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Circuit and method for decompressing compressed elliptic curve points

  • US 6,199,086 B1
  • Filed: 12/24/1997
  • Issued: 03/06/2001
  • Est. Priority Date: 12/24/1997
  • Status: Expired due to Term
First Claim
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1. An elliptic curve processing circuit comprising:

  • a finite field arithmetic logic unit comprising a finite field square circuit, a finite field inverse circuit, a finite field multiplier circuit, and a finite field adder circuit;

    first and second operation registers;

    a storage element; and

    a control unit coupled to the finite field arithmetic logic unit, to the storage element, and to the first and second operation registers, the control unit being programmed to configure the elliptic curve processing circuit to decompress binary information representing a compressed elliptic curve point by;

    (a)loading a plurality of bits representing a corresponding X coordinate into the first operation register;

    (b)coupling the contents of the first operation register to the finite field arithmetic logic unit to compute a first plurality of bits according to an elliptic curve equation and loading the first plurality of bits into the second operation register;

    (c)loading into the storage element and also into a least significant bit position of the second operation register a single bit which represents the compressed Y coordinate of a compressed elliptic curve point;

    (d)coupling the contents of the second operation register and the storage element to the finite field arithmetic logic unit to determine a second plurality of bits which replace the contents of the second operation register, wherein a most significant bit of the second plurality of bits is equal to the single bit representing the compressed Y coordinate; and

    (e)coupling the contents of the first operation register and the second operation register to the finite field arithmetic logic unit to multiply the second plurality of bits in the second operation register by the plurality of bits representing the X coordinate to generate a product which is a third plurality of bits representing a decompressed Y coordinate.

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