Cryptography – Particular algorithmic function encoding
Reexamination Certificate
1997-11-25
2001-10-09
Wright, Norman M. (Department: 2131)
Cryptography
Particular algorithmic function encoding
C380S054000, C713S176000
Reexamination Certificate
active
06301360
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method by which figure-coded data units such as ASCII characters or any other data identifiable in an unambiguous manner can be encoded using changes in a value located at positions calculated with a reversible function within another data entity.
2. Description of the Related Art
Modern communication services and communication options, which may involve networked personal computers, home banking applications, and the Internet, require an increasingly high volume of communication, especially in the entertainment sector which heavily utilizes multimedia and video on demand. In this context, data security is becoming more and more important, as are associated encoding methods for encoding data to be transmitted, especially those methods which can be implemented in a simple manner and without a high computing complexity.
An important aspect of encoding technology is that an unintended receiver does not obtain access to the information that has been encoded. To accomplish this, the information is encoded in such a manner that another receiver which does not have knowledge of certain key parameters cannot decipher this information.
The authors Toshiki Habutso, Yoshifumi Nishio, Iwao Sase and Shinsako Mori describe a secret key cryptosystem using the iteration of a chaotic card. In this method, a key which is used for encoding information is determined by using a chaos function which is found in a chaos card. No other relevant prior art is known.
SUMMARY OF THE INVENTION
The object of the invention is to present an encoding method for figure-coded data units (that are numerical values) which is simple to carry out and offers high security. This method for encoding the data units utilizes a function which cannot be derived by using its function values as a basis.
In general terms the present invention is a method for encoding sequences consisting of figure-coded data units. The invention contains two general steps: 1) occupying a basic matrix with initial values, and 2) encoding figure coded data from the sequence to be encoded into the basic matrix. An at least two-dimensional basic matrix is occupied with values by at least one feedback function such that the value allocated to a respective cell of the matrix at at least one cell index, which specifies the position of the cell in the matrix, is determined by this feedback function.
For encoding the first (figure coded) data unit from the sequence, a value of the matrix cell is changed whose position within the matrix is calculated by applying a first reversible function to the code number (value) of the first data unit of the sequence to be encoded. For encoding the second data unit from the sequence, a value of the matrix cell is changed whose position within the matrix is calculated by applying a second reversible function, which may or may not be the same as the first reversible function applied to the first data unit, to the code number of both the first and second data units. This process may be continued for the remaining figure coded data units of the sequence.
Advantageous developments of the present invention are as follows.
For encoding the first figure coded data unit from the sequence to be encoded, starting from any arbitrary starting cell of the matrix, the cell indices (i.e., the location within the matrix) of a first encoding cell of the basic matrix are found by the first reversible function by combining the cell indices of the start cell in an unambiguous and reversible manner with the code number/value of the first data unit; the value of this first encoding cell is then changed. For encoding the second figure coded unit from the sequence, the value of a second encoding cell of the basic matrix (this basic matrix being now modified by the coding of the first value) is changed; the indices of the second encoding cell result from the application of the unambiguous reversible combination of the second reversible function and the first encoding cell.
For occupying the basic matrix, a chaos function may be used as a feedback function in which a first function value supplied by the function after repeated iterations of the feedback function may depend on the variation of the function after exceeding a predetermined limit value. If the limit value condition cannot be met, the function value which results after a predefined number of iterations may then be used for occupying the matrix with values.
For calculating the matrix indices of the first encoding cell, the code number of the first data unit is added to at least one arbitrary selection of the basic matrix indices.
For the encoding, the value of a respective encoding cell is changed by the number 1 as the encoding value.
The encoding value represents a numerical value by which a cell in the basic matrix, located at a matrix index determined above, may be changed. This value may be 1, for example, and can depend on the number of previously encoded data units: it may also be determined by using an encoding value chaos function (that is distinct from the chaos function that may be used to occupy the basic matrix).
The matrix with the values contained therein is used as a two-dimensional matrix for generating an image, the values stored in each matrix cell being used as color and/or gray-scale values. The encoding value is scaled with the number of absolutely possible color or gray-scale values.
For the purpose of authentication or identification, respectively, the matrix is applied to any image medium, and may be added to any image data record.
For decoding, the type of matrix is made known which is occupied with values, as in the case of the encoding, with knowledge of the first feedback function and how it is applied, resulting in an output matrix. The encoded sequence matrix is compared value by value with the output matrix in order to find any changed values. For decoding a first changed value, the inverse of the reversible function is applied to the matrix indices and thus the code number of the first data unit is found. An analogous procedure is adopted for a second changed value, in the reverse order as used during the encoding.
The method according to the invention especially advantageously specifies an encoding method in which an encoder and a decoder agree on a function, its parameters and starting values, on a transmission (basic) matrix, and on a manner in which the latter is to be occupied with values. It is only with the knowledge of these parameters that a decoding person can build up this basic matrix (unencoded) in order to be able to decipher encoded information by a comparison in this manner. In this method, certain cells of this basic matrix are advantageously changed in dependence on the figure-coded data units and thus only become decodable by a receiver with the knowledge of the basic matrix. However, this basic matrix is not accessible to a third person since it is occupied with values via a multiple-feedback function such as, for example, a chaos function or another suitable complex function.
A simple solution to the problem addressed by the invention, which is therefore easily carried out, is available by using a two-dimensional or multidimensional matrix in which the matrix indices of the encoding cells are combined with the figure codes of the data units by means of a reversible function in an unambiguous manner. To establish the unambiguousness in applying the reversible function, the matrix cells to be encoded advantageously found by considering the preceding encoding cells.
To save computing complexity, it is advantageously provided to carry out the iteration with the feedback function only until a certain limit value is exceeded, where such a limitation occurs depending on the variation of the feedback function.
The method according to the invention may also advantageously be discontinued after a fixed number of iterations and the function value then available is used for encoding in order to avoid convergence problems and associated endless loops in the c
Bocionek Siegfried
Karls Ingolf
Latocha Wanda
Schutt Dieter
Schiff & Hardin & Waite
Seal James
Siemens Aktiengesellschaft
Wright Norman M.
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