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'Paste this code in a Class Module, named clsCryptoFilterBox

Option Explicit
Private Declare Function CryptAcquireContext Lib "advapi32.dll" Alias "CryptAcquireContextA" (phProv As Long, pszContainer As String, pszProvider As String, ByVal dwProvType As Long, ByVal dwFlags As Long) As Long
Private Declare Function CryptCreateHash Lib "advapi32.dll" (ByVal hProv As Long, ByVal Algid As Long, ByVal hKey As Long, ByVal dwFlags As Long, phHash As Long) As Long
Private Declare Function CryptDeriveKey Lib "advapi32.dll" (ByVal hProv As Long, ByVal Algid As Long, ByVal hBaseData As Long, ByVal dwFlags As Long, phKey As Long) As Long
Private Declare Function CryptDestroyHash Lib "advapi32.dll" (ByVal hHash As Long) As Long
Private Declare Function CryptDestroyKey Lib "advapi32.dll" (ByVal hKey As Long) As Long
Private Declare Function CryptEncrypt Lib "advapi32.dll" (ByVal hKey As Long, ByVal hHash As Long, ByVal Final As Long, ByVal dwFlags As Long, ByVal pbData As String, pdwDataLen As Long, ByVal dwBufLen As Long) As Long
Private Declare Function CryptDecrypt Lib "advapi32.dll" (ByVal hKey As Long, ByVal hHash As Long, ByVal Final As Long, ByVal dwFlags As Long, ByVal pbData As String, pdwDataLen As Long) As Long
Private Declare Function CryptExportKey Lib "advapi32.dll" (ByVal hKey As Long, ByVal hExpKey As Long, ByVal dwBlobType As Long, ByVal dwFlags As Long, ByVal pbData As String, pdwDataLen As Long) As Long
Private Declare Function CryptGenKey Lib "advapi32.dll" (ByVal hProv As Long, ByVal Algid As Long, ByVal dwFlags As Long, phKey As Long) As Long
Private Declare Function CryptGetProvParam Lib "advapi32.dll" (ByVal hProv As Long, ByVal dwParam As Long, pbData As Any, pdwDataLen As Long, ByVal dwFlags As Long) As Long
Private Declare Function CryptGetUserKey Lib "advapi32.dll" (ByVal hProv As Long, ByVal dwKeySpec As Long, phUserKey As Long) As Long
Private Declare Function CryptHashData Lib "advapi32.dll" (ByVal hHash As Long, ByVal pbData As String, ByVal dwDataLen As Long, ByVal dwFlags As Long) As Long
Private Declare Function CryptReleaseContext Lib "advapi32.dll" (ByVal hProv As Long, ByVal dwFlags As Long) As Long
Private Declare Function CryptSignHash Lib "advapi32.dll" Alias "CryptSignHashA" (ByVal hHash As Long, ByVal dwKeySpec As Long, ByVal sDescription As String, ByVal dwFlags As Long, ByVal pbSignature As String, pdwSigLen As Long) As Long
Private Declare Function CryptVerifySignature Lib "advapi32.dll" Alias "CryptVerifySignatureA" (ByVal hHash As Long, ByVal pbSignature As String, ByVal dwSigLen As Long, ByVal hPubKey As Long, ByVal sDescription As String, ByVal dwFlags As Long) As Long

'API error function
Private Declare Function GetLastError Lib "kernel32" () As Long

'API memory functions
Private Declare Function GlobalAlloc Lib "kernel32" (ByVal wFlags As Long, ByVal dwBytes As Long) As Long
Private Declare Function GlobalFree Lib "kernel32" (ByVal hMem As Long) As Long
Private Declare Function GlobalLock Lib "kernel32" (ByVal hMem As Long) As Long
Private Declare Function GlobalUnlock Lib "kernel32" (ByVal hMem As Long) As Long
Private Declare Sub CpyMemValAdrFromRefAdr Lib "kernel32" Alias "RtlMoveMemory" (ByVal hpvDest As Any, hpvSource As Any, ByVal cbCopy As Long)
Private Declare Sub CpyMemRefAdrFromValAdr Lib "kernel32" Alias "RtlMoveMemory" (hpvDest As Any, ByVal hpvSource As Any, ByVal cbCopy As Long)

'constants for API memory functions
Private Const GMEM_MOVEABLE = &H2
Private Const GMEM_ZEROINIT = &H40
Private Const GHND = (GMEM_MOVEABLE Or GMEM_ZEROINIT)
    
