[Java.Interop.Tools.JavaCallableWrappers] Support Crc64 package names (…

…#492)

Context: dotnet/android#1580
Context: https://xamarin.github.io/bugzilla-archives/15/15205/bug.html#c1
Context: https://xamarin.github.io/bugzilla-archives/16/16826/bug.html

`JavaNativeTypeManager` [uses MD5 to generate package names][0] for
Java Callable Wrappers, using the hash of the namespace name and the
containing assembly name to produce the Java package name.  This was
because it's perfectly valid for there to be *multiple*
`Example.Name` types within a .NET application, so long as they're
in different assemblies:

	// Lib1.dll
	namespace Example {
	    public class Name : Java.Lang.Object {}
	}

	// Lib2.dll
	namespace Example {
	    public class Name : Java.Lang.Object {}
	}

Because the (default) Java package name is a hash of the namespace
and assembly name, both of these `Example.Name` instances can coexist
because they get separate Java types,
`md5fcf4c1986bf17f9628efcaae404b0b1e.Name` (`md5(Example:Lib1)`) &
`md59dee366f823d92fb98288dda3e25ec49.Name` (`md5(Example:Lib2)`).

This was *never* done for cryptographic purposes.  This was only done
to reduce the likelihood of type name collisions.

Unfortunately, this use of MD5 results in an inability to use
Xamarin.Android on FIPS-enabled machines, because when the **System
cryptography: [Use FIPS compliant algorithms][1] for encryption,
hashing, and signing** setting is enabled on Windows:

!['Use Fips compliant algorithms' setting][2]

then the `System.Security.Cryptography.MD5.Create()` method will
throw `InvalidOperationException`.

In order to support FIPS-enabled machines, use a 64-bit
[Cyclic redundancy check][3] algorithm (CRC64) to instead generate
the Java package names, e.g. `crc64aae7d955a89b38db.Name` and
`crc64217c8705f00a5054.Name`.  A sim:ple implementation using a
lookup table will suffice for our purposes, ported to C# from:

	https://github.com/gityf/crc/blob/8045f50ba6e4193d4ee5d2539025fef26e613c9f/crc/crc64.c

The use of CRC64 avoids the use of MD5, thus permitting execution on
FIPS-enabled Windows machines, and also results in *shorter*
directory names -- as the Java package name is a directory name --
which helps reduce Windows `MAX_PATH` issues.

I also expanded the enum:

	enum PackageNamingPolicy {
	    LowercaseHash = 0,
	    Lowercase = 1,
	    LowercaseWithAssemblyName = 2,
	    LowercaseMD5 = LowercaseHash,
	    LowercaseCrc64 = 3,
	}

Behavior still defaults to `MD5`, as before, but can be changed to
`PackageNamingPolicy.LowercaseCrc64` as needed.

Eventually we will change the default behavior to `LowercaseCrc64`,
and use of MD5 entirely removed.

Further changes will need to be made upstream in
xamarin/xamarin-android to fully integrate support for CRC64.

[0]: xamarin/monodroid@eb04c91
[1]: https://docs.microsoft.com/en-us/windows/security/threat-protection/security-policy-settings/system-cryptography-use-fips-compliant-algorithms-for-encryption-hashing-and-signing
[2]: https://user-images.githubusercontent.com/24926263/38981221-7e0bf7c4-43dc-11e8-8f16-9b6d284a55fb.PNG
[3]: https://en.wikipedia.org/wiki/Cyclic_redundancy_check

src/Java.Interop.Tools.JavaCallableWrappers/Java.Interop.Tools.JavaCallableWrappers.csproj

@@ -35,6 +35,7 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="Properties\AssemblyInfo.cs" />
+    <Compile Include="Java.Interop.Tools.JavaCallableWrappers\Crc64.cs" />
     <Compile Include="Java.Interop.Tools.JavaCallableWrappers\JavaCallableWrapperGenerator.cs" />
     <Compile Include="Java.Interop.Tools.JavaCallableWrappers\JavaTypeScanner.cs" />
     <Compile Include="Java.Interop.Tools.JavaCallableWrappers\TypeNameMapGenerator.cs" />

src/Java.Interop.Tools.JavaCallableWrappers/Java.Interop.Tools.JavaCallableWrappers/Crc64.cs

