diff --git a/.github/workflows/build-test.yml b/.github/workflows/build-test.yml
index d5630331f..463b5d6fb 100644
--- a/.github/workflows/build-test.yml
+++ b/.github/workflows/build-test.yml
@@ -18,11 +18,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, windows-2019, macos-latest]
-        target: [netstandard2.0, netstandard2.1]
-        include:
-          - os: windows-2019
-            target: net45
+        os: [ubuntu-latest, windows-latest, macos-latest]
+        target: [netstandard2.0, netstandard2.1, net6.0]
     env:
       LIB_PROJ: src/ICSharpCode.SharpZipLib/ICSharpCode.SharpZipLib.csproj
     steps:
@@ -31,10 +28,10 @@ jobs:
         ref: ${{ github.events.inputs.tag }}
         fetch-depth: 0
 
-    - name: Setup .NET Core
+    - name: Setup .NET
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: '3.1.x'
+        dotnet-version: '6.0.x'
         
     - name: Show .NET info
       run: dotnet --info
@@ -52,17 +49,17 @@ jobs:
       matrix:
         # Windows testing is combined with code coverage
         os: [ubuntu, macos]
-        target: [netcoreapp3.1]
+        target: [net6.0]
     steps:
     - uses: actions/checkout@v2
       with:
         fetch-depth: 0
 
     - name: Setup .NET Core
-      if: matrix.target == 'netcoreapp3.1'
+      if: matrix.target == 'net6.0'
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: '3.1.x'
+        dotnet-version: '6.0.x'
 
     - name: Restore test dependencies
       run: dotnet restore
@@ -89,7 +86,7 @@ jobs:
     - name: Setup .NET
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: '3.1.x'
+        dotnet-version: '6.0.x'
         
     # NOTE: This is the temporary fix for https://github.com/actions/virtual-environments/issues/1090
     - name: Cleanup before restore
@@ -120,7 +117,7 @@ jobs:
 
   Pack:
     needs: [Build, Test, CodeCov]
-    runs-on: windows-2019
+    runs-on: windows-latest
     env:
       PKG_SUFFIX: ''
       PKG_PROJ: src/ICSharpCode.SharpZipLib/ICSharpCode.SharpZipLib.csproj
@@ -135,14 +132,14 @@ jobs:
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: '5.0.x'
+        dotnet-version: '6.0.x'
         
     - name: Build library for .NET Standard 2.0
       run: dotnet build -c Release -f netstandard2.0 ${{ env.PKG_PROPS }} ${{ env.PKG_PROJ }}
     - name: Build library for .NET Standard 2.1
       run: dotnet build -c Release -f netstandard2.1 ${{ env.PKG_PROPS }} ${{ env.PKG_PROJ }}
-    - name: Build library for .NET Framework 4.5
-      run: dotnet build -c Release -f net45  ${{ env.PKG_PROPS }} ${{ env.PKG_PROJ }}
+    - name: Build library for .NET 6.0
+      run: dotnet build -c Release -f net6.0  ${{ env.PKG_PROPS }} ${{ env.PKG_PROJ }}
 
     - name: Add PR suffix to package
       if: ${{ github.event_name == 'pull_request' }}
diff --git a/benchmark/ICSharpCode.SharpZipLib.Benchmark/ICSharpCode.SharpZipLib.Benchmark.csproj b/benchmark/ICSharpCode.SharpZipLib.Benchmark/ICSharpCode.SharpZipLib.Benchmark.csproj
index 81a8ad598..7688d0ff2 100644
--- a/benchmark/ICSharpCode.SharpZipLib.Benchmark/ICSharpCode.SharpZipLib.Benchmark.csproj
+++ b/benchmark/ICSharpCode.SharpZipLib.Benchmark/ICSharpCode.SharpZipLib.Benchmark.csproj
@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFrameworks>netcoreapp2.1;netcoreapp3.1;net461</TargetFrameworks>
+    <TargetFrameworks>net6.0;netcoreapp3.1;net462</TargetFrameworks>
   </PropertyGroup>
 
