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9

I believe the concept you're looking for is a cryptographical hash. This is a function that takes a (potentially) long input, produces a short (fixed length) output, and for which it is impractical to find two different inputs that generate the same output. It is a fixed function; anyone (including your customer) can generate a hash for any input. How it ...


6

In whitebox cryptography the attacker is supposed to have access to every detail of the computation and the goal of this implementation is to protect the key, to -usually- avoid it is used on a classical no-whitebox implementation on a different platform. The goal is that an attacker having access to the whole computation and intermediate values cannot ...


3

Let $a$ and $b$ be the numbers emited rsp. by person A and person B. $E(x)$ means encoded form of $x$. $E(a)$ and $E(b)$ are publicly known, right? Note that if person A knows $a$, $E(a)$, $E(b)$ and person B knows $b$, $E(a)$, $E(b)$ and it is possible to calculate $a+b$ from $E(a)$ and $E(b)$ (that is what you want to do, right? So it must be possible) ...


2

This is not very secure. You directly leak the symbol distribution, because only the order of symbols changes. For short enough messages this allows easy decryption – e.g. "dr olllWeoH" is quite clearly "Hello World". Even for long messages or binary values, the fact that you leak e.g. a crucial byte may be enough. You also have not defined how the same key ...


1

In cryptography it is common to reason about the probability of an event in the probability space of all the random choices made (i.e. the random bits generated) during an algorithm's execution. So, in this description, "over the random coins of HGD" means the probability is computed over the probability space defined by the random bits used during HGD ...



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