# Tag Info

## Hot answers tagged cryptanalysis

4

Usually cryptographic strength is given as the effective strength in bits of a security primitive. This is related to the amount of tries necessary to break a primitive. So for AES-128 the effective strength is about 126 bits. The number of bits is of course directly related to the number of tries required to perform an attack. This is often given as a power ...

3

When seeing clearly through all the cube "magic", one recognizes the following: All the cube operations are just key-dependent bit permutations. Therefore, the whole cipher is a sequence of key-dependent permutations and XORs with key bits. This admits an algebraic description: For all keys, there is a permutation matrix $A\in\mathbb F_2^{512\times512}$ and ...

3

In your example, $Encryption_1$ is $\textsf{AES}_{CTR}$ and $Encryption_2$ is $\textsf{Salsa20}$. Then, the encryption method you are proposing is $Encryption_1(Encryption_2(plaintext))$, which is in fact a cascade of stream ciphers. Note that, because you simply XOR the streams, this cascade cipher commutes, that is, you will have the same result if you use ...

3

Asmuth and Blakley provided a proof that, assuming the keys for each cryptosystem are chosen independently, breaking their composite cryptosystem is at least as hard as breaking the hardest part of either. [1] Building on their work, cascade ciphers have been shown to in fact be harder to break than the hardest part of either. Admittedly, what you're ...

2

No, of course this is not a good idea. CLCG's were not designed for cryptographic purposes, and there's no reason to expect them to provide cryptographic security. Why would you do that, when there are perfectly good cryptographic-strength PRNGs available? As one simple example, if you use a CLCG built out of two linear congruential generators with the ...

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"Will such security always remain secure?" No. $\:$ In particular, quantum computers will break RSA and elliptic curves. Has it been mathematically proved that these algorithms can not be cracked, or is it a possibility? It is a possibility, since a very-practical algorithm for the Boolean satisfiability problem would be enough to break essentially all ...

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Maarten appears to make it look like it's an impossible (or, at least, an exceedingly difficult task) to recover the two plaintexts. Indeed, if you literally know nothing about the plaintexts, it can be difficult. However, you typically have a reason you are interested in the messages, and hence often have a clue as to what language they might be. If the ...

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Unless you know more about the plaintexts two ciphertexts may not convey all the information to reconstruct the two messages. For instance if you have a bit 0 then both messages may contain a 0 at that location or they may both contain a 1. If you have a 1 message 1 may contain a 0 and message 2 may contain a 1, but it could also be the other way around. ...

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The current way of implementing a (symmetric) cryptographic algorithm as a white-box is to implement it as a network of encoded lookup tables (a good white-box will also have so called 'external encodings' applied, but I'll skip these for now). In this case however, a network of tables is not required (one table will do) and as a result encoding the tables ...

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You say are asking as a learning exercise, to learn how to invent ciphers. The way to learn that is not to try to invent some block cipher and then ask others to break it. The way to learn is to learn cryptanalysis, by breaking other ciphers. See Schneier's self-study course on cryptanalysis for one good resource.

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