diff --git a/Adler32Context.cs b/Adler32Context.cs
index 3cd3ac2..78fc6d5 100644
--- a/Adler32Context.cs
+++ b/Adler32Context.cs
@@ -38,7 +38,7 @@ using Aaru.Helpers;
 namespace Aaru.Checksums
 {
     /// <summary>Implements the Adler-32 algorithm</summary>
-    public class Adler32Context : IChecksum
+    public sealed class Adler32Context : IChecksum
     {
         const ushort ADLER_MODULE = 65521;
         ushort       _sum1, _sum2;
diff --git a/CRC16CCITTContext.cs b/CRC16CCITTContext.cs
index 3c4c748..daa7743 100644
--- a/CRC16CCITTContext.cs
+++ b/CRC16CCITTContext.cs
@@ -32,7 +32,7 @@
 
 namespace Aaru.Checksums
 {
-    public class CRC16CCITTContext : Crc16Context
+    public sealed class CRC16CCITTContext : Crc16Context
     {
         public const ushort CRC16_CCITT_POLY = 0x8408;
         public const ushort CRC16_CCITT_SEED = 0x0000;
diff --git a/CRC16Context.cs b/CRC16Context.cs
index aa59f88..91a1013 100644
--- a/CRC16Context.cs
+++ b/CRC16Context.cs
@@ -41,10 +41,10 @@ namespace Aaru.Checksums
     /// <summary>Implements a CRC16 algorithm</summary>
     public class Crc16Context : IChecksum
     {
-        protected ushort   _finalSeed;
-        protected ushort   _hashInt;
-        protected bool     _inverse;
-        protected ushort[] _table;
+        readonly ushort   _finalSeed;
+        readonly bool     _inverse;
+        readonly ushort[] _table;
+        ushort            _hashInt;
 
         /// <summary>Initializes the CRC16 table with a custom polynomial and seed</summary>
         public Crc16Context(ushort polynomial, ushort seed, ushort[] table, bool inverse)
diff --git a/CRC16IBMContext.cs b/CRC16IBMContext.cs
index 31177db..a9910f0 100644
--- a/CRC16IBMContext.cs
+++ b/CRC16IBMContext.cs
@@ -32,7 +32,7 @@
 
 namespace Aaru.Checksums
 {
-    public class CRC16IBMContext : Crc16Context
+    public sealed class CRC16IBMContext : Crc16Context
     {
         const ushort CRC16_IBM_POLY = 0xA001;
         const ushort CRC16_IBM_SEED = 0x0000;
diff --git a/CRC32Context.cs b/CRC32Context.cs
index 3d8f084..e4c3745 100644
--- a/CRC32Context.cs
+++ b/CRC32Context.cs
@@ -38,7 +38,7 @@ using Aaru.Helpers;
 namespace Aaru.Checksums
 {
     /// <summary>Implements a CRC32 algorithm</summary>
-    public class Crc32Context : IChecksum
+    public sealed class Crc32Context : IChecksum
     {
         const uint CRC32_ISO_POLY = 0xEDB88320;
         const uint CRC32_ISO_SEED = 0xFFFFFFFF;
diff --git a/CRC64Context.cs b/CRC64Context.cs
index 8decdd1..d9bc026 100644
--- a/CRC64Context.cs
+++ b/CRC64Context.cs
@@ -38,7 +38,7 @@ using Aaru.Helpers;
 namespace Aaru.Checksums
 {
     /// <summary>Implements a CRC64 algorithm</summary>
-    public class Crc64Context : IChecksum
+    public sealed class Crc64Context : IChecksum
     {
         public const ulong CRC64_ECMA_POLY = 0xC96C5795D7870F42;
         public const ulong CRC64_ECMA_SEED = 0xFFFFFFFFFFFFFFFF;
diff --git a/FletcherContext.cs b/FletcherContext.cs
index c369180..fed4021 100644
--- a/FletcherContext.cs
+++ b/FletcherContext.cs
@@ -40,7 +40,7 @@ using Aaru.Helpers;
 namespace Aaru.Checksums
 {
     /// <summary>Implements the Fletcher-32 algorithm</summary>
-    public class Fletcher32Context : IChecksum
+    public sealed class Fletcher32Context : IChecksum
     {
         const ushort FLETCHER_MODULE = 0xFFFF;
         ushort       _sum1, _sum2;
@@ -165,7 +165,7 @@ namespace Aaru.Checksums
     }
 
