How to pass Java signed byte into VB6 unsigned program

> Hello everyone

>

> I need to build a client in Java to talk to a VB6

> server. I am the point to pass the encrypt username

> and password into the server. The VB6 code for the

> encryption is

>

> Crypt = Crypt & Chr(Asc(Mid$(Text, Len(Text) - X + 1,

> 1)) Xor &HA3)

> My Java code is

> cryptOutput = cryptOutput + ((char)(((int)

> input.charAt(i)) ^ ((byte)0xa3)));

It was a long time ago since I wrote something in VB, but the VB code and the Java code doesn't do the same thing(?).

kajbja at 2007-7-12 17:30:52 >

> The server doesn't seem to understand my username and

> password. I highly suspect the reason being that Java

> byte is signed and VB6 is unsigned.

>

Whether a byte is signed or unsigned makes no difference UNLESS it is being used in an arithmetic operation such as multiply, divide or remainder. Operations such as add, subtract, OR, AND, XOR give exactly the same bit patterns regardless of the signed or unsigned nature of the arguments.

sabre150a at 2007-7-12 17:30:52 >

> Whether a byte is signed or unsigned makes no

> difference UNLESS it is being used in an arithmetic

> operation such as multiply, divide or remainder.

> Operations such as add, subtract, OR, AND, XOR give

> exactly the same bit patterns regardless of the

> signed or unsigned nature of the arguments.

You are right! But I dont know when the byte then converted to a character, would it make a different?

Because the server keeps rejecting the password I send it... And of course, the password is correct.

BuggyVBa at 2007-7-12 17:30:52 >

I send it using

PrintWriter out = new PrintWriter(soc.getOutputStream(), true);

out.println(msg);

with soc being a Socket class instance

As I said in the post above, I can send normal string like "hello" and the server understands it. But with the encrypt string then it cant :(

BuggyVBa at 2007-7-12 17:30:52 >

When you click on your screen name you get a page that has information about your account and a list of your most recent posts.

> At this point, I dont think it's the crypt function

> anymore... Even more debug work to do...

>

If your crypt function still looks like what it is above then yes, it is an issue. You can verify this by passing it some simple data you can check by hand.

jsalonena at 2007-7-21 21:50:32 >

> My way of doing it is creating a string using

But in Java strings contain characters, not bytes?

Have you tried passing the bytes using an array instead of a string? That's pretty much the only way to guarantee that the bytes are sent as you see them there.

By the way, in Java there are hexadecimal integer constants, for example you can write FD as 0xfd. There's no reason to use Integer.parseInt for this.

> then send this string to the server for

> authentication. Yet the server still refuses my

> connection.

You are saying you get "connection refused?" That is a networking problem. It means you are not allowed to connect at all, most likely because no service is running on the port you are trying to connect to or because there's a firewall or proxy that refuses the connection.

> PS: The server understand me if I send simple string

> like "0123" (I know this because the server has 2

> step authentication, first step is matching a simple

> string, 2nd step is receiving and decoding the user

> name and password... I passed the first step).

OK, so it works with the String "0123." With which string does it not work? The secuence of bytes that you quote?

jsalonena at 2007-7-21 21:50:32 >

> But my crypt("0123") gives different result then Crypt("0123") at the server side.

Do you know what the server's version returns?

Are you sure what the constant you XOR against is supposed to be? I have seen you use A2, A3 and A5.

Have you tried the different implementations of crypt we have shown? In your most recent post there's a problem with bytes in the range 80-FF. They have a negative sign, and when you convert one such byte to a larger type, its sign bit is extended to the higher bytes. This way the byte -42 will come out as -42 and not some positive number. This will cause problems when you cast a negative byte to char: the byte A5 for istance will be converted to the character U+FFA5, which is "HALFWIDTH HANGUL LETTER NIEUN-CIEUC" in the unicode spec. Most likely this is not what the server does!

Because of this issue it's better to not cast anything to byte or use the byte datatype in your implementation of the "crypt" method. Or alternatively it's better not to use the char datatype. It sounds like your protocol involves passing arbitrary binary data, not text, so you should rather use arrays of byte instead of strings.

jsalonena at 2007-7-21 21:50:32 >

> That's why I suspect some byte differences in Java

> and VB that causes the problem...?

No, the difference is between character encodings as I tried to hint in the other thread. The Chr and Asc funtions in VB use what ever code page happens to be configured in Windows, while Java uses the international Unicode standard. It appears to be that your VB code is currently using Windows-1252. On a different computer it might use some other encoding and have different output.

The character '0' corresponds to the code point 48 in both Windows-1252 and in Unicode. When you pass this character to your crypt function, it's code point gets XORed with 0xA5, producing the decimal number 149.

Now, Java converts the number 149 to a character by looking it up in the Unicode standard. From Unicode's table we see that it corresponds to the unprintable control character U+0095, also known as "Message Waiting" as you can verify in http://www.unicode.org/charts/PDF/U0080.pdf This character is unprintable so it can't be seen in your output window.

VB converts the number 149 to a character by looking it up in the Windows-1252 character set. From Microsoft's code table http://www.microsoft.com/globaldev/reference/sbcs/1252.mspx we see that this number corresponds to the bullet character U+2022.

Now the question is do you really need to work with characters at all? Clearly you are dealing with binary data and not text. You should use arrays of bytes.

jsalonena at 2007-7-21 21:50:32 >

Just so everyone who ever has similar problem to me, this is how I do my new crypt function

public static String crypt(String input)

{

int i = 0;

int len = input.length();

int a5 = 0xa3;

byte[] temp = new byte[input.length()];

for (i = 0; i < input.length(); i++)

{

// Original VB code: Crypt = Crypt & Chr(Asc(Mid$(Text, Len(Text) - X + 1, 1)) Xor &HA3)

temp[i] = ((byte)(input.charAt(len - i - 1) ^ a3));

//cryptOutput = cryptOutput + ((char)(((byte)input.charAt(len-i-1)) ^ ((byte)a5)));

//cryptOutput = cryptOutput + ((char)intToPseudoUnsignedByte(((byte)input.charAt(len-i-1)) ^ ((byte)a5)));

}

return (new String(temp));

}

Again, many thanks to jsalonen and martin@work!

BuggyVBa at 2007-7-21 21:50:32 >