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The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5 and up.
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package org.bouncycastle.math.ec;
import java.math.BigInteger;
import java.util.Random;
import org.bouncycastle.util.Arrays;
import org.bouncycastle.util.BigIntegers;
import org.bouncycastle.util.Integers;
public abstract class ECFieldElement
implements ECConstants
{
public abstract BigInteger toBigInteger();
public abstract String getFieldName();
public abstract int getFieldSize();
public abstract ECFieldElement add(ECFieldElement b);
public abstract ECFieldElement addOne();
public abstract ECFieldElement subtract(ECFieldElement b);
public abstract ECFieldElement multiply(ECFieldElement b);
public abstract ECFieldElement divide(ECFieldElement b);
public abstract ECFieldElement negate();
public abstract ECFieldElement square();
public abstract ECFieldElement invert();
public abstract ECFieldElement sqrt();
public ECFieldElement()
{
}
public int bitLength()
{
return toBigInteger().bitLength();
}
public boolean isOne()
{
return bitLength() == 1;
}
public boolean isZero()
{
return 0 == toBigInteger().signum();
}
public ECFieldElement multiplyMinusProduct(ECFieldElement b, ECFieldElement x, ECFieldElement y)
{
return multiply(b).subtract(x.multiply(y));
}
public ECFieldElement multiplyPlusProduct(ECFieldElement b, ECFieldElement x, ECFieldElement y)
{
return multiply(b).add(x.multiply(y));
}
public ECFieldElement squareMinusProduct(ECFieldElement x, ECFieldElement y)
{
return square().subtract(x.multiply(y));
}
public ECFieldElement squarePlusProduct(ECFieldElement x, ECFieldElement y)
{
return square().add(x.multiply(y));
}
public ECFieldElement squarePow(int pow)
{
ECFieldElement r = this;
for (int i = 0; i < pow; ++i)
{
r = r.square();
}
return r;
}
public boolean testBitZero()
{
return toBigInteger().testBit(0);
}
public String toString()
{
return this.toBigInteger().toString(16);
}
public byte[] getEncoded()
{
return BigIntegers.asUnsignedByteArray((getFieldSize() + 7) / 8, toBigInteger());
}
public static abstract class AbstractFp extends ECFieldElement
{
}
public static class Fp extends AbstractFp
{
BigInteger q, r, x;
static BigInteger calculateResidue(BigInteger p)
{
int bitLength = p.bitLength();
if (bitLength >= 96)
{
BigInteger firstWord = p.shiftRight(bitLength - 64);
if (firstWord.longValue() == -1L)
{
return ONE.shiftLeft(bitLength).subtract(p);
}
}
return null;
}
Fp(BigInteger q, BigInteger r, BigInteger x)
{
if (x == null || x.signum() < 0 || x.compareTo(q) >= 0)
{
throw new IllegalArgumentException("x value invalid in Fp field element");
}
this.q = q;
this.r = r;
this.x = x;
}
public BigInteger toBigInteger()
{
return x;
}
/**
* return the field name for this field.
*
* @return the string "Fp".
