# Tag Info

## Hot answers tagged oblivious-transfer

7

### Why use a 1-2 Oblivious Transfer instead of a 1 out of n Oblivious Transfer?

Oblivious transfer is mostly studied as a theoretic construction, as it is an important component in achieving interesting protocols (like secure two-party computation and secure function evaluation). The interest in 1-2 OT is that it is a minimal definition theoretically, and most results that limit themselves to 1-2 are designed to improve some basic ...

6

### Why use a 1-2 Oblivious Transfer instead of a 1 out of n Oblivious Transfer?

the securty of 1-n OT is a function of the security of a 1-2 OT. So in analysis it is easy to use 1-2 OT for security proofs. A 1-n OT is essentially a multiple run of a 1-2 OT. (somewhat like a byte is made of 8 bits) So IMO the question is like asking why use bits when you can use bytes for communication. [it depends on the application]

3

### Randomized Oblivious Transfer

No, as written, your protocol doesn't work -- the problem is that Bob is supposed to be allowed to choose $b$, your protocol selects a random one for him. However, it is close -- here is a modification that I believe does work: First, suppose Alice has her values $(x_0, x_1)$, and Bob has his bit $b$. They run their Random functionality R, and so Alice ...

2

### Are there any differences between PIR, oblivious transfer and differential privacy?

The other answers are good but I thought I would systemize the differences with a single example. Say Bob has a database with 10 entries of the form {name, salary} and Alice would like to query it. With PIR, Alice can retrieve any entry or entries of her choosing (say the 8th entry) without Bob learning which one. The trivial PIR is Alice just retrieves ...

2

### Are there any differences between PIR, oblivious transfer and differential privacy?

In differential privacy the concern is to protect the privacy of a single row of the database. Informally, the DP concept says that everything that can be learned from the database could be learned without access to that row. In a more technical sense, a mechanism respects this property if the distribution of the answers is almost identical (in a very strict ...

2

### Are there any differences between PIR, oblivious transfer and differential privacy?

There is a slight distinction between PIR and OT. From Wikipedia: PIR is a weaker version of 1-out-of-n oblivious transfer, where it is also required that the user should not get information about other database items. In other words, OT is stronger in that the receiver only gets what is requested. Differential privacy is new to me, so I'll read up ...

2

### Is there a group of prime order which could fit the CT-Computational Diffie-Hellman assumption?

The usual technique for having a group of prime size $q$ is to work modulo a prime $p$ such that $q$ divides $p-1$. The target group is then the subgroup of $q$-th roots of $1$ in $\mathbb{Z}_p$. To build such a group, first choose $q$, then selects random values $r$ until you find one such that $p = qr+1$ is prime. This is the way it is defined in the DSA ...

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