@@ -0,0 +1,186 @@
+/*
+ * Originally ported from: https://github.com/gityf/crc/blob/8045f50ba6e4193d4ee5d2539025fef26e613c9f/crc/crc64.c
+ *
+ * Copyright (c) 2012, Salvatore Sanfilippo <antirez at gmail dot com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *   * Redistributions of source code must retain the above copyright notice,
+ *     this list of conditions and the following disclaimer.
+ *   * Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *   * Neither the name of Redis nor the names of its contributors may be used
+ *     to endorse or promote products derived from this software without
+ *     specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE. */
+
+using System;
+using System.Security.Cryptography;
+
+namespace Java.Interop.Tools.JavaCallableWrappers
+{
+	/// <summary>
+	///  CRC64 variant: crc-64-jones 64-bit
+	///  * Poly: 0xad93d23594c935a9
+	/// </summary>
+	public class Crc64 : HashAlgorithm
+	{
+		static readonly ulong [] Table = {
+		    0x0000000000000000, 0x7ad870c830358979,
+		    0xf5b0e190606b12f2, 0x8f689158505e9b8b,
+		    0xc038e5739841b68f, 0xbae095bba8743ff6,
+		    0x358804e3f82aa47d, 0x4f50742bc81f2d04,
+		    0xab28ecb46814fe75, 0xd1f09c7c5821770c,
+		    0x5e980d24087fec87, 0x24407dec384a65fe,
+		    0x6b1009c7f05548fa, 0x11c8790fc060c183,
+		    0x9ea0e857903e5a08, 0xe478989fa00bd371,
+		    0x7d08ff3b88be6f81, 0x07d08ff3b88be6f8,
+		    0x88b81eabe8d57d73, 0xf2606e63d8e0f40a,
+		    0xbd301a4810ffd90e, 0xc7e86a8020ca5077,
+		    0x4880fbd87094cbfc, 0x32588b1040a14285,
+		    0xd620138fe0aa91f4, 0xacf86347d09f188d,
+		    0x2390f21f80c18306, 0x594882d7b0f40a7f,
+		    0x1618f6fc78eb277b, 0x6cc0863448deae02,
+		    0xe3a8176c18803589, 0x997067a428b5bcf0,
+		    0xfa11fe77117cdf02, 0x80c98ebf2149567b,
+		    0x0fa11fe77117cdf0, 0x75796f2f41224489,
+		    0x3a291b04893d698d, 0x40f16bccb908e0f4,
+		    0xcf99fa94e9567b7f, 0xb5418a5cd963f206,
+		    0x513912c379682177, 0x2be1620b495da80e,
+		    0xa489f35319033385, 0xde51839b2936bafc,
+		    0x9101f7b0e12997f8, 0xebd98778d11c1e81,
+		    0x64b116208142850a, 0x1e6966e8b1770c73,
+		    0x8719014c99c2b083, 0xfdc17184a9f739fa,
+		    0x72a9e0dcf9a9a271, 0x08719014c99c2b08,
+		    0x4721e43f0183060c, 0x3df994f731b68f75,
+		    0xb29105af61e814fe, 0xc849756751dd9d87,
+		    0x2c31edf8f1d64ef6, 0x56e99d30c1e3c78f,
+		    0xd9810c6891bd5c04, 0xa3597ca0a188d57d,
+		    0xec09088b6997f879, 0x96d1784359a27100,
