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POAES cryptography in vb6 and c#
 

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    <p>I need a .NET <em>(C# ideally)</em> algorithm that will produce the same results as a <code>vb6</code> one I made to encrypt and <code>decrypt</code> binary files. I've been trying to hunt down code for a week now and have had little success. </p> <p>I started with <a href="http://support.microsoft.com/default.aspx?scid=kb;en-us;821762" rel="nofollow">How to encrypt a string in VB6 decrypt VB.NET</a> but it was only a half solution and it used <code>RC2</code> rather than <code>AES</code>. After some fiddling I got my <code>vb6</code> code to work in <code>AES</code> but I cannot find a way to get <code>c#</code> to produce the same results. I think it has to do with the way I'm making my <code>Key</code> and <code>IV</code>. I've been going over <a href="http://msdn.microsoft.com/en-us/library/93bskf9z.aspx" rel="nofollow">Cryptographic Services</a> my attempts can be broken into two basic types. One where I have tried <code>PasswordDeriveBytes.CryptDeriveKey</code> and trying to make it work with <code>aes</code>. No success at all. And Tries where I tried to mimic it's behavior. Bellow I will post my <code>vb6</code> code and my closest <code>c#</code> attempt. I can't say with 100% certainty that the <code>vb6</code> is perfect so if changes need to be made there I'm open to it. I know there is a way to use p invoke and I know there is a way to make <code>.net dll</code> to be called from my <code>vb apps</code>. I would prefer not to go that way.</p> <p>VB6 Function </p> <pre><code>Public Function Crypt_File(PathToSourceFile As String, PathToDestFile As String, Password As String, HowTo As CryptMethod) As Boolean Const FName As String = "mdlCryptography.Encrypt_file" Dim CryptoContext As Long Dim strProvider As String Dim HashHnd As Long Dim CrypKey As Long Dim Step As Integer Dim CryptBuff As String Dim InFileNum As Long, OutFileNum As Long Dim BytesRemaining As Long, CurrentBufferSize As Long Dim MAX_BUFFER_SIZE As Long Dim DoCryptFinalise As Long Dim Buff As String On Error GoTo Trap: Step = 10 Crypt_File = False If PathToSourceFile = PathToDestFile Then ' Err.Raise 334, FName, "Sourse and Dest Path are the same" End If MAX_BUFFER_SIZE = (2 ^ 20) * 100 '100 MB Buff = vbNullChar strProvider = MS_ENH_RSA_AES_PROV_A &amp; vbNullChar If Not CBool(CryptAcquireContext(CryptoContext, ByVal Buff, ByVal strProvider, PROV_RSA_AES, CRYPT_VERIFYCONTEXT)) Then Err.Raise 33410, FName, "Unable to Acquire Context: " &amp; MS_ENH_RSA_AES_PROV_A End If If Not CBool(CryptCreateHash(CryptoContext, CALG_SHA_256, ByVal 0&amp;, ByVal 0&amp;, HashHnd)) Then Err.Raise 33420, FName, "Unable to Create a hash object. " &amp; MS_ENH_RSA_AES_PROV_A End If If Not CBool(CryptHashData(HashHnd, Password, Len(Password), ByVal 0&amp;)) Then Err.Raise 33430, FName, "Unable to Hash password. " End If If Not CBool(CryptDeriveKey(CryptoContext, CALG_AES_256, HashHnd, ByVal CRYPT_NO_SALT, CrypKey)) Then Err.Raise 33440, FName, "Unable to Derive Key. " End If 'Clear HashHnd If HashHnd &lt;&gt; 0 Then Call CryptDestroyHash(HashHnd) End If HashHnd = 0 'Prep Data For encryption DoCryptFinalise = 0 InFileNum = FreeFile Step = 20 Open PathToSourceFile For Binary Access Read As #InFileNum If LenB(Dir$(PathToDestFile)) &gt; 0 Then Kill PathToDestFile End If OutFileNum = FreeFile Step = 25 Open PathToDestFile For Binary Access Write As #OutFileNum BytesRemaining = LOF(InFileNum) 'Loop through File Chunks Do While BytesRemaining &gt; 0 If BytesRemaining &gt;= MAX_BUFFER_SIZE Then CurrentBufferSize = MAX_BUFFER_SIZE Else CurrentBufferSize = BytesRemaining DoCryptFinalise = 1 End If Buff = String$(CurrentBufferSize, vbNullChar) Get #InFileNum, , Buff If HowTo = CryptMethod.Encrypt Then CryptBuff = EncryptBuffer(CrypKey, DoCryptFinalise, Buff) Else CryptBuff = DecryptBuffer(CrypKey, DoCryptFinalise, Buff) End If Put #OutFileNum, , CryptBuff BytesRemaining = BytesRemaining - CurrentBufferSize Loop Close #InFileNum Close #OutFileNum Crypt_File = True GoTo Fin Trap: