Cryptology ePrint Archive: Report 2021/271

On the CCA Compatibility of Public-Key Infrastructure

Dakshita Khurana and Brent Waters

Abstract: In this work, we study the compatibility of any key generation or setup algorithm. We focus on the specific case of encryption, and say that a key generation algorithm KeyGen is X-compatible (for X \in {CPA, CCA1, CCA2}) if there exist encryption and decryption algorithms that together with KeyGen, result in an X-secure public-key encryption scheme.

We study the following question: Is every CPA-compatible key generation algorithm also CCA-compatible? We obtain the following answers:

- Every sub-exponentially CPA-compatible KeyGen algorithm is CCA1-compatible, assuming the existence of hinting PRGs and sub-exponentially secure keyless collision resistant hash functions. - Every sub-exponentially CPA-compatible KeyGen algorithm is also CCA2-compatible, assuming the existence of non-interactive CCA2 secure commitments, in addition to sub-exponential security of the assumptions listed in the previous bullet.

Here, sub-exponentially CPA-compatible KeyGen refers to any key generation algorithm for which there exist encryption and decryption algorithms that result in a CPA-secure public-key encryption scheme {\em against sub-exponential adversaries}.

This gives a way to perform CCA secure encryption given any public key infrastructure that has been established with only (sub-exponential) CPA security in mind. The resulting CCA encryption makes black-box use of the CPA scheme and all other underlying primitives.

Category / Keywords: public key compatibility, CCA security, non-malleable

Original Publication (in the same form): IACR-PKC-2021

Date: received 3 Mar 2021, last revised 9 Jul 2021

Contact author: dakshita at illinois edu, bwaters at cs utexas edu

Available format(s): PDF | BibTeX Citation

Version: 20210709:164248 (All versions of this report)

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