Cryptology plugin

Comments and discussions about Harry's Filters
sow

Cryptology plugin

Postby sow » Wed Dec 11, 2002 7:00 pm

I do not understand how this works.

With these Encryption/Decryption Filter you are able to encrypt/decrypt picture and video files. All 7 Encryption methods use a 64 bit key. But if you combine e.g. 3 of them you have a 194 bit key.

Since if I apply two 64 bits encyptions it is twice as hard to break as one
64 bit encryption. Which is the same as a 65 bit key. So encrypt threetimes with 64 bit is the same as 65 1/2 bit if we had half bits.


sow/

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Postby HaraldHeim » Thu Dec 12, 2002 9:32 am

When you apply one of the Cryptology filters the image data is encrypted with the values from the eight sliders. These eight sliders can have values from 0 to 255. That's 8 bytes or 8 x 8 bit = 64 bit. When you apply the filter with the same slider values again to the encrypted image or video, it is decrypted.

If you apply two different 64 bit encryptions, it isn't the same as a 65 bit encryption. A 65 bit encryption would mean 8 sliders ranging from 0 to 255 plus an aditional slider which can be set to 0 or 1.

But if you apply two different Cryptology filters each with 8 sliders, it is as if you applied one Cryptology filter with 16 sliders. So 16 x 8 bit = 128 bit.

The reason for this is that if you try to decrypt the image data by trial and error you would first have to decrypt the 64 bit with the one encryption algorithm and then decrypt the other 64 bit with the other algoritm. The problem is however that you don't know how the image should look like after the first decryption. So theoretically it is much stronger protected than 128 bit. Of course you could try to break the encryption in one step by developing an algorithm that is average of both algorithms, but that would need even more time. Besides you don't know which and how many algorithms were used and in which sequence. So that again makes several more bits.

While decrypting by trial and error a decryption program creates thousands of decrypted variations per second. So you can't have a human tell the computer which of the variations is the correct one.

When you try to decrypt a text message at 128 bit, it is quite easy to program a function to check if the decrypted text variations make any sense or not.

But when decrypting image data by trial and error you don't need to just decrypt a few words or lines to find the key as is the case with encrypted text. You have to decrypt at least a large part of the image which takes much more compution time. Besides a function that checks if the decrypted image data makes sense, needs again even much more compution time.

So in that respect the 128 bit are more like 1024 bit when compared to encrypted text messages.

On the other hand a lot of the decrypted variations are quite close to the original. But of course a computer program can't recognize that. So if you are just interested to know what the decrypted image shows and don't want to fully restore it, it might prove even more effective to have some people produce and check decryption variations by hand. That would probably still take several hours or days.

Anyway, who would invest so much time on frustrating work if the encrypted image data isn't of immense importance.


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