B4J Question AES128 ECB Decrypt

[aaronk]

Hi,

I am trying to decrypt a message using AES128 in ECB mode, and not CBC mode.

The data I am trying to decrypt is sent to my B4J as AES-128 in ECB mode, and that data I have put into a string called 'dataToDecrypt' in my code below.

When I run the following code I get the following error:

Waiting for debugger to connect...
Program started.
Error occurred on line: 83 (Main)
javax.crypto.IllegalBlockSizeException: Input length not multiple of 16 bytes
at com.sun.crypto.provider.CipherCore.finalNoPadding(CipherCore.java:1016)
at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:960)
at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:824)
at com.sun.crypto.provider.AESCipher.engineDoFinal(AESCipher.java:436)
at javax.crypto.Cipher.doFinal(Cipher.java:2165)
at anywheresoftware.b4a.agraham.encryption.CipherWrapper.doFinal(CipherWrapper.java:140)
at anywheresoftware.b4a.agraham.encryption.CipherWrapper.Decrypt(CipherWrapper.java:150)
at b4j.example.main._decrypt(main.java:284)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at anywheresoftware.b4a.shell.Shell.runMethod(Shell.java:632)
at anywheresoftware.b4a.shell.Shell.raiseEventImpl(Shell.java:234)
at anywheresoftware.b4a.shell.Shell.raiseEvent(Shell.java:167)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at anywheresoftware.b4a.BA.raiseEvent2(BA.java:91)
at anywheresoftware.b4a.shell.ShellBA.raiseEvent2(ShellBA.java:98)
at anywheresoftware.b4a.BA.raiseEvent(BA.java:78)
at b4j.example.main.main(main.java:29)

Line 83 is: decrypted = C.Decrypt(decrypted, kg.Key, False)

Dim dataToDecrypt As String = "�q�!DAZ��R��:f/�Ŝ��h�U�0h�V��ƅHw��s�Č)�o�yZ��%v��_,"
   
    Dim kg As KeyGenerator
    Dim C As Cipher
    Dim decrypted() As Byte
    Dim BConv As ByteConverter
   
    decrypted = dataToDecrypt.GetBytes("UTF8")
 
    Dim Key As String = "0123456789ABCDEF" ' this is the same key that encrypted the string that was sent

    kg.Initialize("AES")
    kg.KeyFromBytes(Key.GetBytes("UTF8"))
     
    C.Initialize("AES/ECB/NoPadding") ' not 100% sure on the NoPadding part

    decrypted = C.Decrypt(decrypted, kg.Key, False)

    Log("Decrypt = " & BConv.StringFromBytes(decrypted, "UTF8"))

Anyone know where I have gone wrong ?

 

[Erel]

Never convert "random" bytes to string.
Only bytes that represent a string can be converted to a string.

Worth repeating: never convert random bytes to string. It will not work.

Use base64 encoding to convert the bytes to string.

 

[aaronk]

Never convert "random" bytes to string.

I am guessing you mean the encrypted text that I am trying to read, you are calling 'random' text ?

Use base64 encoding to convert the bytes to string.

Not 100% sure on how to do this.. But tried with the code below, but since it's not working I guess I did it wrong.

I should have pointed out, a 3rd party software is sending a UDP message to my B4J app.
This is a ASCII message, and it looks like:

VALUE1//VALUE2//�q�!DAZ��R��:f/�Ŝ��h�U�0h�V��ƅHw��s�Č)�o�yZ��%v��_,

The first 2 values VALUE1 & VALUE2 are in plan text, and the 3rd section is encrypted with AES128 ECB.