Crypt_File = False If Step = 20 Then Close #InFileNum End If If Step = 25 Then Close #InFileNum Close #OutFileNum End If Err.Raise Err.Number, Err.source, Err.Description Fin: If CrypKey &lt;&gt; 0 Then Call CryptDestroyKey(CrypKey) End If If HashHnd &lt;&gt; 0 Then Call CryptDestroyHash(HashHnd) End If End Function Private Function EncryptBuffer(CrypKey As Long, DoCryptFinalise As Long, Buff As String) As String Dim EncDataLength As Long, EnctBuffLen As Long Dim CryptBuff As String EncDataLength = Len(Buff) EnctBuffLen = EncDataLength + AES_BLOCK_SIZE CryptBuff = String$(EnctBuffLen, vbNullChar) LSet CryptBuff = Buff If Not CBool(CryptEncrypt(CrypKey, ByVal 0&amp;, ByVal DoCryptFinalise, ByVal 0&amp;, CryptBuff, EncDataLength, EnctBuffLen)) Then ' Close #InFileNum ' Close #OutFileNum Err.Raise 33450, "mdlCryptography.EncryptBuffer", "Encryption Error" End If EncryptBuffer = Left$(CryptBuff, EncDataLength) End Function Private Function DecryptBuffer(CrypKey As Long, DoCryptFinalise As Long, Buff As String) As String Dim EncDataLength As Long Dim CryptBuff As String EncDataLength = Len(Buff) CryptBuff = String$(EncDataLength, vbNullChar) LSet CryptBuff = Buff If Not CBool(CryptDecrypt(CrypKey, ByVal 0&amp;, ByVal DoCryptFinalise, ByVal 0&amp;, CryptBuff, EncDataLength)) Then ' Close #InFileNum ' Close #OutFileNum Err.Raise 33450, "mdlCryptography.DecryptBuffer", "Decryption Error" End If DecryptBuffer = Left$(CryptBuff, EncDataLength) End Function </code></pre> <p>c# It's very much unrefined</p> <pre><code>private void Crypt(bool DoEn) { int Rfc2898KeygenIterations = 100; int AesKeySizeInBits = 128; byte[] rawPlaintext ;//= System.Text.Encoding.Unicode.GetBytes("This is all clear now!"); byte[] cipherText = null; byte[] plainText = null; using (Aes aes = new AesManaged()) { int KeyStrengthInBytes = aes.KeySize / 8; SHA256 MySHA = new SHA256Cng(); MySHA.Initialize(); plainText = Encoding.ASCII.GetBytes(txtPassword.Text); aes.Key = MySHA.ComputeHash(plainText ); aes.IV = Encoding.ASCII.GetBytes("0000000000000000"); if (DoEn) { //using (FileStream fs = new FileStream(txtOut.Text,FileMode.CreateNew )) using (MemoryStream ms = new MemoryStream()) { using (CryptoStream cs = new CryptoStream(ms, aes.CreateEncryptor(), CryptoStreamMode.Write)) { //using (StreamReader myFile = new StreamReader(txtIn.Text)) //{ // rawPlaintext = System.Text.Encoding.ASCII.GetBytes(myFile.ReadToEnd()); rawPlaintext = File.ReadAllBytes(txtIn.Text); cs.Write(rawPlaintext, 0, rawPlaintext.Length); //} } cipherText = ms.ToArray(); File.WriteAllBytes(txtOut.Text, cipherText); } } else { //using (FileStream fs = new FileStream(txtIn.Text, FileMode.CreateNew)) using (MemoryStream ms = new MemoryStream()) { using (CryptoStream cs = new CryptoStream(ms, aes.CreateDecryptor(), CryptoStreamMode.Write)) { //using (StreamReader myFile = new StreamReader(txtOut.Text)) //{ //string s = myFile.r.ReadToEnd(); rawPlaintext = File.ReadAllBytes(txtOut.Text); //System.Text.Encoding.ASCII.GetBytes(s); //cipherText = new int[rawPlaintext.Length]; cs.Write(rawPlaintext, 0, rawPlaintext.Length); //cs.Write(cipherText, 0, cipherText.Length); //} } cipherText = ms.ToArray(); File.WriteAllBytes(txtIn.Text, cipherText); } } } //string s = System.Text.Encoding.ASCII.GetString(plainText); //Console.WriteLine(s); } </code></pre>
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    1. USRon H
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    1. COmsdn has a simple sample: http://msdn.microsoft.com/en-us/library/system.security.cryptography.aesmanaged.aspx
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      1. USGreg
    2. COAwful lot of code you want us to read.
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      1. USJohn Saunders
    3. COJust in case anyone else finds this useful, the vb code hasn't changed. I used [@HABO's post](http://stackoverflow.com/questions/9237324/encrypting-decrypting-large-files-net) and [@Jon Skeet's post](http://stackoverflow.com/questions/5730863/how-to-use-stream-copyto-on-framework-3-5) to make my c# work with large files.
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