*/
public String getFieldName()
{
return "Fp";
}
public int getFieldSize()
{
return q.bitLength();
}
public BigInteger getQ()
{
return q;
}
public ECFieldElement add(ECFieldElement b)
{
return new Fp(q, r, modAdd(x, b.toBigInteger()));
}
public ECFieldElement addOne()
{
BigInteger x2 = x.add(ECConstants.ONE);
if (x2.compareTo(q) == 0)
{
x2 = ECConstants.ZERO;
}
return new Fp(q, r, x2);
}
public ECFieldElement subtract(ECFieldElement b)
{
return new Fp(q, r, modSubtract(x, b.toBigInteger()));
}
public ECFieldElement multiply(ECFieldElement b)
{
return new Fp(q, r, modMult(x, b.toBigInteger()));
}
public ECFieldElement multiplyMinusProduct(ECFieldElement b, ECFieldElement x, ECFieldElement y)
{
BigInteger ax = this.x, bx = b.toBigInteger(), xx = x.toBigInteger(), yx = y.toBigInteger();
BigInteger ab = ax.multiply(bx);
BigInteger xy = xx.multiply(yx);
return new Fp(q, r, modReduce(ab.subtract(xy)));
}
public ECFieldElement multiplyPlusProduct(ECFieldElement b, ECFieldElement x, ECFieldElement y)
{
BigInteger ax = this.x, bx = b.toBigInteger(), xx = x.toBigInteger(), yx = y.toBigInteger();
BigInteger ab = ax.multiply(bx);
BigInteger xy = xx.multiply(yx);
return new Fp(q, r, modReduce(ab.add(xy)));
}
public ECFieldElement divide(ECFieldElement b)
{
return new Fp(q, r, modMult(x, modInverse(b.toBigInteger())));
}
public ECFieldElement negate()
{
return x.signum() == 0 ? this : new Fp(q, r, q.subtract(x));
}
public ECFieldElement square()
{
return new Fp(q, r, modMult(x, x));
}
public ECFieldElement squareMinusProduct(ECFieldElement x, ECFieldElement y)
{
BigInteger ax = this.x, xx = x.toBigInteger(), yx = y.toBigInteger();
BigInteger aa = ax.multiply(ax);
BigInteger xy = xx.multiply(yx);
return new Fp(q, r, modReduce(aa.subtract(xy)));
}
public ECFieldElement squarePlusProduct(ECFieldElement x, ECFieldElement y)
{
BigInteger ax = this.x, xx = x.toBigInteger(), yx = y.toBigInteger();
BigInteger aa = ax.multiply(ax);
BigInteger xy = xx.multiply(yx);
return new Fp(q, r, modReduce(aa.add(xy)));
}
public ECFieldElement invert()
{
// TODO Modular inversion can be faster for a (Generalized) Mersenne Prime.
return new Fp(q, r, modInverse(x));
}
// D.1.4 91
/**
* return a sqrt root - the routine verifies that the calculation
* returns the right value - if none exists it returns null.
*/
public ECFieldElement sqrt()
{
if (this.isZero() || this.isOne()) // earlier JDK compatibility
{
return this;
}
if (!q.testBit(0))
{
throw new RuntimeException("not done yet");
}
// note: even though this class implements ECConstants don't be tempted to
// remove the explicit declaration, some J2ME environments don't cope.
if (q.testBit(1)) // q == 4m + 3
{
BigInteger e = q.shiftRight(2).add(ECConstants.ONE);
return checkSqrt(new Fp(q, r, x.modPow(e, q)));
}
if (q.testBit(2)) // q == 8m + 5
{
BigInteger t1 = x.modPow(q.shiftRight(3), q);
BigInteger t2 = modMult(t1, x);
BigInteger t3 = modMult(t2, t1);
if (t3.equals(ECConstants.ONE))
{
return checkSqrt(new Fp(q, r, t2));
}
// TODO This is constant and could be precomputed
BigInteger t4 = ECConstants.TWO.modPow(q.shiftRight(2), q);
BigInteger y = modMult(t2, t4);
return checkSqrt(new Fp(q, r, y));
}
// q == 8m + 1
BigInteger legendreExponent = q.shiftRight(1);
if (!(x.modPow(legendreExponent, q).equals(ECConstants.ONE)))
{
return null;
}
BigInteger X = this.x;
BigInteger fourX = modDouble(modDouble(X));
BigInteger k = legendreExponent.add(ECConstants.ONE), qMinusOne = q.subtract(ECConstants.ONE);
BigInteger U, V;
Random rand = new Random();
do
{
BigInteger P;
do
{
P = new BigInteger(q.bitLength(), rand);
}
while (P.compareTo(q) >= 0
|| !modReduce(P.multiply(P).subtract(fourX)).modPow(legendreExponent, q).equals(qMinusOne));
BigInteger[] result = lucasSequence(P, X, k);
U = result[0];
V = result[1];
if (modMult(V, V).equals(fourX))
{
return new ECFieldElement.Fp(q, r, modHalfAbs(V));
}
}
while (U.equals(ECConstants.ONE) || U.equals(qMinusOne));
return null;
}
private ECFieldElement checkSqrt(ECFieldElement z)
{
return z.square().equals(this) ? z : null;
}
private BigInteger[] lucasSequence(
BigInteger P,
BigInteger Q,
