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  Method and device to guarantee the integrity and authenticity of a set of dataRelated Patent Categories: Cryptography, Video CryptographyThe Patent Description & Claims data below is from USPTO Patent Application 20050281406. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] This invention concerns the field of the control of the integrity and authenticity of data, and in particular the downloading of software. [0002] The invention is applied to all those apparatuses that contain at least one central unit such as those currently used in information technology, that is to say, with a processor that has at least a part of its program inside a rewrite memory. BACKGROUND OF THE INVENTION [0003] It is well known that the alteration or the damage of data leaves traces in certain parts of the information processed and stored in a memory, either before or after being processed. It is also known that a simple mathematical technique such as "checksum" is used in order to determine if the data taken into consideration has been modified by establishing a checksum reference. [0004] However, it is possible that the control system has also been altered and that it is no longer able to verify the contents of its memory. Thus, during the course of mathematical operations, the propagation of compensatory random errors may occur, giving an identical result to the one expected. Consequently, verification by the known methods will be inoperative in certain cases. [0005] There is, therefore, a problem that is not solved in a satisfactory manner, which consists in improving the reliability and the security achieved by the known verification methods, particularly when the same unit is in charge of calculating its own checksum and of comparing it with a reference value. [0006] It is well known that, in order to render all data modifications visible, a mono-directional operation is used on the data, that is, an operation that is easy to perform in one direction but almost impossible to perform in the other direction. For example, the operation X.sup.Y is easy to carry out, while the operation .sup.YX is much more difficult. [0007] The term collision-free operation means an operation according to which any different combination of data that is entered gives a similar result. [0008] Within the sphere of this invention, this mono-directional operation is a mathematical application H of a source group towards an object group, in which each x element of the source group is attributed with an H.sub.(x) symbol. These functions are particularly useful when there are functions known as Hash, as they are defined on page 27 of the RSA Laboratories publication "Frequently Asked Questions About Today's Cryptography, v.4.0". The x element can be of any length, but H.sub.(X) always has a series of characters of a fixed length (fixed-size string). Such a function is difficult to invert, that is to say, knowing H.sub.(X) does not generally mean that x can be found. It is said to be more collision-free when it is injective, that is, that H.sub.(Y)=H.sub.(X) leads to y=x, or H.sub.(Y).noteq.H.sub.(X) leads to y.noteq.x. SUMMARY OF THE INVENTION [0009] The aim of this invention is to guarantee that the information contained in a pay-T.V. decoder is, on the one hand, that which the control center has transmitted and, on the other hand, has not been altered. [0010] The aim is achieved through the use of a method to check the integrity and authenticity of a set of memorized data (M1 to Mn) in a pay-T.V. decoding unit, consisting of a decoding unit and a security unit, along with a means of communication (NET, REC) with a control center. [0011] This method consists in: [0012] transmitting the data (M1 to Mn) to the security unit; [0013] calculating a check information (H.sub.X) representative of the result of a function called mono-directional and collision-free, carried out on all or only a part of the data (M1 to Mn); [0014] ciphering the check information (Hx) with a first cipher-key (k1); [0015] establishing the conformity of the check information (Hx) by way of a communication to the control center by one of the means of communication. [0016] In this way, the integrity of the data is no longer checked exclusively by the decoding unit in which the data is stored, but is guaranteed by an external unit, considered impenetrable, the security unit. [0017] According to this invention, the decoder itself can carry out the calculations and transmit the results to the security unit, or transmit the data M1 to Mn to the security unit which will than carry out the calculation of the Hash information. [0018] The cipher-keys used to cipher the information with the control center are contained exclusively in the security unit. The decoder does not have the means to decipher these messages and so modify the data transmitted by the control center when the same messages pass through the decoder. [0019] These security units are generally in the form of smart-cards, and include a memory, a microprocessor and a means of communication. [0020] By means of communication we mean either a two-directional connection by a cable, a modem outlet or a Hertzian-wave connection. The principle means of carrying the data and on which messages directed to the security module are forwarded is included in this term. [0021] The verification operation of the conformity of the check information (Hx) may be carried out in various ways. Continue reading... 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