I am reading this UDP like the following:
(My code now looks like the following)

Private Sub SockUDP_PacketArrived (Packet As UDPPacket)

    Dim msg1 As String     ' This will hold the incoming message
    msg1 = BytesToString(Packet.Data, Packet.Offset, Packet.Length, "UTF8")

    msg1 = msg1.Replace(Chr(10),"")
    msg1 = msg1.Replace(Chr(13),"")

    Dim msg_string() As String = Regex.Split("//",msg1)
   
    Log("Full UDP Message = " & msg1) ' VALUE1//VALUE2//�q�!DAZ��R��:f/�Ŝ��h�U�0h�V��ƅHw��s�Č)�o�yZ��%v��_,
    Log("Encrypted Message = " & msg_string(2)) '  �q�!DAZ��R��:f/�Ŝ��h�U�0h�V��ƅHw��s�Č)�o�yZ��%v��_,

    Dim su As StringUtils
    Dim kg As KeyGenerator
    Dim C As Cipher
       
    Dim Key As String = "0123456789ABCDEF" ' this is the same key that encrypted the string that was sent
       
    kg.Initialize("AES")
    kg.KeyFromBytes(Key.GetBytes("UTF8"))
       
    C.Initialize("AES/ECB/PKCS5Padding")
   
    Dim dataString As String
   
    dataString = su.EncodeBase64(msg_string(2).GetBytes("UTF8"))

    Dim decryptedBytes() As Byte = c.Decrypt(dataString.GetBytes("UTF8"), kg.Key , False)
   
    Log("Decrypt Text = " & BytesToString(decryptedBytes, 0, decryptedBytes.Length, "UTF8")) ' this seems to return the same encrypted text.
   
End Sub

 

[DonManfred]

I should have pointed out, a 3rd party software is sending a UDP message to my B4J app

Is there any Documentation about the UDP Packet?

This is a ASCII message, and it looks like

i dont think this is a ASCII Message. Maybe parts of it are text.

Usually UDP Packets have a "Structure".

 

[aaronk]

Is there any Documentation about the UDP Packet?

Kind of, but need to decrypt the message first.

VALUE1 and VALUE2 are in plan text, and the 3rd part is encrypted. Basically VALUE1 and VALUE2 are telling me information about the user sending the message, and then to read the message the user sent I need to decrypt the 3rd part to read the message.

i dont think this is a ASCII Message.

It's an ASCII message otherwise I wouldn't be able to read the first part of the message.

It sounds to me that the 3rd part of the ASCII message is encrypted wrong, but been told it's meant to be sending the message correctly.

 

[DonManfred]

Dim msg1 As String ' This will hold the incoming message
msg1 = BytesToString(Packet.Data, Packet.Offset, Packet.Length, "UTF8")

I think your problem starts here. You are expecting the hole Packet payload to be a String.
In fact it seems that the message payload, the Packet.Data is binary.

I suggest to start debugging here.

- Get the packet data into a bytearray
- convert the bytearray to a hexstring.
- save the hexstring to a file to upload it here.

Looking at the HEX Dump may reveal more info about the Struct the payload does have.

 

[DonManfred]

- Get the packet data into a bytearray

Sub UDP_PacketArrived (Packet As UDPPacket)
    Dim pkt() As Byte = Packet.Data

convert the bytearray to a hexstring.

    Dim hexdata As String = bc.HexFromBytes(pkt) ' bc is a ByteConverter
    File.WriteString("D:\","DataHEX.txt",hexdata) ' Adapt path...

Please upload such a DataHEX.txt

If would be easier to help if you would point a link to the udp packet documentation of these 3rd party software. Or the name of it.

 

[aaronk]

Please upload such a DataHEX.txt

Attached is the HEX as requested.

The attached is when the remote side sent the message encrypted.

I have made the remote side send the same ASCII message as plain text to compare:

3670BB9F//0//0000754C//00409D27558D//05.03.10//02.00.44//Hello

The difference between the plain text and encrypted text is:

Plain text starts with 3670BB9F//0//
Encrypted text starts with 3670BB9F//1//

So, the following text:

0000754C//00409D27558D//05.03.10//02.00.44//Hello

is the encrypted text:

�q�!DAZ��R��:f/�Ŝ��h�U�0h�V��ƅHw��s�Č)�o�yZ��%v��_,

Just trying to work out how to now decrypt the message to read the same text as the plain text.