 	<ItemGroup>
diff --git a/src/ICSharpCode.SharpZipLib/Encryption/ZipAESStream.cs b/src/ICSharpCode.SharpZipLib/Encryption/ZipAESStream.cs
index 80ce0b4ab..346b5484b 100644
--- a/src/ICSharpCode.SharpZipLib/Encryption/ZipAESStream.cs
+++ b/src/ICSharpCode.SharpZipLib/Encryption/ZipAESStream.cs
@@ -40,7 +40,7 @@ public ZipAESStream(Stream stream, ZipAESTransform transform, CryptoStreamMode m
 		}
 
 		// The final n bytes of the AES stream contain the Auth Code.
-		private const int AUTH_CODE_LENGTH = 10;
+		public const int AUTH_CODE_LENGTH = 10;
 
 		// Blocksize is always 16 here, even for AES-256 which has transform.InputBlockSize of 32.
 		private const int CRYPTO_BLOCK_SIZE = 16;
diff --git a/src/ICSharpCode.SharpZipLib/Encryption/ZipAESTransform.cs b/src/ICSharpCode.SharpZipLib/Encryption/ZipAESTransform.cs
index 6c84be691..32c7b8156 100644
--- a/src/ICSharpCode.SharpZipLib/Encryption/ZipAESTransform.cs
+++ b/src/ICSharpCode.SharpZipLib/Encryption/ZipAESTransform.cs
@@ -1,6 +1,5 @@
 using System;
 using System.Security.Cryptography;
-using ICSharpCode.SharpZipLib.Core;
 
 namespace ICSharpCode.SharpZipLib.Encryption
 {
@@ -9,31 +8,6 @@ namespace ICSharpCode.SharpZipLib.Encryption
 	/// </summary>
 	internal class ZipAESTransform : ICryptoTransform
 	{
-#if NET45
-		class IncrementalHash : HMACSHA1
-		{
-			bool _finalised;
-			public IncrementalHash(byte[] key) : base(key) { }
-			public static IncrementalHash CreateHMAC(string n, byte[] key) => new IncrementalHash(key);
-			public void AppendData(byte[] buffer, int offset, int count) => TransformBlock(buffer, offset, count, buffer, offset);
-			public byte[] GetHashAndReset()
-			{
-				if (!_finalised)
-				{
-					byte[] dummy = new byte[0];
-					TransformFinalBlock(dummy, 0, 0);
-					_finalised = true;
-				}
-				return Hash;
-			}
-		}
-
-		static class HashAlgorithmName
-		{
-			public static string SHA1 = null;
-		}
-#endif
-
 		private const int PWD_VER_LENGTH = 2;
 
 		// WinZip use iteration count of 1000 for PBKDF2 key generation
@@ -137,91 +111,67 @@ public int TransformBlock(byte[] inputBuffer, int inputOffset, int inputCount, b
 		/// <summary>
 		/// Returns the 2 byte password verifier
 		/// </summary>
-		public byte[] PwdVerifier
-		{
-			get
-			{
-				return _pwdVerifier;
-			}
-		}
+		public byte[] PwdVerifier => _pwdVerifier;
 
 		/// <summary>
 		/// Returns the 10 byte AUTH CODE to be checked or appended immediately following the AES data stream.
 		/// </summary>
-		public byte[] GetAuthCode()
-		{
-			if (_authCode == null)
-			{
-				_authCode = _hmacsha1.GetHashAndReset();
-			}
-			return _authCode;
-		}
+		public byte[] GetAuthCode() => _authCode ?? (_authCode = _hmacsha1.GetHashAndReset());
 
