Add one-shot CFB encrypt/decrypt to SymmetricAlgorithm

Adds the CFB versions similar to the already-added ECB and CBC versions.

Co-authored-by: Jeremy Barton <jbarton@microsoft.com>

Author: vcsjones

src/libraries/Common/src/Internal/Cryptography/Helpers.cs

@@ -30,14 +30,9 @@ internal static partial class Helpers
             return (byte[])(src.Clone());
         }
 
-        public static int GetPaddingSize(this SymmetricAlgorithm algorithm, CipherMode mode, int feedbackSizeBits)
+        public static int GetPaddingSize(this SymmetricAlgorithm algorithm, CipherMode mode, int feedbackSizeInBits)
         {
-            // CFB8 does not require any padding at all
-            // otherwise, it is always required to pad for block size
-            if (mode == CipherMode.CFB && feedbackSizeBits == 8)
-                return 1;
-
-            return algorithm.BlockSize / 8;
+            return (mode == CipherMode.CFB ? feedbackSizeInBits : algorithm.BlockSize) / 8;
         }
 
         internal static bool TryCopyToDestination(ReadOnlySpan<byte> source, Span<byte> destination, out int bytesWritten)

src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/AES/AesCipherOneShotTests.cs

@@ -1124,6 +1124,7 @@ private static void TestAesTransformDirectKey(
             {
                 aes.Mode = cipherMode;
                 aes.Padding = paddingMode;
+                aes.Key = key;
 
                 if (feedbackSize.HasValue)
                 {
@@ -1135,16 +1136,19 @@ private static void TestAesTransformDirectKey(
 
                 if (cipherMode == CipherMode.ECB)
                 {
-                    aes.Key = key;
                     liveOneShotDecryptBytes = aes.DecryptEcb(cipherBytes, paddingMode);
                     liveOneShotEncryptBytes = aes.EncryptEcb(plainBytes, paddingMode);
                 }
                 else if (cipherMode == CipherMode.CBC)
                 {
-                    aes.Key = key;
                     liveOneShotDecryptBytes = aes.DecryptCbc(cipherBytes, iv, paddingMode);
                     liveOneShotEncryptBytes = aes.EncryptCbc(plainBytes, iv, paddingMode);
                 }
+                else if (cipherMode == CipherMode.CFB)
+                {
+                    liveOneShotDecryptBytes = aes.DecryptCfb(cipherBytes, iv, paddingMode, feedbackSizeInBits: feedbackSize.Value);
+                    liveOneShotEncryptBytes = aes.EncryptCfb(plainBytes, iv, paddingMode, feedbackSizeInBits: feedbackSize.Value);
+                }
             }
 
             Assert.Equal(cipherBytes, liveEncryptBytes);

src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/AES/AesCipherTests.cs

@@ -531,6 +531,7 @@ private static void TestDESTransformDirectKey(
             {
                 des.Mode = cipherMode;
                 des.Padding = paddingMode;
+                des.Key = key;
 
                 if (feedbackSize.HasValue)
                 {
@@ -540,17 +541,23 @@ private static void TestDESTransformDirectKey(
                 liveEncryptBytes = DESEncryptDirectKey(des, key, iv, plainBytes);
                 liveDecryptBytes = DESDecryptDirectKey(des, key, iv, cipherBytes);
 
-                if (cipherMode == CipherMode.ECB)
-                {
-                    des.Key = key;
-                    liveOneShotDecryptBytes = des.DecryptEcb(cipherBytes, paddingMode);
-                    liveOneShotEncryptBytes = des.EncryptEcb(plainBytes, paddingMode);
-                }
-                else if (cipherMode == CipherMode.CBC)
+                if (DESFactory.OneShotSupported)
                 {
-                    des.Key = key;
-                    liveOneShotDecryptBytes = des.DecryptCbc(cipherBytes, iv, paddingMode);
-                    liveOneShotEncryptBytes = des.EncryptCbc(plainBytes, iv, paddingMode);
+                    if (cipherMode == CipherMode.ECB)
+                    {
+                        liveOneShotDecryptBytes = des.DecryptEcb(cipherBytes, paddingMode);
+                        liveOneShotEncryptBytes = des.EncryptEcb(plainBytes, paddingMode);
+                    }
+                    else if (cipherMode == CipherMode.CBC)
+                    {
+                        liveOneShotDecryptBytes = des.DecryptCbc(cipherBytes, iv, paddingMode);
+                        liveOneShotEncryptBytes = des.EncryptCbc(plainBytes, iv, paddingMode);
+                    }
+                    else if (cipherMode == CipherMode.CFB)
+                    {
+                        liveOneShotDecryptBytes = des.DecryptCfb(cipherBytes, iv, paddingMode, feedbackSizeInBits: feedbackSize.Value);
+                        liveOneShotEncryptBytes = des.EncryptCfb(plainBytes, iv, paddingMode, feedbackSizeInBits: feedbackSize.Value);
+                    }
                 }
             }
 

src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/DES/DESCipherOneShotTests.cs

@@ -6,13 +6,12 @@ namespace System.Security.Cryptography.Encryption.Des.Tests
     public interface IDESProvider
     {
         DES Create();
+        bool OneShotSupported { get; }
     }
 
     public static partial class DESFactory
     {
-        public static DES Create()
-        {
-            return s_provider.Create();
-        }
+        public static DES Create() => s_provider.Create();
+        public static bool OneShotSupported => s_provider.OneShotSupported;
     }
 }

src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/DES/DESCipherTests.cs

@@ -90,6 +90,26 @@ public void DecryptOneShot_Array(byte[] plaintext, byte[] ciphertext, PaddingMod
         public void EncryptOneShot_Array(byte[] plaintext, byte[] ciphertext, PaddingMode padding, CipherMode mode) =>
             EncryptOneShot_ArrayTest(plaintext, ciphertext, padding, mode);
 
+        [Fact]
+        public void EncryptOneShot_CfbNotSupported()
+        {
+            using (SymmetricAlgorithm alg = CreateAlgorithm())
+            {
+                Assert.ThrowsAny<CryptographicException>(() =>
+                    alg.TryEncryptCfb(ReadOnlySpan<byte>.Empty, IV, Span<byte>.Empty, out _));
+            }
+        }
+
+        [Fact]
+        public void DecryptOneShot_CfbNotSupported()
+        {
+            using (SymmetricAlgorithm alg = CreateAlgorithm())
+            {
+                Assert.ThrowsAny<CryptographicException>(() =>
+                    alg.TryDecryptCfb(ReadOnlySpan<byte>.Empty, IV, Span<byte>.Empty, out _));
+            }
+        }
+
         public static IEnumerable<object[]> TestCases
         {
             get