+		    0x19b9e91b09fcea8b, 0x636199d339c963f2,
+		    0xdf7adabd7a6e2d6f, 0xa5a2aa754a5ba416,
+		    0x2aca3b2d1a053f9d, 0x50124be52a30b6e4,
+		    0x1f423fcee22f9be0, 0x659a4f06d21a1299,
+		    0xeaf2de5e82448912, 0x902aae96b271006b,
+		    0x74523609127ad31a, 0x0e8a46c1224f5a63,
+		    0x81e2d7997211c1e8, 0xfb3aa75142244891,
+		    0xb46ad37a8a3b6595, 0xceb2a3b2ba0eecec,
+		    0x41da32eaea507767, 0x3b024222da65fe1e,
+		    0xa2722586f2d042ee, 0xd8aa554ec2e5cb97,
+		    0x57c2c41692bb501c, 0x2d1ab4dea28ed965,
+		    0x624ac0f56a91f461, 0x1892b03d5aa47d18,
+		    0x97fa21650afae693, 0xed2251ad3acf6fea,
+		    0x095ac9329ac4bc9b, 0x7382b9faaaf135e2,
+		    0xfcea28a2faafae69, 0x8632586aca9a2710,
+		    0xc9622c4102850a14, 0xb3ba5c8932b0836d,
+		    0x3cd2cdd162ee18e6, 0x460abd1952db919f,
+		    0x256b24ca6b12f26d, 0x5fb354025b277b14,
+		    0xd0dbc55a0b79e09f, 0xaa03b5923b4c69e6,
+		    0xe553c1b9f35344e2, 0x9f8bb171c366cd9b,
+		    0x10e3202993385610, 0x6a3b50e1a30ddf69,
+		    0x8e43c87e03060c18, 0xf49bb8b633338561,
+		    0x7bf329ee636d1eea, 0x012b592653589793,
+		    0x4e7b2d0d9b47ba97, 0x34a35dc5ab7233ee,
+		    0xbbcbcc9dfb2ca865, 0xc113bc55cb19211c,
+		    0x5863dbf1e3ac9dec, 0x22bbab39d3991495,
+		    0xadd33a6183c78f1e, 0xd70b4aa9b3f20667,
+		    0x985b3e827bed2b63, 0xe2834e4a4bd8a21a,
+		    0x6debdf121b863991, 0x1733afda2bb3b0e8,
+		    0xf34b37458bb86399, 0x8993478dbb8deae0,
+		    0x06fbd6d5ebd3716b, 0x7c23a61ddbe6f812,
+		    0x3373d23613f9d516, 0x49aba2fe23cc5c6f,
+		    0xc6c333a67392c7e4, 0xbc1b436e43a74e9d,
+		    0x95ac9329ac4bc9b5, 0xef74e3e19c7e40cc,
+		    0x601c72b9cc20db47, 0x1ac40271fc15523e,
+		    0x5594765a340a7f3a, 0x2f4c0692043ff643,
+		    0xa02497ca54616dc8, 0xdafce7026454e4b1,
+		    0x3e847f9dc45f37c0, 0x445c0f55f46abeb9,
+		    0xcb349e0da4342532, 0xb1eceec59401ac4b,
+		    0xfebc9aee5c1e814f, 0x8464ea266c2b0836,
+		    0x0b0c7b7e3c7593bd, 0x71d40bb60c401ac4,
+		    0xe8a46c1224f5a634, 0x927c1cda14c02f4d,
+		    0x1d148d82449eb4c6, 0x67ccfd4a74ab3dbf,
+		    0x289c8961bcb410bb, 0x5244f9a98c8199c2,
+		    0xdd2c68f1dcdf0249, 0xa7f41839ecea8b30,
+		    0x438c80a64ce15841, 0x3954f06e7cd4d138,
+		    0xb63c61362c8a4ab3, 0xcce411fe1cbfc3ca,
+		    0x83b465d5d4a0eece, 0xf96c151de49567b7,
+		    0x76048445b4cbfc3c, 0x0cdcf48d84fe7545,
+		    0x6fbd6d5ebd3716b7, 0x15651d968d029fce,
+		    0x9a0d8ccedd5c0445, 0xe0d5fc06ed698d3c,
+		    0xaf85882d2576a038, 0xd55df8e515432941,
