Module java.base
Package java.security.spec

Class ECFieldF2m

  • All Implemented Interfaces:
    ECField

    public class ECFieldF2m
extends Object
implements ECField
    This immutable class defines an elliptic curve (EC) characteristic 2 finite field.
    Since:
    1.5
    See Also:
    ECField

    • Constructor Summary

      Constructors 
      Constructor Description
      ECFieldF2m​(int m)
      Creates an elliptic curve characteristic 2 finite field which has 2^m elements with normal basis.
      ECFieldF2m​(int m, int[] ks)
      Creates an elliptic curve characteristic 2 finite field which has 2^m elements with polynomial basis.
      ECFieldF2m​(int m, BigInteger rp)
      Creates an elliptic curve characteristic 2 finite field which has 2^m elements with polynomial basis.

    • Constructor Detail

      • ECFieldF2m

        public ECFieldF2m​(int m)
        Creates an elliptic curve characteristic 2 finite field which has 2^m elements with normal basis.
        Parameters:
        m - with 2^m being the number of elements.
        Throws:
        IllegalArgumentException - if m is not positive.

      • ECFieldF2m

        public ECFieldF2m​(int m,
                  BigInteger rp)
        Creates an elliptic curve characteristic 2 finite field which has 2^m elements with polynomial basis. The reduction polynomial for this field is based on rp whose i-th bit corresponds to the i-th coefficient of the reduction polynomial.

        Note: A valid reduction polynomial is either a trinomial (X^m + X^k + 1 with m > k >= 1) or a pentanomial (X^m + X^k3 + X^k2 + X^k1 + 1 with m > k3 > k2 > k1 >= 1).

        Parameters:
        m - with 2^m being the number of elements.
        rp - the BigInteger whose i-th bit corresponds to the i-th coefficient of the reduction polynomial.
        Throws:
        NullPointerException - if rp is null.
        IllegalArgumentException - if m is not positive, or rp does not represent a valid reduction polynomial.

      • ECFieldF2m

        public ECFieldF2m​(int m,
                  int[] ks)
        Creates an elliptic curve characteristic 2 finite field which has 2^m elements with polynomial basis. The reduction polynomial for this field is based on ks whose content contains the order of the middle term(s) of the reduction polynomial. Note: A valid reduction polynomial is either a trinomial (X^m + X^k + 1 with m > k >= 1) or a pentanomial (X^m + X^k3 + X^k2 + X^k1 + 1 with m > k3 > k2 > k1 >= 1), so ks should have length 1 or 3.
        Parameters:
        m - with 2^m being the number of elements.
        ks - the order of the middle term(s) of the reduction polynomial. Contents of this array are copied to protect against subsequent modification.
        Throws:
        NullPointerException - if ks is null.
        IllegalArgumentException - ifm is not positive, or the length of ks is neither 1 nor 3, or values in ks are not between m-1 and 1 (inclusive) and in descending order.

    • Method Detail

      • getFieldSize

        public int getFieldSize​()
        Returns the field size in bits which is m for this characteristic 2 finite field.
        Specified by:
        getFieldSize in interface ECField
        Returns:
        the field size in bits.

      • getM

        public int getM​()
        Returns the value m of this characteristic 2 finite field.
        Returns:
        m with 2^m being the number of elements.

      • getReductionPolynomial

        public BigInteger getReductionPolynomial​()
        Returns a BigInteger whose i-th bit corresponds to the i-th coefficient of the reduction polynomial for polynomial basis or null for normal basis.
        Returns:
        a BigInteger whose i-th bit corresponds to the i-th coefficient of the reduction polynomial for polynomial basis or null for normal basis.

      • getMidTermsOfReductionPolynomial

        public int[] getMidTermsOfReductionPolynomial​()
        Returns an integer array which contains the order of the middle term(s) of the reduction polynomial for polynomial basis or null for normal basis.
        Returns:
        an integer array which contains the order of the middle term(s) of the reduction polynomial for polynomial basis or null for normal basis. A new array is returned each time this method is called.

      • equals

        public boolean equals​(Object obj)
        Compares this finite field for equality with the specified object.
        Overrides:
        equals in class Object
        Parameters:
        obj - the object to be compared.
        Returns:
        true if obj is an instance of ECFieldF2m and both m and the reduction polynomial match, false otherwise.
        See Also:
        Object.hashCode(), HashMap