summary refs log tree commit diff
path: root/crypto/src/math/ec
diff options
context:
space:
mode:
Diffstat (limited to 'crypto/src/math/ec')
-rw-r--r--crypto/src/math/ec/ECFieldElement.cs9
-rw-r--r--crypto/src/math/ec/custom/djb/Curve25519Field.cs51
-rw-r--r--crypto/src/math/ec/custom/gm/SM2P256V1Field.cs55
-rw-r--r--crypto/src/math/ec/custom/sec/SecP128R1Field.cs46
-rw-r--r--crypto/src/math/ec/custom/sec/SecP160R1Field.cs53
-rw-r--r--crypto/src/math/ec/custom/sec/SecP160R2Field.cs65
-rw-r--r--crypto/src/math/ec/custom/sec/SecP192K1Field.cs62
-rw-r--r--crypto/src/math/ec/custom/sec/SecP192R1Field.cs53
-rw-r--r--crypto/src/math/ec/custom/sec/SecP224K1Field.cs62
-rw-r--r--crypto/src/math/ec/custom/sec/SecP224R1Field.cs49
-rw-r--r--crypto/src/math/ec/custom/sec/SecP256K1Field.cs60
-rw-r--r--crypto/src/math/ec/custom/sec/SecP256R1Field.cs55
-rw-r--r--crypto/src/math/ec/custom/sec/SecP384R1Field.cs61
-rw-r--r--crypto/src/math/ec/custom/sec/SecP521R1Field.cs57
-rw-r--r--crypto/src/math/ec/rfc7748/X25519Field.cs76
-rw-r--r--crypto/src/math/ec/rfc7748/X448Field.cs80
-rw-r--r--crypto/src/math/ec/rfc8032/Ed25519.cs2
-rw-r--r--crypto/src/math/ec/rfc8032/Ed448.cs2
18 files changed, 159 insertions, 739 deletions
diff --git a/crypto/src/math/ec/ECFieldElement.cs b/crypto/src/math/ec/ECFieldElement.cs
index ef10dbf90..ed530b6b7 100644
--- a/crypto/src/math/ec/ECFieldElement.cs
+++ b/crypto/src/math/ec/ECFieldElement.cs
@@ -1,7 +1,6 @@
 using System;
 using System.Diagnostics;
 
-using Org.BouncyCastle.Math.Raw;
 using Org.BouncyCastle.Utilities;
 
 namespace Org.BouncyCastle.Math.EC
@@ -434,13 +433,7 @@ namespace Org.BouncyCastle.Math.EC
 
         protected virtual BigInteger ModInverse(BigInteger x)
         {
-            int bits = FieldSize;
-            int len = (bits + 31) >> 5;
-            uint[] p = Nat.FromBigInteger(bits, q);
-            uint[] n = Nat.FromBigInteger(bits, x);
-            uint[] z = Nat.Create(len);
-            Mod.Invert(p, n, z);
-            return Nat.ToBigInteger(len, z);
+            return BigIntegers.ModOddInverse(q, x);
         }
 
         protected virtual BigInteger ModMult(BigInteger x1, BigInteger x2)
diff --git a/crypto/src/math/ec/custom/djb/Curve25519Field.cs b/crypto/src/math/ec/custom/djb/Curve25519Field.cs
index 4e4cfbaa5..0006acd94 100644
--- a/crypto/src/math/ec/custom/djb/Curve25519Field.cs
+++ b/crypto/src/math/ec/custom/djb/Curve25519Field.cs
@@ -70,56 +70,7 @@ namespace Org.BouncyCastle.Math.EC.Custom.Djb
 
         public static void Inv(uint[] x, uint[] z)
         {
-            /*
-             * Raise this element to the exponent 2^255 - 21
-             *
-             * Breaking up the exponent's binary representation into "repunits", we get:
-             * { 250 1s } { 1 0s } { 1 1s } { 1 0s } { 2 1s }
-             *
-             * Therefore we need an addition chain containing 1, 2, 250 (the lengths of the repunits)
-             * We use: [1], [2], 3, 5, 10, 15, 25, 50, 75, 125, [250]
-             */
-
-            if (0 != IsZero(x))
-                throw new ArgumentException("cannot be 0", "x");
-
-            uint[] x1 = x;
-            uint[] x2 = Nat256.Create();
-            Square(x1, x2);
-            Multiply(x2, x1, x2);
-            uint[] x3 = Nat256.Create();
-            Square(x2, x3);
-            Multiply(x3, x1, x3);
-            uint[] x5 = x3;
-            SquareN(x3, 2, x5);
-            Multiply(x5, x2, x5);
-            uint[] x10 = Nat256.Create();
-            SquareN(x5, 5, x10);
-            Multiply(x10, x5, x10);
-            uint[] x15 = Nat256.Create();
-            SquareN(x10, 5, x15);
-            Multiply(x15, x5, x15);
-            uint[] x25 = x5;
-            SquareN(x15, 10, x25);
-            Multiply(x25, x10, x25);
-            uint[] x50 = x10;
-            SquareN(x25, 25, x50);
-            Multiply(x50, x25, x50);
-            uint[] x75 = x15;
-            SquareN(x50, 25, x75);
-            Multiply(x75, x25, x75);
-            uint[] x125 = x25;
-            SquareN(x75, 50, x125);
-            Multiply(x125, x50, x125);
-            uint[] x250 = x50;
-            SquareN(x125, 125, x250);
-            Multiply(x250, x125, x250);
-
-            uint[] t = x250;
-            SquareN(t, 2, t);
-            Multiply(t, x1, t);
-            SquareN(t, 3, t);
-            Multiply(t, x2, z);
+            Mod.CheckedModOddInverse(P, x, z);
         }
 
         public static int IsZero(uint[] x)
diff --git a/crypto/src/math/ec/custom/gm/SM2P256V1Field.cs b/crypto/src/math/ec/custom/gm/SM2P256V1Field.cs
index 55596b844..38743189a 100644
--- a/crypto/src/math/ec/custom/gm/SM2P256V1Field.cs
+++ b/crypto/src/math/ec/custom/gm/SM2P256V1Field.cs
@@ -57,60 +57,7 @@ namespace Org.BouncyCastle.Math.EC.Custom.GM
 
