Cryptology ePrint Archive: Report 2016/763

Human Public-Key Encryption

Houda Ferradi and Rémi Géraud and David Naccache

Abstract: This paper proposes a public-key cryptosystem and a short password encryption mode, where traditional hardness assumptions are replaced by specific refinements of the CAPTCHA concept called Decisional and Existential CAPTCHAs.

The public-key encryption method, achieving 128-bit security, typically requires from the sender to solve one CAPTCHA. The receiver does not need to resort to any human aid.

A second symmetric encryption method allows to encrypt messages using very short passwords shared between the sender and the receiver. Here, a simple 5-character alphanumeric password provides sufficient security for all practical purposes.

We conjecture that the automatic construction of Decisional and Existential CAPTCHAs is possible and provide candidate ideas for their implementation.

Category / Keywords:

Date: received 8 Aug 2016

Contact author: remi geraud at ens fr

Available format(s): PDF | BibTeX Citation

Version: 20160810:204348 (All versions of this report)

Short URL:

[ Cryptology ePrint archive ]