Encrypt a small string to later Decrypt

[no1biscuit]

Ok I have a item that requires a password. it is 5-8 numeric numbers. I am wanting to encrypt it in such away that it is secure and produces a small enough encrypted string that it can be written in the item's cabinet. I initially did the whole turn to ASC and add or subtract Chars from it but one of the people here spent and evening decrypting it so that is useless now. I looked at a bunch of Cryptography examples but they all seem to put them in a byte array. This app will be installed on select machines so if some sort of generic key file is required that is fine as long as the same key is on every machine.


Thanks for any input you may have.

Thom

 

[realm174]

Something I came across on the internet a while ago, which you probably came across as well based on your post. It does meet your requirements of being quite small, and using a unique key. Ever since I've come across that, I've been using it in just about every app I'm writing that requires anything at all to be encrypted (saved passwords, sensitive data, etc.. ). Hopefully this will help you:

Imports System.Security.Cryptography
Imports System.IO
Imports System.Text

Module MyEncryption
    Public Function EncryptString128Bit(ByVal vstrTextToBeEncrypted As String, _
                                        ByVal vstrEncryptionKey As String) As String

        Dim bytValue() As Byte
        Dim bytKey() As Byte
        Dim bytEncoded() As Byte
        Dim bytIV() As Byte = {121, 241, 10, 1, 132, 74, 11, 39, 255, 91, 45, 78, 14, 211, 22, 62}
        Dim intLength As Integer
        Dim intRemaining As Integer
        Dim objMemoryStream As New MemoryStream()
        Dim objCryptoStream As CryptoStream
        Dim objRijndaelManaged As RijndaelManaged


        '   **********************************************************************
        '   ******  Strip any null character from string to be encrypted    ******
        '   **********************************************************************

        vstrTextToBeEncrypted = StripNullCharacters(vstrTextToBeEncrypted)

        '   **********************************************************************
        '   ******  Value must be within ASCII range (i.e., no DBCS chars)  ******
        '   **********************************************************************

        bytValue = Encoding.ASCII.GetBytes(vstrTextToBeEncrypted.ToCharArray)

        intLength = Len(vstrEncryptionKey)

        '   ********************************************************************
        '   ******   Encryption Key must be 256 bits long (32 bytes)      ******
        '   ******   If it is longer than 32 bytes it will be truncated.  ******
        '   ******   If it is shorter than 32 bytes it will be padded     ******
        '   ******   with upper-case Xs.                                  ****** 
        '   ********************************************************************

        If intLength >= 32 Then
            vstrEncryptionKey = Strings.Left(vstrEncryptionKey, 32)
        Else
            intLength = Len(vstrEncryptionKey)
            intRemaining = 32 - intLength
            vstrEncryptionKey = vstrEncryptionKey & Strings.StrDup(intRemaining, "X")
        End If

        bytKey = Encoding.ASCII.GetBytes(vstrEncryptionKey.ToCharArray)

        objRijndaelManaged = New RijndaelManaged()

        '   ***********************************************************************
        '   ******  Create the encryptor and write value to it after it is   ******
        '   ******  converted into a byte array                              ******
        '   ***********************************************************************

        Try

            objCryptoStream = New CryptoStream(objMemoryStream, _
              objRijndaelManaged.CreateEncryptor(bytKey, bytIV), _
              CryptoStreamMode.Write)
            objCryptoStream.Write(bytValue, 0, bytValue.Length)

            objCryptoStream.FlushFinalBlock()

            bytEncoded = objMemoryStream.ToArray
            objMemoryStream.Close()
            objCryptoStream.Close()
        Catch



        End Try

        '   ***********************************************************************
        '   ******   Return encryptes value (converted from  byte Array to   ******
        '   ******   a base64 string).  Base64 is MIME encoding)             ******
        '   ***********************************************************************

        Return Convert.ToBase64String(bytEncoded)

    End Function




    Public Function DecryptString128Bit(ByVal vstrStringToBeDecrypted As String, _
                                        ByVal vstrDecryptionKey As String) As String

        Dim bytDataToBeDecrypted() As Byte
        Dim bytTemp() As Byte
        Dim bytIV() As Byte = {121, 241, 10, 1, 132, 74, 11, 39, 255, 91, 45, 78, 14, 211, 22, 62}
        Dim objRijndaelManaged As New RijndaelManaged()
        Dim objMemoryStream As MemoryStream
        Dim objCryptoStream As CryptoStream
        Dim bytDecryptionKey() As Byte

        Dim intLength As Integer
        Dim intRemaining As Integer
        'Dim intCtr As Integer
        Dim strReturnString As String = String.Empty
        'Dim achrCharacterArray() As Char
        'Dim intIndex As Integer

        '   *****************************************************************
        '   ******   Convert base64 encrypted value to byte array      ******
        '   *****************************************************************

        bytDataToBeDecrypted = Convert.FromBase64String(vstrStringToBeDecrypted)

        '   ********************************************************************
        '   ******   Encryption Key must be 256 bits long (32 bytes)      ******
        '   ******   If it is longer than 32 bytes it will be truncated.  ******
        '   ******   If it is shorter than 32 bytes it will be padded     ******
        '   ******   with upper-case Xs.                                  ****** 
        '   ********************************************************************

        intLength = Len(vstrDecryptionKey)

        If intLength >= 32 Then
            vstrDecryptionKey = Strings.Left(vstrDecryptionKey, 32)
        Else
            intLength = Len(vstrDecryptionKey)
            intRemaining = 32 - intLength
            vstrDecryptionKey = vstrDecryptionKey & Strings.StrDup(intRemaining, "X")
        End If

        bytDecryptionKey = Encoding.ASCII.GetBytes(vstrDecryptionKey.ToCharArray)

        ReDim bytTemp(bytDataToBeDecrypted.Length)

        objMemoryStream = New MemoryStream(bytDataToBeDecrypted)

        '   ***********************************************************************
        '   ******  Create the decryptor and write value to it after it is   ******
        '   ******  converted into a byte array                              ******
        '   ***********************************************************************

        Try

            objCryptoStream = New CryptoStream(objMemoryStream, _
               objRijndaelManaged.CreateDecryptor(bytDecryptionKey, bytIV), _
               CryptoStreamMode.Read)

            objCryptoStream.Read(bytTemp, 0, bytTemp.Length)

            objCryptoStream.FlushFinalBlock()
            objMemoryStream.Close()
            objCryptoStream.Close()

        Catch

        End Try

        '   *****************************************
        '   ******   Return decypted value     ******
        '   *****************************************

        Return StripNullCharacters(Encoding.ASCII.GetString(bytTemp))

    End Function


    Public Function StripNullCharacters(ByVal vstrStringWithNulls As String) As String

        Dim intPosition As Integer
        Dim strStringWithOutNulls As String

        intPosition = 1
        strStringWithOutNulls = vstrStringWithNulls

        Do While intPosition > 0
            intPosition = InStr(intPosition, vstrStringWithNulls, vbNullChar)

            If intPosition > 0 Then
                strStringWithOutNulls = Left$(strStringWithOutNulls, intPosition - 1) & _
                                  Right$(strStringWithOutNulls, Len(strStringWithOutNulls) - intPosition)
            End If

            If intPosition > strStringWithOutNulls.Length Then
                Exit Do
            End If
        Loop

        Return strStringWithOutNulls

    End Function


End Module

Cheers,

Realm174

http://sites.google.com/site/mymediadatabase/

 

[no1biscuit]

This is a super easy script as you said. I have seen similar ones but my problem is the encrypted value I would like no more than 15 digits long. Any suggestions?

Thanks
Thom