FYI: Encryption thru the built-in cryptology

VB supplies a strongly-encrypted service provider, the System.Security.Cryptography namespace.

Unfortunately, after reading all the MSDN articles and the posts on these boards, I was none-the-better off with implementing those classes as when I started.

It appears that people have been having a hard time understanding, much less implementing, this namespace.

Well, my job required that I learn it, so I did. Because of the immense effort required, I wanted to provide my code here so that some other people will not have to go through the headache I had to go through.

You may use it, as long as you follow the terms laid out in the beginning...

VB Code:

''Cryptography wrapper classes
    ''Programmed by Keith Ratliff
    '' (c) 2003 Keith Ratliff
    ''Uses code from the RSA library
    '' - additional copyrights may need including with your application
    ''You may use these classes, or modifications of them royalty-free under the 
    '' following terms:
    '' 1) You must state somewhere within your program that you are using
    ''    encryption routines supplied by Keith Ratliff
    '' 2) You must email me ([email protected]) with the name of the 
    ''    application and Web site of that application
    '' 3) You may not sell these routines in a non-compiled code
    '' 4) If your program is a DLL, the parent program must comply with term 1
    '' 5) This copyright and notice must remain intact.
 
    'to use this function, do something like this:
    'Dim objCP As CryptoPass
    'objCP = CreateHash(txtPassword.Text)
    'MsgBox(DecryptHash(objCP))
 
    'The objCP will contain a .Hash and .Salt
    'You need both to decrypt, so if you are storing the encrypted
    'values, store both
 
    'Constants:
    Const KeyLen = 31   '0-based key length
    Const HKeyLen = 15  'half that size (also 0-based)
 
    'Create Salt Function
    ' Salt is a generic term for random bits.
    Private Function CreateSalt(ByVal size As Integer) As String
        ' Create a cryptographically generated random number using the 
        ' cryptographic service provider
        Dim rng As New System.Security.Cryptography.RNGCryptoServiceProvider()
        ' Create a buffer to hold this information
        Dim buff(size) As Byte
        ' Fill the buffer with salt
        rng.GetBytes(buff)
        ' Convert to a string for returning.
        ' Due to null-handling, we will not use this again
        Return Convert.ToBase64String(buff)
    End Function
 
    'Create Key Function
    ' Uses the input key to create a cryptographic key in a byte array
    Private Function CreateKey(ByVal Key() As Byte) As Byte()
        'Create our object that will generate the key, based on the application name and 
        '  supplied key
        Dim objPDB As New System.Security.Cryptography.PasswordDeriveBytes(Application.ProductName, Key)
        'Send our key back as a byte array
        Return objPDB.GetBytes(KeyLen + 1)
    End Function
 
    'Create Salt Function
    'Same as other function, except that it creates salt based on the 
    'KeySize constant and returns as a byte array.
    Private Function CreateSalt() As Byte()
        Dim abytSalt(KeyLen) As Byte
        Dim rng As System.Security.Cryptography.RandomNumberGenerator = System.Security.Cryptography.RandomNumberGenerator.Create()
        rng.GetBytes(abytSalt)
        Return abytSalt
    End Function
 
