| 摘要 |
The invention relates to an apparatus and method for enhancing the security of selected information associated with a negotiable document, such as the monetary value of a cheque. In the invention, one or more security features are printed or applied onto the cheque. One such security feature is an encrypted control code. The preferred embodiment employs a secret key cryptographic scheme to encrypt the monetary value and thereby generate a first control code which is printed on tile cheque. When the cheque is presented for payment, a validator, such as bank or cheque cle aring house, employs a verification system having a copy of the encryption key to read the monetary value from the cheque and re-encrypt it according to said scheme to generate a second control code. The cheque is not honoured if the first and second control codes are not identical.Another security feature is a security image, composed, for instance, from a foreground image of the monetary value superimposed over a background motif image. The security image has a number of hidden attributes, such as the relative aspect ratios, absolute and relative dimensions of the underlying foreground and background images, that are preselected and used when printing the security image. When the cheque is presented for payment a teller can visually inspect the security image for compliance with certain of the preselected attributes. The preferred validation system can also electronically scan the security image for the hidden attributes. This comparison makes it difficult for a forger to copy, for instance, the monetary value of the eheque and add a significant digit to it because some of the foregoing preselected image attributes are liable to change and be detected. The composite image serves as a back-up security when verification of the encrypted control code is not possible.
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