internal static BigInteger evenModPow(BigInteger _base, BigInteger exponent,
BigInteger modulus)
{
// PRE: (base > 0), (exponent > 0), (modulus > 0) and (modulus even)
// STEP 1: Obtain the factorization 'modulus'= q * 2^j.
int j = modulus.getLowestSetBit();
BigInteger q = modulus.shiftRight(j);
// STEP 2: Compute x1 := base^exponent (mod q).
BigInteger x1 = oddModPow(_base, exponent, q);
// STEP 3: Compute x2 := base^exponent (mod 2^j).
BigInteger x2 = pow2ModPow(_base, exponent, j);
// STEP 4: Compute q^(-1) (mod 2^j) and y := (x2-x1) * q^(-1) (mod 2^j)
BigInteger qInv = modPow2Inverse(q, j);
BigInteger y = (x2.subtract(x1)).multiply(qInv);
inplaceModPow2(y, j);
if (y.sign < 0)
{
y = y.add(BigInteger.getPowerOfTwo(j));
}
// STEP 5: Compute and return: x1 + q * y
return(x1.add(q.multiply(y)));
}
public static BigInteger karatsuba(BigInteger op1, BigInteger op2)
{
BigInteger temp;
if (op2.numberLength > op1.numberLength) {
temp = op1;
op1 = op2;
op2 = temp;
}
if (op2.numberLength < whenUseKaratsuba) {
return multiplyPAP(op1, op2);
}
/* Karatsuba: u = u1*B + u0
* v = v1*B + v0
* u*v = (u1*v1)*B^2 + ((u1-u0)*(v0-v1) + u1*v1 + u0*v0)*B + u0*v0
*/
// ndiv2 = (op1.numberLength / 2) * 32
int ndiv2 = (int)(op1.numberLength & 0xFFFFFFFE) << 4;
BigInteger upperOp1 = op1.shiftRight(ndiv2);
BigInteger upperOp2 = op2.shiftRight(ndiv2);
BigInteger lowerOp1 = op1.subtract(upperOp1.shiftLeft(ndiv2));
BigInteger lowerOp2 = op2.subtract(upperOp2.shiftLeft(ndiv2));
BigInteger upper = karatsuba(upperOp1, upperOp2);
BigInteger lower = karatsuba(lowerOp1, lowerOp2);
BigInteger middle = karatsuba( upperOp1.subtract(lowerOp1),
lowerOp2.subtract(upperOp2));
middle = middle.add(upper).add(lower);
middle = middle.shiftLeft(ndiv2);
upper = upper.shiftLeft(ndiv2 << 1);
return upper.add(middle).add(lower);
}
private static bool millerRabin(BigInteger n, int t)
{
// PRE: n >= 0, t >= 0
BigInteger x; // x := UNIFORM{2...n-1}
BigInteger y; // y := x^(q * 2^j) mod n
BigInteger n_minus_1 = n.subtract(BigInteger.ONE); // n-1
int bitLength = n_minus_1.bitLength(); // ~ log2(n-1)
// (q,k) such that: n-1 = q * 2^k and q is odd
int k = n_minus_1.getLowestSetBit();
BigInteger q = n_minus_1.shiftRight(k);
Random rnd = new Random();
for (int i = 0; i < t; i++)
{
// To generate a witness 'x', first it use the primes of table
if (i < primes.Length)
{
x = BIprimes[i];
}
else /*
* It generates random witness only if it's necesssary. Note
* that all methods would call Miller-Rabin with t <= 50 so
* this part is only to do more robust the algorithm
*/
{
do
{
x = new BigInteger(bitLength, rnd);
} while ((x.compareTo(n) >= BigInteger.EQUALS) || (x.sign == 0) ||
x.isOne());
}
y = x.modPow(q, n);
if (y.isOne() || y.Equals(n_minus_1))
{
continue;
}
for (int j = 1; j < k; j++)
{
if (y.Equals(n_minus_1))
{
continue;
}
y = y.multiply(y).mod(n);
if (y.isOne())
{
return(false);
}
}
if (!y.Equals(n_minus_1))
{
return(false);
}
}
return(true);
}
public static BigInteger karatsuba(BigInteger op1, BigInteger op2)
{
BigInteger temp;
if (op2.numberLength > op1.numberLength)
{
temp = op1;
op1 = op2;
op2 = temp;
}
if (op2.numberLength < whenUseKaratsuba)
{
return(multiplyPAP(op1, op2));
}
/* Karatsuba: u = u1*B + u0
* v = v1*B + v0
* u*v = (u1*v1)*B^2 + ((u1-u0)*(v0-v1) + u1*v1 + u0*v0)*B + u0*v0
*/
// ndiv2 = (op1.numberLength / 2) * 32
int ndiv2 = (int)(op1.numberLength & 0xFFFFFFFE) << 4;
BigInteger upperOp1 = op1.shiftRight(ndiv2);
BigInteger upperOp2 = op2.shiftRight(ndiv2);
BigInteger lowerOp1 = op1.subtract(upperOp1.shiftLeft(ndiv2));
BigInteger lowerOp2 = op2.subtract(upperOp2.shiftLeft(ndiv2));
BigInteger upper = karatsuba(upperOp1, upperOp2);
BigInteger lower = karatsuba(lowerOp1, lowerOp2);
BigInteger middle = karatsuba(upperOp1.subtract(lowerOp1),
lowerOp2.subtract(upperOp2));
middle = middle.add(upper).add(lower);
middle = middle.shiftLeft(ndiv2);
upper = upper.shiftLeft(ndiv2 << 1);
return(upper.add(middle).add(lower));
}
internal static BigInteger evenModPow(BigInteger _base, BigInteger exponent,
BigInteger modulus)
{
// PRE: (base > 0), (exponent > 0), (modulus > 0) and (modulus even)
// STEP 1: Obtain the factorization 'modulus'= q * 2^j.
int j = modulus.getLowestSetBit();
BigInteger q = modulus.shiftRight(j);
// STEP 2: Compute x1 := base^exponent (mod q).
BigInteger x1 = oddModPow(_base, exponent, q);
// STEP 3: Compute x2 := base^exponent (mod 2^j).
BigInteger x2 = pow2ModPow(_base, exponent, j);
// STEP 4: Compute q^(-1) (mod 2^j) and y := (x2-x1) * q^(-1) (mod 2^j)
BigInteger qInv = modPow2Inverse(q, j);
BigInteger y = (x2.subtract(x1)).multiply(qInv);
inplaceModPow2(y, j);
if (y.sign < 0) {
y = y.add(BigInteger.getPowerOfTwo(j));
}
// STEP 5: Compute and return: x1 + q * y
return x1.add(q.multiply(y));
}