    'Create Hash function
    'Takes the inputted text and makes a hash and salt value from it
    ' In these functions, the salt is used to determine the key (randomly)
    ' To decrypt, the salt has to be preserved which is the primary purpose
    ' of the CryptoPass class.
    Private Function CreateHash(ByVal sToEncrypt As String) As CryptoPass
        Dim abytKey(KeyLen) As Byte
        Dim PwdAndSalt As String       ' Will store our password, appended with salt
        Dim objSalt() As Byte = CreateSalt()       ' Get a byte array of salt
        PwdAndSalt = sToEncrypt    'Put our string in the PwdAndSalt string
        PwdAndSalt += Chr(0)       'Place a null-terminator in the string manually
        Dim tmpString As String    'For use with the BtoS function
        BtoS(objSalt, tmpString)       'Convert the Salt Byte array to a string
        PwdAndSalt += tmpString    'Add the salt to the end of the PwdAndSalt string
        Dim abytEnc(255) As Byte       'Byte array for the encrypted data
        Dim tmpByte(255) As Byte          'Byte array for the buffer
        ' Create a buffer to allow the cryptography provider to do its thing
        Dim objBuffer As New System.IO.MemoryStream(tmpByte, 0, tmpByte.Length, True, True)
        ' Change our PwdAndSalt array to a byte array (for use in the cryptography provider)
        StoB(PwdAndSalt, tmpByte)
        ' Create a Symmetric Algorithm Provider (Key Keeper)
        Dim objSymm As System.Security.Cryptography.SymmetricAlgorithm = System.Security.Cryptography.SymmetricAlgorithm.Create("Rijndael")
        ' Create the key based on the salt
        abytKey = CreateKey(objSalt)
        objSymm.Key = abytKey
        ' Save the salt for returning from the function since we are about to truncate it
        CreateHash = New CryptoPass()
        CreateHash.Salt = objSalt
        ' And truncate to the shorter length for the IV
        ReDim Preserve objSalt(HKeyLen)
        ' And assign to the IV
        objSymm.IV = objSalt
        ' Create the stream object and give it our SymmetricAlgorithm so that it creates
        ' a hash we can decrypt later
        Dim objCrypto As New System.Security.Cryptography.CryptoStream(objBuffer, objSymm.CreateEncryptor(), Security.Cryptography.CryptoStreamMode.Write)
        ' Have it do it's thing and output to the buffer
        objCrypto.Write(tmpByte, 0, tmpByte.Length)
        ' Tell it to expand to the rest of the buffer using padding
        objCrypto.FlushFinalBlock()
        ' Create a variable to keep the hash
        Dim hashedPwd As String
        ' Reset the buffer pointer
        objBuffer.Seek(0, IO.SeekOrigin.Begin)
        ' Retrieve the buffer as a byte array to the abytEnc byte array
        abytEnc = objBuffer.GetBuffer()
        ' Convert the byte array to a string
        BtoS(abytEnc, hashedPwd)
        ' Store in the object
        CreateHash.Hash = hashedPwd
        ' Close the crypto provider. We cannot close it before now since we needed the 
        '   buffer and closing the provider also closes the buffer.
        objCrypto.Close()
    End Function
 
    'Decrypt Function.
    ' Expects the hash and the salt used to create the hash
    ' Uses the CryptoPass class for this
    Private Function DecryptPasswordHash(ByVal objCP As CryptoPass) As String
        ' Recreate our Symmetric Algorithm using the settings from the encryption routine
        Dim objSymm As System.Security.Cryptography.SymmetricAlgorithm = System.Security.Cryptography.SymmetricAlgorithm.Create("Rijndael")
        Dim abytKey(KeyLen) As Byte
        abytKey = CreateKey(objCP.Salt)
        objSymm.Key = abytKey
        Dim objSalt() As Byte = objCP.Salt
        ReDim Preserve objSalt(HKeyLen)
        objSymm.IV = objSalt
 
        ' Create a byte array so that we can pass the hash in to the buffer
        Dim tmpByte() As Byte
        ' Fill the byte array with the contents of the Hash from the CP object
        StoB(objCP.Hash, tmpByte)
        ' And now, create that buffer
        Dim objBuffer As New System.IO.MemoryStream(tmpByte, 0, tmpByte.Length, True, True)
        ' Create a decryptor using our Symmetric Alorithm
        Dim csDecrypted As New System.Security.Cryptography.CryptoStream(objBuffer, objSymm.CreateDecryptor(), System.Security.Cryptography.CryptoStreamMode.Read)
        ' Create a stream reader buffer to read from the csDecrypted, the decrypted value
        Dim objBuffer2 As New System.IO.StreamReader(csDecrypted)
        ' Create a string to hold the decrypted value and read it
        Dim tmpString As String
        tmpString = objBuffer2.ReadToEnd()
        ' We dont need the decrytor any more, or the buffer, so close them
        ' Remember that closing the cryptostream also closes the buffer
        csDecrypted.Close()
        tmpString = tmpString.Substring(0, tmpString.IndexOf(Chr(0)))
        'our original string had a termination character.
        'Once this is decrypted, attempting to use it results in expected behaviour, since it still has a null
        'terminator, but since the btos function converts all of the byte stream (not stopping at the first instance
        'of null) it will have a wrong .length size. This fixes that.
        Return tmpString
    End Function
 
