# Tag Info

3

In here, it is 1-2 oblivious transfer meaning that for each $i$, the receiver gets $A'_{i1}$ or $A'_{i2}$ but the sender does not know which. The length of the elements $A'_{ij}$ is not important as long as you choose a correct oblivious transfer protocol.

0

We consider a server $S$ and a bunch of users $U_1, \dots, U_n$. What you want: Users should be able to send queries to the server and receive replies. The users should be able to register identities with the server. Any reply $m'$ that a user accepts as coming from the server in response to a query $m$ from that user, really came from the server in ...

3

The scheme is secure against chosen-plaintext attacks up to $2^{|R|/2}$ queries. Indeed, given this number of queries, it is likely that every encryption call yields a new value $R$, which has never used as part of the permutation input. However, when this bound is reached, some problems occur. Suppose you encrypt the same message $M$ as many as ...

5

Given: The attacker can call PRP() and the inverse function prp() on any message of his choosing. PRP is a pseudorandom permutation indistinguishable to the attacker from a random permutation. Assuming R and K are "sufficiently large", perfectly random, and never leaked to the attacker -- in particular, during a chosen-ciphertext attack, the decryptor only ...

2

Your protocol is good (assuming an honest-but-curious adversary model). As DrLecter pointed out, each party will need to publish their sum of shares. To recover the answer, each party then simply xors all published values.

0

One potential consideration is that combinations of security principles may have unintended vulnerabilities. This is not to say they you cannot combine such approaches, but most combinations have been well studied and then recommended by trusted 3rd parties (academic or governmental or institutional). While not in the same domain has hash functions, the ...

2

One potential issue with this strategy revolves around compliance. You might be subject to various regulations (such as Government/DoD regulations) that prohibit unsafe hash functions. You might have a very unpleasant experience trying to explain to the audit team how using MD5 as part of user authentication does not mean "the terrorists win!"... In the best ...

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