     /// <summary>Implements the Fletcher-16 algorithm</summary>
-    public class Fletcher16Context : IChecksum
+    public sealed class Fletcher16Context : IChecksum
     {
         const byte FLETCHER_MODULE = 0xFF;
         byte       _sum1, _sum2;
diff --git a/MD5Context.cs b/MD5Context.cs
index 4852b3b..95ff00b 100644
--- a/MD5Context.cs
+++ b/MD5Context.cs
@@ -38,7 +38,7 @@ using Aaru.CommonTypes.Interfaces;
 namespace Aaru.Checksums
 {
     /// <summary>Wraps up .NET MD5 implementation to a Init(), Update(), Final() context.</summary>
-    public class Md5Context : IChecksum
+    public sealed class Md5Context : IChecksum
     {
         readonly MD5 _provider;
 
diff --git a/Register.cs b/Register.cs
index 9ad89ce..99f7760 100644
--- a/Register.cs
+++ b/Register.cs
@@ -44,7 +44,7 @@ using Aaru.CommonTypes.Interfaces;
 
 namespace Aaru.Checksums
 {
-    public class Register : IPluginRegister
+    public sealed class Register : IPluginRegister
     {
         public List<Type> GetAllChecksumPlugins() => Assembly.
                                                      GetExecutingAssembly().GetTypes().
diff --git a/SHA1Context.cs b/SHA1Context.cs
index 86e4b14..a054b2a 100644
--- a/SHA1Context.cs
+++ b/SHA1Context.cs
@@ -38,7 +38,7 @@ using Aaru.CommonTypes.Interfaces;
 namespace Aaru.Checksums
 {
     /// <summary>Wraps up .NET SHA1 implementation to a Init(), Update(), Final() context.</summary>
-    public class Sha1Context : IChecksum
+    public sealed class Sha1Context : IChecksum
     {
         readonly SHA1 _provider;
 
diff --git a/SHA256Context.cs b/SHA256Context.cs
index 2ed98f0..bc7d232 100644
--- a/SHA256Context.cs
+++ b/SHA256Context.cs
@@ -38,7 +38,7 @@ using Aaru.CommonTypes.Interfaces;
 namespace Aaru.Checksums
 {
     /// <summary>Wraps up .NET SHA256 implementation to a Init(), Update(), Final() context.</summary>
-    public class Sha256Context : IChecksum
+    public sealed class Sha256Context : IChecksum
     {
         readonly SHA256 _provider;
 
diff --git a/SHA384Context.cs b/SHA384Context.cs
index db85bec..945720e 100644
--- a/SHA384Context.cs
+++ b/SHA384Context.cs
@@ -38,7 +38,7 @@ using Aaru.CommonTypes.Interfaces;
 namespace Aaru.Checksums
 {
     /// <summary>Wraps up .NET SHA384 implementation to a Init(), Update(), Final() context.</summary>
-    public class Sha384Context : IChecksum
+    public sealed class Sha384Context : IChecksum
     {
         readonly SHA384 _provider;
 
diff --git a/SHA512Context.cs b/SHA512Context.cs
index 1c9f243..d0040d7 100644
--- a/SHA512Context.cs
+++ b/SHA512Context.cs
@@ -38,7 +38,7 @@ using Aaru.CommonTypes.Interfaces;
 namespace Aaru.Checksums
 {
     /// <summary>Wraps up .NET SHA512 implementation to a Init(), Update(), Final() context.</summary>
-    public class Sha512Context : IChecksum
+    public sealed class Sha512Context : IChecksum
     {
         readonly SHA512 _provider;
 
diff --git a/SpamSumContext.cs b/SpamSumContext.cs
index a4ff46d..5e1c769 100644
--- a/SpamSumContext.cs
+++ b/SpamSumContext.cs
@@ -47,7 +47,7 @@ using Aaru.CommonTypes.Interfaces;
 namespace Aaru.Checksums
 {
     /// <summary>Implements the SpamSum fuzzy hashing algorithm.</summary>
-    public class SpamSumContext : IChecksum
+    public sealed class SpamSumContext : IChecksum
     {
         const uint ROLLING_WINDOW   = 7;
         const uint MIN_BLOCKSIZE    = 3;