CryptEncrypt/CryptDecrypt WinAPI functions fail when called from vb.net - vb.net

Question

Any help with the following greatly appreciated.....
I have some C++ code I've inherited which decrypts certain structures/byte arrays; I've been trying to write a test program in VB.net which exactly mimics the C++ decryption routine using the same functions, ie. using the WinAPI Crypto calls; in testing, CryptAcquireContext, CryptCreateHash, CryptHashData and CryptDeriveKey all succeed;
However, both the CryptEncrypt and CryptDecrypt functions fail with the Invalid Parameter error, even in the most simple scenario;
(I am aware of the System.Security.Cryptography namespace...and I will resort to this...but the C++ code includes structures with unions, and for testing, it seemed better to try the WinAPI route first)
the sample code is below...I am on Win7x64 sp1, vs 2010 sp1...
Private Sub cmdTest(sender As System.Object, e As System.EventArgs) Handles cmdtest.Click
Dim hCrypt As IntPtr
Dim hSecretHash, hUserHash As IntPtr
Dim hSecretKey As IntPtr
Dim success As Boolean
If CryptAcquireContext(hCrypt, vbNullString, MS_DEF_PROV, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT) Then
'create hash
success = CryptCreateHash(hCrypt, CALG_MD5, 0, 0, hSecretHash)
'hash stage 1
success = CryptHashData(hSecretHash, Encoding.ASCII.GetBytes("yyyyyy"), "xxxxxx".length, 0)
success = CryptHashData(hSecretHash, Encoding.ASCII.GetBytes("yyyyyy"), "yyyyyy".length, 0)
'derive key
success = CryptDeriveKey(hCrypt, CALG_RC4, hSecretHash, 0, hSecretKey)
Dim newb(127) As Byte
Dim teststring As String = "Testing"
Dim testbytes() As Byte = Encoding.ASCII.GetBytes(teststring)
Buffer.BlockCopy(testbytes, 0, newb, 0, testbytes.Length)
Dim inputlength As UShort = Convert.ToUInt16(testbytes.Length)
Dim newblength As UShort = CUShort(newb.Length)
Dim bufferlength As UShort = newblength
'---------------BOTH THESE FAIL (all above OK)
success = CryptEncrypt(hSecretKey, 0, True, 0, newb, newblength, inputlength)
success = CryptDecrypt(hSecretKey, 0, True, 0, newb, newblength)
'--------------------------------------------
'Destroy the user keycode
CryptDestroyHash(hUserHash)
'Destroy the secret key
CryptDestroyKey(hSecretKey)
CryptDestroyHash(hSecretHash)
'Release the provider
CryptReleaseContext(hCrypt, 0)
End If
End Sub
Public Const ALG_CLASS_DATA_ENCRYPT As Int32 = 24576
Public Const ALG_CLASS_HASH As Int32 = 32768
Public Const ALG_TYPE_ANY As Int32 = 0
Public Const ALG_SID_RC4 As Int32 = 1
Public Const ALG_SID_RC2 As Int32 = 2
Public Const ALG_SID_MD5 As Int32 = 3
Public Const ALG_SID_SHA1 As Int32 = 4
Public Const ALG_SID_MAC As Int32 = 5
Public Const ALG_SID_HMAC As Int32 = 9
Public Const ALG_TYPE_BLOCK As Int32 = 1536
Public Const ALG_TYPE_STREAM As Int32 = 2048
Public Const CALG_MD5 As Int32 = ALG_CLASS_HASH + ALG_TYPE_ANY + ALG_SID_MD5
Public Const CALG_RC2 As Int32 = ALG_CLASS_DATA_ENCRYPT + ALG_TYPE_BLOCK + ALG_SID_RC2
Public Const CALG_RC4 As Int32 = ALG_CLASS_DATA_ENCRYPT + ALG_TYPE_STREAM + ALG_SID_RC4
Public Const CALG_SHA1 As Int32 = ALG_CLASS_HASH + ALG_TYPE_ANY + ALG_SID_SHA1
Public Const CALG_MAC As Int32 = ALG_CLASS_HASH + ALG_TYPE_ANY + ALG_SID_MAC
Public Const CALG_HMAC As Int32 = ALG_CLASS_HASH + ALG_TYPE_ANY + ALG_SID_HMAC
Public Const PROV_RSA_FULL As Int32 = &H1
Public Const CRYPT_VERIFYCONTEXT As Int32 = &HF0000000
Public Const HP_ALGID As Int32 = 1
Public Const HP_HASHVAL As Int32 = 2
Public Const HP_HASHSIZE As Int32 = 4
Public Const HP_HMAC_INFO As Int32 = 5
Public Const MS_DEF_PROV As String = "Microsoft Base Cryptographic Provider v1.0"
'Imported Functions:
<DllImport("advapi32.dll", CharSet:=CharSet.Auto, SetLastError:=True)> _
Public Shared Function CryptAcquireContext( _
ByRef hProv As IntPtr, _
ByVal pszContainer As String, _
ByVal pszProvider As String, _
ByVal dwProvType As Int32, _
ByVal dwFlags As Int32 _
) As Boolean
End Function
<DllImport("advapi32.dll", SetLastError:=True)>
Public Shared Function CryptEncrypt( _
ByVal hKey As IntPtr, _
ByVal hHash As IntPtr, _
ByVal Final As Boolean, _
ByVal dwFlags As UShort, _
pbData() As Byte, _
pdwDataLen As UShort, _
ByVal dwBufLen As UShort) As Boolean
End Function
<DllImport("advapi32.dll", SetLastError:=True, CharSet:=CharSet.Unicode)>
Public Shared Function CryptDecrypt( _
ByVal hKey As IntPtr, _
ByVal hHash As IntPtr, _
ByVal Final As Boolean, _
ByVal dwFlags As UShort, _
pbData() As Byte, _
pdwDataLen As UShort _
) As Boolean
End Function
<DllImport("advapi32.dll", SetLastError:=True)> _
Public Shared Function CryptCreateHash( _
ByVal hProv As IntPtr, _
ByVal Algid As Int32, _
ByVal hKey As IntPtr, _
ByVal dwFlags As Int32, _
ByRef phHash As IntPtr _
) As Boolean
End Function
<DllImport("advapi32.dll", SetLastError:=True)> _
Public Shared Function CryptDestroyHash( _
ByVal hHash As IntPtr _
) As Boolean
End Function
<DllImport("advapi32.dll", SetLastError:=True)> _
Public Shared Function CryptHashData( _
ByVal hHash As IntPtr, _
ByVal pbData() As Byte, _
ByVal dwDataLen As Int32, _
ByVal dwFlags As Int32 _
) As Boolean
End Function
<DllImport("advapi32.dll", setlasterror:=True)> _
Public Shared Function CryptDeriveKey( _
ByVal hProv As IntPtr, _
ByVal Algid As Integer, _
ByVal hBaseData As IntPtr, _
ByVal dwflags As Integer, _
ByRef phKey As IntPtr) As <MarshalAs(UnmanagedType.Bool)> Boolean
End Function
<DllImport("advapi32.dll", SetLastError:=True)> _
Public Shared Function CryptDestroyKey( _
ByVal hKey As IntPtr _
) As Boolean
End Function

Answer 1

The Final parameter of CryptEncrypt is a BOOL, which is a 32-bit int. Try changing the parameter to Final as int32,or use MarshalAs(UnmanagedType.Bool)

Answer 2

Could be more things, but immediately ByVal dwFlags As UShort looks off to me.
The msdn lists that parameter as:
DWORD dwFlags,
A DWORD is 4 bytes, so would be an Int32 or Integer (in VB.NET)