Secret-key-controlled reversible circuit and corresponding method of data processing
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Abstract
A combinatorial key-dependent network suitable for the encryption/decryption of data on buses and in memories of data-processing devices, has a number of layers, where each layer has a number of elementary building blocks operating on very small block sizes. A generic building block acts on a small number of input data bits, which are divided into two groups of m and n bits, respectively. The m input bits, which are passed to the output intact, are used to select k out of 2mk key bits by a multiplexer circuit; the k bits are then used to select an (n×n)-bit reversible transformation acting on the remaining n input bits to produce the corresponding n output bits. The total number of the key bits in the building block is thus 2mk, which can easily he made larger that m+n. An inverse building block is the same except that the reversible transformations are replaced by their inverses.
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Citations
82 Claims
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1-41. -41. (canceled)
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42. A combinatorial key-dependent network for encryption/decryption of input digital data of word size N into output digital data of the same word size, comprising at least two layers, each layer comprising at least an elementary building block, each building block operating on an input block of bits having a word size n+m smaller than or equal to said word size N, for generating an output block of bits, said building block comprising:
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a multiplexer circuit, receiving on a control input a first portion m of said block of bits, for selecting k out of 2mk key bits on a k-bit output of said multiplexer circuit, said first portion of bits being transferred intact to an output of said building block; and
a transformation circuit, for transforming a remaining portion n of said input block of bits into transformed bits according to a reversible transformation chosen, by means of said selected k bits, among a plurality of reversible transformations implemented in said transformation circuit. - View Dependent Claims (43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 81, 82)
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69. A block for secret-key-controlled cryptographic functions, operating on an input block of bits for generating an output block of bits comprising:
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a multiplexer circuit receiving on a control input a first portion of m bits of said block of bits, for selecting k out of 2mk key bits on a k-bit output of said multiplexer circuit, said first portion of bits being transferred intact to an output of said building block; and
a transformation circuit for transforming a remaining portion of said input block of bits into transformed bits, according to a reversible transformation chosen, by means of said selected k bits, among a plurality of reversible transformations implemented in said transformation circuit. - View Dependent Claims (70, 71, 72, 73, 74, 75, 76)
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77. A method for encryption/decryption of input digital data of word size N into an output digital data of the same word size, comprising;
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a) dividing said input digital data into blocks of bits, each having a word size n+m smaller than said word size N, each block of bits being divided into a first portion m and a second portion n;
b) for each block of bits;
b1) addressing a lookup table containing 2mk key bits, by means of said first portion m of bits, for selecting k out of 2mk key bits, transferring intact said first portion m of bits to a first portion of transformed bits;
b2) selecting, by means of said selected k bits, a reversible transformation among a plurality of reversible transformations;
b3) applying said reversible transformation to said second portion n of bits, thus generating a second portion of transformed bits;
c) collecting the transformed bits from each block into said output digital data. - View Dependent Claims (78, 79, 80)
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Specification