[ExI] The second step towards immortality

[Martin Sustrik]

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On 02/01/14 23:05, Adrian Tymes wrote:

>> AFAIU, what you get by such observation is some number of 
>> plaintext-cyphertext pairs (not of your choosing).
> 
> No, you get the decryption function, keys included.  Ain't no
> cipher that can keep it secure at that point.  (This does exclude
> ciphers where there is no decryption algorithm, but there needs to
> be one in this use case.)

I see, you mean reverse-engeneering the decryption algo. As already
said, rigrous crypto analysis would be needed, but my gut feeling is
that reverse-engineering shouldn't be possible.

The conceptual model for the proof can be something like this:
Attacker sees the output and can track the program back so that he
sees how the output was generated. However, given that processing is
done in encrypted form, what he sees is millions of randomly-looking
operations on randomly-looking data. His goal is to modify the program
in such a way that a different output is generated (say a valid
bitcoin transfer to his account). Thus, what he is going to do is to
alter pieces of the program to see what happens... And the formal
proof of the scheme should prove that such endeavour would basically
be equivalent to brute-forcing the cypher, i.e. would require 2^128
attemps or somesuch.

In any case, I believe that we have drifted too far away from the
original topic and this discussion would fit better to some
crypto-related mailing list.

Martin
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