I used the following code to write the encrypted text and also logged the incoming data to the IDE log:

Sub UDP_PacketArrived (Packet As UDPPacket)
       
    Dim pkt() As Byte = Packet.Data
        
    Dim bc As ByteConverter
    Dim hexdata As String = bc.HexFromBytes(pkt) ' bc is a ByteConverter
    File.WriteString("c:\","DataHEX.txt",hexdata) ' Adapt path...
    
    Dim msg1 As String     ' This will hold the incoming message
    msg1 = BytesToString(Packet.Data, Packet.Offset, Packet.Length, "UTF8")
    
    Log(msg1)
End Sub

It Logs:

Looks like it split the message?

Any help on working out how to decrypt the message would be great.

 

[DonManfred]

Just trying to work out how to now decrypt the message to read the same text as the plain text.

you need to split out the msgpayload (which is binary (probably the encrypted bytes)

    Dim hex As String = "33363730424239462F2F312F2F8971C5072144415AEEEE5212B7B13A662F84C59C99E71D68D17F55BF30680DB556E2ADC4C6854877A3C17384C48C132903E66FAA795AD0E3812576F4EC0F5F2C000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000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    Log("Length HEX: "&hex.Length)
    
    Dim raw() As Byte = bc.HexToBytes(hex)
    bb.Initialize
    bb.Append(raw)
    Dim binaryflag() As Byte = Array As Byte(0x33, 0x36, 0x37, 0x30, 0x42, 0x42, 0x39, 0x46, 0x2f,0x2f,0x31,0x2f,0x2f)
    If bb.IndexOf(binaryflag) > -1 Then
        Log("Binary-Flag found")
        Log("Searching for next zero byte (0x0)")
        Log(bb.IndexOf2(Array As Byte(0x0),13)) ' i expect the encrypted message ends with a zerobyte. here just logging the position
        Log("Substract binarymessage")
        Dim msgbytes() As Byte = bb.SubArray2(13,bb.IndexOf2(Array As Byte(0x0),13)) ' use the index of the zerobyte to mark the "end". 
        Log("Message Bytes extracted. Length: "&msgbytes.Length)
        File.WriteBytes("E:\","messageraw.bin",msgbytes)
    End If

I guess you now need to decrypt THIS bytes....

PS: bb is a

    Private bb As B4XBytesBuilder

from the B4XCollections lib.

 

[DonManfred]

Any help on working out how to decrypt the message would be great

Do you know the password used for enryption of the message using AES ECB?

 

[aaronk]

Do you know the password used for enryption of the message using AES ECB?

0123456789ABCDEF

 

[aaronk]

I am not 100% sure if this is correct..

I tried using:

Sub Decrypt
    
    Dim hex As String = "33363730424239462F2F312F2F8971C5072144415AEEEE5212B7B13A662F84C59C99E71D68D17F55BF30680DB556E2ADC4C6854877A3C17384C48C132903E66FAA795AD0E3812576F4EC0F5F2C000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000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   
    Dim bb As B4XBytesBuilder
    Dim bc As ByteConverter
    Dim kg As KeyGenerator
    Dim C As Cipher
    Dim BConv As ByteConverter
    
    Log("Length HEX: " & hex.Length) ' logs Length HEX: 16000
    
    Dim raw() As Byte = bc.HexToBytes(hex)
    bb.Initialize
    bb.Append(raw)
    Dim binaryflag() As Byte = Array As Byte(0x33, 0x36, 0x37, 0x30, 0x42, 0x42, 0x39, 0x46, 0x2f,0x2f,0x31,0x2f,0x2f)
    If bb.IndexOf(binaryflag) > -1 Then
        Log("Binary-Flag found")
        Log("Searching for next zero byte (0x0)") 
        Log(bb.IndexOf2(Array As Byte(0x0),13)) 'logs 77
        Log("Substract binarymessage")
        Dim msgbytes() As Byte = bb.SubArray2(13,bb.IndexOf2(Array As Byte(0x0),13)) ' use the index of the zerobyte to mark the "end".
        Log("Message Bytes extracted. Length: " & msgbytes.Length) ' Message Bytes extracted. Length: 64
        File.WriteBytes("c:\","messageraw.txt",msgbytes) ' file attached
    End If

    Dim Key As String = "0123456789ABCDEF" ' this is the same key that encrypted the string that was sent

    kg.Initialize("AES")
    kg.KeyFromBytes(Key.GetBytes("UTF8"))
    
    C.Initialize("AES/ECB/NoPadding")

    msgbytes = C.Decrypt(msgbytes, kg.Key, False)

    Log("Decrypted Plain text: " & BConv.StringFromBytes(msgbytes, "UTF8"))

End Sub

I attached the messageraw.txt file it created.

