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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 1.8 and up.
package org.bouncycastle.math.ec.custom.djb;
import java.math.BigInteger;
import java.security.SecureRandom;
import org.bouncycastle.math.raw.Mod;
import org.bouncycastle.math.raw.Nat;
import org.bouncycastle.math.raw.Nat256;
import org.bouncycastle.util.Pack;
public class Curve25519Field
{
private static final long M = 0xFFFFFFFFL;
// 2^255 - 19
static final int[] P = new int[]{ 0xFFFFFFED, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF,
0xFFFFFFFF, 0x7FFFFFFF };
private static final int P7 = 0x7FFFFFFF;
private static final int[] PExt = new int[]{ 0x00000169, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000,
0x00000000, 0x00000000, 0xFFFFFFED, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF,
0x3FFFFFFF };
private static final int PInv = 0x13;
public static void add(int[] x, int[] y, int[] z)
{
Nat256.add(x, y, z);
if (Nat256.gte(z, P))
{
subPFrom(z);
}
}
public static void addExt(int[] xx, int[] yy, int[] zz)
{
Nat.add(16, xx, yy, zz);
if (Nat.gte(16, zz, PExt))
{
subPExtFrom(zz);
}
}
public static void addOne(int[] x, int[] z)
{
Nat.inc(8, x, z);
if (Nat256.gte(z, P))
{
subPFrom(z);
}
}
public static int[] fromBigInteger(BigInteger x)
{
int[] z = Nat256.fromBigInteger(x);
while (Nat256.gte(z, P))
{
Nat256.subFrom(P, z);
}
return z;
}
public static void half(int[] x, int[] z)
{
if ((x[0] & 1) == 0)
{
Nat.shiftDownBit(8, x, 0, z);
}
else
{
Nat256.add(x, P, z);
Nat.shiftDownBit(8, z, 0);
}
}
public static void inv(int[] x, int[] z)
{
Mod.checkedModOddInverse(P, x, z);
}
public static int isZero(int[] x)
{
int d = 0;
for (int i = 0; i < 8; ++i)
{
d |= x[i];
}
d = (d >>> 1) | (d & 1);
return (d - 1) >> 31;
}
public static void multiply(int[] x, int[] y, int[] z)
{
int[] tt = Nat256.createExt();
Nat256.mul(x, y, tt);
reduce(tt, z);
}
public static void multiplyAddToExt(int[] x, int[] y, int[] zz)
{
Nat256.mulAddTo(x, y, zz);
if (Nat.gte(16, zz, PExt))
{
subPExtFrom(zz);
}
}
public static void negate(int[] x, int[] z)
{
if (0 != isZero(x))
{
Nat256.sub(P, P, z);
}
else
{
Nat256.sub(P, x, z);
}
}
public static void random(SecureRandom r, int[] z)
{
byte[] bb = new byte[8 * 4];
do
{
r.nextBytes(bb);
Pack.littleEndianToInt(bb, 0, z, 0, 8);
z[7] &= P7;
}
while (0 == Nat.lessThan(8, z, P));
}
public static void randomMult(SecureRandom r, int[] z)
{
do
{
random(r, z);
}
while (0 != isZero(z));
}
public static void reduce(int[] xx, int[] z)
{
// assert xx[15] >>> 30 == 0;
int xx07 = xx[7];
Nat.shiftUpBit(8, xx, 8, xx07, z, 0);
int c = Nat256.mulByWordAddTo(PInv, xx, z) << 1;
int z7 = z[7];
c += (z7 >>> 31) - (xx07 >>> 31);
z7 &= P7;
z7 += Nat.addWordTo(7, c * PInv, z);
z[7] = z7;
if (Nat256.gte(z, P))
{
subPFrom(z);
}
}
public static void reduce27(int x, int[] z)
{
// assert x >>> 26 == 0;
int z7 = z[7];
int c = (x << 1 | z7 >>> 31);
z7 &= P7;
z7 += Nat.addWordTo(7, c * PInv, z);
z[7] = z7;
if (Nat256.gte(z, P))
{
subPFrom(z);
}
}
public static void square(int[] x, int[] z)
{
int[] tt = Nat256.createExt();
Nat256.square(x, tt);
reduce(tt, z);
}
public static void squareN(int[] x, int n, int[] z)
{
// assert n > 0;
int[] tt = Nat256.createExt();
Nat256.square(x, tt);
reduce(tt, z);
while (--n > 0)
{
Nat256.square(z, tt);
reduce(tt, z);
}
}
public static void subtract(int[] x, int[] y, int[] z)
{
int c = Nat256.sub(x, y, z);
if (c != 0)
{
addPTo(z);
}
}
public static void subtractExt(int[] xx, int[] yy, int[] zz)
{
int c = Nat.sub(16, xx, yy, zz);
if (c != 0)
{
addPExtTo(zz);
}
}
public static void twice(int[] x, int[] z)
{
Nat.shiftUpBit(8, x, 0, z);
if (Nat256.gte(z, P))
{
subPFrom(z);
}
}
private static int addPTo(int[] z)
{
long c = (z[0] & M) - PInv;
z[0] = (int)c;
c >>= 32;
if (c != 0)
{
c = Nat.decAt(7, z, 1);
}
c += (z[7] & M) + ((P7 + 1) & M);
z[7] = (int)c;
c >>= 32;
return (int)c;
}
private static int addPExtTo(int[] zz)
{
long c = (zz[0] & M) + (PExt[0] & M);
zz[0] = (int)c;
c >>= 32;
if (c != 0)
{
c = Nat.incAt(8, zz, 1);
}
c += (zz[8] & M) - PInv;
zz[8] = (int)c;
c >>= 32;
if (c != 0)
{
c = Nat.decAt(15, zz, 9);
}
c += (zz[15] & M) + ((PExt[15] + 1) & M);
zz[15] = (int)c;
c >>= 32;
return (int)c;
}
private static int subPFrom(int[] z)
{
long c = (z[0] & M) + PInv;
z[0] = (int)c;
c >>= 32;
if (c != 0)
{
c = Nat.incAt(7, z, 1);
}
c += (z[7] & M) - ((P7 + 1) & M);
z[7] = (int)c;
c >>= 32;
return (int)c;
}
private static int subPExtFrom(int[] zz)
{
long c = (zz[0] & M) - (PExt[0] & M);
zz[0] = (int)c;
c >>= 32;
if (c != 0)
{
c = Nat.decAt(8, zz, 1);
}
c += (zz[8] & M) + PInv;
zz[8] = (int)c;
c >>= 32;
if (c != 0)
{
c = Nat.incAt(15, zz, 9);
}
c += (zz[15] & M) - ((PExt[15] + 1) & M);
zz[15] = (int)c;
c >>= 32;
return (int)c;
}
}