VBA Code explantion

[sauce1979]

Hi there. I have jsut joined this forum and would like an explanation for a tutorial I amd doing from an VBA programming book. The code below is the code for two command buttons on a simple encryption applicaiton. My area of concern are the lines (in bold) in both button click events. When the chr function is used to convert a character code back to a character -1 and +1 are entered in chr parenthesis. If I remove -1 or +1 the text is not encrypted. Could someone explain why this is the case. Any help would be much appreciated.

Regards
sauce1979

Private Sub cmdDecrypt_Click()
Dim sDecryptedCharacter As String
Dim sDecryptedMessage As String
Dim iCounter As Integer
' Check if user enters text
If txtAreaWrite <> "" Then
' Iterate through each character in the message.
For iCounter = 1 To Len(txtAreaWrite.Value)
sDecryptedCharacter = Asc(Mid(txtAreaWrite.Value, iCounter, 1))
' Convert the character code (shifted by -1) back
' to a character.
sDecryptedCharacter = Chr(sDecryptedCharacter - 1)
' Add the decrypted character to the new decrypted message.
sDecryptedMessage = sDecryptedMessage + sDecryptedCharacter
Next iCounter
' Display the decrypted message.
txtAreaWrite.Value = sDecryptedMessage
End If
End Sub


Private Sub cmdEncrypt_Click()
Dim sEncryptedCharacter As String
Dim sEncryptedMessage As String
Dim iCounter As Integer
If txtAreaWrite.Value <> "" Then
' Iterate through each character in the message.
For iCounter = 1 To Len(txtAreaWrite.Value)
' Convert one character at a time to its equivalent
' character code.
sEncryptedCharacter = Asc(Mid(txtAreaWrite.Value, iCounter, 1))
' Convert the character code (shifted by 1) back
' to a character.
sEncryptedCharacter = Chr(sEncryptedCharacter + 1)
' Add the encrypted character to the new encrypted message.
sEncryptedMessage = sEncryptedMessage + sEncryptedCharacter
Next iCounter
' Display the encrypted message.
txtAreaWrite.Value = sEncryptedMessage
End If
End Sub

 

[georgedwilkinson]

You should take a look at an ASCII chart.

When you add 1 to the ASCII value of a "character", you are actually saying to use the next letter. So if I encrypt the letter "B" with this algorithm, I would expect to see the letter "A".

I prefer to use an encryption routine similar to this that multiplies the ASCII of the character times 2. It makes it a little harder to "read" the encrypted characters (because not all the characters are visible).

The use of the word "shifted" in the comments is mis-leading. Multiplying by 2 is actually "shifting" (i.e. moving the bits to the right). All this algorithm does is uses an adjacent letter in the alphbet...not very encrypted at all.

 

[sauce1979]

Thanks!! Much clearer now.

 

[georgedwilkinson]

Glad to help.