I am guessing this created the encrypted text I am trying to decrypt, as bytes into that file ?

I then tried to decrypt the message (the bytes from messageraw.txt), but looks like it didn't do it.

I have been told this is working in VB / C# with the following:

' struct that holds the buffer and count of bytes in it and some other stuff
Public Structure XepQData_Class

        Public EPProtocol As Protocol
        Public EP As IPEndPoint
        Public RmtTcpSess As XepTcpObject
        Public RmtUdpClient As UdpClient
        Public IOBuff() As Byte
        Public NumBytesInBuff As Integer

    End Structure

'define a variable from that struct:
    Dim XepQData As New XepQData_Class

' code to pass the message to the aes decryption is as follows:
    Dim crypt As New AES(AESkey)
    crypt.Decrypt(XepQData.IOBuff, XepQData.NumBytesInBuff)

Public Class AES
    Dim cAES As RijndaelManaged

    Public Sub New(ByVal AESkey As Byte())

        Dim InitVector() As Byte = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}

        cAES = New RijndaelManaged
        cAES.BlockSize = 128
        cAES.KeySize = 128
        cAES.Mode = CipherMode.ECB
        cAES.IV = InitVector
        cAES.Padding = PaddingMode.Zeros
        cAES.Key = AESkey

    End Sub


    Public Sub Decrypt(ByRef cBytes As Byte(), ByVal NumBytes As Integer)

        Dim PlainBytes(IOBuffSize) As Byte
        Dim i As Integer
        Dim cDecryptor As ICryptoTransform = cAES.CreateDecryptor()

        ' Skip over the first 13 bytes - they are already in the plain.
        For i = 13 To NumBytes - 16 Step 16
            cDecryptor.TransformBlock(cBytes, i, 16, PlainBytes, i)
        Next

        Array.Copy(PlainBytes, 13, cBytes, 13, NumBytes - 13)

    End Sub


    Public Sub Encrypt(ByRef cBytes As Byte(), ByRef NumBytes As Integer)

        Dim EncryptedBytes(IOBuffSize) As Byte
        Dim i As Integer

        ' pad to a multiple of 16
        Dim numPadBytes As Integer = 16 - ((NumBytes - 13) Mod 16)
        ReDim Preserve cBytes(NumBytes + numPadBytes - 1)
        For i = NumBytes To NumBytes + numPadBytes - 1
            cBytes(i) = 0
        Next i

        NumBytes += numPadBytes

        Dim cEncryptor As ICryptoTransform = cAES.CreateEncryptor()

        ' Skip over the first 13 bytes - they are left in the plain.
        For i = 13 To NumBytes - 1 Step 16
            cEncryptor.TransformBlock(cBytes, i, 16, EncryptedBytes, i)
        Next

        Array.Copy(EncryptedBytes, 13, cBytes, 13, NumBytes - 13)

    End Sub
End Class

“AES” is a class that is defined based on the windows’ RijndaelManaged class (https://docs.microsoft.com/en-us/do...ography.rijndaelmanaged?view=netframework-4.8) which is basically the code as above.

Not 100% sure on how to do the same thing in B4X (I thought I was doing something very similar already but guess not since it's not working).

0123456789ABCDEF is the AES key that was used to encrypt the message.

