Ja koristim jednu gotovu klasu skinuo sa neta. Jednostavno to je jedna klasa, koju pozovem crc32-ujem nesto i upisem key u bazu sledeci put kqada proveravam neki novi fajl koji unosim, uporedim crc32 i ako je isti... ma kontas vec kako ide. evo ti cele klase:
Code:
Option Strict On
Option Explicit On
Imports System.Security.Cryptography
Namespace xous.Security.Cryptography
Public Class CRC32
Inherits HashAlgorithm
Private Const _DefaultPolynomial As Integer = &HEDB88320
#Region " Member Variables "
Private _Table() As Integer
Private _CRC32 As Integer = &HFFFFFFFF
Private _Polynomial As Integer
#End Region
#Region " Contructors "
Public Sub New()
Me.HashSizeValue = 32 ' CRC32 is a 32bit hash
_Polynomial = _DefaultPolynomial
Initialize()
End Sub
Public Sub New(ByVal Polynomial As Integer)
_Polynomial = Polynomial
End Sub
#End Region
#Region " HashAlgorithm "
Protected Overrides Sub HashCore(ByVal array() As Byte, ByVal ibStart As Integer, ByVal cbSize As Integer)
Dim intLookup As Integer
For i As Integer = 0 To cbSize - 1
intLookup = (_CRC32 And &HFF) Xor array(i)
'This is a workaround for a right bit-shift because vb.net
'does not support unsigned Integers, so _CRC32 >> 8
'gives the wrong value (any better fixes?)
_CRC32 = ((_CRC32 And &HFFFFFF00) \ &H100) And &HFFFFFF
_CRC32 = _CRC32 Xor _Table(intLookup)
Next i
End Sub
Protected Overrides Function HashFinal() As Byte()
Return BitConverter.GetBytes(Not _CRC32)
End Function
Public Overrides Sub Initialize()
_CRC32 = &HFFFFFFFF
_Table = BuildTable(_Polynomial)
End Sub
#End Region
#Region " Helper Methods "
''' <returns>The CRC32 Table based on the Polynomial given</returns>
Private Shared Function BuildTable(ByVal Polynomial As Integer) As Integer()
Dim Table(255) As Integer
Dim Value As Integer
For I As Integer = 0 To 255
Value = I
For X As Integer = 0 To 7
If (Value And 1) = 1 Then
'This is a workaround for a right bit-shift because vb.net
'does not support unsigned Integers, so _CRC32 >> 1
'gives the wrong value (any better fixes?)
Value = Convert.ToInt32(((Value And &HFFFFFFFE) \ 2&) And &H7FFFFFFF)
Value = Value Xor Polynomial
Else
'Same as above.
Value = Convert.ToInt32(((Value And &HFFFFFFFE) \ 2&) And &H7FFFFFFF)
End If
Next
Table(I) = Value
Next
Return Table
End Function
#End Region
End Class
End Namespace
A pozivas je ovako:
Code:
Dim crc As New xous.Security.Cryptography.CRC32
Dim fs As New FileStream(fl, FileMode.Open)
Dim CRC32 As Integer = BitConverter.ToInt32(crc.ComputeHash(CType(fs, Stream)), 0)
fs.Close()
Dim crcresult As String = String.Format("{0:X8}", CRC32)
gde ti je fl recimo putanja do fajla...
nadam se da ce koristiti.
E sad ja sa ovim proveravam fajlove... i to lepo radi... mislim da bi trebalo nekako da dataset ili vec to sto imas memorijski pretvoris u fajl, hashujes ga zatim upises kod a promenljivu koja sadrzi fajl ubijes... i taj postupak ponavljas svaki put kada ti je ovo potrebno. Ne znam dali je hash direktno na dataset ili vec sta koristis moguc, tj dali uvek daje iste rezultate na razlicitim masinama i slicno...
***If there is a will, there is a way***
Pitanje o hash-iranju objekta