         public static void Inv(uint[] x, uint[] z)
         {
-            /*
-             * Raise this element to the exponent 2^256 - 2^224 - 2^96 + 2^64 - 3
-             *
-             * Breaking up the exponent's binary representation into "repunits", we get:
-             * { 31 1s } { 1 0s } { 128 1s } { 32 0s } { 62 1s } { 1 0s } { 1 1s }
-             *
-             * We use an addition chain for the beginning: [1], 2, [4], 6, 12, 24, 30, [31] 
-             */
-
-            if (0 != IsZero(x))
-                throw new ArgumentException("cannot be 0", "x");
-
-            uint[] x1 = x;
-            uint[] x2 = Nat256.Create();
-            Square(x1, x2);
-            Multiply(x2, x1, x2);
-            uint[] x4 = Nat256.Create();
-            SquareN(x2, 2, x4);
-            Multiply(x4, x2, x4);
-            uint[] x6 = Nat256.Create();
-            SquareN(x4, 2, x6);
-            Multiply(x6, x2, x6);
-            uint[] x12 = x2;
-            SquareN(x6, 6, x12);
-            Multiply(x12, x6, x12);
-            uint[] x24 = Nat256.Create();
-            SquareN(x12, 12, x24);
-            Multiply(x24, x12, x24);
-            uint[] x30 = x12;
-            SquareN(x24, 6, x30);
-            Multiply(x30, x6, x30);
-            uint[] x31 = x6;
-            Square(x30, x31);
-            Multiply(x31, x1, x31);
-
-            uint[] t = x24;
-            SquareN(x31, 32, t);
-            Multiply(t, x31, t);
-            SquareN(t, 31, t);
-            Multiply(t, x31, t);
-            SquareN(t, 31, t);
-            Multiply(t, x31, t);
-            SquareN(t, 31, t);
-            Multiply(t, x31, t);
-            SquareN(t, 4, t);
-            Multiply(t, x4, t);
-            SquareN(t, 63, t);
-            Multiply(t, x31, t);
-            SquareN(t, 31, t);
-            Multiply(t, x31, t);
-            SquareN(t, 2, t);
-
-            // NOTE that x1 and z could be the same array
-            Multiply(x1, t, z);
+            Mod.CheckedModOddInverse(P, x, z);
         }
 
         public static void Half(uint[] x, uint[] z)
diff --git a/crypto/src/math/ec/custom/sec/SecP128R1Field.cs b/crypto/src/math/ec/custom/sec/SecP128R1Field.cs
index 23ea361a0..03a07f79b 100644
--- a/crypto/src/math/ec/custom/sec/SecP128R1Field.cs
+++ b/crypto/src/math/ec/custom/sec/SecP128R1Field.cs
@@ -70,51 +70,7 @@ namespace Org.BouncyCastle.Math.EC.Custom.Sec
 
         public static void Inv(uint[] x, uint[] z)
         {
-            /*
-             * Raise this element to the exponent 2^128 - 2^97 - 3
-             *
-             * Breaking up the exponent's binary representation into "repunits", we get:
-             * { 30 1s } { 1 0s } { 95 1s } { 1 0s } { 1 1s }
-             *
-             * We use an addition chain for the beginning: [1], 2, 3, [5], 10, 20, [30]
-             */
-
-            if (0 != IsZero(x))
-                throw new ArgumentException("cannot be 0", "x");
-
-            uint[] x1 = x;
-            uint[] x2 = Nat128.Create();
-            Square(x1, x2);
-            Multiply(x2, x1, x2);
-            uint[] x3 = Nat128.Create();
-            Square(x2, x3);
-            Multiply(x3, x1, x3);
-            uint[] x5 = x3;
-            SquareN(x3, 2, x5);
-            Multiply(x5, x2, x5);
-            uint[] x10 = x2;
-            SquareN(x5, 5, x10);
-            Multiply(x10, x5, x10);
-            uint[] x20 = Nat128.Create();
-            SquareN(x10, 10, x20);
-            Multiply(x20, x10, x20);
-            uint[] x30 = x20;
-            SquareN(x20, 10, x30);
-            Multiply(x30, x10, x30);
-
-            uint[] t = x10;
-            SquareN(x30, 31, t);
-            Multiply(t, x30, t);
-            SquareN(t, 30, t);
-            Multiply(t, x30, t);
-            SquareN(t, 30, t);
-            Multiply(t, x30, t);
-            SquareN(t, 5, t);
-            Multiply(t, x5, t);
-            SquareN(t, 2, t);
-
-            // NOTE that x1 and z could be the same array
-            Multiply(x1, t, z);
+            Mod.CheckedModOddInverse(P, x, z);
         }
 
         public static int IsZero(uint[] x)
diff --git a/crypto/src/math/ec/custom/sec/SecP160R1Field.cs b/crypto/src/math/ec/custom/sec/SecP160R1Field.cs
index 139cd80d6..31c957301 100644
--- a/crypto/src/math/ec/custom/sec/SecP160R1Field.cs
+++ b/crypto/src/math/ec/custom/sec/SecP160R1Field.cs
@@ -74,58 +74,7 @@ namespace Org.BouncyCastle.Math.EC.Custom.Sec
 
         public static void Inv(uint[] x, uint[] z)
         {
-            /*
-             * Raise this element to the exponent 2^160 - 2^31 - 3
-             *
-             * Breaking up the exponent's binary representation into "repunits", we get:
-             * { 128 1s } { 1 0s } { 29 1s } { 1 0s } { 1 1s }
-             *
-             * Therefore we need an addition chain containing 1, 29, 128 (the lengths of the repunits)
-             * We use: [1], 2, 3, 6, 12, 24, 27, [29], 32, 64, [128]
-             */
-
-            if (0 != IsZero(x))
-                throw new ArgumentException("cannot be 0", "x");
-
-            uint[] x1 = x;
-            uint[] x2 = Nat160.Create();
-            Square(x1, x2);
-            Multiply(x2, x1, x2);
-            uint[] x3 = Nat160.Create();
-            Square(x2, x3);
-            Multiply(x3, x1, x3);
-            uint[] x6 = Nat160.Create();
-            SquareN(x3, 3, x6);
-            Multiply(x6, x3, x6);
-            uint[] x12 = Nat160.Create();
-            SquareN(x6, 6, x12);
-            Multiply(x12, x6, x12);
-            uint[] x24 = x6;
-            SquareN(x12, 12, x24);
-            Multiply(x24, x12, x24);
-            uint[] x27 = x12;
-            SquareN(x24, 3, x27);
-            Multiply(x27, x3, x27);
-            uint[] x29 = x24;
-            SquareN(x27, 2, x29);
-            Multiply(x29, x2, x29);
-            uint[] x32 = x2;
-            SquareN(x29, 3, x32);
-            Multiply(x32, x3, x32);
-            uint[] x64 = x3;
-            SquareN(x32, 32, x64);
-            Multiply(x64, x32, x64);
-            uint[] x128 = x27;
-            SquareN(x64, 64, x128);
-            Multiply(x128, x64, x128);
-
-            uint[] t = x128;
-            SquareN(t, 30, t);
-            Multiply(t, x29, t);
-            SquareN(t, 2, t);
-
-            // NOTE that x1 and z could be the same array
-            Multiply(x1, t, z);
+            Mod.CheckedModOddInverse(P, x, z);
         }
 
