diff options
Diffstat (limited to 'core/src/main/java/org/spongycastle/math/ec/custom/djb/Curve25519Field.java')
| -rw-r--r-- | core/src/main/java/org/spongycastle/math/ec/custom/djb/Curve25519Field.java | 254 |
1 files changed, 254 insertions, 0 deletions
diff --git a/core/src/main/java/org/spongycastle/math/ec/custom/djb/Curve25519Field.java b/core/src/main/java/org/spongycastle/math/ec/custom/djb/Curve25519Field.java new file mode 100644 index 00000000..2fe484e1 --- /dev/null +++ b/core/src/main/java/org/spongycastle/math/ec/custom/djb/Curve25519Field.java @@ -0,0 +1,254 @@ +package org.spongycastle.math.ec.custom.djb; + +import java.math.BigInteger; + +import org.spongycastle.math.raw.Nat; +import org.spongycastle.math.raw.Nat256; + +public class Curve25519Field +{ + private static final long M = 0xFFFFFFFFL; + + // 2^255 - 2^4 - 2^1 - 1 + 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 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 (Nat256.isZero(x)) + { + Nat256.zero(z); + } + else + { + Nat256.sub(P, x, 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; + } +} |