diff --git a/Crypto/src/crypto/modes/gcm/GcmUtilities.cs b/Crypto/src/crypto/modes/gcm/GcmUtilities.cs
new file mode 100644
index 000000000..8da125641
--- /dev/null
+++ b/Crypto/src/crypto/modes/gcm/GcmUtilities.cs
@@ -0,0 +1,149 @@
+using System;
+
+using Org.BouncyCastle.Crypto.Utilities;
+using Org.BouncyCastle.Utilities;
+
+namespace Org.BouncyCastle.Crypto.Modes.Gcm
+{
+ internal abstract class GcmUtilities
+ {
+ internal static byte[] OneAsBytes()
+ {
+ byte[] tmp = new byte[16];
+ tmp[0] = 0x80;
+ return tmp;
+ }
+
+ internal static uint[] OneAsUints()
+ {
+ uint[] tmp = new uint[4];
+ tmp[0] = 0x80000000;
+ return tmp;
+ }
+
+ internal static uint[] AsUints(byte[] bs)
+ {
+ uint[] us = new uint[4];
+ us[0] = Pack.BE_To_UInt32(bs, 0);
+ us[1] = Pack.BE_To_UInt32(bs, 4);
+ us[2] = Pack.BE_To_UInt32(bs, 8);
+ us[3] = Pack.BE_To_UInt32(bs, 12);
+ return us;
+ }
+
+ internal static void Multiply(byte[] block, byte[] val)
+ {
+ byte[] tmp = Arrays.Clone(block);
+ byte[] c = new byte[16];
+
+ for (int i = 0; i < 16; ++i)
+ {
+ byte bits = val[i];
+ for (int j = 7; j >= 0; --j)
+ {
+ if ((bits & (1 << j)) != 0)
+ {
+ Xor(c, tmp);
+ }
+
+ bool lsb = (tmp[15] & 1) != 0;
+ ShiftRight(tmp);
+ if (lsb)
+ {
+ // R = new byte[]{ 0xe1, ... };
+ //GCMUtilities.Xor(tmp, R);
+ tmp[0] ^= (byte)0xe1;
+ }
+ }
+ }
+
+ Array.Copy(c, 0, block, 0, 16);
+ }
+
+ // P is the value with only bit i=1 set
+ internal static void MultiplyP(uint[] x)
+ {
+ bool lsb = (x[3] & 1) != 0;
+ ShiftRight(x);
+ if (lsb)
+ {
+ // R = new uint[]{ 0xe1000000, 0, 0, 0 };
+ //Xor(v, R);
+ x[0] ^= 0xe1000000;
+ }
+ }
+
+ internal static void MultiplyP8(uint[] x)
+ {
+// for (int i = 8; i != 0; --i)
+// {
+// MultiplyP(x);
+// }
+
+ uint lsw = x[3];
+ ShiftRightN(x, 8);
+ for (int i = 7; i >= 0; --i)
+ {
+ if ((lsw & (1 << i)) != 0)
+ {
+ x[0] ^= (0xe1000000 >> (7 - i));
+ }
+ }
+ }
+
+ internal static void ShiftRight(byte[] block)
+ {
+ int i = 0;
+ byte bit = 0;
+ for (;;)
+ {
+ byte b = block[i];
+ block[i] = (byte)((b >> 1) | bit);
+ if (++i == 16) break;
+ bit = (byte)(b << 7);
+ }
+ }
+
+ internal static void ShiftRight(uint[] block)
+ {
+ int i = 0;
+ uint bit = 0;
+ for (;;)
+ {
+ uint b = block[i];
+ block[i] = (b >> 1) | bit;
+ if (++i == 4) break;
+ bit = b << 31;
+ }
+ }
+
+ internal static void ShiftRightN(uint[] block, int n)
+ {
+ int i = 0;
+ uint bit = 0;
+ for (;;)
+ {
+ uint b = block[i];
+ block[i] = (b >> n) | bit;
+ if (++i == 4) break;
+ bit = b << (32 - n);
+ }
+ }
+
+ internal static void Xor(byte[] block, byte[] val)
+ {
+ for (int i = 15; i >= 0; --i)
+ {
+ block[i] ^= val[i];
+ }
+ }
+
+ internal static void Xor(uint[] block, uint[] val)
+ {
+ for (int i = 3; i >= 0; --i)
+ {
+ block[i] ^= val[i];
+ }
+ }
+ }
+}
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