         public static int IsZero(uint[] x)
diff --git a/crypto/src/math/ec/custom/sec/SecP160R2Field.cs b/crypto/src/math/ec/custom/sec/SecP160R2Field.cs
index bc36d9de1..55f02e438 100644
--- a/crypto/src/math/ec/custom/sec/SecP160R2Field.cs
+++ b/crypto/src/math/ec/custom/sec/SecP160R2Field.cs
@@ -74,70 +74,7 @@ namespace Org.BouncyCastle.Math.EC.Custom.Sec
 
         public static void Inv(uint[] x, uint[] z)
         {
-            /*
-             * Raise this element to the exponent 2^160 - 2^32 - 2^14 - 2^12 - 2^9 - 2^8 - 2^7 - 2^3 - 2^2 - 3
-             *
-             * Breaking up the exponent's binary representation into "repunits", we get:
-             * { 127 1s } { 1 0s } { 17 1s } "010110001110001"
-             *
-             * Therefore we need an addition chain containing 1, 2, 3, 17, 127 (the lengths of the repunits)
-             * We use: 1, 2, 3, 6, 12, 15, [17], 34, 68, 102, 119, 125, [127]
-             */
-
-            if (0 != IsZero(x))
-                throw new ArgumentException("cannot be 0", "x");
-
-            uint[] x1 = x;
-            uint[] x2 = Nat160.Create();
-            Square(x1, x2);
-            Multiply(x2, x1, x2);
-            uint[] x3 = Nat160.Create();
-            Square(x2, x3);
-            Multiply(x3, x1, x3);
-            uint[] x6 = Nat160.Create();
-            SquareN(x3, 3, x6);
-            Multiply(x6, x3, x6);
-            uint[] x12 = Nat160.Create();
-            SquareN(x6, 6, x12);
-            Multiply(x12, x6, x12);
-            uint[] x15 = x12;
-            SquareN(x12, 3, x15);
-            Multiply(x15, x3, x15);
-            uint[] x17 = x15;
-            SquareN(x15, 2, x17);
-            Multiply(x17, x2, x17);
-            uint[] x34 = Nat160.Create();
-            SquareN(x17, 17, x34);
-            Multiply(x34, x17, x34);
-            uint[] x68 = Nat160.Create();
-            SquareN(x34, 34, x68);
-            Multiply(x68, x34, x68);
-            uint[] x102 = x68;
-            SquareN(x68, 34, x102);
-            Multiply(x102, x34, x102);
-            uint[] x119 = x34;
-            SquareN(x102, 17, x119);
-            Multiply(x119, x17, x119);
-            uint[] x125 = x102;
-            SquareN(x119, 6, x125);
-            Multiply(x125, x6, x125);
-            uint[] x127 = x6;
-            SquareN(x125, 2, x127);
-            Multiply(x127, x2, x127);
-
-            uint[] t = x127;
-            SquareN(t, 18, t);
-            Multiply(t, x17, t);
-            SquareN(t, 2, t);
-            Multiply(t, x1, t);
-            SquareN(t, 3, t);
-            Multiply(t, x2, t);
-            SquareN(t, 6, t);
-            Multiply(t, x3, t);
-            SquareN(t, 4, t);
-
-            // NOTE that x1 and z could be the same array
-            Multiply(x1, t, z);
+            Mod.CheckedModOddInverse(P, x, z);
         }
 
         public static int IsZero(uint[] x)
diff --git a/crypto/src/math/ec/custom/sec/SecP192K1Field.cs b/crypto/src/math/ec/custom/sec/SecP192K1Field.cs
index 30d53f7dc..23bd732bd 100644
--- a/crypto/src/math/ec/custom/sec/SecP192K1Field.cs
+++ b/crypto/src/math/ec/custom/sec/SecP192K1Field.cs
@@ -75,67 +75,7 @@ namespace Org.BouncyCastle.Math.EC.Custom.Sec
 
         public static void Inv(uint[] x, uint[] z)
         {
-            /*
-             * Raise this element to the exponent 2^192 - 2^32 - 2^12 - 2^8 - 2^7 - 2^6 - 2^3 - 3
-             *
-             * Breaking up the exponent's binary representation into "repunits", we get:
-             * { 159 1s } { 1 0s } { 19 1s } { 1 0s } { 3 1s } "000110101"
-             *
-             * Therefore we need an addition chain containing 1, 2, 3, 19, 159 (the lengths of the repunits)
-             * We use: [1], [2], [3], 6, 12, 18, [19], 38, 76, 152, 158, [159]
-             */
-
-            if (0 != IsZero(x))
-                throw new ArgumentException("cannot be 0", "x");
-
-            uint[] x1 = x;
-            uint[] x2 = Nat192.Create();
-            Square(x1, x2);
-            Multiply(x2, x1, x2);
-            uint[] x3 = Nat192.Create();
-            Square(x2, x3);
-            Multiply(x3, x1, x3);
-            uint[] x6 = Nat192.Create();
-            SquareN(x3, 3, x6);
-            Multiply(x6, x3, x6);
-            uint[] x12 = Nat192.Create();
-            SquareN(x6, 6, x12);
-            Multiply(x12, x6, x12);
-            uint[] x18 = x12;
-            SquareN(x12, 6, x18);
-            Multiply(x18, x6, x18);
-            uint[] x19 = x18;
-            Square(x18, x19);
-            Multiply(x19, x1, x19);
-            uint[] x38 = Nat192.Create();
-            SquareN(x19, 19, x38);
-            Multiply(x38, x19, x38);
-            uint[] x76 = Nat192.Create();
-            SquareN(x38, 38, x76);
-            Multiply(x76, x38, x76);
-            uint[] x152 = x38;
-            SquareN(x76, 76, x152);
-            Multiply(x152, x76, x152);
-            uint[] x158 = x76;
-            SquareN(x152, 6, x158);
-            Multiply(x158, x6, x158);
-            uint[] x159 = x6;
-            Square(x158, x159);
-            Multiply(x159, x1, x159);
-
-            uint[] t = x159;
-            SquareN(t, 20, t);
-            Multiply(t, x19, t);
-            SquareN(t, 4, t);
-            Multiply(t, x3, t);
-            SquareN(t, 5, t);
-            Multiply(t, x2, t);
-            SquareN(t, 2, t);
-            Multiply(t, x1, t);
-            SquareN(t, 2, t);
-
-            // NOTE that x1 and z could be the same array
-            Multiply(x1, t, z);
+            Mod.CheckedModOddInverse(P, x, z);
         }
 
