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**2013/690**

**Title:**

Obfuscation ==> (IND-CPA Security =/=> Circular Security)

**Authors:**
Antonio Marcedone, Claudio Orlandi

**Abstract:**

Circular security is an important notion for public-key encryption schemes and is needed by several cryptographic protocols. In circular security the adversary is given an extra ``hint’’ consisting of a cycle of encryption of secret keys i.e., (E_{pk_1}(sk_2),…, E_{pk_n}(sk_1)). A natural question is whether every IND-CPA encryption scheme is also circular secure. It is trivial to see that this is not the case when n=1. In 2010 a separation for n=2 was shown by [ABBC10,GH10] under standard assumptions in bilinear groups. In this paper we finally settle the question showing that for every n there exist an IND-CPA secure scheme which is not n-circular secure. Our result relies on the recent progress in program obfuscation.

**ePrint:**
https://eprint.iacr.org/2013/690

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