Re: Crypto API using RC2 instead of RC4?
From: Matt (mtaylor_at_gladstonemrm.com)
Date: 11/23/05
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Date: 23 Nov 2005 10:16:45 -0800
Looks like I jumped the gun a bit.
I've run it through a random string generator to really test it and it
still generates an error every so often.
Below is the Decrypt function if anybody is able to figure out what is
wrong.
I'm tearing my hair out.
Its the call to the CryptDecrypt API that is causing the problem.
I'm not entirely sure what you mean by the padding mode Valery?
I'm sure I haven't changed anything like that.
*** Code Starts ***
Private Function CryptoDecrypt(intHashType As Integer, _
intCipherType As Integer) As Boolean
Dim lngHashHnd As Long ' Hash handle
Dim lngkey As Long
Dim lngRetCode As Long ' return value from an API call
Dim lngHashType As Long
Dim lngLen As Long
Dim lngAlgoType As Long
Dim lngHExchgKey As Long
Dim lngEncDataLength As Long
Dim lngEnctBuffLen As Long
Dim strEncBuffer As String
Dim strOutData As String
Dim strPassword As String
'--------------------------- Initialize
variables-------------------------------
CryptoDecrypt = False ' preset to FALSE
Erase g_abytOutData()
strOutData = ""
strEncBuffer = ""
strPassword = ""
lngHashType = CALG_SHA1
lngAlgoType = CALG_RC2
'----------------------- Aquire the provider
handle---------------------------
If g_lngCryptoContext = 0 Then
If Not GetProvider Then
Call Class_Terminate ' Failed. Time to leave.
Exit Function
End If
End If
On Error GoTo CryptoDecrypt_Error
'---------------------- convert password to
string-----------------------------
If UBound(g_abytPassword) > 0 Then
strPassword = ByteArrayToString(g_abytPassword())
End If
'----------------------- Create a hash
object----------------------------------
If Not CBool(CryptCreateHash(g_lngCryptoContext, lngHashType, ByVal
0&, _
ByVal 0&, lngHashHnd)) Then
Err.Raise vbObjectError + 6, "clsCryptoAPIWrapper.CryptoDecrypt",
"Error: " & CStr(GetLastError) & " during CryptCreateHash!"
End If
'------------------------- Hash in the password
text----------------------------
If Not CBool(CryptHashData(lngHashHnd, strPassword,
Len(strPassword), ByVal 0&)) Then
Err.Raise vbObjectError + 7, "clsCryptoAPIWrapper.CryptoDecrypt",
"Error: " & CStr(GetLastError) & " during CryptHashData!"
End If
'-------------- Create a session key from the hash
object--------------------
If Not CBool(CryptDeriveKey(g_lngCryptoContext, lngAlgoType, _
lngHashHnd, ByVal CRYPT_NO_SALT, lngkey)) Then
Err.Raise vbObjectError + 8, "clsCryptoAPIWrapper.CryptoDecrypt",
"Error: " & CStr(GetLastError) & " during CryptDeriveKey!"
End If
'----------------------- Destroy hash
object--------------------------------
If lngHashHnd <> 0 Then
lngRetCode = CryptDestroyHash(lngHashHnd)
End If
lngHashHnd = 0
'------------------------- Prepare data for
decryption.-----------------------
lngEncDataLength = Len(g_strInData)
lngEnctBuffLen = lngEncDataLength * 2
strEncBuffer = String$(lngEnctBuffLen, vbNullChar)
LSet strEncBuffer = g_strInData
'--------------------- Decrypt the text
data---------------------------------
If Not CBool(CryptDecrypt(lngkey, ByVal 0&, ByVal 1&, ByVal 0&, _
strEncBuffer, lngEncDataLength)) Then
Err.Raise vbObjectError + 9, "clsCryptoAPIWrapper.CryptoDecrypt",
"Bytes required:" & CStr(lngEnctBuffLen) & vbCrLf & vbCrLf & _
"Error: " & CStr(GetLastError) & " during CryptEncrypt!"
End If
'--------------- Return the decrypted data string in a byte
array-------------
strOutData = Mid$(strEncBuffer, 1, lngEncDataLength)
g_abytOutData = StringToByteArray(strOutData)
CryptoDecrypt = True ' Successful finish
CleanUp:
' -------------------------Destroy session
key.-----------------------------
If lngkey <> 0 Then
lngRetCode = CryptDestroyKey(lngkey)
End If
'-------------------------- Destroy key exchange key
handle---------------------
If lngHExchgKey <> 0 Then
lngRetCode = CryptDestroyKey(lngHExchgKey)
End If
'---------------------------- Destroy hash
object--------------------------------
If lngHashHnd <> 0 Then
lngRetCode = CryptDestroyHash(lngHashHnd)
End If
'----------------------------- Empty
variables-----------------------------------
lngHashHnd = 0
strPassword = String$(250, 0)
Exit Function
CryptoDecrypt_Error:
' -------------------------Destroy session
key.-----------------------------
If lngkey <> 0 Then
lngRetCode = CryptDestroyKey(lngkey)
End If
'-------------------------- Destroy key exchange key
handle---------------------
If lngHExchgKey <> 0 Then
lngRetCode = CryptDestroyKey(lngHExchgKey)
End If
'---------------------------- Destroy hash
object--------------------------------
If lngHashHnd <> 0 Then
lngRetCode = CryptDestroyHash(lngHashHnd)
End If
'----------------------------- Empty
variables-----------------------------------
lngHashHnd = 0
strPassword = String$(250, 0)
Err.Raise vbObjectError + 10, "clsCryptoAPIWrapper.CryptoDecrypt",
"Error: " & CStr(Err.Number) & " " & Err.Description & vbCrLf & _
vbCrLf & "A critical error ocurred during the decryption
process."
End Function
*** Code Ends ***
- Next message: lelteto: "Re: CryptAcquireContext _sometimes_ fails with NTE_PROVIDER_DLL_FA"
- Previous message: Mick J.: "access control on key containers"
- In reply to: Matt: "Re: Crypto API using RC2 instead of RC4?"
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- Reply: Valery Pryamikov: "Re: Crypto API using RC2 instead of RC4?"
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