Class SM9G2Point

java.lang.Object
org.bouncycastle.math.ec.sm9.SM9G2Point
public class SM9G2Point extends Object
Affine point of the group G2 for SM9: the sextic twist E'(F_p2): y^2 = x^3 + 5u (GM/T 0044.5-2016). Immutable. G1 by contrast is an ordinary prime-field curve handled by ECCurve.Fp.

  • Method Details

    • isInfinity

      public boolean isInfinity()

    • add

      public SM9G2Point add(SM9G2Point o)

    • multiply

      public SM9G2Point multiply(BigInteger k)
      Scalar multiplication by a Montgomery ladder, maintaining the invariant r1 = r0 + this and returning [k]this. The loop runs a fixed, scalar-independent number of iterations (the group order bit length) doing exactly one point addition and one doubling per bit, so it removes the Hamming-weight and bit-length leaks of the plain double-and-add it replaces.

      NOTE: this is a hardening, not a full constant-time guarantee. The per-bit if/else selects which running point is updated (a data-dependent branch), the INFINITY fast paths in add(SM9G2Point)/twice() make the leading-zero prefix of the scalar cheaper (leaking its most-significant-bit position), and the underlying F_p2 arithmetic is BigInteger-based and not itself constant time. It is used only for the two secret scalars in offline KGC key derivation ([ks]P2 and [t2]P2); a fully constant-time G2 would need a uniform, sentinel-free point representation over a fixed-limb F_p2.

    • getEncoded

      public byte[] getEncoded()
      Uncompressed encoding 0x04 || x || y, each F_p2 coordinate written high dimension first (u-coefficient then constant), 32 bytes per F_p component; 129 bytes total.

    • decode

      public static SM9G2Point decode(byte[] enc)

    • equals

      public boolean equals(Object other)
      Overrides:
      equals in class Object

    • hashCode

      public int hashCode()
      Overrides:
      hashCode in class Object