File Encryption

darknuke

darknuke

Well-known member
Joined
Oct 3, 2003
Messages
68
What cryptography method I would use for the encryption AND decryption of a file via a specified key? (I searched on the forum for this topic, but what Im looking for didnt come up)

Example:

Program A encrypts file A using the key wiehr234hih

Program A outputs (encrypted) file B

User A does not know the key, but tries the key 293ywah

Program B is decrypted, but is not the original file because it is corrupted due to the incorrect key given

User B knows the key, so inputs the key wiehr234hih

Program B is decrypted correctly
 
This is the module that I use. It should return you a decypted text with no validation...

and as an added bonus, this is XML safe :)

Code: 
Imports System
Imports System.IO
Imports System.Xml
Imports System.Text
Imports System.Security.Cryptography

 Namespace: YourCompany.Utils.Encryption
 Uses DES private key and vector to provide HTTP / XMLDOM - safe base64 string encryption
 Encrypted string such as account info, passwords, etc can be safely placed in XML element
 for transmission over the wire without any illegal characters

Public Class Encryption64

     Use DES CryptoService with Private key pair
    Private key() As Byte = {}  we are going to pass in the key portion in our method calls
    Private IV() As Byte = {&H12, &H34, &H56, &H78, &H90, &HAB, &HCD, &HEF}

    Public Function DecryptFromBase64String(ByVal stringToDecrypt As String, ByVal sEncryptionKey As String) As String
        Dim inputByteArray(stringToDecrypt.Length) As Byte
         Note: The DES CryptoService only accepts certain key byte lengths
         We are going to make things easy by insisting on an 8 byte legal key length

        Try
            key = System.Text.Encoding.UTF8.GetBytes(Left(sEncryptionKey, 8))
            Dim des As New DESCryptoServiceProvider()
             we have a base 64 encoded string so first must decode to regular unencoded (encrypted) string
            inputByteArray = Convert.FromBase64String(stringToDecrypt)
             now decrypt the regular string
            Dim ms As New MemoryStream()
            Dim cs As New CryptoStream(ms, des.CreateDecryptor(key, IV), CryptoStreamMode.Write)
            cs.Write(inputByteArray, 0, inputByteArray.Length)
            cs.FlushFinalBlock()
            Dim encoding As System.Text.Encoding = System.Text.Encoding.UTF8
            Return encoding.GetString(ms.ToArray())
        Catch e As Exception
            Return e.Message
        End Try
    End Function

    Public Function EncryptToBase64String(ByVal stringToEncrypt As String, ByVal SEncryptionKey As String) As String
        Try
            key = System.Text.Encoding.UTF8.GetBytes(Left(SEncryptionKey, 8))
            Dim des As New DESCryptoServiceProvider()
             convert our input string to a byte array
            Dim inputByteArray() As Byte = Encoding.UTF8.GetBytes(stringToEncrypt)
            now encrypt the bytearray
            Dim ms As New MemoryStream()
            Dim cs As New CryptoStream(ms, des.CreateEncryptor(key, IV), CryptoStreamMode.Write)
            cs.Write(inputByteArray, 0, inputByteArray.Length)
            cs.FlushFinalBlock()
             now return the byte array as a "safe for XMLDOM" Base64 String
            Return Convert.ToBase64String(ms.ToArray())
        Catch e As Exception
            Return e.Message
        End Try
    End Function

End Class
 
opps sorry. But how different can it really be. At the lowest level you still have to read in an array of bytes from a file and write to a new one...
 
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