**SEMINAR
NOTICE**

**IND-CCVA
: Indistinguishability Against Chosen Ciphertext Verification Attack**

**Sumit
Kumar Pandey, C.R.Rao Institute**

**DATE
& TIME : 23 August 2013,**
**4PM
VENUE: SEMINAR ROOM, SCIS**

**Abstract**

The
definition of IND-CCA security model for public key encryption allows
an adversary to obtain (adaptively) decryption of ciphertexts of its
choice. That is, the adversary is given oracle access to the
decryption function correspondingto the decryption key in use. The
adversary may make queries that do not correspond to a valid
ciphertext, and the answer will be accordingly (i.e., a special
“failure” symbol). In this talk, we investigate the case where we
restrict the oracle to only determine if the query made is a valid
ciphertext or not. That is, the oracle will

output 1 if the query
string is a valid ciphertext (do not output the corresponding
plaintext) and output 0 otherwise. We call this oracle as “ciphertext
verification oracle” and the corresponding security model as
Indistinguishability against chosen ciphertext verification attack
(IND-CCVA). We point out that this seemingly weaker security model is
meaningful, clear and useful to the extent where we motivate that
certain cryptographic functionalities can be achieved by ensuring the
IND-CCVA security where as IND-CPA is not sufficient and IND-CCA
provides more than necessary. We support our claim by providing
nontrivial construction (existing/new) of:

public key encryption schemes that are IND-CCVA secure but not IND-CCA secure,

– public key encryption schemes that are IND-CPA secure but not IND-CCVA secure.

– public key encryption schemes that are IND-CCA1 secure but not IND-CCVA secure.

Our discoveries are another manifestation of the subtleties that make the study of security notions for public key encryption schemes so attractive and are important towards achieving the definitional clarity of the target security.The speaker did his Masters in Mathematics from IIT Bombay and then did Masters in Computer Science from ISI Kolkata. After that, he has been pursuing PhD in Computer Science from ISI Kolkata itself. He joined CR RAO AIMSCS in September 2012 as an Assistant Professor. His research area includes "Encryption, Signature, Signcryption schemes, Elliptic Curve Cryptography, Pairings and Provable Security" .