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Re: Cartcam block cipher - C implementation

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Oleg Khovayko

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Oct 22, 2008, 6:50:19 AM10/22/08
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After first look, in ~3 minutes, I see following weaknesses:

1. Weak keys:
If all key values are x*32, then in the all iterations,
rotation shift values (mod1, mod2) always will be 0.
Hence, rotation block will be not work for these weak keys.

2. Obvious:
If key is "all 0-s", and plaintext also "all 0-s", cyphertext also will
be "all 0-s".

3. In the cipher, you make 128 rounds, and in the each round you make
addition/subtraction.

Do you know, code:

for(i = 0; i <= 127; i++)
x += y;

absolutely equals to:
x += y << 8;

Make attention, lowest byte of x is unchanged after this operation.

This is serious weakness, and I assume, linear cryptanalysis will be
effective against this cipher.


Thank you,

Oleg H.

Ertugrul Söylemez

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Oct 24, 2008, 1:34:46 AM10/24/08
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Oleg Khovayko <"[my_last_name]"@gmail.com> wrote:

> Do you know, code:
>
> for(i = 0; i <= 127; i++)
> x += y;
>
> absolutely equals to:
> x += y << 8;

x += y << 7;

> Make attention, lowest byte of x is unchanged after this operation.

Almost. Its highest bit could be changed.

Greets,
Ertugrul.

--
nightmare = unsafePerformIO (getWrongWife >>= sex)

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