This thread is for discussions of Encrypt/Decrypt.

Hello,
i'm doing a small app to create encrypt keys, and i'm used your example, except in Chr$ i got an error and just used Chr, and it works fine.the problem is, after create encrypt word, and saved to a file, when reading the encrypted word i can't decrypt.......any idea???
thanks very much for your time

The problem with the chr(0) can be solved by this process.

The pseudocode is like this. In the final encrypted text, the chr(0) cuts the rest of the string. We can
mark those positions and decrypt accordingly.

In our encrypted text we can include these characters in the front.

flag & noOfFaults & pos(1), .....pos(n),

flag indicated that the problem occured. noofFaults indicated the total number of faults and pos(1),..pos(n) indicates the positions of faults. In the decryption process we will first replace those positions with chr(0) and decrypt accordingly.


Option Explicit

'Set to True to make the password case-sensitive
#Const CASE_SENSITIVE_PASSWORD = False

Private Sub cmdEncrypt_Click()
    Dim buffText As String
    Dim lngFileEnd As Integer
    
    ' You can encrypt twice for extra security
    buffText = EncryptText((txtText), txtPassword)
    buffText = EncryptTextFinal((buffText), txtPassword)
    
    Dim path As String
    path = App.path & "\a.txt"
    'writing the contents to a file
        'opening the file and writing contents
        Open path For Binary Access Write As #1
     
        lngFileEnd = LOF(1) + 1
     'putting data into file
        Put #1, lngFileEnd, buffText
    Close #1
    
    txtText = buffText
    
    cmdEncrypt.Enabled = False
    cmdDecrypt.Enabled = True
    
End Sub

Private Sub cmdDecrypt_Click()
    txtText = DecryptTextFault((txtText), txtPassword)
    txtText = DecryptText((txtText), txtPassword)
    
    cmdEncrypt.Enabled = True
    cmdDecrypt.Enabled = False
End Sub

'Encrypt text finally
Private Function EncryptTextFinal(strText As String, ByVal strPwd As String)
    Dim i As Integer, c As Integer
    Dim strBuff As String
    
    Dim jhamela As Integer
    Dim noFault As Integer

      jhamela = 0
      noFault = 0
    
#If Not CASE_SENSITIVE_PASSWORD Then

    'Convert password to upper case
    'if not case-sensitive
    strPwd = UCase(strPwd)

#End If

    'Encrypt string
    If Len(strPwd) Then
        For i = 1 To Len(strText)
            c = Asc(Mid(strText, i, 1))
            c = c + Asc(Mid(strPwd, (i Mod Len(strPwd)) + 1, 1))
            
            Dim addBuff As String
            
            'checking for faulty position
            
            If Chr(c And &HFF) = Chr(0) Then
              'marking of a faulty portion
              jhamela = 1
              noFault = noFault + 1
            
              addBuff = Trim(addBuff) & Trim(Str(i)) & ","
              
              
              strBuff = strBuff & "0"
            Else
              strBuff = strBuff & Chr(c And &HFF)
            End If
            
        Next i
    End If
        
        Dim jhBuff As String
        
    If jhamela = 1 Then
      jhBuff = "1"
      strBuff = Trim(jhBuff) & Trim(Str(noFault)) & "," & Trim(addBuff) & Trim(strBuff)
    Else
      jhBuff = "0"
      strBuff = Trim(jhBuff) & Trim(strBuff)
    End If

    EncryptTextFinal = strBuff
    
End Function


'Encrypt text
Private Function EncryptText(strText As String, ByVal strPwd As String)
    Dim i As Integer, c As Integer
    Dim strBuff As String
    
    Dim jhamela As Integer
    Dim noFault As Integer

      jhamela = 0
      noFault = 0
    
#If Not CASE_SENSITIVE_PASSWORD Then

    'Convert password to upper case
    'if not case-sensitive
    strPwd = UCase(strPwd)

#End If

    'Encrypt string
    If Len(strPwd) Then
        For i = 1 To Len(strText)
            c = Asc(Mid(strText, i, 1))
            c = c + Asc(Mid(strPwd, (i Mod Len(strPwd)) + 1, 1))
            strBuff = strBuff & Chr(c And &HFF)
           
        Next i
    Else
        strBuff = strText
    End If
    EncryptText = strBuff
End Function

'Decrypt text encrypted with EncryptText
Private Function DecryptText(strText As String, ByVal strPwd As String)
    Dim i As Integer, c As Integer
    Dim strBuff As String

#If Not CASE_SENSITIVE_PASSWORD Then

    'Convert password to upper case
    'if not case-sensitive
    strPwd = UCase(strPwd)