BigInteger k)
{
// TODO Research and apply "common-multiplicand multiplication here"
int n = k.bitLength();
int s = k.getLowestSetBit();
// assert k.testBit(s);
BigInteger Uh = ECConstants.ONE;
BigInteger Vl = ECConstants.TWO;
BigInteger Vh = P;
BigInteger Ql = ECConstants.ONE;
BigInteger Qh = ECConstants.ONE;
for (int j = n - 1; j >= s + 1; --j)
{
Ql = modMult(Ql, Qh);
if (k.testBit(j))
{
Qh = modMult(Ql, Q);
Uh = modMult(Uh, Vh);
Vl = modReduce(Vh.multiply(Vl).subtract(P.multiply(Ql)));
Vh = modReduce(Vh.multiply(Vh).subtract(Qh.shiftLeft(1)));
}
else
{
Qh = Ql;
Uh = modReduce(Uh.multiply(Vl).subtract(Ql));
Vh = modReduce(Vh.multiply(Vl).subtract(P.multiply(Ql)));
Vl = modReduce(Vl.multiply(Vl).subtract(Ql.shiftLeft(1)));
}
}
Ql = modMult(Ql, Qh);
Qh = modMult(Ql, Q);
Uh = modReduce(Uh.multiply(Vl).subtract(Ql));
Vl = modReduce(Vh.multiply(Vl).subtract(P.multiply(Ql)));
Ql = modMult(Ql, Qh);
for (int j = 1; j <= s; ++j)
{
Uh = modMult(Uh, Vl);
Vl = modReduce(Vl.multiply(Vl).subtract(Ql.shiftLeft(1)));
Ql = modMult(Ql, Ql);
}
return new BigInteger[]{ Uh, Vl };
}
protected BigInteger modAdd(BigInteger x1, BigInteger x2)
{
BigInteger x3 = x1.add(x2);
if (x3.compareTo(q) >= 0)
{
x3 = x3.subtract(q);
}
return x3;
}
protected BigInteger modDouble(BigInteger x)
{
BigInteger _2x = x.shiftLeft(1);
if (_2x.compareTo(q) >= 0)
{
_2x = _2x.subtract(q);
}
return _2x;
}
protected BigInteger modHalf(BigInteger x)
{
if (x.testBit(0))
{
x = q.add(x);
}
return x.shiftRight(1);
}
protected BigInteger modHalfAbs(BigInteger x)
{
if (x.testBit(0))
{
x = q.subtract(x);
}
return x.shiftRight(1);
}
protected BigInteger modInverse(BigInteger x)
{
return BigIntegers.modOddInverse(q, x);
}
protected BigInteger modMult(BigInteger x1, BigInteger x2)
{
return modReduce(x1.multiply(x2));
}
protected BigInteger modReduce(BigInteger x)
{
if (r != null)
{
boolean negative = x.signum() < 0;
if (negative)
{
x = x.abs();
}
int qLen = q.bitLength();
boolean rIsOne = r.equals(ECConstants.ONE);
while (x.bitLength() > (qLen + 1))
{
BigInteger u = x.shiftRight(qLen);
BigInteger v = x.subtract(u.shiftLeft(qLen));
if (!rIsOne)
{
u = u.multiply(r);
}
x = u.add(v);
}
while (x.compareTo(q) >= 0)
{
x = x.subtract(q);
}
if (negative && x.signum() != 0)
{
x = q.subtract(x);
}
}
else
{
x = x.mod(q);
}
return x;
}
protected BigInteger modSubtract(BigInteger x1, BigInteger x2)
{
BigInteger x3 = x1.subtract(x2);
if (x3.signum() < 0)
{
x3 = x3.add(q);
}
return x3;
}
public boolean equals(Object other)
{
if (other == this)
{
return true;
}
if (!(other instanceof ECFieldElement.Fp))
{
return false;
}
ECFieldElement.Fp o = (ECFieldElement.Fp)other;
return q.equals(o.q) && x.equals(o.x);
}
public int hashCode()
{
return q.hashCode() ^ x.hashCode();
}
}
public static abstract class AbstractF2m extends ECFieldElement
{
public ECFieldElement halfTrace()
{
int m = this.getFieldSize();
if ((m & 1) == 0)
{
throw new IllegalStateException("Half-trace only defined for odd m");
}
// ECFieldElement ht = this;
// for (int i = 1; i < m; i += 2)
// {
// ht = ht.squarePow(2).add(this);
// }
int n = (m + 1) >>> 1;
int k = 31 - Integers.numberOfLeadingZeros(n);
int nk = 1;
ECFieldElement ht = this;
while (k > 0)
{
ht = ht.squarePow(nk << 1).add(ht);
nk = n >>> --k;
if (0 != (nk & 1))
{
ht = ht.squarePow(2).add(this);
}
}
return ht;
}
public boolean hasFastTrace()
{
return false;
}
public int trace()
{
int m = this.getFieldSize();
// ECFieldElement tr = this;
// for (int i = 1; i < m; ++i)
// {
// tr = tr.square().add(this);
// }
int k = 31 - Integers.numberOfLeadingZeros(m);
int mk = 1;
ECFieldElement tr = this;
while (k > 0)
{
tr = tr.squarePow(mk).add(tr);
mk = m >>> --k;
if (0 != (mk & 1))
{
tr = tr.square().add(this);
}
}
if (tr.isZero())
{
return 0;
}
if (tr.isOne())
{
return 1;
}
throw new IllegalStateException("Internal error in trace calculation");
}
}
/**
* Class representing the Elements of the finite field
* F2m in polynomial basis (PB)
* representation. Both trinomial (TPB) and pentanomial (PPB) polynomial
* basis representations are supported. Gaussian normal basis (GNB)
* representation is not supported.