'constants for Cryptography API functions
Private Const MS_DEF_PROV = "Microsoft Base Cryptographic Provider v1.0"
Private Const PROV_RSA_FULL = 1
Private Const CRYPT_NEWKEYSET = &H8
Private Const PP_CONTAINER = 6
Private Const AT_KEYEXCHANGE = 1
Private Const AT_SIGNATURE = 2

Private Const SIMPLEBLOB = 1

Private Const ALG_CLASS_DATA_ENCRYPT = 24576
Private Const ALG_CLASS_HASH = 32768
Private Const ALG_TYPE_ANY = 0
Private Const ALG_TYPE_BLOCK = 1536
Private Const ALG_TYPE_STREAM = 2048
Private Const ALG_SID_RC2 = 2
Private Const ALG_SID_RC4 = 1
Private Const ALG_SID_MD5 = 3

Private Const CALG_MD5 = ((ALG_CLASS_HASH Or ALG_TYPE_ANY) Or ALG_SID_MD5)
Private Const CALG_RC2 = ((ALG_CLASS_DATA_ENCRYPT Or ALG_TYPE_BLOCK) Or ALG_SID_RC2)
Private Const CALG_RC4 = ((ALG_CLASS_DATA_ENCRYPT Or ALG_TYPE_STREAM) Or ALG_SID_RC4)

'constants from WinErr.h
Private Const NTE_NO_KEY As Long = -2146893811 '0x8009000DL
Private Const NTE_BAD_SIGNATURE As Long = -2146893818

'clsCryptoFilterBox constants
Private Const CFB_BUSY = 0
Private Const CFB_READY = 1
Private Const CFB_VALID = 2

Private Const ENCRYPT_ALGORITHM = CALG_RC4
Private Const ENCRYPT_BLOCK_SIZE = 1

Private Const CRYPT_EXPORTABLE = 1

'private property buffers
Private sInBuffer As String
Private sOutBuffer As String
Private sPassword As String
Private sSignature As String
Private lStatus As Long
Public Property Get InBuffer() As String
    InBuffer = sInBuffer
End Property
Public Property Let InBuffer(vNewValue As String)
    sInBuffer = vNewValue
End Property
Public Property Get OutBuffer() As String
    OutBuffer = sOutBuffer
End Property
Public Property Get Signature() As String
    Signature = sSignature
End Property
Public Property Let Signature(vNewValue As String)
    sSignature = vNewValue
End Property
Public Sub Sign()
'Create a signature for Inbuffer and place in Signature

Dim sContainer As String, sDescription As String, sProvider As String, lHCryptprov As Long
Dim lHHash As Long, lResult As Long, lSignatureLen As Long

On Error GoTo ErrSign
    
'switch Status property
lStatus = CFB_BUSY

'init Signature property
sSignature = ""

'Get handle to the default provider.
sContainer = vbNullChar
sProvider = MS_DEF_PROV & vbNullChar
If Not CBool(CryptAcquireContext(lHCryptprov, ByVal sContainer, ByVal sProvider, PROV_RSA_FULL, 0)) Then
    MsgBox ("Error " & CStr(GetLastError) & " during CryptAcquireContext!")
    GoTo ReleaseHandles:
End If

'Create a hash object.
If Not CBool(CryptCreateHash(lHCryptprov, CALG_MD5, 0, 0, lHHash)) Then
    MsgBox ("Error " & CStr(GetLastError) & " during CryptCreateHash!")
    GoTo ReleaseHandles:
End If

If Not CBool(CryptHashData(lHHash, sInBuffer, Len(sInBuffer), 0)) Then
    MsgBox ("Error " & CStr(GetLastError) & " during CryptHashData!")
    GoTo ReleaseHandles:
End If

'Sign hash object.
'Determine size of signature.
sDescription = vbNullChar
lResult = CryptSignHash(lHHash, AT_SIGNATURE, sDescription, 0, sSignature, lSignatureLen)

sSignature = String(lSignatureLen, vbNullChar)

'Sign hash object (with signature key).
If Not CBool(CryptSignHash(lHHash, AT_SIGNATURE, sDescription, 0, sSignature, lSignatureLen)) Then
    MsgBox ("Error " & CStr(GetLastError()) & " during CryptSignHash")
    GoTo ReleaseHandles:
End If

ReleaseHandles:
'Destroy hash object.
If lHHash Then lResult = CryptDestroyHash(lHHash)
'Release provider handle.
If lHCryptprov Then lResult = CryptReleaseContext(lHCryptprov, 0)

