Rc4 encrypt/decrypt fonction

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Ce code sert a encrypter ou decrypter des strings avec un mot de passe. Baser sur le RC4.

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Source / Exemple : 


Public Function RC4Encrypt(text As String, encryptkey As String)
    Dim sbox(256)
    Dim key(256)
    Dim temp As Integer
    Dim a As Long
    Dim i As Integer
    Dim j As Integer
    Dim k As Integer
    Dim cipherby As Integer
    Dim cipher As String
    
    i = 0
    j = 0
    
    RC4Initialize encryptkey, key, sbox
    
    For a = 1 To Len(text)
        i = (i + 1) Mod 256
        j = (j + sbox(i)) Mod 256
        temp = sbox(i)
        sbox(i) = sbox(j)
        sbox(j) = temp

        k = sbox((sbox(i) + sbox(j)) Mod 256)

        cipherby = (Asc(Mid$(text, a, 1))) Xor k
        If Len(Hex(cipherby)) = 1 Then
            cipher = cipher & "0" & Hex(cipherby)
        Else
            cipher = cipher & Hex(cipherby)
        End If
    Next

    RC4Encrypt = cipher
End Function

Public Function RC4Decrypt(text, encryptkey)
    Dim sbox(256) As Integer
    Dim key(256) As Integer
    Dim Text2 As String
    Dim temp As Integer
    Dim a As Long
    Dim i As Integer
    Dim j As Integer
    Dim k As Long
    Dim w As Integer
    Dim cipherby As Integer
    Dim cipher As String
    
    For w = 1 To Len(text) Step 2
        Text2 = Text2 & Chr(Dec(Mid$(text, w, 2)))
    Next
    
    i = 0
    j = 0

    RC4Initialize encryptkey, key, sbox

    For a = 1 To Len(Text2)
        i = (i + 1) Mod 256
        j = (j + sbox(i)) Mod 256
        temp = sbox(i)
        sbox(i) = sbox(j)
        sbox(j) = temp

        k = sbox((sbox(i) + sbox(j)) Mod 256)

        cipherby = Asc(Mid$(Text2, a, 1)) Xor k
        cipher = cipher & Chr(cipherby)
    Next
    
    RC4Decrypt = cipher
End Function

Public Function RC4Initialize(strPwd, ByRef key, ByRef sbox)
    Dim tempSwap
    Dim a
    Dim b
    Dim intlength As Long

    intlength = Len(strPwd)
    For a = 0 To 255
        key(a) = Asc(Mid$(strPwd, a Mod intlength + 1, 1))
        sbox(a) = a
    Next

    b = 0
    For a = 0 To 255
        b = (b + sbox(a) + key(a)) Mod 256
        tempSwap = sbox(a)
        sbox(a) = sbox(b)
        sbox(b) = tempSwap
    Next
End Function
    
Public Function Dec(number) As String
    Dim base As String
    Dim iLen As Integer
    Dim iReturn As Long
    Dim i As Long
    Dim iTemp As String
    
    base = "0123456789ABCDEF"
    iLen = Len(number)
    
    For i = 0 To iLen - 1
        iTemp = Mid$(number, iLen - i, 1)
        iReturn = iReturn + (16 ^ i) * (InStr(1, base, iTemp) - 1)
    Next
    
    Dec = iReturn
End Function

Conclusion :


Utiliser comme ceci:

StringEncrypte = RC4Encrypt("message secret", "mot de passe")
StringDecrypte = RC4Decrypt(StringEncrypte, "mot de passe")

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