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Basically you are talking about “superencipherment”. This has a long history in cyptography, but it eats up space like crazy. Your observation of PK cyptography being vulnerable is true. Solving 'Prime' would bring the house down.


2

They rely on problems not so different as you might think. They are based either in the factoring problem or in the discrete logarithm problem, which have a deep connection between each other. Once you have an algorithm that can efficiently solve one, you most likely would be able to adapt it to reproduce an answer for the other in polynomial time. Thus ...


6

I don't know about computing things in parallel, so I will ignore that part of the question. First, please note that the encryption algorithm is rarely the the weak point of the security. It is far more likely that you will have problems with the implementation, some spyware installed on your computer, a weak password (If you use qwerty as your password, ...


0

It seems the result is specifically for multiple encryption with a single cipher (like in 3DES). It probably applies for different ciphers as well, but key and block sizes would need to be equal. You might get a lower bound by using the minimum key size, but don't quote me on that. However, I don't think this is really relevant for a practical ...


2

What you propose is called Double Encryption. With two independent keys, it is vulnerable to meet-in-the-middle attacks as described in another comment. I just add that this attack can be performed almost memoryless. Details are in the answer to similar question about Double-DES.


5

I won't say someone would be able to break it 'easily'; however it won't be anywhere as difficult as with a true 128 bit cipher (or even 120 bit cipher; your construction ignores 8 of the key bits). Here's an outline of how the attack would work: we assume we know the plaintext and the ciphertext, and are trying to recover the key. When we do is encrypt ...


3

The actual security would probably be about 65 bits. A meet-in-the-middle attack can be used to find the keys of both ciphers in less time than naive brute force. The attack would decrypt the ciphertext with all the 64 bit l keys of the outer cipher, encrypt the plaintext with all the 56 bit keys of the inner cipher, then look for matches. It only requires ...


7

EEE and EDE are effectively the same in terms of security. EDE is used because it is "backwards compatible:" by setting all three keys to be the same, it becomes equivalent to just single encryption (E) with that key.


1

Two things to consider: encryption and authentication. In general you can only say that a cascade of ciphers is as secure as its weakest link. If the encryption in NaCL had a side-channel attack, it might leak information about the plaintext, whether or not the ciphertext is sent through TLS. Authentication, on the other hand, is additive. If you can ...



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