    'Converts a string to a byte array
    Private Function StoB(ByVal inString As String, ByRef outBytes() As Byte)
        ReDim outBytes(inString.Length)
        Dim i As Integer
        For i = 0 To inString.Length - 1
            outBytes(i) = Asc(inString.Substring(i, 1))
        Next
    End Function
 
    'converts a byte array to a string. Does not stop at the first null character
    Private Function BtoS(ByVal inBytes() As Byte, ByRef outString As String)
        outString = ""
        Dim i As Integer
        For i = 0 To inBytes.Length - 1
            outString += Chr(inBytes(i))
        Next
    End Function
 
    'CryptoPass class. For keeping the hash with the salt
    Private Class CryptoPass
        Private _Hash As String
        Private _Salt As Byte()
        Public Property Hash() As String
            Get
                Return _Hash
            End Get
            Set(ByVal Value As String)
                _Hash = Value
            End Set
        End Property
 
        Public Property Salt() As Byte()
            Get
                Return _Salt
            End Get
            Set(ByVal Value As Byte())
                _Salt = Value
            End Set
        End Property
    End Class

FYI:

Here is how I store and retreive the info once generated, using the Registry:

VB Code:

'To save
        Dim objCP As CryptoPass
        objCP = CreateHash(txtPassword.Text)
        SetRegistryValue("Hash", objCP.Hash)
        Dim sTmp As String
        BtoS(objCP.Salt, sTmp)
        SetRegistryValue("Salt", sTmp)
 
 
'and to load
        objPassword.Hash = GetRegistryValue("Hash")
        Dim sTmp As String = GetRegistryValue("Salt")
        Dim sByte(0) As Byte
        StoB(sTmp, sByte)
        'the registry appends a null terminator, so we need to dispose of it
        ReDim Preserve sByte(31)
        objPassword.Salt = sByte
        txtPassword.Text = DecryptPasswordHash(objPassword)

And the helper Functions:

VB Code:

Private Function GetRegistryValue(ByVal inKey As String) As String
        Dim objKey As Microsoft.Win32.RegistryKey = Microsoft.Win32.Registry.CurrentUser
        If Not objKey.OpenSubKey("SOFTWARE\" & Application.ProductName) Is Nothing Then objKey = objKey.OpenSubKey("SOFTWARE\" & Application.ProductName)
        If objKey.GetValue(inKey, "") = "" Then Return ""
        Return KillLBCode(objKey.GetValue(inKey, ""))
    End Function
 
    Private Sub SetRegistryValue(ByVal inKey As String, ByVal inValue As String)
        Dim objKey As Microsoft.Win32.RegistryKey = Microsoft.Win32.Registry.CurrentUser
        objKey.CreateSubKey("SOFTWARE\" & Application.ProductName)
        If Not objKey.OpenSubKey("SOFTWARE\" & Application.ProductName) Is Nothing Then objKey = objKey.OpenSubKey("SOFTWARE\" & Application.ProductName, True)
        objKey.SetValue(inKey, inValue.Replace(Chr(13) & Chr(10), "#_#"))
    End Sub
 
 
    Private Function KillLBCode(ByVal inText As String) As String   ''Converts #_# to vbCrLf
        Return inText.Replace("#_#", Chr(13) & Chr(10))
    End Function