Android Question Encrypt on Android - Decrypt on .Net

pereskjo

Member
Licensed User
Hi, I need to send a encrypted String from Android Phone to Windows computer.
So I need a B4A Encrypt , and C# / vb.net Decrypt code.
I have tried various DES, 3DES libraries.
So if any one of you have got this right, please post the code below.
 

pereskjo

Member
Licensed User

Not any luck yet. Tried Rijandel code in link, but the B4A code generate different output each time i input "hello world" ??
added
Dim bc As ByteConverter
Return bc.StringFromBytes(encrypted,"UTF-8")
is that wrong?

B4A:
B4X:
Sub Button1_Click
    ToastMessageShow("Encrypted = " & Encrypt("hello world"),False)
End Sub

Sub Encrypt(dataToEncrypt As String) As String
    Dim kg As KeyGenerator
    Dim C As Cipher
    Dim encrypted() As Byte
 
    kg.Initialize("AES")
    kg.KeyFromBytes("5TGB&YHN7UJM(IK<".GetBytes("UTF8"))
  
    C.Initialize("AES/CBC/PKCS7Padding")
      C.InitialisationVector = "!QAZ2WSX#EDC4RFV".GetBytes("UTF8")
    encrypted = C.Encrypt(dataToEncrypt.GetBytes("UTF8"), kg.Key, False)
    Dim bc As ByteConverter
    Return bc.StringFromBytes(encrypted,"UTF-8")
End Sub

Please help if any of you got B4A -> .Net encrypd decrypt working.
 
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Jeffrey Cameron

Well-Known Member
Licensed User
I usually hex encode the bytes but you could base-64 or post the bytes directly. I use this for URI parameters, for example, .NET CODE:
B4X:
    Public Shared Function AESDecrypt(ByVal HexString As String) As String
        Dim poBytes As New List(Of Byte)
        Dim piIndex As Integer
        Dim pyResult() As Byte

        Try
            For piIndex = 0 To HexString.Length - 1 Step 2
                Dim psChars As String
                psChars = HexString.Substring(piIndex, 2)
                poBytes.Add(Convert.ToInt32(psChars, 16))
            Next

            ' decrypt it
            Dim poAES As New System.Security.Cryptography.AesManaged

            poAES.IV = System.Text.UTF8Encoding.UTF8.GetBytes(ConfigurationManager.AppSettings("AesIV"))
            poAES.Key = System.Text.UTF8Encoding.UTF8.GetBytes(ConfigurationManager.AppSettings("AesKey"))
            pyResult = poAES.CreateDecryptor().TransformFinalBlock(poBytes.ToArray, 0, poBytes.Count)
            poAES.Clear()

            Return System.Text.UTF8Encoding.UTF8.GetString(pyResult)

        Catch ex As Exception
            clsLogError.WriteToLog("WebCore.AESDecrypt", "RTE attempting AES decrypt of string: " & ex.Message & "<br />Input: [&nbsp;<b>" & HexString & "</b>&nbsp;]")
            Return ""
        End Try

    End Function

    Public Shared Function AESEncrypt(ByVal PlainText As String) As String
        Dim pyBytes() As Byte
        Dim pyResult() As Byte
        Dim piIndex As Integer
        Dim poResult As New System.Text.StringBuilder

        pyBytes = System.Text.UTF8Encoding.UTF8.GetBytes(PlainText)

        ' Encrypt it
        Dim poAES As New System.Security.Cryptography.AesManaged

        poAES.IV = System.Text.UTF8Encoding.UTF8.GetBytes(ConfigurationManager.AppSettings("AesIV"))
        poAES.Key = System.Text.UTF8Encoding.UTF8.GetBytes(ConfigurationManager.AppSettings("AesKey"))
        pyResult = poAES.CreateEncryptor().TransformFinalBlock(pyBytes, 0, pyBytes.Length)
        ' convert it to a HEX string
        For piIndex = 0 To pyResult.Length - 1
            poResult.Append(pyResult(piIndex).ToString("X2"))
        Next

        Return poResult.ToString
    End Function

B4A Code:
B4X:
' Note:  REQUIRES:   Encryption, B4XEncryption, ByteConverter, StringUtils libraries

' In Starter module:
 Public Const PART_3 As String = "16RANDOMBYTESOne"   ' command line parameter encryption
 Public Const PART_4 As String = "16RANDOMBYTESTwo"

' in a module:

'Takes a plain string and returns as HEX-ENCODED string of the encrytped text.
Public Sub AES_Encrypt(DataToEncrypt As String) As String
    Dim poKG As KeyGenerator
    Dim poCy As Cipher
    Dim poBC As ByteConverter
    Dim poData() As Byte

    ' doing AES
    poCy.Initialize("AES/CBC/PKCS7Padding")
    ' set InitializationVector value
    poCy.InitialisationVector = poBC.StringToBytes(Starter.PART_3, "utf8")
    ' Generate a key
    poKG.Initialize("AES")
    poKG.KeyFromBytes(poBC.StringToBytes(Starter.PART_4, "utf8"))
    ' encrypt the string into a byte array   
    poData = poCy.Encrypt(poBC.StringToBytes(DataToEncrypt, "utf8"), poKG.Key, True)
    ' convert the byte array to a HEX string and return it
    Return poBC.HexFromBytes(poData)
End Sub

' Takes a HEX-ENCODED string of the encrytped text and returns the plain text.
Public Sub AES_Decrypt(HexEncodedString As String) As String
    Dim poKG As KeyGenerator
    Dim poCy As Cipher
    Dim poBC As ByteConverter
    Dim poData() As Byte

    poData = poBC.HexToBytes(HexEncodedString)
    ' doing AES
    poCy.Initialize("AES/CBC/PKCS7Padding")
    ' set InitializationVector value
    poCy.InitialisationVector = poBC.StringToBytes(Starter.PART_3, "utf8")
    ' Generate a key
    poKG.Initialize("AES")
    poKG.KeyFromBytes(poBC.StringToBytes(Starter.PART_4, "utf8"))
    ' encrypt the string into a byte array   
    poData = poCy.Decrypt(poBC.HexToBytes(HexEncodedString), poKG.Key, True)
    ' Convert it back to utf8 string
    Return BytesToString(poData, 0, poData.Length, "utf8")
End Sub
 
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pereskjo

Member
Licensed User
Awesome Jeffrey, Thanks.:)
Just changed your ConfigurationManager.AppSettings with a 16 char long string for iv and key, and it worked.
 
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