'switch Status property
lStatus = CFB_READY

Exit Sub

ErrSign:
MsgBox ("ErrSign " & Error$)
GoTo ReleaseHandles
End Sub

Public Sub Validate()
'Validate InBuffer with Signature and assign Status with result
Dim bValid As Boolean, sContainer As String, sDescription As String, sProvider As String
Dim lDataLen As Long, lDataPoint As Long, lHCryptprov As Long, lHHash As Long
Dim lResult As Long, lSignatureLen As Long, lHCryptKey As Long

ReDim aByteData(0) As Byte

On Error GoTo ErrValidate

'switch Status property
lStatus = CFB_BUSY

'init internal valid flag
bValid = True

'Get handle to the default provider.
sContainer = vbNullChar
sProvider = MS_DEF_PROV & vbNullChar
If Not CBool(CryptAcquireContext(lHCryptprov, ByVal sContainer, ByVal sProvider, PROV_RSA_FULL, 0)) Then
    bValid = False
    MsgBox ("Error " & CStr(GetLastError) & " during CryptAcquireContext!")
    GoTo ReleaseHandles:
End If

'Create a hash object.
If Not CBool(CryptCreateHash(lHCryptprov, CALG_MD5, 0, 0, lHHash)) Then
    bValid = False
    MsgBox ("Error " & CStr(GetLastError) & " during CryptCreateHash!")
    GoTo ReleaseHandles:
End If

'Add data to hash object.
If Not CBool(CryptHashData(lHHash, sInBuffer, Len(sInBuffer), 0)) Then
    bValid = False
    MsgBox ("Error " & CStr(GetLastError) & " during CryptHashData!")
    GoTo ReleaseHandles:
End If

'Determine size of signature.
'sDescription = vbNullChar
'lResult = CryptSignHash(lHHash, AT_SIGNATURE, sDescription, 0, 0, lSignatureLen)

'Get handle to signature key.
If Not CBool(CryptGetUserKey(lHCryptprov, AT_SIGNATURE, lHCryptKey)) Then
    bValid = False
    MsgBox ("Error " & CStr(GetLastError) & " during CryptGetUserKey!")
    GoTo ReleaseHandles:
End If

lSignatureLen = Len(sSignature)

'Verify signature.
If Not CBool(CryptVerifySignature(lHHash, sSignature, lSignatureLen, lHCryptKey, sDescription, 0)) Then

    If GetLastError = NTE_BAD_SIGNATURE Then
        bValid = False
        GoTo ReleaseHandles:
    Else
        bValid = False
        MsgBox ("Error " & CStr(GetLastError) & " during CryptVerifySignature!")
        GoTo ReleaseHandles:
    End If

End If

ReleaseHandles:
'Release signature key.
If lHCryptKey Then lResult = CryptDestroyKey(lHCryptKey)
'Destroy hash object.
If lHHash Then lResult = CryptDestroyHash(lHHash)
'Release provider handle.
If lHCryptprov Then lResult = CryptReleaseContext(lHCryptprov, 0)

Select Case bValid
    Case True
        lStatus = CFB_VALID
    Case Else
        lStatus = CFB_READY
End Select

Exit Sub

ErrValidate:
MsgBox ("ErrValidate " & Error$)
Resume

End Sub
Public Sub Encrypt()
'Encrypt InBuffer into OutBuffer

Dim lHExchgKey As Long, lHCryptprov As Long, lHHash As Long, lHkey As Long
Dim lResult As Long, sContainer As String, sProvider As String, sCryptBuffer As String
Dim lCryptLength As Long, lCryptBufLen As Long

On Error GoTo ErrEncrypt

'switch Status property
lStatus = CFB_BUSY

'Get handle to the default provider
sContainer = vbNullChar
sProvider = vbNullChar
sProvider = MS_DEF_PROV & vbNullChar
If Not CBool(CryptAcquireContext(lHCryptprov, ByVal sContainer, ByVal sProvider, PROV_RSA_FULL, 0)) Then
    MsgBox ("Error " & CStr(GetLastError) & " during CryptAcquireContext!")
    GoTo Done
End If

'Create a hash object.
If Not CBool(CryptCreateHash(lHCryptprov, CALG_MD5, 0, 0, lHHash)) Then
    MsgBox ("Error " & CStr(GetLastError) & " during CryptCreateHash!")
    GoTo Done
End If

'Hash in the password data.
If Not CBool(CryptHashData(lHHash, sPassword, Len(sPassword), 0)) Then
    MsgBox ("Error " & CStr(GetLastError) & " during CryptHashData!")
    GoTo Done
End If

