How is HexToBase64 used? - GameCreators Forum

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traumvogel

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Posted: 19th Jan 2018 23:07

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Can someone give an example for using this function?
I know that the input must be a hex encoded string: How is this input interpreted? Always two hex characters interpreted as one byte?

I want to xor encrypt a string with a key. Problem is that if a character of the string to be encrypted is the same character as the current character from the key being used the resulting code is 0 and this cannot be put into the result encoded string because this is automatically interpreted as end of the resulting encoded string even if it should be continued with more data. Does someone understand what I mean?

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puzzler2018

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Posted: 19th Jan 2018 23:17 Edited at: 19th Jan 2018 23:18

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XOR -
11001100
= 00110011

Inverts the binary diits

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puzzler2018

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Posted: 19th Jan 2018 23:32

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so encrypting with a key like decimal 129 which is ultimately binary 1000001

XOR 129 with any character there after

ASC(32) = 00100000
XOR with
128 = 10000001
= 10100001

Keeps the 1's in the binary code where there is only 1 in either two of the binary
If both are any 1s in the two would result in 0

ASC(130) = 1000010
XOR with
127 = 1000001
= 0000011

Still mind boggled !

https://en.wikipedia.org/wiki/Bitwise_operation

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traumvogel

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Posted: 19th Jan 2018 23:53

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Thanks! In the meantime I found out. HexToBase64 takes pairs of hex characters.
My encryption function now looks like this:

+ Code Snippet

function encryptString(input$ as string, key$ as string)
	output$ = ""
	
	// Get the encryption code length
	codeLen = Len(key$)
	
	//loop through the bytes and encrypt them
	codeCounter = 0
	for n = 1 to Len(input$)
		inc codeCounter, 1
		if codeCounter > codeLen then codeCounter = 1
		coded = Asc(mid(input$, n, 1)) ~~ Asc(mid(key$, codeCounter, 1))
		if Len(Hex(coded)) = 1
			output$ = output$ + "0" + Hex(coded)
		else
			output$ = output$ + Hex(coded)
		endif
	next n
	output$ = HexToBase64(output$)
endfunction output$

Works as intended.

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puzzler2018

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Posted: 19th Jan 2018 23:56

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That will work

Great stuff

ps. dont use the same key through any encryption - can be hacked with seconds

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traumvogel

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Posted: 20th Jan 2018 18:28

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I know this solution is weak. I use it to transport passwords for user authentication using the AppGameKit multiuser networking functions from client to server. Currently it is only a little chat app experiment. But there has to be user authentication and it is really a pity that the AppGameKit multiuser net functions do not use SSL... Maybe there will be some better encryption possibilities in the future?

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Qugurun

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Posted: 22nd Jan 2018 08:49 Edited at: 23rd Jan 2018 12:17

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traumvogel, please show your decryption function. Thx!

What does this symbol do?

https://www.instagram.com/qugurun/

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Phaelax

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Posted: 24th Jan 2018 13:49

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mid will return a substring of input$ starting at Nth position and contain a length of only 1 character. ASC will then convert that string character into its integer ASCII value (see http://www.asciitable.com/).

The second line does the same thing just with different values. And the double tildes (squiggles) is the bitwise XOR operation.

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traumvogel

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Posted: 27th Jan 2018 00:24

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The decryption function I implemented not in AppGameKit but in PHP. Rather easy there:

+ Code Snippet

function xor_string($string, $key) {
    $str_len = strlen($string);
    $key_len = strlen($key);

    for($i = 0; $i < $str_len; $i++) {
        $string[$i] = $string[$i] ^ $key[$i % $key_len];
    }

    return $string;
}

I have no decryption function available in AGK. I am not sure how to implement it. The problem is the non-existance of binary strings like in PHP, that is a AppGameKit string cannot contain a zero "0" character.

But what I would like much more is a more secure encryption function. XOR is way too weak...

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