How to make an Encode function based on this Decode function?

Question

How to make an Encode function based on this Decode function? I got the source code for the Decode function on the internet but I need the Encode function.

All my attempts to make it failed and the original coder isn't available at the moment.

The (original) code:

byte Decode(byte EncodedByte)
{
    EncodedByte ^= (byte)194;
    EncodedByte = (byte)((EncodedByte << 4) | (EncodedByte >> 4));
    return EncodedByte;
}

score 4 · Answer 1 · answered Sep 15 '10 at 13:45

4

Just some quick back of the napkin coding the answer should be

byte Encode(byte DecodedByte)
{
    DecodedByte = (byte)((DecodedByte << 4) | (DecodedByte >> 4));
    DecodedByte ^= (byte)194;
    return DecodedByte;
}

Also I agree with Alex this is a trivial Encryption method. Anyone who knows the algorithm can trivially decrypt your message. I would not rely on it for any sensitive information and if this is code for public use some countries have laws that data must have some form of encryption. If I was a judge for the person suing you for a data breach I would call this more of a obfuscation technique then a encryption technique.

answered Sep 15 '10 at 13:45

Scott Chamberlain

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Thank you, Henrik was first though. +1. – lesderid Sep 15 '10 at 13:48
1

Came up with the same myself - ran a unit test on all possible bytes and it successfully works (as if you had a doubt ;)) – Rudu Sep 15 '10 at 13:50
1

Henrik and I posted about 15 seconds apart. If I had not changed my EncodedBytes to Decoded bytes I would have been first ;p – Scott Chamberlain Sep 15 '10 at 13:51
1

About your edit, I agree. I'm dealing with a file format that I didn't make so I can't really do anything about it. – lesderid Sep 15 '10 at 13:51
Sorry for not accepting your answer. But you've got 3 upvotes. :P – lesderid Sep 15 '10 at 13:54

score 1 · Accepted Answer · answered Sep 15 '10 at 13:44

1


byte Encode(byte EncodedByte) 
{ 
    EncodedByte = (byte)((EncodedByte << 4) | (EncodedByte >> 4)); 
    EncodedByte ^= (byte)194; 
    return EncodedByte; 
}

answered Sep 15 '10 at 13:44

Henrik

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I didn't knew it's this easy. Thank you very much! – lesderid Sep 15 '10 at 13:47

score 0 · Answer 3 · edited May 23 '17 at 12:01

0

Why do not you use normal encryption/decryption functions of c#?

Encrypt and decrypt a string

edited May 23 '17 at 12:01

Community

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answered Sep 15 '10 at 13:43

Alex Reitbort

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Why would I? This code is converted from C++ and this way works perfect. Also, I have no idea how I would convert this to 'normal encryption/decryption functions'. – lesderid Sep 15 '10 at 13:44
1

This isn't very helpful - he's likely dealing with data created through some other process that has to use this approach. – Rudu Sep 15 '10 at 13:49
Indeed, see Scott's answer's comments. – lesderid Sep 15 '10 at 13:51

How to make an Encode function based on this Decode function?

3 Answers3