         public static int IsZero(uint[] x)
diff --git a/crypto/src/math/ec/custom/sec/SecP192R1Field.cs b/crypto/src/math/ec/custom/sec/SecP192R1Field.cs
index 2061d1359..a4fb4bb76 100644
--- a/crypto/src/math/ec/custom/sec/SecP192R1Field.cs
+++ b/crypto/src/math/ec/custom/sec/SecP192R1Field.cs
@@ -74,58 +74,7 @@ namespace Org.BouncyCastle.Math.EC.Custom.Sec
 
         public static void Inv(uint[] x, uint[] z)
         {
-            /*
-             * Raise this element to the exponent 2^192 - 2^64 - 1
-             *
-             * Breaking up the exponent's binary representation into "repunits", we get:
-             * { 127 1s } { 1 0s } { 62 1s } { 1 0s } { 1 1s }
-             *
-             * Therefore we need an addition chain containing 1, 62, 127 (the lengths of the repunits)
-             * We use: [1], 2, 3, 6, 12, 24, 30, 32, [62], 65, [127]
-             */
-
-            if (0 != IsZero(x))
-                throw new ArgumentException("cannot be 0", "x");
-
-            uint[] x1 = x;
-            uint[] x2 = Nat192.Create();
-            Square(x1, x2);
-            Multiply(x2, x1, x2);
-            uint[] x3 = Nat192.Create();
-            Square(x2, x3);
-            Multiply(x3, x1, x3);
-            uint[] x6 = Nat192.Create();
-            SquareN(x3, 3, x6);
-            Multiply(x6, x3, x6);
-            uint[] x12 = Nat192.Create();
-            SquareN(x6, 6, x12);
-            Multiply(x12, x6, x12);
-            uint[] x24 = Nat192.Create();
-            SquareN(x12, 12, x24);
-            Multiply(x24, x12, x24);
-            uint[] x30 = x12;
-            SquareN(x24, 6, x30);
-            Multiply(x30, x6, x30);
-            uint[] x32 = x6;
-            SquareN(x30, 2, x32);
-            Multiply(x32, x2, x32);
-            uint[] x62 = x2;
-            SquareN(x32, 30, x62);
-            Multiply(x62, x30, x62);
-            uint[] x65 = x24;
-            SquareN(x62, 3, x65);
-            Multiply(x65, x3, x65);
-            uint[] x127 = x3;
-            SquareN(x65, 62, x127);
-            Multiply(x127, x62, x127);
-
-            uint[] t = x127;
-            SquareN(t, 63, t);
-            Multiply(t, x62, t);
-            SquareN(t, 2, t);
-
-            // NOTE that x1 and z could be the same array
-            Multiply(x1, t, z);
+            Mod.CheckedModOddInverse(P, x, z);
         }
 
         public static int IsZero(uint[] x)
diff --git a/crypto/src/math/ec/custom/sec/SecP224K1Field.cs b/crypto/src/math/ec/custom/sec/SecP224K1Field.cs
index d20ac63f3..5d4237708 100644
--- a/crypto/src/math/ec/custom/sec/SecP224K1Field.cs
+++ b/crypto/src/math/ec/custom/sec/SecP224K1Field.cs
@@ -76,67 +76,7 @@ namespace Org.BouncyCastle.Math.EC.Custom.Sec
 
         public static void Inv(uint[] x, uint[] z)
         {
-            /*
-             * Raise this element to the exponent 2^224 - 2^32 - 2^12 - 2^11 - 2^9 - 2^7 - 2^4 - 5
-             *
-             * Breaking up the exponent's binary representation into "repunits", we get:
-             * { 191 1s } { 1 0s } { 19 1s } "0010101101011"
-             *
-             * Therefore we need an addition chain containing 1, 2, 19, 191 (the lengths of the repunits)
-             * We use: [1], [2], 4, 5, 9, 10, [19], 38, 76, 152, 190 [191]
-             */
-
-            if (0 != IsZero(x))
-                throw new ArgumentException("cannot be 0", "x");
-
-            uint[] x1 = x;
-            uint[] x2 = Nat224.Create();
-            Square(x1, x2);
-            Multiply(x2, x1, x2);
-            uint[] x4 = Nat224.Create();
-            SquareN(x2, 2, x4);
-            Multiply(x4, x2, x4);
-            uint[] x5 = Nat224.Create();
-            Square(x4, x5);
-            Multiply(x5, x1, x5);
-            uint[] x9 = x5;
-            SquareN(x5, 4, x9);
-            Multiply(x9, x4, x9);
-            uint[] x10 = x4;
-            Square(x9, x10);
-            Multiply(x10, x1, x10);
-            uint[] x19 = x10;
-            SquareN(x10, 9, x19);
-            Multiply(x19, x9, x19);
-            uint[] x38 = x9;
-            SquareN(x19, 19, x38);
-            Multiply(x38, x19, x38);
-            uint[] x76 = Nat224.Create();
-            SquareN(x38, 38, x76);
-            Multiply(x76, x38, x76);
-            uint[] x152 = Nat224.Create();
-            SquareN(x76, 76, x152);
-            Multiply(x152, x76, x152);
-            uint[] x190 = x76;
-            SquareN(x152, 38, x190);
-            Multiply(x190, x38, x190);
-            uint[] x191 = x38;
-            Square(x190, x191);
-            Multiply(x191, x1, x191);
-
-            uint[] t = x191;
-            SquareN(t, 20, t);
-            Multiply(t, x19, t);
-            SquareN(t, 3, t);
-            Multiply(t, x1, t);
-            SquareN(t, 2, t);
-            Multiply(t, x1, t);
-            SquareN(t, 3, t);
-            Multiply(t, x2, t);
-            SquareN(t, 2, t);
-            Multiply(t, x1, t);
-            SquareN(t, 3, t);
-            Multiply(t, x2, z);
+            Mod.CheckedModOddInverse(P, x, z);
         }
 
         public static int IsZero(uint[] x)
diff --git a/crypto/src/math/ec/custom/sec/SecP224R1Field.cs b/crypto/src/math/ec/custom/sec/SecP224R1Field.cs
index 06d451c2b..dde291d5e 100644
--- a/crypto/src/math/ec/custom/sec/SecP224R1Field.cs
+++ b/crypto/src/math/ec/custom/sec/SecP224R1Field.cs
@@ -75,54 +75,7 @@ namespace Org.BouncyCastle.Math.EC.Custom.Sec
 