+		    0x5a3569bd451db2ca, 0x20ed197575283bb3,
+		    0xc49581ead523e8c2, 0xbe4df122e51661bb,
+		    0x3125607ab548fa30, 0x4bfd10b2857d7349,
+		    0x04ad64994d625e4d, 0x7e7514517d57d734,
+		    0xf11d85092d094cbf, 0x8bc5f5c11d3cc5c6,
+		    0x12b5926535897936, 0x686de2ad05bcf04f,
+		    0xe70573f555e26bc4, 0x9ddd033d65d7e2bd,
+		    0xd28d7716adc8cfb9, 0xa85507de9dfd46c0,
+		    0x273d9686cda3dd4b, 0x5de5e64efd965432,
+		    0xb99d7ed15d9d8743, 0xc3450e196da80e3a,
+		    0x4c2d9f413df695b1, 0x36f5ef890dc31cc8,
+		    0x79a59ba2c5dc31cc, 0x037deb6af5e9b8b5,
+		    0x8c157a32a5b7233e, 0xf6cd0afa9582aa47,
+		    0x4ad64994d625e4da, 0x300e395ce6106da3,
+		    0xbf66a804b64ef628, 0xc5bed8cc867b7f51,
+		    0x8aeeace74e645255, 0xf036dc2f7e51db2c,
+		    0x7f5e4d772e0f40a7, 0x05863dbf1e3ac9de,
+		    0xe1fea520be311aaf, 0x9b26d5e88e0493d6,
+		    0x144e44b0de5a085d, 0x6e963478ee6f8124,
+		    0x21c640532670ac20, 0x5b1e309b16452559,
+		    0xd476a1c3461bbed2, 0xaeaed10b762e37ab,
+		    0x37deb6af5e9b8b5b, 0x4d06c6676eae0222,
+		    0xc26e573f3ef099a9, 0xb8b627f70ec510d0,
+		    0xf7e653dcc6da3dd4, 0x8d3e2314f6efb4ad,
+		    0x0256b24ca6b12f26, 0x788ec2849684a65f,
+		    0x9cf65a1b368f752e, 0xe62e2ad306bafc57,
+		    0x6946bb8b56e467dc, 0x139ecb4366d1eea5,
+		    0x5ccebf68aecec3a1, 0x2616cfa09efb4ad8,
+		    0xa97e5ef8cea5d153, 0xd3a62e30fe90582a,
+		    0xb0c7b7e3c7593bd8, 0xca1fc72bf76cb2a1,
+		    0x45775673a732292a, 0x3faf26bb9707a053,
+		    0x70ff52905f188d57, 0x0a2722586f2d042e,
+		    0x854fb3003f739fa5, 0xff97c3c80f4616dc,
+		    0x1bef5b57af4dc5ad, 0x61372b9f9f784cd4,
+		    0xee5fbac7cf26d75f, 0x9487ca0fff135e26,
+		    0xdbd7be24370c7322, 0xa10fceec0739fa5b,
+		    0x2e675fb4576761d0, 0x54bf2f7c6752e8a9,
+		    0xcdcf48d84fe75459, 0xb71738107fd2dd20,
+		    0x387fa9482f8c46ab, 0x42a7d9801fb9cfd2,
+		    0x0df7adabd7a6e2d6, 0x772fdd63e7936baf,
+		    0xf8474c3bb7cdf024, 0x829f3cf387f8795d,
+		    0x66e7a46c27f3aa2c, 0x1c3fd4a417c62355,
+		    0x935745fc4798b8de, 0xe98f353477ad31a7,
+		    0xa6df411fbfb21ca3, 0xdc0731d78f8795da,
+		    0x536fa08fdfd90e51, 0x29b7d047efec8728,
+		};
+
+		ulong crc;
+
+		public override void Initialize () { }
+
+		protected override void HashCore (byte [] array, int ibStart, int cbSize)
+		{
+			for (int i = ibStart; i < cbSize; i++) {
+				crc = Table [(byte) (crc ^ array [i])] ^ (crc >> 8);
+			}
+		}
+
+		protected override byte [] HashFinal () => BitConverter.GetBytes (crc);
+	}
+}