 

[OliverA]

Something is not right (which can be on my part). But when I encrypt

0000754C//00409D27558D//05.03.10//02.00.44//Hello

using the key

0123456789ABCDEF

the hex output of the encrypted text is

CB517EF65D218017C806EE2D4CF03E1A7859FD08E48E1F1D799E9A8D8593041ED6BC07D879092756A99BE059CA98BFEB45D7BF25523DE1FEA630E97414F8BD97

That's nowhere near

8971C5072144415AEEEE5212B7B13A662F84C59C99E71D68D17F55BF30680DB556E2ADC4C6854877A3C17384C48C132903E66FAA795AD0E3812576F4EC0F5F2C

Also, de-crypting that string (the one starting with 8971C5...) with that key produces the gibberish you see in your code. I even tried (it should make no difference, and it did not) splitting up the packet manually as the VB code that you gave.

Conclusion: We are not using the same key. How are you converting your key to a byte array? Are you sure you are using the key you are posting?

My code:

'Non-UI application (console / server application)
#Region Project Attributes
    #CommandLineArgs:
    #MergeLibraries: True
#End Region

#AdditionalJar: bcprov-jdk15on-160.jar
'        External Libraries:
'            #AdditionalJar: bcprov-jdk15on-160
'            Library can be found here: https://www.bouncycastle.org/download/bcprov-jdk15on-160.jar

Sub Process_Globals
  
End Sub

Sub AppStart (Args() As String)
    Dim joSecurity As JavaObject
    joSecurity.InitializeStatic("java.security.Security")
#if B4J
    Dim jo As JavaObject
    jo.InitializeNewInstance("org.bouncycastle.jce.provider.BouncyCastleProvider", Null)
    joSecurity.RunMethod("addProvider", Array As Object (jo))
#else if B4A
    ' Seems to just work as of Android 5.1 (oldest version I have)
'    Dim jo As JavaObject
'    jo.InitializeNewInstance("org.spongycastle.jce.provider.BouncyCastleProvider", Null)
'    joSecurity.RunMethod("insertProviderAt", Array As Object (jo, 1))
#else
    LOG("ERROR: UNSUPPORTED PLATFORM")
    Return
#End If

  
    Dim hex As String = "33363730424239462F2F312F2F8971C5072144415AEEEE5212B7B13A662F84C59C99E71D68D17F55BF30680DB556E2ADC4C6854877A3C17384C48C132903E66FAA795AD0E3812576F4EC0F5F2C000000"
  
    Dim hexCurated As String = "8971C5072144415AEEEE5212B7B13A662F84C59C99E71D68D17F55BF30680DB556E2ADC4C6854877A3C17384C48C132903E66FAA795AD0E3812576F4EC0F5F2C"
    'Dim hexCurated As String = "8971C5072144415AEEEE5212B7B13A66"
    Dim bc As ByteConverter
    Dim pktHeader() As Byte = bc.HexToBytes("33363730424239462F2F312F2F")
    Log(bc.StringFromBytes(pktHeader, "ASCII"))
    Dim pktData() As Byte = bc.HexToBytes(hexCurated)
    Log(BytesToString(pktData, 0, pktData.Length, "ASCII"))
    Log(pktData.Length)
    Dim kg As KeyGenerator
    Dim C As Cipher
    kg.Initialize("AES")
    kg.KeyFromBytes("0123456789ABCDEF".GetBytes("ASCII"))
      
    C.Initialize("AES/ECB/ZeroBytePadding")
  
    Dim decryptedBytes() As Byte = C.Decrypt(pktData, kg.Key, False)
    Log(bc.HexFromBytes(decryptedBytes))
    Log(bc.StringFromBytes(decryptedBytes, "ASCII"))
  
    Dim textToEncrypt As String = "0000754C//00409D27558D//05.03.10//02.00.44//Hello"
    Dim textBytes() As Byte = textToEncrypt.GetBytes("ASCII")
    Log($"textBytes.Length = ${textBytes.Length}"$)
    Log(bc.HexFromBytes(textBytes))
    Dim textEncryptedBytes() As Byte = C.Encrypt(textBytes, kg.Key, False)
    Log($"textEncryptedBytes.Length = ${textEncryptedBytes.Length}"$)
    Log(bc.HexFromBytes(textEncryptedBytes))
  