         public static void Inv(uint[] x, uint[] z)
         {
-            /*
-             * Raise this element to the exponent 2^224 - 2^96 - 1
-             *
-             * Breaking up the exponent's binary representation into "repunits", we get:
-             * { 127 1s } { 1 0s } { 96 1s }
-             *
-             * Therefore we need an addition chain containing 96, 127 (the lengths of the repunits)
-             * We use: 1, 2, 3, 6, 12, 24, 48, [96], 120, 126, [127]
-             */
-
-            if (0 != IsZero(x))
-                throw new ArgumentException("cannot be 0", "x");
-
-            uint[] x1 = x;
-            uint[] x2 = Nat224.Create();
-            Square(x1, x2);
-            Multiply(x2, x1, x2);
-            uint[] x3 = x2;
-            Square(x2, x3);
-            Multiply(x3, x1, x3);
-            uint[] x6 = Nat224.Create();
-            SquareN(x3, 3, x6);
-            Multiply(x6, x3, x6);
-            uint[] x12 = x3;
-            SquareN(x6, 6, x12);
-            Multiply(x12, x6, x12);
-            uint[] x24 = Nat224.Create();
-            SquareN(x12, 12, x24);
-            Multiply(x24, x12, x24);
-            uint[] x48 = x12;
-            SquareN(x24, 24, x48);
-            Multiply(x48, x24, x48);
-            uint[] x96 = Nat224.Create();
-            SquareN(x48, 48, x96);
-            Multiply(x96, x48, x96);
-            uint[] x120 = x48;
-            SquareN(x96, 24, x120);
-            Multiply(x120, x24, x120);
-            uint[] x126 = x24;
-            SquareN(x120, 6, x126);
-            Multiply(x126, x6, x126);
-            uint[] x127 = x6;
-            Square(x126, x127);
-            Multiply(x127, x1, x127);
-
-            uint[] t = x127;
-            SquareN(t, 97, t);
-            Multiply(t, x96, z);
+            Mod.CheckedModOddInverse(P, x, z);
         }
 
         public static int IsZero(uint[] x)
diff --git a/crypto/src/math/ec/custom/sec/SecP256K1Field.cs b/crypto/src/math/ec/custom/sec/SecP256K1Field.cs
index 2193c94e6..acdb1f362 100644
--- a/crypto/src/math/ec/custom/sec/SecP256K1Field.cs
+++ b/crypto/src/math/ec/custom/sec/SecP256K1Field.cs
@@ -76,65 +76,7 @@ namespace Org.BouncyCastle.Math.EC.Custom.Sec
 
         public static void Inv(uint[] x, uint[] z)
         {
-            /*
-             * Raise this element to the exponent 2^256 - 2^32 - 2^9 - 2^8 - 2^7 - 2^6 - 2^4 - 3
-             *
-             * Breaking up the exponent's binary representation into "repunits", we get:
-             * { 223 1s } { 1 0s } { 22 1s } { 4 0s } { 1 1s } { 1 0s } { 2 1s } { 1 0s } { 1 1s }
-             *
-             * Therefore we need an addition chain containing 1, 2, 22, 223 (the lengths of the repunits)
-             * We use: [1], [2], 3, 6, 9, 11, [22], 44, 88, 176, 220, [223]
-             */
-
-            if (0 != IsZero(x))
-                throw new ArgumentException("cannot be 0", "x");
-
-            uint[] x1 = x;
-            uint[] x2 = Nat256.Create();
-            Square(x1, x2);
-            Multiply(x2, x1, x2);
-            uint[] x3 = Nat256.Create();
-            Square(x2, x3);
-            Multiply(x3, x1, x3);
-            uint[] x6 = Nat256.Create();
-            SquareN(x3, 3, x6);
-            Multiply(x6, x3, x6);
-            uint[] x9 = x6;
-            SquareN(x6, 3, x9);
-            Multiply(x9, x3, x9);
-            uint[] x11 = x9;
-            SquareN(x9, 2, x11);
-            Multiply(x11, x2, x11);
-            uint[] x22 = Nat256.Create();
-            SquareN(x11, 11, x22);
-            Multiply(x22, x11, x22);
-            uint[] x44 = x11;
-            SquareN(x22, 22, x44);
-            Multiply(x44, x22, x44);
-            uint[] x88 = Nat256.Create();
-            SquareN(x44, 44, x88);
-            Multiply(x88, x44, x88);
-            uint[] x176 = Nat256.Create();
-            SquareN(x88, 88, x176);
-            Multiply(x176, x88, x176);
-            uint[] x220 = x88;
-            SquareN(x176, 44, x220);
-            Multiply(x220, x44, x220);
-            uint[] x223 = x44;
-            SquareN(x220, 3, x223);
-            Multiply(x223, x3, x223);
-
-            uint[] t = x223;
-            SquareN(t, 23, t);
-            Multiply(t, x22, t);
-            SquareN(t, 5, t);
-            Multiply(t, x1, t);
-            SquareN(t, 3, t);
-            Multiply(t, x2, t);
-            SquareN(t, 2, t);
-
-            // NOTE that x1 and z could be the same array
-            Multiply(x1, t, z);
+            Mod.CheckedModOddInverse(P, x, z);
         }
 
         public static int IsZero(uint[] x)
diff --git a/crypto/src/math/ec/custom/sec/SecP256R1Field.cs b/crypto/src/math/ec/custom/sec/SecP256R1Field.cs
index eadc7ee58..668efc895 100644
--- a/crypto/src/math/ec/custom/sec/SecP256R1Field.cs
+++ b/crypto/src/math/ec/custom/sec/SecP256R1Field.cs
@@ -70,60 +70,7 @@ namespace Org.BouncyCastle.Math.EC.Custom.Sec
 
         public static void Inv(uint[] x, uint[] z)
         {
-            /*
-             * Raise this element to the exponent 2^256 - 2^224 + 2^192 + 2^96 - 3
-             *
-             * Breaking up the exponent's binary representation into "repunits", we get:
-             * { 32 1s } { 31 0s } { 1 1s } { 96 0s } { 94 1s } { 1 0s } { 1 1s }
-             *
-             * Therefore we need an addition chain containing 1, 32, 94 (the lengths of the repunits)
-             * We use: [1], 2, 4, 8, 16, [32], 64, 80, 88, 92, [94]
-             */
-
-            if (0 != IsZero(x))
-                throw new ArgumentException("cannot be 0", "x");
-
-            uint[] x1 = x;
-            uint[] x2 = Nat256.Create();
-            Square(x1, x2);
-            Multiply(x2, x1, x2);
-            uint[] x4 = Nat256.Create();
-            SquareN(x2, 2, x4);
-            Multiply(x4, x2, x4);
-            uint[] x8 = Nat256.Create();
-            SquareN(x4, 4, x8);
-            Multiply(x8, x4, x8);
-            uint[] x16 = Nat256.Create();
-            SquareN(x8, 8, x16);
-            Multiply(x16, x8, x16);
-            uint[] x32 = Nat256.Create();
-            SquareN(x16, 16, x32);
-            Multiply(x32, x16, x32);
-            uint[] x64 = Nat256.Create();
-            SquareN(x32, 32, x64);
-            Multiply(x64, x32, x64);
-            uint[] x80 = x64;
-            SquareN(x64, 16, x80);
-            Multiply(x80, x16, x80);
-            uint[] x88 = x16;
-            SquareN(x80, 8, x88);
-            Multiply(x88, x8, x88);
-            uint[] x92 = x8;
-            SquareN(x88, 4, x92);
-            Multiply(x92, x4, x92);
-            uint[] x94 = x4;
-            SquareN(x92, 2, x94);
-            Multiply(x94, x2, x94);
-
-            uint[] t = x32;
-            SquareN(t, 32, t);
-            Multiply(t, x1, t);
-            SquareN(t, 190, t);
-            Multiply(t, x94, t);
-            SquareN(t, 2, t);
-
-            // NOTE that x1 and z could be the same array
-            Multiply(x1, t, z);
+            Mod.CheckedModOddInverse(P, x, z);
         }
 
