Decrypt should take into account unpadding for the final output if padding is specified.

Author: scott-xu

src/Renci.SshNet/Security/Cryptography/BlockCipher.cs

@@ -1,6 +1,9 @@
 using System;
 
+using Org.BouncyCastle.Crypto.Paddings;
+
 using Renci.SshNet.Security.Cryptography.Ciphers;
+using Renci.SshNet.Security.Cryptography.Ciphers.Paddings;
 
 namespace Renci.SshNet.Security.Cryptography
 {
@@ -153,6 +156,12 @@ public override byte[] Decrypt(byte[] input, int offset, int length)
                 throw new InvalidOperationException("Encryption error.");
             }
 
+            if (_padding is PKCS7Padding)
+            {
+                var paddingLength = new Pkcs7Padding().PadCount(output);
+                Array.Resize(ref output, output.Length - paddingLength);
+            }
+
             return output;
         }
 

test/Renci.SshNet.Tests/Classes/Security/Cryptography/BlockCipherTest.cs

@@ -56,17 +56,19 @@ public void EncryptShouldTakeIntoAccountPaddingForLengthOfInputBufferPassedToEnc
         }
 
         [TestMethod]
-        public void DecryptShouldTakeIntoAccountPaddingForLengthOfOutputBufferPassedToDecryptBlock()
+        public void DecryptShouldTakeIntoAccountUnPaddingForTheFinalOutput()
         {
-            var input = new byte[] { 0x2c, 0x1a, 0x05, 0x00, 0x68 };
-            var output = new byte[] { 0x0a, 0x00, 0x03, 0x02, 0x06, 0x08, 0x07, 0x05 };
+            var input = new byte[] { 0x0a, 0x00, 0x03, 0x02, 0x06, 0x08, 0x07, 0x05 };
+            var output = new byte[] { 0x2c, 0x1a, 0x05, 0x00, 0x68 };
+            var padding = new byte[] { 0x03, 0x03, 0x03 };
             var key = new byte[] { 0x17, 0x78, 0x56, 0xe1, 0x3e, 0xbd, 0x3e, 0x50, 0x1d, 0x79, 0x3f, 0x0f, 0x55, 0x37, 0x45, 0x54 };
             var blockCipher = new BlockCipherStub(key, 8, null, new PKCS7Padding())
             {
                 DecryptBlockDelegate = (inputBuffer, inputOffset, inputCount, outputBuffer, outputOffset) =>
                     {
                         Assert.AreEqual(8, outputBuffer.Length);
                         Buffer.BlockCopy(output, 0, outputBuffer, 0, output.Length);
+                        Buffer.BlockCopy(padding, 0, outputBuffer, output.Length, padding.Length);
                         return inputBuffer.Length;
                     }
             };