src/Java.Interop.Tools.JavaCallableWrappers/Test/Java.Interop.Tools.JavaCallableWrappers-Tests.csproj

@@ -38,6 +38,8 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="Java.Interop.Tools.JavaCallableWrappers\JavaCallableWrapperGeneratorTests.cs" />
+    <Compile Include="Java.Interop.Tools.JavaCallableWrappers\Crc64Tests.cs" />
+    <Compile Include="Java.Interop.Tools.JavaCallableWrappers\JavaNativeTypeManagerTests.cs" />
     <Compile Include="Java.Interop.Tools.JavaCallableWrappers\TypeNameMapGeneratorTests.cs" />
     <Compile Include="Java.Interop.Tools.JavaCallableWrappers\SupportDeclarations.cs" />
     <Compile Include="Android.App\ActivityAttribute.cs" />

src/Java.Interop.Tools.JavaCallableWrappers/Test/Java.Interop.Tools.JavaCallableWrappers/Crc64Tests.cs

@@ -0,0 +1,36 @@
+using System.Text;
+using Java.Interop.Tools.JavaCallableWrappers;
+using NUnit.Framework;
+
+namespace Java.Interop.Tools.JavaCallableWrappersTests
+{
+	[TestFixture]
+	public class Crc64Tests
+	{
+		static string ToHash (string value)
+		{
+			var data = Encoding.UTF8.GetBytes (value);
+			using (var crc = new Crc64 ()) {
+				var hash = crc.ComputeHash (data);
+				var buf = new StringBuilder (hash.Length * 2);
+				foreach (var b in hash)
+					buf.AppendFormat ("{0:x2}", b);
+				return buf.ToString ();
+			}
+		}
+
+		[Test]
+		public void Hello ()
+		{
+			var actual = ToHash ("hello");
+			Assert.AreEqual ("a27666cb10ddb0d6", actual);
+		}
+
+		[Test]
+		public void XmlDocument ()
+		{
+			var actual = ToHash ("System.Xml.XmlDocument, System.Xml");
+			Assert.AreEqual ("2fbc43b3a95193ae", actual);
+		}
+	}
+}

src/Java.Interop.Tools.JavaCallableWrappers/Test/Java.Interop.Tools.JavaCallableWrappers/JavaNativeTypeManagerTests.cs

@@ -0,0 +1,56 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Java.Interop.Tools.TypeNameMappings;
+using NUnit.Framework;
+
+namespace Java.Interop.Tools.JavaCallableWrappersTests
+{
+	[TestFixture]
+	public class JavaNativeTypeManagerTests
+	{
+		PackageNamingPolicy existingValue;
+
+		[SetUp]
+		public void SetUp ()
+		{
+			existingValue = JavaNativeTypeManager.PackageNamingPolicy;
+		}
+
+		[TearDown]
+		public void TearDown ()
+		{
+			JavaNativeTypeManager.PackageNamingPolicy = existingValue;
+		}
+
+		[Test]
+		public void MD5 ()
+		{
+			JavaNativeTypeManager.PackageNamingPolicy = PackageNamingPolicy.LowercaseMD5;
+			Assert.AreEqual ("md5acb69d261d9efeb0927dd7ff443b9a3a", JavaNativeTypeManager.GetPackageName (typeof (string)));
+		}
+
+		[Test]
+		public void Crc64 ()
+		{
+			JavaNativeTypeManager.PackageNamingPolicy = PackageNamingPolicy.LowercaseCrc64;
+			Assert.AreEqual ("crc640005e817d0491b19", JavaNativeTypeManager.GetPackageName (typeof (string)));
+		}
+
+		[Test]
+		public void Lowercase ()
+		{
+			JavaNativeTypeManager.PackageNamingPolicy = PackageNamingPolicy.Lowercase;
+			Assert.AreEqual ("system", JavaNativeTypeManager.GetPackageName (typeof (string)));
+		}
+
+		[Test]
+		public void LowercaseWithAssemblyName ()
+		{
+			JavaNativeTypeManager.PackageNamingPolicy = PackageNamingPolicy.LowercaseWithAssemblyName;
+			Assert.AreEqual ("assembly_mscorlib.system", JavaNativeTypeManager.GetPackageName (typeof (string)));
+		}
+	}
+}

src/Java.Interop.Tools.TypeNameMappings/Java.Interop.Tools.TypeNameMappings/JavaNativeTypeManager.cs