         public static int IsZero(uint[] x)
diff --git a/crypto/src/math/ec/custom/sec/SecP384R1Field.cs b/crypto/src/math/ec/custom/sec/SecP384R1Field.cs
index 9b20db1b0..cddb46895 100644
--- a/crypto/src/math/ec/custom/sec/SecP384R1Field.cs
+++ b/crypto/src/math/ec/custom/sec/SecP384R1Field.cs
@@ -77,66 +77,7 @@ namespace Org.BouncyCastle.Math.EC.Custom.Sec
 
         public static void Inv(uint[] x, uint[] z)
         {
-            /*
-             * Raise this element to the exponent 2^384 - 2^128 - 2^96 + 2^32 - 3
-             *
-             * Breaking up the exponent's binary representation into "repunits", we get:
-             * { 255 1s } { 1 0s } { 32 1s } { 64 0s } { 30 1s } { 1 0s } { 1 1s }
-             *
-             * Therefore we need an addition chain containing 1, 30, 32, 255 (the lengths of the repunits)
-             * We use: [1], 2, 3, 6, 12, 24, [30], [32], 62, 124, 248, 254, [255]
-             */
-
-            if (0 != IsZero(x))
-                throw new ArgumentException("cannot be 0", "x");
-
-            uint[] x1 = x;
-            uint[] x2 = Nat.Create(12);
-            Square(x1, x2);
-            Multiply(x2, x1, x2);
-            uint[] x3 = Nat.Create(12);
-            Square(x2, x3);
-            Multiply(x3, x1, x3);
-            uint[] x6 = Nat.Create(12);
-            SquareN(x3, 3, x6);
-            Multiply(x6, x3, x6);
-            uint[] x12 = x3;
-            SquareN(x6, 6, x12);
-            Multiply(x12, x6, x12);
-            uint[] x24 = Nat.Create(12);
-            SquareN(x12, 12, x24);
-            Multiply(x24, x12, x24);
-            uint[] x30 = x12;
-            SquareN(x24, 6, x30);
-            Multiply(x30, x6, x30);
-            uint[] x32 = x24;
-            SquareN(x30, 2, x32);
-            Multiply(x32, x2, x32);
-            uint[] x62 = x2;
-            SquareN(x32, 30, x62);
-            Multiply(x62, x30, x62);
-            uint[] x124 = Nat.Create(12);
-            SquareN(x62, 62, x124);
-            Multiply(x124, x62, x124);
-            uint[] x248 = x62;
-            SquareN(x124, 124, x248);
-            Multiply(x248, x124, x248);
-            uint[] x254 = x124;
-            SquareN(x248, 6, x254);
-            Multiply(x254, x6, x254);
-            uint[] x255 = x6;
-            Square(x254, x255);
-            Multiply(x255, x1, x255);
-
-            uint[] t = x255;
-            SquareN(t, 33, t);
-            Multiply(t, x32, t);
-            SquareN(t, 94, t);
-            Multiply(t, x30, t);
-            SquareN(t, 2, t);
-
-            // NOTE that x1 and z could be the same array
-            Multiply(x1, t, z);
+            Mod.CheckedModOddInverse(P, x, z);
         }
 
         public static int IsZero(uint[] x)
diff --git a/crypto/src/math/ec/custom/sec/SecP521R1Field.cs b/crypto/src/math/ec/custom/sec/SecP521R1Field.cs
index 10b98fc21..0f1922f36 100644
--- a/crypto/src/math/ec/custom/sec/SecP521R1Field.cs
+++ b/crypto/src/math/ec/custom/sec/SecP521R1Field.cs
@@ -56,62 +56,7 @@ namespace Org.BouncyCastle.Math.EC.Custom.Sec
 
         public static void Inv(uint[] x, uint[] z)
         {
-            /*
-             * Raise this element to the exponent 2^521 - 3
-             *
-             * Breaking up the exponent's binary representation into "repunits", we get:
-             * { 519 1s } { 1 0s } { 1 1s }
-             *
-             * Therefore we need an addition chain containing 1, 519 (the lengths of the repunits)
-             * We use: [1], 2, 4, 8, 16, 32, 64, 128, 256, 512, 516, 518, [519]
-             */
-
-            if (0 != IsZero(x))
-                throw new ArgumentException("cannot be 0", "x");
-
-            uint[] x1 = x;
-            uint[] x2 = Nat.Create(17);
-            Square(x1, x2);
-            Multiply(x2, x1, x2);
-            uint[] x4 = Nat.Create(17);
-            SquareN(x2, 2, x4);
-            Multiply(x4, x2, x4);
-            uint[] x8 = Nat.Create(17);
-            SquareN(x4, 4, x8);
-            Multiply(x8, x4, x8);
-            uint[] x16 = Nat.Create(17);
-            SquareN(x8, 8, x16);
-            Multiply(x16, x8, x16);
-            uint[] x32 = x8;
-            SquareN(x16, 16, x32);
-            Multiply(x32, x16, x32);
-            uint[] x64 = x16;
-            SquareN(x32, 32, x64);
-            Multiply(x64, x32, x64);
-            uint[] x128 = x32;
-            SquareN(x64, 64, x128);
-            Multiply(x128, x64, x128);
-            uint[] x256 = x64;
-            SquareN(x128, 128, x256);
-            Multiply(x256, x128, x256);
-            uint[] x512 = x128;
-            SquareN(x256, 256, x512);
-            Multiply(x512, x256, x512);
-            uint[] x516 = x256;
-            SquareN(x512, 4, x516);
-            Multiply(x516, x4, x516);
-            uint[] x518 = x4;
-            SquareN(x516, 2, x518);
-            Multiply(x518, x2, x518);
-            uint[] x519 = x2;
-            Square(x518, x519);
-            Multiply(x519, x1, x519);
-
-            uint[] t = x519;
-            SquareN(t, 2, t);
-
-            // NOTE that x1 and z could be the same array
-            Multiply(x1, t, z);
+            Mod.CheckedModOddInverse(P, x, z);
         }
 
         public static int IsZero(uint[] x)
diff --git a/crypto/src/math/ec/rfc7748/X25519Field.cs b/crypto/src/math/ec/rfc7748/X25519Field.cs
index 6843e274a..ffede563b 100644
--- a/crypto/src/math/ec/rfc7748/X25519Field.cs
+++ b/crypto/src/math/ec/rfc7748/X25519Field.cs
@@ -1,6 +1,8 @@
 using System;
 using System.Diagnostics;
 
