from the sender of the mail items. The invention also relates to franking apparatus for carrying out the method.

Currently used postage payment systems for franking machines fall into two categories. In one category, in which the postage is prepaid, the franking machine is constructed and operated to securely maintain a record of credit remaining available to a user of the machine and the machine is controlled to lock if and when the credit level decreases to a predetermined low value. Consequently if this low credit level is reached and the machine locks, the machine is unable to be used for further franking until such time as payment has been received by the postal authority for additional credit and the new credit value has been entered in the machine. In the other category in which a post payment method is used, the meter is read periodically and the user invoiced accordingly, use of the franking machine is constrained by controls which lock the machine when total postage value used exceeds a predetermined limit. In both of these categories of system it is necessary for the franking machine to incorporate security measures to prevent fraudulent use of the machine. In order to maintain the integrity of the security complex control systems are used in the internal operation of the machine and the franking machine is constructed to be physically robust and is provided with sealing devices to prevent unauthorised access to the interior of the machine. In addition to the security maintained in the franking machine, the postal authorities operate an elaborate manual procedure for checking franked mail items which necessitates restriction of location at which franked mail can be posted by any sender. The maintenance of security in the franking machine increases the cost of the franking machine and this together with restrictive posting procedures tends to limit the use of franking machines to those users which have a relatively large volume of postal usage.

Broadly the invention relates to a system of franking mail items comprising printing franking data in machine readable form on said mail items by senders of said items, said franking data including at least data relating to a postage charge for the item encoded in a secure manner to prevent unauthorised printing of said data relating to the postal charge and identification data; utilizing a data reading device to read said imprinted franking data from the mail items at a postal authority location to provide data signals relating to each mail item; utilizing said data signals to generate a transaction record for each of the franked items and utilizing said transaction records to generate a billing account for each sender of franked mail items.

EP 0 132 782 discloses a system for printing postage indicia on mail items in which the indicia is printed in plain form and in encrypted form. Encryption of the postage indicia is effected by use of a base seed number which is modified by postage data such as postage amount and date. When the item is received by a postal authority, the indicia in plain form is read and is encrypted in the same manner as at the sending station. The resulting encrypted form is then compared with the encrypted form read from the item to validate the indicia on the item. According to US-A-3 792 446, data transfer to a franking machine is secured by pseudo-random numbers individually issued and compared.

According to one aspect of the invention there is provided a method of franking mail items in a franking machine in which encrypted data is printed in machine readable form on the mail items comprising the steps of generating a pseudo-random number relating to a franking transaction; forming a data block containing at least said pseudo-random number and data relating to a postal charge for said mail item; encrypting said data block; printing in machine readable form on the mail item (10) data (12) representing said encrypted data block together with identification data identifying a location at which the mail items are franked and with identification data identifying said franking machine, and carrying out, at a postal authority location, the steps of machine reading the printed data representing the identification data and the encrypted data block (12); selecting from a record of decryption keys a decryption key corresponding to said identification data identifying said franking machine; utilising said selected decryption key to decrypt said encrypted data block read from the mail item (10) and checking validity of the pseudo-random number contained in said data block.

In accordance with a second aspect of the invention there is provided franking apparatus including a franking machine having printing means (16) to print encrypted data in machine readable form on mail items having means (18) to generate a pseudo-random number for each franking transaction; means (18) to form a data block by combining said pseudo-random number with a postal value selected for franking the mail item; means for encrypting said data block; and in which the printing means (16) is operated to print in machine readable form on the mail item franking data representing said data block together with identification data identifying a location at which the mail item is franked and identification data identifying said franking machine, and having at a postal authority location, reading means to read the printed franking data representing said data block and the identification data; means to select from a record of decryption keys a decryption key corresponding to the identification data identifying said franking machine; means operable to utilise said selected decryption key to decrypt said data block read from the mail item and means to check the validity of the pseudo-random number.

