Add common interface for padding (#420)

Algorithms.Tests/Crypto/Paddings/Pkcs7PaddingTests.cs

@@ -141,10 +141,20 @@ public void RemovePadding_WhenInvalidPadding_ShouldThrowArgumentException()
             .WithMessage("Invalid padding");
     }
 
+    [Test]
+    public void GetPaddingCount_WhenArrayIsNull_ShouldThrowArgumentNullException()
+    {
+        var padding = new Pkcs7Padding(DefaultBlockSize);
+
+        Action act = () => padding.GetPaddingCount(null!);
+
+        act.Should().Throw<ArgumentNullException>();
+    }
+
     [Test]
     public void GetPaddingCount_WhenInputArrayIsValid_ShouldReturnCorrectPaddingCount()
     {
-        var paddingSize = 5;
+        const int paddingSize = 5;
         var size32Input = new byte[32];
 
         for (var i = 0; i < paddingSize; i++)

Algorithms.Tests/Crypto/Paddings/TbcPaddingTests.cs

@@ -128,7 +128,7 @@ public void GetPaddingBytes_WhenCalledWithPaddedData_ShouldReturnCorrectPaddingC
         var paddedData = new byte[] { 0x01, 0x02, 0x03, 0xff, 0xff };
         const int expectedPaddingCount = 2;
 
-        var result = padding.GetPaddingBytes(paddedData);
+        var result = padding.GetPaddingCount(paddedData);
 
         result.Should().Be(expectedPaddingCount);
     }
@@ -138,7 +138,7 @@ public void GetPaddingBytes_WhenCalledWithUnpaddedData_ShouldReturnZero()
     {
         var unpaddedData = new byte[] { 0x01, 0x02, 0x03 };
 
-        Action action = () => padding.GetPaddingBytes(unpaddedData);
+        Action action = () => padding.GetPaddingCount(unpaddedData);
 
         action.Should().Throw<ArgumentException>()
             .WithMessage("No padding found");
@@ -149,7 +149,7 @@ public void GetPaddingBytes_WhenCalledWithEmptyArray_ShouldReturnZero()
     {
         var emptyData = Array.Empty<byte>();
 
-        Action action = () => padding.GetPaddingBytes(emptyData);
+        Action action = () => padding.GetPaddingCount(emptyData);
 
         action.Should().Throw<ArgumentException>()
             .WithMessage("No padding found.");

Algorithms/Crypto/Paddings/IBlockCipherPadding.cs

@@ -0,0 +1,39 @@
+using System;
+
+namespace Algorithms.Crypto.Paddings;
+
+/// <summary>
+/// A common interface that all block cipher padding schemes should follow.
+/// </summary>
+public interface IBlockCipherPadding
+{
+    /// <summary>
+    /// Adds padding bytes to the end of the given block of the data and returns the number of bytes that were added.
+    /// </summary>
+    /// <param name="inputData">The input data array that needs padding.</param>
+    /// <param name="inputOffset">The offset in the input array where the padding should start.</param>
+    /// <returns>The number of bytes added.</returns>
+    /// <remarks>
+    /// This method expects that the input parameter <paramref name="inputData"/> contains the last block of plain text
+    /// that needs to be padded. This means that the value of <paramref name="inputData"/> has to have the same value as
+    /// the last block of plain text. The reason for this is that some modes such as the <see cref="TbcPadding"/> base the
+    /// padding value on the last byte of the plain text.
+    /// </remarks>
+    public int AddPadding(byte[] inputData, int inputOffset);
+
+    /// <summary>
+    /// Removes the padding bytes from the given block of data and returns the original data as a new array.
+    /// </summary>
+    /// <param name="inputData">The input data array containing the padding.</param>
+    /// <returns>The input data without the padding as a new byte array.</returns>
+    /// <exception cref="ArgumentException">Thrown when the input data has invalid padding.</exception>
+    public byte[] RemovePadding(byte[] inputData);
+
+    /// <summary>
+    /// Gets the number of padding bytes in the input data.
+    /// </summary>
+    /// <param name="input">The input data array that has padding.</param>
+    /// <returns>The number of padding bytes in the input data.</returns>
+    /// <exception cref="ArgumentException">Thrown when the input data has invalid padding.</exception>
+    public int GetPaddingCount(byte[] input);
+}

Algorithms/Crypto/Paddings/Iso10126D2Padding.cs

@@ -19,7 +19,7 @@ namespace Algorithms.Crypto.Paddings;
 /// the end of the data.
 /// </para>
 /// </summary>
-public class Iso10126D2Padding
+public class Iso10126D2Padding : IBlockCipherPadding
 {
     /// <summary>
     /// Adds random padding to the input data array to make it a multiple of the block size according to the

Algorithms/Crypto/Paddings/Iso7816D4Padding.cs

@@ -28,7 +28,7 @@ namespace Algorithms.Crypto.Paddings;
 /// depend on any specific character encoding or representation.
 /// </para>
 /// </summary>
-public class Iso7816D4Padding
+public class Iso7816D4Padding : IBlockCipherPadding
 {
     /// <summary>
     /// Adds padding to the input data according to the ISO 7816-4 standard.

Algorithms/Crypto/Paddings/Pkcs7Padding.cs

@@ -20,7 +20,7 @@ namespace Algorithms.Crypto.Paddings;
 /// padding, such as AES.
 /// </para>
 /// </summary>
-public class Pkcs7Padding
+public class Pkcs7Padding : IBlockCipherPadding
 {
     private readonly int blockSize;
 

Algorithms/Crypto/Paddings/TbcPadding.cs

@@ -15,7 +15,7 @@ namespace Algorithms.Crypto.Paddings;
 /// The padding bytes are added at the end of the data block until the desired length is reached.
 /// </para>
 /// </summary>
-public class TbcPadding
+public class TbcPadding : IBlockCipherPadding
 {
     /// <summary>
     /// Adds padding to the input array according to the TBC standard.
@@ -121,7 +121,7 @@ public byte[] RemovePadding(byte[] input)
     /// avoid branching. If the input array is not padded or has an invalid padding, the method may return incorrect
     /// results.
     /// </remarks>
-    public int GetPaddingBytes(byte[] input)
+    public int GetPaddingCount(byte[] input)
     {
         var length = input.Length;
 

Algorithms/Crypto/Paddings/X932Padding.cs

@@ -18,7 +18,7 @@ namespace Algorithms.Crypto.Paddings;
 /// bytes.
 /// </para>
 /// </summary>
-public class X932Padding
+public class X932Padding : IBlockCipherPadding
 {
     private readonly bool useRandomPadding;