+using Org.BouncyCastle.Math.Raw;
+
 namespace Org.BouncyCastle.Math.EC.Rfc7748
 {
     public abstract class X25519Field
@@ -11,6 +13,8 @@ namespace Org.BouncyCastle.Math.EC.Rfc7748
         private const int M25 = 0x01FFFFFF;
         private const int M26 = 0x03FFFFFF;
 
+        private static readonly uint[] P32 = new uint[]{ 0xFFFFFFEDU, 0xFFFFFFFFU, 0xFFFFFFFFU, 0xFFFFFFFFU,
+            0xFFFFFFFFU, 0xFFFFFFFFU, 0xFFFFFFFFU, 0x7FFFFFFFU };
         private static readonly int[] RootNegOne = { 0x020EA0B0, 0x0386C9D2, 0x00478C4E, 0x0035697F, 0x005E8630,
             0x01FBD7A7, 0x0340264F, 0x01F0B2B4, 0x00027E0E, 0x00570649 };
 
@@ -128,6 +132,14 @@ namespace Org.BouncyCastle.Math.EC.Rfc7748
             }
         }
 
+        [CLSCompliantAttribute(false)]
+        public static void Decode(uint[] x, int xOff, int[] z)
+        {
+            Decode128(x, xOff, z, 0);
+            Decode128(x, xOff + 4, z, 5);
+            z[9] &= M24;
+        }
+
         public static void Decode(byte[] x, int xOff, int[] z)
         {
             Decode128(x, xOff, z, 0);
@@ -135,6 +147,17 @@ namespace Org.BouncyCastle.Math.EC.Rfc7748
             z[9] &= M24;
         }
 
+        private static void Decode128(uint[] x, int xOff, int[] z, int zOff)
+        {
+            uint t0 = x[xOff + 0], t1 = x[xOff + 1], t2 = x[xOff + 2], t3 = x[xOff + 3];
+
+            z[zOff + 0] = (int)t0 & M26;
+            z[zOff + 1] = (int)((t1 <<  6) | (t0 >> 26)) & M26;
+            z[zOff + 2] = (int)((t2 << 12) | (t1 >> 20)) & M25;
+            z[zOff + 3] = (int)((t3 << 19) | (t2 >> 13)) & M26;
+            z[zOff + 4] = (int)(t3 >> 7);
+        }
+
         private static void Decode128(byte[] bs, int off, int[] z, int zOff)
         {
             uint t0 = Decode32(bs, off + 0);
@@ -158,12 +181,30 @@ namespace Org.BouncyCastle.Math.EC.Rfc7748
             return n;
         }
 
+        [CLSCompliantAttribute(false)]
+        public static void Encode(int[] x, uint[] z, int zOff)
+        {
+            Encode128(x, 0, z, zOff);
+            Encode128(x, 5, z, zOff + 4);
+        }
+
         public static void Encode(int[] x, byte[] z, int zOff)
         {
             Encode128(x, 0, z, zOff);
             Encode128(x, 5, z, zOff + 16);
         }
 
+        private static void Encode128(int[] x, int xOff, uint[] z, int zOff)
+        {
+            uint x0 = (uint)x[xOff + 0], x1 = (uint)x[xOff + 1], x2 = (uint)x[xOff + 2], x3 = (uint)x[xOff + 3],
+                x4 = (uint)x[xOff + 4];
+
+            z[zOff + 0] =  x0        | (x1 << 26);
+            z[zOff + 1] = (x1 >>  6) | (x2 << 20);
+            z[zOff + 2] = (x2 >> 12) | (x3 << 13);
+            z[zOff + 3] = (x3 >> 19) | (x4 <<  7);
+        }
+
         private static void Encode128(int[] x, int xOff, byte[] bs, int off)
         {
             uint x0 = (uint)x[xOff + 0], x1 = (uint)x[xOff + 1], x2 = (uint)x[xOff + 2];
@@ -185,15 +226,36 @@ namespace Org.BouncyCastle.Math.EC.Rfc7748
 
         public static void Inv(int[] x, int[] z)
         {
-            // z = x^(p-2) = x^7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEB
-            // (250 1s) (1 0s) (1 1s) (1 0s) (2 1s)
-            // Addition chain: [1] [2] 3 5 10 15 25 50 75 125 [250]
+            //int[] x2 = Create();
+            //int[] t = Create();
+            //PowPm5d8(x, x2, t);
+            //Sqr(t, 3, t);
+            //Mul(t, x2, z);
 
-            int[] x2 = Create();
             int[] t = Create();
-            PowPm5d8(x, x2, t);
-            Sqr(t, 3, t);
-            Mul(t, x2, z);
+            uint[] u = new uint[8];
+
+            Copy(x, 0, t, 0);
+            Normalize(t);
+            Encode(t, u, 0);
+
+            Mod.ModOddInverse(P32, u, u);
+
+            Decode(u, 0, z);
+        }
+
+        public static void InvVar(int[] x, int[] z)
+        {
+            int[] t = Create();
+            uint[] u = new uint[8];
+
+            Copy(x, 0, t, 0);
+            Normalize(t);
+            Encode(t, u, 0);
+
+            Mod.ModOddInverseVar(P32, u, u);
+
+            Decode(u, 0, z);
         }
 
         public static int IsZero(int[] x)
diff --git a/crypto/src/math/ec/rfc7748/X448Field.cs b/crypto/src/math/ec/rfc7748/X448Field.cs
index 240518cde..4d3be5cda 100644
--- a/crypto/src/math/ec/rfc7748/X448Field.cs
+++ b/crypto/src/math/ec/rfc7748/X448Field.cs
@@ -1,6 +1,8 @@
 using System;
 using System.Diagnostics;
 
+using Org.BouncyCastle.Math.Raw;
+
 namespace Org.BouncyCastle.Math.EC.Rfc7748
 {
     [CLSCompliantAttribute(false)]
@@ -10,6 +12,10 @@ namespace Org.BouncyCastle.Math.EC.Rfc7748
 
         private const uint M28 = 0x0FFFFFFFU;
 