A method of and apparatus for carrying out the invention will now be described by way of example with reference to the drawings in which:- <ul id="ul0001" list-style="none" compact="compact"><li>Figure 1 shows a franking impression on a mail item</li><li>Figure 2 is a flow diagram of the operation of a franking machine</li><li>Figure 3 is a flow diagram of procedures carried out at a postal authority centre and</li><li>Figure 4 is a block diagram of franking apparatus.</li></ul>

Referring first to Figure 1, a franking printed onto a mail item 10 comprises two parts indicated as 11 and 12. The part 11 consists of a typical franking such as is applied by current franking machines to enable visual inspection of a mail item to ascertain that it has been correctly franked with a value of postage appropriate to the size or weight of the item, the destination of the item and the postal service such as surface mail or airmail required by the sender. The franking consists of a predetermined pattern as governed by rules laid down by the postal authority and usually includes not only the value of postage but also the date of franking and the licence number of the franking machine. At the time of printing the franking additional information such as a slogan 13 may be printed on the mail item alongside the franking. In addition the franking impression includes the portion 12 consisting of an impression in a coded form which can be read by machine. The coded impression may take a number of forms, the form illustrated consisting of a bar code in which data is represented in binary notation by spaced bars of one or other of two widths. In printing the franking, it is usual for the mail item, an envelope in this present example, to be fed in a direction left to right as seen in Figure 1 in which the upper edge 14 engages and is guided by a guide on the franking machine and the right hand edge 15 is the leading edge of the envelope. These edges 14 and 15 of the mail item serve as datum edges for the positioning of the franking impression on the item. The bars of the bar code, in the portion 12 of the franking, extend transversely to the direction of feeding of the mail item and are spaced apart in the direction of feeding of the mail item. The portion 12 may consist of a single row of bars or where the quantity of data to be represented would require an unduly long row of bars, the data may be represented by bars arranged in a number of rows, for example two rows, as shown in Figure 1. It will be appreciated that instead of printing directly onto the envelope, the mail item on which printing is effected may comprise an adhesive label for subsequent application to an envelope or parcel. Conveniently, the franking may be printed by a thermal print head 16 (Figure 4) which has a plurality of print elements disposed along a line extending transversely to the direction of feeding of the mail item. The print elements are selectively energised in synchronism with the feeding of the mail item in such a manner as to achieve printing of the required franking impression. Since the portion 12 consisting of coded data is required to be read by machine it is desirable to check the printing of the bar code by a reading device 17 positioned upstream and immediately adjacent the print head. The data represented by the bar code in the portion 12 of the franking impression includes date of franking, postage value and franking machine identification which conveniently may be the licence number of the franking machine. In addition the despatch postal area code is included and the destination postal code may be included. In order to ensure that the data, particularly that relating to the postage value, is valid and is secure from attempts to fraudulently print or tamper with that data, the data is formed into a secure code or data block. This is effected by causing the franking machine to generate a pseudo random number and to combine this with at least the postal value to form a data block. This data block is then encrypted using a secure encryption key held in non-volatile memory in the franking machine. The licence number of the franking machine and the despatch and destination areas codes are combined with the secure data block after encryption. The pseudo random numbers are generated in a sequence so that successive numbers of the sequence are used for each franking transaction. A franking transaction may comprise franking of an individual mail item or may comprise franking of all mail items during a predetermined time period, for example one day. Thus, in the latter instance, the pseudo random number is reset for each day and this may be effected by an algorithm triggered by resetting the date in the franking machine. Thus the data block for each franking transaction is unique. As will be seen from Figure 4, the franking machine includes electronic circuits 18 operable to control operation of the print head 16 and to receive output signals from the reading device 17. Non-volatile memory 19 is provided to store the licence number of the franking machine and any other data which may be required in the operation of the machine. The circuits 18 are operable under the control of software programs to generate pseudo random numbers in sequence and to form a data block by combining a postage charge value input on a keyboard 20, or from another source, and to utilise an encryption key held in a secure location of memory 19 to encrypt the data block and then carry out a printing operation in which franking data including the encrypted data block is printed in the form of a bar code on the mail item fed past the print head 16.

