6

Secure cryptographic protocols that can be executed by humans are considered in this paper: http://link.springer.com/chapter/10.1007%2F3-540-45682-1_4 (Hopper and Blum, "Secure Human Identification Protocols"). Reading the abstract, it sounds like they don't fully solve the problem. I suspect a satisfying solution is not known, but if you want to look into ...


5

I believe you are talking about the existence of information-theoretically (unconditionally) secure key agreement schemes. You can prove that such schemes cannot be achieved with only authenticated channels from Alice to Bob and Bob to Alice. Nevertheless, if Alice, Bob, and Eve are in possession of some sort of correlated randomness, then it may be ...


2

No. What is a key exchange? Both parties have a private random sequence (that they've generated for themselves) plus possibly some public random sequence (that the eavesdropper can also see). Then they want to communicate so that the other party learns something about the probability distribution of their sequence that the eavesdropper doesn't. But whatever ...


2

The Wikipedia page on "Post-quantum cryptography" provides a list of proposals for PKE resistant to quantum attacks. Quantum algorithms can solve DL in finite abelian groups (as well as a few nonabelian and infinite abelian ones), so they get very close to the spirit of the question you are asking. The learning with errors problem mentioned by one of the ...


2

The Cæsar and Vigenère cipher are breakable. While some private key ciphers such as RC4, SNOW and SNOW2 (which are quite safe if used properly) can in principle be used by hand (albeit very slowly), public key ciphers usually require modular exponentiation of (very) large integers, which seems out of reach even for a determined individual. (Rabin's cipher ...


1

Let me elaborate on @domotorp's answer, since a natural first objection might be, "We're talking about secure key exchange -- who said anything about requiring randomness?" The point is that public-key cryptography requires an asymmetry in the difficulty of computing a function: it's supposed to be hard to compute except if you have a special "key". It's ...


1

I am not an expert on this subject, but it looks to me like the question makes some assumptions that may or may not be valid. The question claims that the Needham-Schroeder-Lowe protocol is SK-secure. However, I don't know whether there is any known proof that Needham-Schroeder-Lowe is SK-secure. The paper that was cited in the question does not appear to ...


1

Check Supersingular Isogeny Key Exchnage for some nice work on a Diffie-Hellman like Key Exchange based on isogenies between supersingular elliptic curves. This will compute computationally secure key. The authors mention that even though the key exchange is secure it will most likely be interesting purely for research/ pedagogical reasons. There also is a ...


1

If we look at a related topic, namely interactive identification protocols, we get a problem that has been well-studied. Unfortunately there are no known protocols that are both secure (against attacks by computers) yet where ordinary humans can reasonably execute the protocol mentally without the aid of the computer. There have been lots of proposals, but ...


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