+        private static readonly uint[] P32 = new uint[]{ 0xFFFFFFFFU, 0xFFFFFFFFU, 0xFFFFFFFFU, 0xFFFFFFFFU,
+            0xFFFFFFFFU, 0xFFFFFFFFU, 0xFFFFFFFFU, 0xFFFFFFFEU, 0xFFFFFFFFU, 0xFFFFFFFFU, 0xFFFFFFFFU, 0xFFFFFFFFU,
+            0xFFFFFFFFU, 0xFFFFFFFFU };
+
         protected X448Field() {}
 
         public static void Add(uint[] x, uint[] y, uint[] z)
@@ -129,6 +135,12 @@ namespace Org.BouncyCastle.Math.EC.Rfc7748
             }
         }
 
+        public static void Decode(uint[] x, int xOff, uint[] z)
+        {
+            Decode224(x, xOff, z, 0);
+            Decode224(x, xOff + 7, z, 8);
+        }
+
         public static void Decode(byte[] x, int xOff, uint[] z)
         {
             Decode56(x, xOff, z, 0);
@@ -141,6 +153,21 @@ namespace Org.BouncyCastle.Math.EC.Rfc7748
             Decode56(x, xOff + 49, z, 14);
         }
 
+        private static void Decode224(uint[] x, int xOff, uint[] z, int zOff)
+        {
+            uint x0 = x[xOff + 0], x1 = x[xOff + 1], x2 = x[xOff + 2], x3 = x[xOff + 3];
+            uint x4 = x[xOff + 4], x5 = x[xOff + 5], x6 = x[xOff + 6];
+
+            z[zOff + 0] = x0 & M28;
+            z[zOff + 1] = (x0 >> 28 | x1 <<  4) & M28;
+            z[zOff + 2] = (x1 >> 24 | x2 <<  8) & M28;
+            z[zOff + 3] = (x2 >> 20 | x3 << 12) & M28;
+            z[zOff + 4] = (x3 >> 16 | x4 << 16) & M28;
+            z[zOff + 5] = (x4 >> 12 | x5 << 20) & M28;
+            z[zOff + 6] = (x5 >>  8 | x6 << 24) & M28;
+            z[zOff + 7] = x6 >> 4;
+        }
+
         private static uint Decode24(byte[] bs, int off)
         {
             uint n = bs[off];
@@ -166,6 +193,12 @@ namespace Org.BouncyCastle.Math.EC.Rfc7748
             z[zOff + 1] = (lo >> 28) | (hi << 4);
         }
 
+        public static void Encode(uint[] x, uint[] z, int zOff)
+        {
+            Encode224(x, 0, z, zOff);
+            Encode224(x, 8, z, zOff + 7);
+        }
+
         public static void Encode(uint[] x, byte[] z, int zOff)
         {
             Encode56(x, 0, z, zOff);
@@ -178,6 +211,20 @@ namespace Org.BouncyCastle.Math.EC.Rfc7748
             Encode56(x, 14, z, zOff + 49);
         }
 
+        private static void Encode224(uint[] x, int xOff, uint[] z, int zOff)
+        {
+            uint x0 = x[xOff + 0], x1 = x[xOff + 1], x2 = x[xOff + 2], x3 = x[xOff + 3];
+            uint x4 = x[xOff + 4], x5 = x[xOff + 5], x6 = x[xOff + 6], x7 = x[xOff + 7];
+
+            z[zOff + 0] =  x0        | (x1 << 28);
+            z[zOff + 1] = (x1 >>  4) | (x2 << 24);
+            z[zOff + 2] = (x2 >>  8) | (x3 << 20);
+            z[zOff + 3] = (x3 >> 12) | (x4 << 16);
+            z[zOff + 4] = (x4 >> 16) | (x5 << 12);
+            z[zOff + 5] = (x5 >> 20) | (x6 <<  8);
+            z[zOff + 6] = (x6 >> 24) | (x7 <<  4);
+        }
+
         private static void Encode24(uint n, byte[] bs, int off)
         {
             bs[  off] = (byte)(n      );
@@ -202,14 +249,35 @@ namespace Org.BouncyCastle.Math.EC.Rfc7748
 
         public static void Inv(uint[] x, uint[] z)
         {
-            // z = x^(p-2) = x^(2^448 - 2^224 - 3)
-            // (223 1s) (1 0s) (222 1s) (1 0s) (1 1s)
-            // Addition chain: [1] 2 3 6 9 18 19 37 74 111 [222] [223]
+            //uint[] t = Create();
+            //PowPm3d4(x, t);
+            //Sqr(t, 2, t);
+            //Mul(t, x, z);
 
             uint[] t = Create();
-            PowPm3d4(x, t);
-            Sqr(t, 2, t);
-            Mul(t, x, z);
+            uint[] u = new uint[14];
+
+            Copy(x, 0, t, 0);
+            Normalize(t);
+            Encode(t, u, 0);
+
+            Mod.ModOddInverse(P32, u, u);
+
+            Decode(u, 0, z);
+        }
+
+        public static void InvVar(uint[] x, uint[] z)
+        {
+            uint[] t = Create();
+            uint[] u = new uint[14];
+
+            Copy(x, 0, t, 0);
+            Normalize(t);
+            Encode(t, u, 0);
+
+            Mod.ModOddInverseVar(P32, u, u);
+
+            Decode(u, 0, z);
         }
 
         public static int IsZero(uint[] x)
diff --git a/crypto/src/math/ec/rfc8032/Ed25519.cs b/crypto/src/math/ec/rfc8032/Ed25519.cs
index 95ba43472..3a39ae53d 100644
--- a/crypto/src/math/ec/rfc8032/Ed25519.cs
+++ b/crypto/src/math/ec/rfc8032/Ed25519.cs
@@ -754,7 +754,7 @@ namespace Org.BouncyCastle.Math.EC.Rfc8032
 
                         X25519Field.Add(q.z, q.z, x);
                         // TODO[ed25519] Batch inversion
-                        X25519Field.Inv(x, y);
+                        X25519Field.InvVar(x, y);
                         X25519Field.Mul(q.x, y, x);
                         X25519Field.Mul(q.y, y, y);
 
diff --git a/crypto/src/math/ec/rfc8032/Ed448.cs b/crypto/src/math/ec/rfc8032/Ed448.cs
index 12f24c1ff..c1202dc02 100644
--- a/crypto/src/math/ec/rfc8032/Ed448.cs
+++ b/crypto/src/math/ec/rfc8032/Ed448.cs
@@ -702,7 +702,7 @@ namespace Org.BouncyCastle.Math.EC.Rfc8032
                     {
                         PointExt q = points[i];
                         // TODO[ed448] Batch inversion
-                        X448Field.Inv(q.z, q.z);
+                        X448Field.InvVar(q.z, q.z);
                         X448Field.Mul(q.x, q.z, q.x);
                         X448Field.Mul(q.y, q.z, q.y);