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Rob-HagueRob-Hague
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Increase test coverage for AesCipher (#1232)
* Increase test coverage for AesCipher The tests were generated by a script which is also added for posterity. The script works by running "openssl enc [...]" (via WSL) to generate the expected encrypted values, and also verifies those values against the .NET BCL implementation as an extra validation (it uncovered a difference in CFB mode between the two relating to the feedback size). * Fix OfbCipherMode It was an exact copy of CfbCipherMode
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‎src/Renci.SshNet/Security/Cryptography/Ciphers/Modes/OfbCipherMode.cs‎

Lines changed: 2 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -50,14 +50,13 @@ public override int EncryptBlock(byte[] inputBuffer, int inputOffset, int inputC
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_ = Cipher.EncryptBlock(IV, 0, IV.Length, _ivOutput, 0);
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Buffer.BlockCopy(_ivOutput, 0, IV, 0, IV.Length);
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for (var i = 0; i < _blockSize; i++)
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{
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outputBuffer[outputOffset + i] = (byte)(_ivOutput[i] ^ inputBuffer[inputOffset + i]);
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}
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Buffer.BlockCopy(IV, _blockSize, IV, 0, IV.Length - _blockSize);
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Buffer.BlockCopy(outputBuffer, outputOffset, IV, IV.Length - _blockSize, _blockSize);
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return _blockSize;
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}
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‎test/Renci.SshNet.Tests/Classes/Security/Cryptography/Ciphers/AesCipherTest.Gen.cs.txt‎

Lines changed: 142 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,142 @@
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// Used to generate tests in AesCipherTest.cs
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// The script works by running "openssl enc [...]" (via WSL) to generate the
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// expected encrypted values, and also verifies those values against the .NET
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// BCL implementation as an extra validation before generating the tests.
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Dictionary<string, (string, CipherMode?)> modes = new()
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{
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["ecb"] = ("mode: null", CipherMode.ECB),
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["cbc"] = ("new CbcCipherMode((byte[])iv.Clone())", CipherMode.CBC),
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["cfb"] = ("new CfbCipherMode((byte[])iv.Clone())", CipherMode.CFB),
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["ctr"] = ("new CtrCipherMode((byte[])iv.Clone())", null),
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["ofb"] = ("new OfbCipherMode((byte[])iv.Clone())", CipherMode.OFB),
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};
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Random random = new(123);
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using IndentedTextWriter tw = new(Console.Out);
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foreach ((string mode, (string modeCode, CipherMode? bclMode)) in modes)
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{
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foreach (int keySize in new int[] { 128, 192, 256 })
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{
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foreach (int inputLength in new int[] { 16, 32, 64 })
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{
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byte[] input = new byte[inputLength];
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random.NextBytes(input);
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byte[] key = new byte[keySize / 8];
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random.NextBytes(key);
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byte[] iv = new byte[16];
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random.NextBytes(iv);
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StringBuilder openSslCmd = new();
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openSslCmd.Append($"echo -n -e '{string.Join("", input.Select(b => $"\\x{b:x2}"))}' |");
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openSslCmd.Append($" openssl enc -e -aes-{keySize}-{mode}");
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openSslCmd.Append($" -K {Convert.ToHexString(key)}");
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if (mode != "ecb")
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{
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openSslCmd.Append($" -iv {Convert.ToHexString(iv)}");
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}
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openSslCmd.Append(" -nopad");
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ProcessStartInfo pi = new("wsl", openSslCmd.ToString())
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{
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RedirectStandardOutput = true,
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RedirectStandardError = true,
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};
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byte[] expected;
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string error;
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using (MemoryStream ms = new())
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{
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var p = Process.Start(pi);
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p.StandardOutput.BaseStream.CopyTo(ms);
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error = p.StandardError.ReadToEnd();
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p.WaitForExit();
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expected = ms.ToArray();
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}
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tw.WriteLine("[TestMethod]");
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tw.WriteLine($"public void AES_{mode.ToUpper()}_{keySize}_Length{inputLength}()");
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tw.WriteLine("{");
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tw.Indent++;
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WriteBytes(input);
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WriteBytes(key);
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if (mode != "ecb")
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{
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WriteBytes(iv);
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}
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tw.WriteLine();
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if (!string.IsNullOrWhiteSpace(error))
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{
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tw.WriteLine($"// {openSslCmd}");
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tw.WriteLine($"Assert.Fail(@\"{error}\");");
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tw.Indent--;
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tw.WriteLine("}");
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tw.WriteLine();
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continue;
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}
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tw.WriteLine($"// {openSslCmd} | hd"); // pipe to hexdump
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WriteBytes(expected);
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tw.WriteLine();
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tw.WriteLine($"var actual = new AesCipher(key, {modeCode}, padding: null).Encrypt(input);");
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tw.WriteLine();
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tw.WriteLine($"CollectionAssert.AreEqual(expected, actual);");
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if (bclMode is not null and not CipherMode.OFB)
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{
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// Verify the OpenSSL result is the same as the .NET BCL, just to be sure
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Aes bcl = Aes.Create();
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bcl.Key = key;
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bcl.IV = iv;
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bcl.Mode = bclMode.Value;
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bcl.Padding = PaddingMode.None;
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bcl.FeedbackSize = 128; // .NET is CFB8 by default, OpenSSL is CFB128
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byte[] bclBytes = bcl.CreateEncryptor().TransformFinalBlock(input, 0, input.Length);
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if (!bclBytes.AsSpan().SequenceEqual(expected))
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{
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tw.WriteLine();
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tw.WriteLine(@"Assert.Inconclusive(@""OpenSSL does not match the .NET BCL");
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tw.Indent++;
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tw.WriteLine($@"OpenSSL: {Convert.ToHexString(expected)}");
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tw.WriteLine($@"BCL: {Convert.ToHexString(bclBytes)}"");");
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tw.Indent--;
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}
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}
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tw.WriteLine();
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tw.WriteLine($"var decrypted = new AesCipher(key, {modeCode}, padding: null).Decrypt(actual);");
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tw.WriteLine();
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tw.WriteLine($"CollectionAssert.AreEqual(input, decrypted);");
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tw.Indent--;
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tw.WriteLine("}");
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tw.WriteLine();
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}
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}
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}
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void WriteBytes(byte[] bytes, [CallerArgumentExpression(nameof(bytes))] string name = null)
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{
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tw.WriteLine($"var {name} = new byte[]");
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tw.WriteLine("{");
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tw.Indent++;
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foreach (byte[] chunk in bytes.Chunk(16))
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{
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tw.WriteLine(string.Join(", ", chunk.Select(b => $"0x{b:x2}")) + ',');
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}
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tw.Indent--;
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tw.WriteLine("};");
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}

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