Figure 2 illustrates steps in the franking machine operation from which it will be seen that after encryption of the data block, the portion 12 of the franking impression is printed and, immediately thereafter, is read by the reading device. The output of the reading device is compared with the data block intended to be printed. If the comparison indicates that the printed bar code correctly represents the data block, the operation of the franking machine continues so as to print the visually readable portion 11 of the franking impression and the mail item 10 bearing a complete franking impression 11, 12 and, where desired, a slogan or the like 13 is fed from the franking machine. However if the comparison indicates that the data block is not correctly represented by the printing, printing of the remainder of the franking impression is terminated and a fault message is displayed on the franking machine. The output of the reading device in respect of the whole of the portion 12 of the franking impression may be compared with the whole of the data block intended to be printed. However the processing of the data in the comparison operation may take a length of time such that a pause would be required before continuing after a correct comparison to print the visually readable portion 11 of the franking impression. In order to enable the printing of the entire franking impression to be continuous and uninterrupted, the comparison may be carried out on a probability basis and be in respect of only a leading part of the portion 12 of the franking impression. If a comparison in respect of this part of the portion 12 indicates that this part is correct, a decision would be made to continue printing and the visually readable portion would be printed immediately following printing of the machine readable portion in a continuous printing operation. While such a partial comparison would not check the entire portion 12, on a probability basis, if this part has been correctly printed by the printing device, the printing device will continue to function correctly to print the remainder of the portion 12 and the partial comparison will provide an adequate and sufficient check of the printing.

The postage value and destination code are input to the franking machine by the user, or from another station in a mailing system of which the franking machine is a part. The date of franking may be set automatically from a clock device in the franking machine and the licence number is read from a location of non-volatile memory where it is stored.

The licence numbers and corresponding users secure encryption keys are held in a data base accessible by mail handling apparatus at a postal authority location. Referring to Figure 3, when the franked mail item 10 is received at the postal authority location, it is fed into an automatic mail handling apparatus. The apparatus includes a suitable code reader for reading the bar code of the portion 12 of the franking impression. Upon reading the licence number from the portion 12 of the franking impression, the data base is accessed to obtain the secure encryption key associated with that licence number and the key is utilised to decrypt the secure data block represented by the bar code of portion 12 of the franking impression. Validation checks are carried out on the data within the block to check validity of the data. The validity checks include a check to ensure that the data read from the secure block is error free, a check on the pseudo random number to ensure that it is a valid current pseudo random number, a check that the licence number of the machine relates to a current account with the postal authority and a check that the date and value of franking have allowable values. If the validation checks indicate that the coded franking impression is valid and acceptable by the postal authority the mail item is fed for sorting and handling in the usual manner. If the portion 12 of the franking impression includes destination data for the mail item, reading of this destination data by the code reader may be utilised to control mechanical sorting apparatus to direct the mail item to an appropriate destination area bin. In the event that either the reading of the code portion 12 indicates a faulty reading of the data or the validity check on data in the secure data block indicates that the data is not valid, the mail item is directed to a station where a manual check of the franking impression can be effected. If, from the manual check, the franking impression is judged to be valid the franking and destination details are entered manually at a keyboard terminal and the item is re-introduced into the mechanical handling system. On the other hand, if it appears that the franking impression is invalid and possibly results from an attempted fraudulent action, the mail item may be passed to a supervisor for attention. The franking data read from the portion 12 of the franking impression and after decryption of the secure data block, together with similar franking data entered manually on the keyboard terminal is utilised to enter the postal charge for the mail item as a transaction on a computerised accounting system. Billing of users of the franking machines may be effected from the accounting system and in addition reports concerning usage of the mail handling system may be produced for management and other purposes.