Score:2

Can CPA secure scheme be converted to CCA secure?

us flag
Naz

I would like to know if there are some methods or techniques that can convert a public key encryption scheme from CPA secure to CCA secure?

ckamath avatar
ag flag
See [Naor-Yung](http://www.cs.umd.edu/~jkatz/gradcrypto2/NOTES/lecture7.pdf) and [Fujisaki-Okamoto](https://cs.uni-paderborn.de/fileadmin/informatik/fg/cuk/Lehre/Abschlussarbeiten/Bachelorarbeiten/2014/BA_Lippert_FOT_final.pdf) transformations.
Patriot avatar
cn flag
@Occams_Trimmer Why not offer a full answer instead of just a comment?
Score:2
ag flag

There are several compilers that take a CPA-secure PKE and produce a CCA-secure PKE. I am aware of two.

The first (possibly the earliest) is the Naor-Yung transformation [NY], which uses a non-interactive zero-knowledge proof (NIKZ) for this purpose. Since we know how to construct NIZKs from a variety of hardness assumptions (e.g., quadratic residuosity, LWE etc.) and in the random-oracle model, we get CCA-secure PKE under these additional assumptions.

The second and arguably the more efficient/practical transformation is the Fujisaki-Okamoto transformation, which is proved secure in the random-oracle model. In fact, one can as well start with a OW-secure PKE.

[FO]: Fujisaki and Okamoto, Secure Integration of Asymmetric and Symmetric Encryption Schemes, JoC'13

[NY]: Naor and Yung, Public-key Cryptosystems Provably Secure against Chosen Ciphertext Attacks, STOC'90

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