@@ -5,11 +5,11 @@
 using System.Security.Cryptography;
 using System.Text;
 using Android.Runtime;
+using Java.Interop.Tools.JavaCallableWrappers;
 
 #if HAVE_CECIL
 using Mono.Cecil;
 using Java.Interop.Tools.Cecil;
-using Java.Interop.Tools.JavaCallableWrappers;
 #endif  // HAVE_CECIL
 
 namespace Java.Interop.Tools.TypeNameMappings
@@ -19,9 +19,14 @@ namespace Java.Interop.Tools.TypeNameMappings
 	public
 #endif
 	enum PackageNamingPolicy {
-		LowercaseHash,
-		Lowercase,
-		LowercaseWithAssemblyName,
+		/// <summary>
+		/// A hashed package name, currently defaults to LowercaseMD5
+		/// </summary>
+		LowercaseHash = 0,
+		Lowercase = 1,
+		LowercaseWithAssemblyName = 2,
+		LowercaseMD5 = LowercaseHash,
+		LowercaseCrc64 = 3,
 	}
 
 #if HAVE_CECIL
@@ -195,8 +200,13 @@ public static string GetPackageName (Type type)
 				return type.Namespace.ToLowerInvariant ();
 			case PackageNamingPolicy.LowercaseWithAssemblyName:
 				return "assembly_" + (assemblyName.Replace ('.', '_') + "." + type.Namespace).ToLowerInvariant ();
+			case PackageNamingPolicy.LowercaseCrc64:
+				using (var crc = new Crc64 ())
+					return "crc64" + ToHash (type.Namespace + ":" + assemblyName, crc);
+			case PackageNamingPolicy.LowercaseMD5:
 			default:
-				return "md5" + ToMd5 (type.Namespace + ":" + assemblyName);
+				using (var md5 = MD5.Create ())
+					return "md5" + ToHash (type.Namespace + ":" + assemblyName, md5);
 			}
 		}
 
@@ -515,8 +525,13 @@ public static string GetPackageName (TypeDefinition type)
 				return type.Namespace.ToLowerInvariant ();
 			case PackageNamingPolicy.LowercaseWithAssemblyName:
 				return "assembly_" + (type.GetPartialAssemblyName ().Replace ('.', '_') + "." + type.Namespace).ToLowerInvariant ();
+			case PackageNamingPolicy.LowercaseCrc64:
+				using (var crc = new Crc64 ())
+					return "crc64" + ToHash (type.Namespace + ":" + type.GetPartialAssemblyName (), crc);
+			case PackageNamingPolicy.LowercaseMD5:
 			default:
-				return "md5" + ToMd5 (type.Namespace + ":" + type.GetPartialAssemblyName ());
+				using (var md5 = MD5.Create ())
+					return "md5" + ToHash (type.Namespace + ":" + type.GetPartialAssemblyName (), md5);
 			}
 		}
 #endif
@@ -583,16 +598,14 @@ static IEnumerable<MethodDefinition> GetBaseConstructors (TypeDefinition type)
 		}
 #endif  // HAVE_CECIL
 
-		static string ToMd5 (string value)
+		static string ToHash (string value, HashAlgorithm algorithm)
 		{
 			var data = Encoding.UTF8.GetBytes (value);
-			using (var md5 = MD5.Create ()) {
-				var hash    = md5.ComputeHash (data);
-				var buf     = new StringBuilder (hash.Length * 2);
-				foreach (var b in hash)
-					buf.AppendFormat ("{0:x2}", b);
-				return buf.ToString ();
-			}
+			var hash = algorithm.ComputeHash (data);
+			var buf  = new StringBuilder (hash.Length * 2);
+			foreach (var b in hash)
+				buf.AppendFormat ("{0:x2}", b);
+			return buf.ToString ();
 		}
 
 		static string ToLowerCase (string value)