 		#region ICryptoTransform Members
 
 		/// <summary>
-		/// Not implemented.
+		/// Transform final block and read auth code
 		/// </summary>
 		public byte[] TransformFinalBlock(byte[] inputBuffer, int inputOffset, int inputCount)
 		{
-			if (inputCount > 0)
-			{
-				throw new NotImplementedException("TransformFinalBlock is not implemented and inputCount is greater than 0");
+			var buffer = Array.Empty<byte>();
+
+			// FIXME: When used together with `ZipAESStream`, the final block handling is done inside of it instead
+			// This should not be necessary anymore, and the entire `ZipAESStream` class should be replaced with a plain `CryptoStream`
+			if (inputCount != 0) {
+				if (inputCount > ZipAESStream.AUTH_CODE_LENGTH)
+				{
+					// At least one byte of data is preceeding the auth code
+					int finalBlock = inputCount - ZipAESStream.AUTH_CODE_LENGTH;
+					buffer = new byte[finalBlock];
+					TransformBlock(inputBuffer, inputOffset, finalBlock, buffer, 0);
+				}
+				else if (inputCount < ZipAESStream.AUTH_CODE_LENGTH)
+					throw new Zip.ZipException("Auth code missing from input stream");
+
+				// Read the authcode from the last 10 bytes
+				_authCode = _hmacsha1.GetHashAndReset();
 			}
-			return Empty.Array<byte>();
+			
+
+			return buffer;
 		}
 
 		/// <summary>
 		/// Gets the size of the input data blocks in bytes.
 		/// </summary>
-		public int InputBlockSize
-		{
-			get
-			{
-				return _blockSize;
-			}
-		}
+		public int InputBlockSize => _blockSize;
 
 		/// <summary>
 		/// Gets the size of the output data blocks in bytes.
 		/// </summary>
-		public int OutputBlockSize
-		{
-			get
-			{
-				return _blockSize;
-			}
-		}
+		public int OutputBlockSize => _blockSize;
 
 		/// <summary>
 		/// Gets a value indicating whether multiple blocks can be transformed.
 		/// </summary>
-		public bool CanTransformMultipleBlocks
-		{
-			get
-			{
-				return true;
-			}
-		}
+		public bool CanTransformMultipleBlocks => true;
 
 		/// <summary>
 		/// Gets a value indicating whether the current transform can be reused.
 		/// </summary>
-		public bool CanReuseTransform
-		{
-			get
-			{
-				return true;
-			}
-		}
+		public bool CanReuseTransform => true;
 
 		/// <summary>
 		/// Cleanup internal state.
 		/// </summary>
-		public void Dispose()
-		{
-			_encryptor.Dispose();
-		}
+		public void Dispose() => _encryptor.Dispose();
 
 		#endregion ICryptoTransform Members
 	}
diff --git a/src/ICSharpCode.SharpZipLib/ICSharpCode.SharpZipLib.csproj b/src/ICSharpCode.SharpZipLib/ICSharpCode.SharpZipLib.csproj
index e736ad1cc..0dfc04003 100644
--- a/src/ICSharpCode.SharpZipLib/ICSharpCode.SharpZipLib.csproj
+++ b/src/ICSharpCode.SharpZipLib/ICSharpCode.SharpZipLib.csproj
@@ -1,8 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;netstandard2.1;net45</TargetFrameworks>
-    <SignAssembly>True</SignAssembly>
+    <TargetFrameworks>netstandard2.0;netstandard2.1;net6.0</TargetFrameworks>
+    <IsTrimmable>true</IsTrimmable>
+    <EnableTrimAnalyzer>true</EnableTrimAnalyzer>
+    <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>../../assets/ICSharpCode.SharpZipLib.snk</AssemblyOriginatorKeyFile>
     <GeneratePackageOnBuild>true</GeneratePackageOnBuild>
 		<GenerateDocumentationFile>true</GenerateDocumentationFile>
@@ -11,8 +13,8 @@
   
