org.bouncycastle.math.ec.rfc7748.X25519 Maven / Gradle / Ivy
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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 to JDK 1.7. Note: this package includes the IDEA and NTRU encryption algorithms.
package org.bouncycastle.math.ec.rfc7748;
public abstract class X25519
{
private static final int C_A = 486662;
private static final int C_A24 = (C_A + 2)/4;
// 0x1
// private static final int[] S_x = new int[] { 1, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
// 0x215132111D8354CB52385F46DCA2B71D440F6A51EB4D1207816B1E0137D48290
private static final int[] PsubS_x = new int[]{ 0x03D48290, 0x02C7804D, 0x01207816, 0x028F5A68, 0x00881ED4, 0x00A2B71D,
0x0217D1B7, 0x014CB523, 0x0088EC1A, 0x0042A264 };
private static int[] precompBase = null;
private static int decode32(byte[] bs, int off)
{
int n = bs[off] & 0xFF;
n |= (bs[++off] & 0xFF) << 8;
n |= (bs[++off] & 0xFF) << 16;
n |= bs[++off] << 24;
return n;
}
private static void decodeScalar(byte[] k, int kOff, int[] n)
{
for (int i = 0; i < 8; ++i)
{
n[i] = decode32(k, kOff + i * 4);
}
n[0] &= 0xFFFFFFF8;
n[7] &= 0x7FFFFFFF;
n[7] |= 0x40000000;
}
private static void pointDouble(int[] x, int[] z)
{
int[] A = X25519Field.create();
int[] B = X25519Field.create();
X25519Field.apm(x, z, A, B);
X25519Field.sqr(A, A);
X25519Field.sqr(B, B);
X25519Field.mul(A, B, x);
X25519Field.sub(A, B, A);
X25519Field.mul(A, C_A24, z);
X25519Field.add(z, B, z);
X25519Field.mul(z, A, z);
}
public synchronized static void precompute()
{
if (precompBase != null)
{
return;
}
precompBase = new int[X25519Field.SIZE * 252];
int[] xs = precompBase;
int[] zs = new int[X25519Field.SIZE * 251];
int[] x = X25519Field.create(); x[0] = 9;
int[] z = X25519Field.create(); z[0] = 1;
int[] n = X25519Field.create();
int[] d = X25519Field.create();
X25519Field.apm(x, z, n, d);
int[] c = X25519Field.create(); X25519Field.copy(d, 0, c, 0);
int off = 0;
for (;;)
{
X25519Field.copy(n, 0, xs, off);
if (off == (X25519Field.SIZE * 251))
{
break;
}
pointDouble(x, z);
X25519Field.apm(x, z, n, d);
X25519Field.mul(n, c, n);
X25519Field.mul(c, d, c);
X25519Field.copy(d, 0, zs, off);
off += X25519Field.SIZE;
}
int[] u = X25519Field.create();
X25519Field.inv(c, u);
for (;;)
{
X25519Field.copy(xs, off, x, 0);
X25519Field.mul(x, u, x);
// X25519Field.normalize(x);
X25519Field.copy(x, 0, precompBase, off);
if (off == 0)
{
break;
}
off -= X25519Field.SIZE;
X25519Field.copy(zs, off, z, 0);
X25519Field.mul(u, z, u);
}
}
public static void scalarMult(byte[] k, int kOff, byte[] u, int uOff, byte[] r, int rOff)
{
int[] n = new int[8]; decodeScalar(k, kOff, n);
int[] x1 = X25519Field.create(); X25519Field.decode(u, uOff, x1);
int[] x2 = X25519Field.create(); X25519Field.copy(x1, 0, x2, 0);
int[] z2 = X25519Field.create(); z2[0] = 1;
int[] x3 = X25519Field.create(); x3[0] = 1;
int[] z3 = X25519Field.create();
int[] t1 = X25519Field.create();
int[] t2 = X25519Field.create();
// assert n[7] >>> 30 == 1;
int bit = 254, swap = 1;
do
{
X25519Field.apm(x3, z3, t1, x3);
X25519Field.apm(x2, z2, z3, x2);
X25519Field.mul(t1, x2, t1);
X25519Field.mul(x3, z3, x3);
X25519Field.sqr(z3, z3);
X25519Field.sqr(x2, x2);
X25519Field.sub(z3, x2, t2);
X25519Field.mul(t2, C_A24, z2);
X25519Field.add(z2, x2, z2);
X25519Field.mul(z2, t2, z2);
X25519Field.mul(x2, z3, x2);
X25519Field.apm(t1, x3, x3, z3);
X25519Field.sqr(x3, x3);
X25519Field.sqr(z3, z3);
X25519Field.mul(z3, x1, z3);
--bit;
int word = bit >>> 5, shift = bit & 0x1F;
int kt = (n[word] >>> shift) & 1;
swap ^= kt;
X25519Field.cswap(swap, x2, x3);
X25519Field.cswap(swap, z2, z3);
swap = kt;
}
while (bit >= 3);
// assert swap == 0;
for (int i = 0; i < 3; ++i)
{
pointDouble(x2, z2);
}
X25519Field.inv(z2, z2);
X25519Field.mul(x2, z2, x2);
X25519Field.normalize(x2);
X25519Field.encode(x2, r, rOff);
}
public static void scalarMultBase(byte[] k, int kOff, byte[] r, int rOff)
{
precompute();
int[] n = new int[8]; decodeScalar(k, kOff, n);
int[] x0 = X25519Field.create();
// int[] x1 = X25519Field.create(); X25519Field.copy(S_x, 0, x1, 0);
int[] x1 = X25519Field.create(); x1[0] = 1;
int[] z1 = X25519Field.create(); z1[0] = 1;
int[] x2 = X25519Field.create(); X25519Field.copy(PsubS_x, 0, x2, 0);
int[] z2 = X25519Field.create(); z2[0] = 1;
int[] A = x1;
int[] B = z1;
int[] C = x0;
int[] D = A;
int[] E = B;
// assert n[7] >>> 30 == 1;
int off = 0, bit = 3, swap = 1;
do
{
X25519Field.copy(precompBase, off, x0, 0);
off += X25519Field.SIZE;
int word = bit >>> 5, shift = bit & 0x1F;
int kt = (n[word] >>> shift) & 1;
swap ^= kt;
X25519Field.cswap(swap, x1, x2);
X25519Field.cswap(swap, z1, z2);
swap = kt;
X25519Field.apm(x1, z1, A, B);
X25519Field.mul(x0, B, C);
X25519Field.carry(A);
X25519Field.apm(A, C, D, E);
X25519Field.sqr(D, D);
X25519Field.sqr(E, E);
X25519Field.mul(z2, D, x1);
X25519Field.mul(x2, E, z1);
}
while (++bit < 255);
// assert swap == 1;
for (int i = 0; i < 3; ++i)
{
pointDouble(x1, z1);
}
X25519Field.inv(z1, z1);
X25519Field.mul(x1, z1, x1);
X25519Field.normalize(x1);
X25519Field.encode(x1, r, rOff);
}
}
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