#End If

    

    'Decrypt string
    If Len(strPwd) Then
        For i = 1 To Len(strText)
            c = Asc(Mid(strText, i, 1))
            c = c - Asc(Mid(strPwd, (i Mod Len(strPwd)) + 1, 1))
            strBuff = strBuff & Chr(c And &HFF)
        Next i
    Else
        strBuff = strText
    End If
    DecryptText = strBuff
End Function

'Decrypt text encrypted with EncryptText
Private Function DecryptTextFault(strText As String, ByVal strPwd As String)
    Dim i As Integer, c As Integer
    Dim strBuff As String

#If Not CASE_SENSITIVE_PASSWORD Then

    'Convert password to upper case
    'if not case-sensitive
    strPwd = UCase(strPwd)

#End If

    'getting the first portion and finding the faulty positions
    Dim jhText As String
    Dim mainText As String
    Dim noFault As Integer
    Dim pos(100) As Integer
    
    mainText = strText
    
    jhText = Mid(strText, 1, 1)
    'MsgBox jhText
    
    If jhText = "1" Then
      'getting the jhamelas
      
      Dim jhNo As String
      jhNo = ""
      
      Dim j As Integer
      j = 2
      Do
        
        jhNo = jhNo & Trim(Mid(mainText, j, 1))
        j = j + 1
        
      Loop While Mid(mainText, j, 1) <> ","
      
      noFault = CInt(jhNo)
      
      
      'looping through the maintext for finding the positions
        'MsgBox j
      For i = 1 To noFault
        Do
          
          pos(i) = pos(i) & Trim(Mid(mainText, j, 1))
          j = j + 1
          
        Loop While Mid(mainText, j, 1) <> ","
        
        'MsgBox pos(i) & "and current j " & j
        
      Next i
 
      'now correction of the main text and getting our desired text
      
      mainText = Mid(mainText, j + 1, Len(mainText))
      
      j = 1 'updating the current position
      
      'going to faulty positions and correcting those
      Dim correctedMainText As String
      
      correctedMainText = ""
                 
        For i = 1 To noFault
          j = pos(i)
          'previous text
          correctedMainText = Trim(Mid(mainText, 1, j - 1))
          'faulty text
          correctedMainText = correctedMainText & Chr(0)
          'trailing text
          correctedMainText = correctedMainText & Trim(Mid(mainText, j + 1, Len(mainText)))
          
          mainText = correctedMainText
        Next i
        
        mainText = correctedMainText

      
      
    Else
      mainText = Mid(strText, 2, Len(strText))
    End If

    'Decrypt string
    If Len(strPwd) Then
        For i = 1 To Len(mainText)
            c = Asc(Mid(mainText, i, 1))
            c = c - Asc(Mid(strPwd, (i Mod Len(strPwd)) + 1, 1))
            strBuff = strBuff & Chr(c And &HFF)
        Next i
    Else
        strBuff = strText
    End If
    DecryptTextFault = strBuff
End Function

hi,

I have been trying to use your code for my application in C#,but i am less successful.

Could you please post the code in C#?

Thanks in advance.

Regards

Anuradha

hi,

i implemented the code and it encrypts correctly,but when i decrypt it it still gives me weird characters and not the string that i had passed to encrypt function.

Can you please guide me in the same.

 

 

Dear Anuradha

This  is the  C#  Code

class Class1
    {
        // Encryption Method
        public object EncryptText(string strText, string strPwd)
        {
            int i;
            int c;
            string strBuff = "";


            // Convert User Password to upper case
            strPwd = strPwd.ToUpper();

            for (i = 0; i < (strText.Length); i++)
            {
                c = Convert.ToInt32(char.Parse(strText.Substring(i, 1)));
                c = c + Convert.ToInt32(char.Parse(strPwd.Substring((i % (strPwd.Length)), 1)));

                strBuff = strBuff + Chr(c & 255);
            }
            return strBuff;
        }

        // Decryption Method
        public object DecryptText(string strText, string strPwd)
        {
            int i;
            int c;
            string strBuff = "";


            // Convert User Password to upper case
            strPwd = strPwd.ToUpper();

            for (i = 0; i < (strText.Length); i++)
            {
                c = Convert.ToInt32(char.Parse(strText.Substring(i, 1)));
                c = c - Convert.ToInt32(char.Parse(strPwd.Substring((i % (strPwd.Length)), 1)));

                strBuff = strBuff + Chr(c & 255);
            }
            return strBuff;
        }


        char Chr(int n)
        {
            return (char)n;
        }
    }

regards


Amila

 looks good lemme try it