*/
public static class F2m extends AbstractF2m
{
/**
* Indicates gaussian normal basis representation (GNB). Number chosen
* according to X9.62. GNB is not implemented at present.
*/
public static final int GNB = 1;
/**
* Indicates trinomial basis representation (TPB). Number chosen
* according to X9.62.
*/
public static final int TPB = 2;
/**
* Indicates pentanomial basis representation (PPB). Number chosen
* according to X9.62.
*/
public static final int PPB = 3;
/**
* TPB or PPB.
*/
private int representation;
/**
* The exponent m of F2m.
*/
private int m;
private int[] ks;
/**
* The LongArray holding the bits.
*/
LongArray x;
/**
* Constructor for PPB.
* @param m The exponent m of
* F2m.
* @param k1 The integer k1 where xm +
* xk3 + xk2 + xk1 + 1
* represents the reduction polynomial f(z).
* @param k2 The integer k2 where xm +
* xk3 + xk2 + xk1 + 1
* represents the reduction polynomial f(z).
* @param k3 The integer k3 where xm +
* xk3 + xk2 + xk1 + 1
* represents the reduction polynomial f(z).
* @param x The BigInteger representing the value of the field element.
*/
F2m(
int m,
int k1,
int k2,
int k3,
BigInteger x)
{
if (x == null || x.signum() < 0 || x.bitLength() > m)
{
throw new IllegalArgumentException("x value invalid in F2m field element");
}
if ((k2 == 0) && (k3 == 0))
{
this.representation = TPB;
this.ks = new int[]{ k1 };
}
else
{
if (k2 >= k3)
{
throw new IllegalArgumentException(
"k2 must be smaller than k3");
}
if (k2 <= 0)
{
throw new IllegalArgumentException(
"k2 must be larger than 0");
}
this.representation = PPB;
this.ks = new int[]{ k1, k2, k3 };
}
this.m = m;
this.x = new LongArray(x);
}
F2m(int m, int[] ks, LongArray x)
{
this.m = m;
this.representation = (ks.length == 1) ? TPB : PPB;
this.ks = ks;
this.x = x;
}
public int bitLength()
{
return x.degree();
}
public boolean isOne()
{
return x.isOne();
}
public boolean isZero()
{
return x.isZero();
}
public boolean testBitZero()
{
return x.testBitZero();
}
public BigInteger toBigInteger()
{
return x.toBigInteger();
}
public String getFieldName()
{
return "F2m";
}
public int getFieldSize()
{
return m;
}
public ECFieldElement add(final ECFieldElement b)
{
// No check performed here for performance reasons. Instead the
// elements involved are checked in ECPoint.F2m
// checkFieldElements(this, b);
LongArray iarrClone = (LongArray)this.x.clone();
F2m bF2m = (F2m)b;
iarrClone.addShiftedByWords(bF2m.x, 0);
return new F2m(m, ks, iarrClone);
}
public ECFieldElement addOne()
{
return new F2m(m, ks, x.addOne());
}
public ECFieldElement subtract(final ECFieldElement b)
{
// Addition and subtraction are the same in F2m
return add(b);
}
public ECFieldElement multiply(final ECFieldElement b)
{
// Right-to-left comb multiplication in the LongArray
// Input: Binary polynomials a(z) and b(z) of degree at most m-1
// Output: c(z) = a(z) * b(z) mod f(z)
// No check performed here for performance reasons. Instead the
// elements involved are checked in ECPoint.F2m
// checkFieldElements(this, b);
return new F2m(m, ks, x.modMultiply(((F2m)b).x, m, ks));
