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Editing a cipher

Hello,

My scenario is as follows:

I have a program that generates ciphertext, message-hash, key pair, (RSA) and I need to model a simple attack.

Everything is fine, but one of the attacks I am having trouble with: I need to somehow 'modify' the byte array containing the ciphertext and prove that the receiver of the message propper will be able to detect the interference.

Whats the best way to do this though? if I access elements like:

array[4] = (byte) 0x0;

then I run into 'data must start with a zero' padding errors. Which, although alerting the receiver to a problem, avoids the true aim of my test, -hash authentication.

My only workaround in mind is to have this 'adversary' create his own cipher from scratch based on his own message.

Thanks in advance,
Matt
Dec 16 '08 #1
2 1325
Nepomuk
3,112 Expert 2GB
Hi Matt!
Our Posting Guidelines, Things that are generally unacceptable state:
Things that are generally unacceptable
  • ...
  • Posts containing any information or questions on how to hack or crack or produce code with some other malicious intent. Note however that security topics whose intent is generally not malicious but rather is discussing methods of improving security are allowed.
  • ...
Now, although I'm quite happy to believe your intent is not harmful, this information could clearly be used in a malicious way except if you are accessing them from the same program. Therefore I'm sorry, but we're not going to help you here unless it can certainly not be used in a malicious way. If however you post some of your code that proves both are from the same program, we might be able to help.

Greetings,
Nepomuk (Moderator)
Dec 16 '08 #2
Oh dear, makes sense.

Time is short so I've resorted to my backup plan and so my modelled adversary will just cipher his own message and overwrite the original cipher; I presume that no matter what I did, the resulting effect on the program would have been failure to decrypt, resulting in error of sorts.

I suspect it will be enough of a proof.

Thanks for your time and the time of all those that read my problem.

God Speed.
Dec 17 '08 #3

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