Re: An hash-Encryption algorithm



Kristian Gjøsteen <kristiag+news@xxxxxxxxxxxx> wrote in news:0hesa3-
abu1.ln1@xxxxxxxxxxxxxxxxxxxxx:

> Neo <neoscandal@xxxxxxxxx> wrote:
>>Kristian Gjøsteen <kristiag+news@xxxxxxxxxxxx> wrote in
>>news:uo7qa3-j1m1.ln1@xxxxxxxxxxxxxxxxxxxxx:
>>
>>> You are getting somewhere. Now you are just missing a somewhat
>>> subtle point: Encrypt two messages P1(1,...,n) and P2(1,..m) with
>>> the same key K(0). Find the expression for the first ciphertext
>>> blocks C1(1) and C2(1) and compute their exclusive ors. What do you
>>> find?
>>>
>>
>>Hmm.. according to my design that would imply ( consider
pa,ca,pb,cb)...
>>
>> ca xor cb = (pa xor (ka(0) + salt1)) xor (pb xor (kb(0) + salt2))
>>
>> |_______________________| |______________________|
>> ciphertext1 block 1 ciphertext2 block 1
>>
>>I dont see how this may be simplified...
>
> Now you have this thing called "salt" in there. It wasn't there
> yesterday!

It was!
------------copypaste start------------
>>K(0) = user entered key + salt (which is added plainly into the
>>encrypted file header)
>>
>>K(1) = MD5(K(0))
>>
>>C1 = K(1) XOR P1
>>
>>for n = 2 onwards..
------------copypaste end--------------
>
>>Note that salts are generated at the time of encryption .. and
>>thoeretically no two salts would match. Thus no two encryptions would
>>use similar keys during the first round.
>
> Exactly. You need to be a bit careful about how you add your salts to
> the message. The above looks a bit shaky.

Hmm.. what would be a "non-shaky" version of adding the saly. XORing
perhaps?

>
> Your "salt" is commonly called a nonce or iv in this context:
>
.