    Dim textLength As Int  = textBytes.Length
    Log($"textLength = ${textLength}"$)
    Dim byteBlocks As Int = textLength / 16
    If (textLength Mod 16) > 0 Then byteBlocks = byteBlocks + 1
    Log($"byteBlocks * 16 = ${byteBlocks *16}"$)
    Dim textPadded(byteBlocks * 16) As Byte
    bc.ArrayCopy(textBytes, 0, textPadded, 0, textBytes.Length)
    Log($"textPadded.Length = ${textPadded.Length}"$)
    Log(bc.HexFromBytes(textPadded))
    For x = 0 To byteBlocks - 1
        Dim buffer(16) As Byte
        bc.ArrayCopy(textPadded, x * 16, buffer, 0, 16)
        Dim bufferEncrypted() As Byte = C.Encrypt(buffer, kg.Key, False)
        Log($"bufferEncrypted: ${bc.HexFromBytes(bufferEncrypted)}"$)
    Next
  
End Sub

'Return true to allow the default exceptions handler to handle the uncaught exception.
Sub Application_Error (Error As Exception, StackTrace As String) As Boolean
    Return True
End Sub

 

[aaronk]

Conclusion: We are not using the same key. How are you converting your key to a byte array? Are you sure you are using the key you are posting?

Looks like I was sending the encryption key to remote side (setting the encryption key for encoding the message) wrong. Looks like I sent it as 0123456789ABCDEF and not encoding it as a base64binary key.

Should have sent MDEyMzQ1Njc4OUFCQ0RFRg==
and not 0123456789ABCDEF

Soon as I sent it as the base64 key I could then decrypt the message.

@DonManfred thanks heaps for your help.

 

[DonManfred]

@DonManfred thanks heaps for your help.

you should click on LIKE link on the helpful post(s)

 

[DonManfred]

Soon as I sent it as the base64 key I could then decrypt the message.

Great you got it sorted

 

[avalle]

@OliverA When I try your code above it compiles well but the line below triggers an error:

    C.Initialize("AES/ECB/ZeroBytePadding")

java.security.NoSuchAlgorithmException: Cannot find any provider supporting AES/ECB/ZeroBytePadding

Any idea why?
I compiled with B4J with Java 8 with the following Libraries enabled: ByteConverter 1.10, Encryption 1.10, JavaObject 2.06, jCore 7.50

Thanks
Andrea

 

[OliverA]

Any idea why?

1) You need

#AdditionalJar: bcprov-jdk15on-160.jar

2) You need

Dim joSecurity As JavaObject
joSecurity.InitializeStatic("java.security.Security")
#if B4J
Dim jo As JavaObject
jo.InitializeNewInstance("org.bouncycastle.jce.provider.BouncyCastleProvider", Null)
joSecurity.RunMethod("addProvider", Array As Object (jo))
#else if B4A
' Seems to just work as of Android 5.1 (oldest version I have)
' Dim jo As JavaObject
' jo.InitializeNewInstance("org.spongycastle.jce.provider.BouncyCastleProvider", Null)
' joSecurity.RunMethod("insertProviderAt", Array As Object (jo, 1))
#else
LOG("ERROR: UNSUPPORTED PLATFORM")
Return
#End If

1) That's the Bouncy Castle library that you need for ZeroPadding. Look at the code above for the link for that library. Put it in the Additional Libraries folder
2) That's needed to load/enable the Bouncy Castle library
The code runs fine on my end.

 

[avalle]

I fully copied your sample so everything was already there.
I also had the BC Jar in the External Library folder.

The issue indeed was that #MergeLibraries must be set to False

 

[OliverA]

The issue indeed was that #MergeLibraries must be set to False

Odd. Not here. Neither Amazon's Corretto (JDK 1.8.0_212), nor the JDK 11 provided by @Erel do this on my end (notice the code above has #MergeLibraries: True). May be due to another issue (may be worth another post?). I actually still had B4J 6.8 running here and updated to 7.51 without any changes in results (meaning, it just works here).