'Derive a session key from the hash object.
If Not CBool(CryptDeriveKey(lHCryptprov, ENCRYPT_ALGORITHM, lHHash, 0, lHkey)) Then
    MsgBox ("Error " & CStr(GetLastError) & " during CryptDeriveKey!")
    GoTo Done
End If

'Destroy the hash object.
CryptDestroyHash (lHHash)
lHHash = 0

'Prepare a string buffer for the CryptEncrypt function
lCryptLength = Len(sInBuffer)
lCryptBufLen = lCryptLength * 2
sCryptBuffer = String(lCryptBufLen, vbNullChar)
LSet sCryptBuffer = sInBuffer

'Encrypt data
If Not CBool(CryptEncrypt(lHkey, 0, 1, 0, sCryptBuffer, lCryptLength, lCryptBufLen)) Then
    MsgBox ("bytes required:" & CStr(lCryptLength))
    MsgBox ("Error " & CStr(GetLastError) & " during CryptEncrypt!")
    'GoTo Done
End If

sOutBuffer = Mid$(sCryptBuffer, 1, lCryptLength)
    
Done:

'Destroy session key.
If (lHkey) Then lResult = CryptDestroyKey(lHkey)

'Release key exchange key handle.
If lHExchgKey Then CryptDestroyKey (lHExchgKey)

'Destroy hash object.
If lHHash Then CryptDestroyHash (lHHash)

'Release provider handle.
If lHCryptprov Then lResult = CryptReleaseContext(lHCryptprov, 0)

'switch Status property
lStatus = CFB_READY

Exit Sub

ErrEncrypt:

MsgBox ("ErrEncrypt " & Error$)
Resume

End Sub
Public Sub Decrypt()
'Decrypt InBuffer into OutBuffer
Dim lHExchgKey As Long, lHCryptprov As Long, lHHash As Long, lHkey As Long
Dim lResult As Long, sContainer As String, sProvider As String
Dim sCryptBuffer As String, lCryptBufLen As Long, lCryptPoint As Long
Dim lPasswordPoint As Long, lPasswordCount As Long
    
On Error GoTo ErrDecrypt

'switch Status property
lStatus = CFB_BUSY
        
'Init sOutBuffer
sOutBuffer = ""

'Get handle to the default provider.
sContainer = vbNullChar
sProvider = vbNullChar
sProvider = MS_DEF_PROV & vbNullChar
If Not CBool(CryptAcquireContext(lHCryptprov, ByVal sContainer, ByVal sProvider, PROV_RSA_FULL, 0)) Then
    MsgBox ("Error " & CStr(GetLastError) & " during CryptAcquireContext!")
    GoTo Done
End If

'Create a hash object.
If Not CBool(CryptCreateHash(lHCryptprov, CALG_MD5, 0, 0, lHHash)) Then
    MsgBox ("Error " & CStr(GetLastError) & " during CryptCreateHash!")
    GoTo Done
End If

'Hash in the password data.
If Not CBool(CryptHashData(lHHash, sPassword, Len(sPassword), 0)) Then
    MsgBox ("Error " & CStr(GetLastError) & " during CryptHashData!")
    GoTo Done
End If
    
'Derive a session key from the hash object.
If Not CBool(CryptDeriveKey(lHCryptprov, ENCRYPT_ALGORITHM, lHHash, 0, lHkey)) Then
    MsgBox ("Error " & CStr(GetLastError) & " during CryptDeriveKey!")
    GoTo Done
End If

'Destroy the hash object.
CryptDestroyHash (lHHash)
lHHash = 0

'Prepare sCryptBuffer for CryptDecrypt
lCryptBufLen = Len(sInBuffer) * 2
sCryptBuffer = String(lCryptBufLen, vbNullChar)
LSet sCryptBuffer = sInBuffer

'Decrypt data
If Not CBool(CryptDecrypt(lHkey, 0, 1, 0, sCryptBuffer, lCryptBufLen)) Then
    MsgBox ("bytes required:" & CStr(lCryptBufLen))
    MsgBox ("Error " & CStr(GetLastError) & " during CryptDecrypt!")
    GoTo Done
End If

'Apply decrypted string from sCryptBuffer to private buffer for OutBuffer property
sOutBuffer = Mid$(sCryptBuffer, 1, Len(sInBuffer))

Done:

'Destroy session key.
If (lHkey) Then lResult = CryptDestroyKey(lHkey)