}
public ECFieldElement multiplyMinusProduct(ECFieldElement b, ECFieldElement x, ECFieldElement y)
{
return multiplyPlusProduct(b, x, y);
}
public ECFieldElement multiplyPlusProduct(ECFieldElement b, ECFieldElement x, ECFieldElement y)
{
LongArray ax = this.x, bx = ((F2m)b).x, xx = ((F2m)x).x, yx = ((F2m)y).x;
LongArray ab = ax.multiply(bx, m, ks);
LongArray xy = xx.multiply(yx, m, ks);
if (ab == ax || ab == bx)
{
ab = (LongArray)ab.clone();
}
ab.addShiftedByWords(xy, 0);
ab.reduce(m, ks);
return new F2m(m, ks, ab);
}
public ECFieldElement divide(final ECFieldElement b)
{
// There may be more efficient implementations
ECFieldElement bInv = b.invert();
return multiply(bInv);
}
public ECFieldElement negate()
{
// -x == x holds for all x in F2m
return this;
}
public ECFieldElement square()
{
return new F2m(m, ks, x.modSquare(m, ks));
}
public ECFieldElement squareMinusProduct(ECFieldElement x, ECFieldElement y)
{
return squarePlusProduct(x, y);
}
public ECFieldElement squarePlusProduct(ECFieldElement x, ECFieldElement y)
{
LongArray ax = this.x, xx = ((F2m)x).x, yx = ((F2m)y).x;
LongArray aa = ax.square(m, ks);
LongArray xy = xx.multiply(yx, m, ks);
if (aa == ax)
{
aa = (LongArray)aa.clone();
}
aa.addShiftedByWords(xy, 0);
aa.reduce(m, ks);
return new F2m(m, ks, aa);
}
public ECFieldElement squarePow(int pow)
{
return pow < 1 ? this : new F2m(m, ks, x.modSquareN(pow, m, ks));
}
public ECFieldElement invert()
{
return new ECFieldElement.F2m(this.m, this.ks, this.x.modInverse(m, ks));
}
public ECFieldElement sqrt()
{
return (x.isZero() || x.isOne()) ? this : squarePow(m - 1);
}
/**
* @return the representation of the field
* F2m, either of
* TPB (trinomial
* basis representation) or
* PPB (pentanomial
* basis representation).
*/
public int getRepresentation()
{
return this.representation;
}
/**
* @return the degree m of the reduction polynomial
* f(z).
*/
public int getM()
{
return this.m;
}
/**
* @return TPB: The integer k where xm +
* xk + 1 represents the reduction polynomial
* f(z).
* PPB: The integer k1 where xm +
* xk3 + xk2 + xk1 + 1
* represents the reduction polynomial f(z).
*/
public int getK1()
{
return this.ks[0];
}
/**
* @return TPB: Always returns 0
* PPB: The integer k2 where xm +
* xk3 + xk2 + xk1 + 1
* represents the reduction polynomial f(z).
*/
public int getK2()
{
return this.ks.length >= 2 ? this.ks[1] : 0;
}
/**
* @return TPB: Always set to 0
* PPB: The integer k3 where xm +
* xk3 + xk2 + xk1 + 1
* represents the reduction polynomial f(z).
*/
public int getK3()
{
return this.ks.length >= 3 ? this.ks[2] : 0;
}
public boolean equals(Object anObject)
{
if (anObject == this)
{
return true;
}
if (!(anObject instanceof ECFieldElement.F2m))
{
return false;
}
ECFieldElement.F2m b = (ECFieldElement.F2m)anObject;
return ((this.m == b.m)
&& (this.representation == b.representation)
&& Arrays.areEqual(this.ks, b.ks)
&& (this.x.equals(b.x)));
}
public int hashCode()
{
return x.hashCode() ^ m ^ Arrays.hashCode(ks);
}
}
}
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