Electrical computers and digital processing systems: support – Data processing protection using cryptography
Reexamination Certificate
1999-12-09
2004-07-20
Smithers, Matthew (Department: 2137)
Electrical computers and digital processing systems: support
Data processing protection using cryptography
C713S193000, C705S060000, C705S401000
Reexamination Certificate
active
06766455
ABSTRACT:
BACKGROUND OF THE INVENTION
The subject invention relates generally to systems for carrying out cryptographic processes and, more particularly, to systems and methods for increasing the security of such systems; particularly such systems used to verify the payment of postage.
Cryptographic systems have many applications both for the secure transmission of information and for the authentication and verification of the source of information. One such application is the verification of postage.
The vast majority of the Posts around the world require prepayment for postal services provided by the Posts. Prepayment, however, requires verifiable evidence of paid postage. The traditional postage stamp is a prime example of such evidence.
Another is the use of postage meters, which alleviate some shortcomings of postage stamps. The first postage meters were mechanical devices which securely coupled printing and accounting functions. The mechanical meter, which was perfected over the years, became a widespread basic business machine. The accounting and machine control functions were computerized when electronic postage meters were introduced in the late seventies. This enabled new features, including departmental accounting and computerized meter resetting. However, the fundamental security of postage evidencing remained the same; depending on two features: 1) physical security of the printing process, i.e., printing of postage evidence can not occur without appropriate accounting, and 2) forensic delectability, i.e., fraudulent postal indicia can be distinguished from legitimate indicia.
Coupling the printing and accounting mechanism within a secure tamper-evident enclosure provides physical security of printing. Inspection of the device normally reveals tampering. Effective forensic delectability of fraudulent postal indicia depends on non-availability of alternative mechanisms suitable for forging indicia. Until recently, serious attempts to generate fraudulent indicia using an alternate printing mechanism were detectable.
Today, the possible use of readily available, inexpensive computer-driven printers for printing postage evidence offers new opportunities for customer convenience and substantial cost advantages. However, the use of such printers requires new ways of verifying postage evidence, as was first suggested in U.S. Pat. Nos. 4,641,347, 4,641,346, 4,757,537, and 4,775,246. At that time, it was realized that the security of postage evidencing depends on the security of the information printed in the indicium, including message authentication and integrity.
U.S. Pat. No. 4,831,555 and 4,725,718 extended this idea to unsecured printing of postage; disclosing the necessity that at least some of the information in the indicium must appear random to a party not in possession of some secret. Such random looking information is commonly referred to as a digital token.
The basis of postal revenue security in the digital world is two new requirements: 1) security of the digital token generating process, i.e., digital tokens can not be generated without appropriate accounting, and 2) automatic delectability, i.e., fraudulent digital tokens can be detected by automatic means.
A cryptographic transformation applied to selected data on the mailpiece produces the digital token. The data may include postage value, date, postal code of the geographical deposit area, recipient address information, meter data, and piece count. Such data is commonly referred to as postal data. The secret used to generate the digital token is generally a cryptographic key held within the accounting device. A verifier, with access to a verifying key corresponding to the accounting device secret, validates the digital token. Several cryptographic algorithms and protocols have been considered for this purpose. U.S. Pat. No. 4,853,961 describes critical aspects of public-key cryptography for mailing applications. See José Pastor, CRYPTOPOST, A Universal Information-Based Franking System for Automated Mail Processing, Proceedings of the Fourth Advanced Technology Conference of the U.S. Postal Service, Vol. I, pp. 429-442, November 1990. See also José Pastor, CRYPTOPOST, A Cryptographic Application to Mail Processing, Journal of Cryptology, 3 (2), pp. 137-146, November 1990.
Two methods of presenting a postal verifier with fraudulent evidence of payment are a counterfeited indicium and a copied indicium. The former is an unpaid indicium that appears legitimate; in particular which will satisfy a cryptographic verification process. The latter is a replica of a legitimate paid indicium. Such counterfeit indicia will necessarily satisfy any cryptographic verification process and must be detected by other means; e.g. duplicate mailpiece numbers, etc., which form no part of the present invention. The present invention addresses the prevention of counterfeit indicium.
A counterfeit indicium can be detected by verifying the digital token. Verification proves that the digital token was generated by a cryptographic algorithm with access to the secret meter key. The information printed in the indicium and access to a verifying key are sufficient for the detection of counterfeited indicia as long as the secret meter key is confidential. In a public-key system, a digital signature provides the data authentication and integrity check. In a symmetric-key system a message authentication code (MAC) provides a similar check.
Assuming integrity of the verification software and hardware, only a compromised meter secret-key can produce verifiable counterfeit indicia. Meters can be compromised by violating the physical protection of the key by tampering, or by deriving the key from indicia data by cryptanalysis. Generally, tampering is detectable if the physical protection of the secure component of the postage metering system is adequate, for example as set forth in FIPS 140-1, Security Requirements for Cryptographic Modules, National Institute for Standards and Technology, January 1994, and protection against physical tampering forms no part of the subject invention.
In general various cryptographic operations for generating digital tokens to authenticate postal indicia and to verify such indicia are well known and details of various systems need not be discussed further here for an understanding of the subject invention except to note that robustness of all such operations against cryptanalysis depends on the difficulty of solving certain mathematical problems, for example, discrete logarithm problems or factoring a large composite number. (see: The USPS published draft specifications: The INFORMATION BASED INDICIA PROGRAM (IBIP) INDICIUM SPECIFICATION, dated Jun. 13, 1996; The INFORMATION BASED INDICIA PROGRAM POSTAL SECURITY DEVICE SPECIFICATION, dated Jun. 13, 1996; and The INFORMATION BASED INDICIA PROGRAM HOST SYSTEM SPECIFICATION, dated Oct. 9, 1996, which together define the U.S.P.S.'s proposed requirements for a postage payment system based upon cryptographically secured indicia.)
As part of its proposed Information-Based Indicia Program (IBIP), the USPS has proposed 1024 bit RSA, 1024 bit DSS or 160 bit ECDSA as a measure of robustness.
Presently, there are two postage metering types: closed systems and open systems. In a closed system, the system functionality is solely dedicated to metering activity. An open system metering device is a postage evidencing device with a non-dedicated printer that is not securely coupled to a secure accounting module. Open system indicia printed by the non-dedicated printer are made secure by including addressee information in the encrypted evidence of postage printed on the mailpiece for subsequent verification. Examples of open system metering devices include personal computer (PC) based devices with single/multi-tasking operating systems, multi-user applications and digital printers.
Conventional closed system mechanical and electronic postage meters have heretofore secured the link between printing and accounting. The integrity of the physical meter box has been monitored by periodi
Chaclas Angelo N.
Fields Courtney D.
Lemm Brian A.
Pitney Bowes Inc.
Smithers Matthew
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