'Release key exchange key handle.
If lHExchgKey Then CryptDestroyKey (lHExchgKey)

'Destroy hash object.
If lHHash Then CryptDestroyHash (lHHash)

'Release provider handle.
If lHCryptprov Then lResult = CryptReleaseContext(lHCryptprov, 0)

'switch Status property
lStatus = CFB_READY

Exit Sub

ErrDecrypt:
MsgBox ("ErrDecrypt " & Error$)
GoTo Done

End Sub
Public Property Get Status() As Long
    Status = lStatus
End Property
Private Function InitUser() As Long
    Dim lHCryptprov As Long, lHCryptKey As Long, avProviderData(1000) As Byte
    Dim lProviderDataAddress As Long, lProviderDataLen As Long, lDataSize As Long
    Dim lResult As Long, sContainer As String, sProvider As String
    Dim sUserName As String, lPoint As Long, lMemHandle As Long
    Dim lReturn As Long, sBuffer As String
    
    On Error GoTo ErrInitUser
    'prepare string buffers
    
    sContainer = vbNullChar
    sProvider = MS_DEF_PROV & vbNullChar
    
    'Attempt to acquire a handle to the default key container.
    If Not CBool(CryptAcquireContext(lHCryptprov, ByVal sContainer, ByVal sProvider, PROV_RSA_FULL, 0)) Then
        
        'Create default key container.
        If Not CBool(CryptAcquireContext(lHCryptprov, ByVal sContainer, ByVal sProvider, PROV_RSA_FULL, CRYPT_NEWKEYSET)) Then
            MsgBox ("Error creating key container! " & CStr(GetLastError))
            Exit Function
        End If
        
        'Get name of default key container.
        lProviderDataLen = Len(avProviderData(0)) * (UBound(avProviderData) + 1)
        If Not CBool(CryptGetProvParam(lHCryptprov, PP_CONTAINER, avProviderData(0), lProviderDataLen, 0)) Then
            MsgBox ("Error getting user name! " & CStr(GetLastError))
            avProviderData(0) = 0
        End If
        
        'Get sUserName from avProviderData()
        lPoint = LBound(avProviderData)
        While lPoint <= UBound(avProviderData)
            If avProviderData(lPoint) <> 0 Then
                sUserName = sUserName & Chr$(avProviderData(lPoint))
            Else
                lPoint = UBound(avProviderData)
            End If
            lPoint = lPoint + 1
        Wend
        
        MsgBox ("Create key container " & sUserName)
        
    End If
    
    'Attempt to get handle to signature key
    If Not CBool(CryptGetUserKey(lHCryptprov, AT_SIGNATURE, lHCryptKey)) Then
        If GetLastError = NTE_NO_KEY Then
            MsgBox ("Create key exchange key pair")
            If Not CBool(CryptGenKey(lHCryptprov, AT_SIGNATURE, 0, lHCryptKey)) Then
                MsgBox ("Error during CryptGenKey! " & CStr(GetLastError))
                Exit Function
            Else
                lResult = CryptDestroyKey(lHCryptprov)
            End If
        Else
            MsgBox ("Error during CryptGetUserKey! " & CStr(GetLastError))
            Exit Function
        End If
    End If

    'Attempt to get handle to exchange key
    If Not CBool(CryptGetUserKey(lHCryptprov, AT_KEYEXCHANGE, lHCryptKey)) Then
        If GetLastError = NTE_NO_KEY Then
            MsgBox ("Create key exchange key pair")
            If Not CBool(CryptGenKey(lHCryptprov, AT_KEYEXCHANGE, 0, lHCryptKey)) Then
                MsgBox ("Error during CryptGenKey! " & CStr(GetLastError))
                Exit Function
            Else
                lResult = CryptDestroyKey(lHCryptprov)
            End If
        Else
            MsgBox ("Error during CryptGetUserKey! " & CStr(GetLastError))
            Exit Function
        End If
    End If
    
    'release handle to provider
    lResult = CryptReleaseContext(lHCryptprov, 0)
    InitUser = True

Exit Function

ErrInitUser:
    MsgBox ("ErrInitUser " & Error$)
    Resume

End Function
Private Sub Class_Initialize()
    If InitUser = True Then
        MsgBox ("InitUser OK")
    Else
        MsgBox ("InitUser failed")
    End If
End Sub
Public Property Get Password() As String
    Password = sPassword
End Property
Public Property Let Password(vNewValue As String)
    sPassword = vNewValue
End Property


 
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