   <!-- Nuget specific tags -->
   <PropertyGroup>
-    <Version>1.3.3</Version>
-    <FileVersion>$(Version).11</FileVersion>
+    <Version>1.4.0</Version>
+    <FileVersion>$(Version).12</FileVersion>
     <AssemblyVersion>$(FileVersion)</AssemblyVersion>
     <PackageId>SharpZipLib</PackageId>
     <Company>ICSharpCode</Company>
@@ -22,11 +24,11 @@
 		<PackageProjectUrl>http://icsharpcode.github.io/SharpZipLib/</PackageProjectUrl>
 		<PackageIcon>images/sharpziplib-nuget-256x256.png</PackageIcon>
     <RepositoryUrl>https://github.com/icsharpcode/SharpZipLib</RepositoryUrl>
-    <Copyright>Copyright © 2000-2021 SharpZipLib Contributors</Copyright>
+    <Copyright>Copyright © 2000-2022 SharpZipLib Contributors</Copyright>
     <PackageTags>Compression Library Zip GZip BZip2 LZW Tar</PackageTags>
     <NeutralLanguage>en-US</NeutralLanguage>
     <PackageReleaseNotes>
-Please see https://github.com/icsharpcode/SharpZipLib/wiki/Release-1.3.3 for more information.</PackageReleaseNotes>
+Please see https://github.com/icsharpcode/SharpZipLib/wiki/Release-1.4.0 for more information.</PackageReleaseNotes>
     <PackageProjectUrl>https://github.com/icsharpcode/SharpZipLib</PackageProjectUrl> 
   </PropertyGroup>
 
@@ -34,11 +36,6 @@ Please see https://github.com/icsharpcode/SharpZipLib/wiki/Release-1.3.3 for mor
 		<PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.0.0" PrivateAssets="All" />
 	</ItemGroup>
 
-	<ItemGroup Condition=" '$(TargetFramework)' == 'net45' ">
-		<PackageReference Include="System.Memory" Version="4.5.4" />
-		<PackageReference Include="System.Threading.Tasks.Extensions" Version="4.5.2" />
-	</ItemGroup>
-
 	<ItemGroup Condition=" '$(TargetFramework)' == 'netstandard2.0' ">
 		<PackageReference Include="System.Memory" Version="4.5.4" />
 		<PackageReference Include="System.Threading.Tasks.Extensions" Version="4.5.2" />
diff --git a/test/ICSharpCode.SharpZipLib.Tests/ICSharpCode.SharpZipLib.Tests.csproj b/test/ICSharpCode.SharpZipLib.Tests/ICSharpCode.SharpZipLib.Tests.csproj
index 4a46e84f2..73ef2eb0d 100644
--- a/test/ICSharpCode.SharpZipLib.Tests/ICSharpCode.SharpZipLib.Tests.csproj
+++ b/test/ICSharpCode.SharpZipLib.Tests/ICSharpCode.SharpZipLib.Tests.csproj
@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Library</OutputType>
-		<TargetFrameworks>netcoreapp3.1;net46</TargetFrameworks>
+		<TargetFrameworks>net6.0;net462</TargetFrameworks>
     <ApplicationIcon />
     <StartupObject />
     <SignAssembly>true</SignAssembly>
@@ -13,9 +13,9 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.9.1" />
-    <PackageReference Include="nunit" Version="3.13.1" />
-    <PackageReference Include="nunit.console" Version="3.12.0" />
-    <PackageReference Include="NUnit3TestAdapter" Version="3.17.0" />
+    <PackageReference Include="nunit" Version="3.13.3" />
+    <PackageReference Include="nunit.console" Version="3.15.0" />
+    <PackageReference Include="NUnit3TestAdapter" Version="4.2.1" />
     <PackageReference Include="System.Text.Encoding.CodePages" Version="4.4.0" />
     <PackageReference Include="System.ValueTuple" Version="4.5.0" />
   </ItemGroup>