# 1 out of n oblivious transfer

So I read some stuff about oblivious transfer and came a ross that 1 out of 2 OT can be used as a black box to build 1 out of n OT. At first it seemed trivial just feeding in 4 messages and 2 chooser bits but then I realized it's not that trivial since it doesn't guarantee security. How is 1 out of 2 OT used to build 1 out of 4 OT if we can use 1 out of 2 OT as a black box?

• However, if L is the minimum length over the n messages, then it's significantly harder when the 1-out-of-2 OTs must be for strings of less than L$\cdot$n/2 bits. ​ (I don't know of any nice way of handling that restriction.) ​ ​ ​ ​ – user991 Oct 21 '16 at 12:17
• @RickyDemer Sorry; I didn't understand what problem you are referring to. The 1-out-of-2 OTs I am referring to are for strings of length $n$ where $n$ is the security parameter (for transferring keys). If you are asking what can be done with lower communication complexity, then I agree; this is an interesting problem. – Yehuda Lindell Oct 23 '16 at 12:45